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Centre National de la Recherche Scientifique, UMR 6558, Laboratoire des Biomembranes et Signalisation Cellulaire, Faculty of Sciences, University of Poitiers, 86022 Poitiers cedex, France
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ABSTRACT |
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 TOP
 ABSTRACT
 INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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Calcium current was recorded
from ventricular cardiomyocytes of rats at various stages of postnatal
development using the whole cell patch-clamp technique. In cultured
3-day-old neonatal cells, the current carried by Ca2+ or
Ba2+ (5 mM) was not completely inhibited by 2 µM
nifedipine. A residual current was activated in the same voltage range
as the L-type, nifedipine-sensitive Ca2+ current, but its
steady-state inactivation was negatively shifted by 16 mV. This
nifedipine-resistant calcium current was not further inhibited by other
organic calcium current antagonists such as PN200-110, verapamil, and
diltiazem nor by nickel, 
-conotoxin, or tetrodotoxin. It was
completely blocked by cadmium and increased by isoproterenol and
forskolin. This current was >20% of total calcium current in
ventricular myocytes freshly isolated from neonatal rats, and it
decreased during postnatal maturation, disappearing at the adult stage.
This suggests that this current could be caused by an isoform of the
L-type calcium channel expressed in a way that reflects the
developmental stage of the rat heart.
rats; heart; development; Ca2+ channel isoform
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INTRODUCTION |
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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POSTNATAL CARDIAC DEVELOPMENT is characterized by a rapid withdrawal of myocytes from the cell cycle after birth (22), with growth assumed to take place via the enlargement of preexisting myocytes as a result of a large increase in protein synthesis (33). The myocyte phenotype shifts from a fetal phenotype to a more differentiated phenotype to attain the completely differentiated stage of adult cardiac cells with respect to metabolic processes (23), contractile protein functions (27), and excitation-contraction coupling mechanisms (35).
In this way, important developmental changes take place in relation to cellular electrophysiological properties during the postnatal growth period (39). For example, it has been reported that the activity of the rat cardiac Na+/Ca2+ exchanger (19, 31) and the density of the inward rectifier K+ current (24) are increased, whereas the activity of the Na+/H+ exchanger (15) is decreased during this period. Some discrepancies, however, have appeared in the literature in relation to developmental changes in the cardiac L-type calcium current (ICa-L). The density of this current has been shown in different studies either to remain constant (12, 35) or to decrease (6).
The major entry pathway of calcium into cardiac cells is assumed to be
via voltage-activated calcium channels (VACC). The electrophysiological
properties of these channels have been extensively characterized in
terms of their voltage dependence, inactivation, single-channel
conductance, and pharmacology, such that several types of channels
(named L, N, P/Q, R, and T) have been identified (10, 20,
25). Subsequent biochemical and molecular biology studies have
established the structure of these channels as multi-subunit complexes
composed of an ion-conducting 
1-subunit protein
associated with 2-, 
-, 
-, and 
-regulatory
subunits. Calcium currents are classically divided into two classes,
low- and high-voltage-activated calcium channels (LVACC and HVACC), as
a function of their voltage dependence.
In mammalian heart, two types of calcium currents have been reported, which show a cell-specific distribution. The T-type low-voltage-activated calcium current (ICa-T) is expressed in the heart's conduction system as well as in pacemaker and atrial cells. It has also been shown in rat ventricular cardiomyocytes at the fetal and neonatal stages of development, but it disappears during postnatal maturation (40). This current has also been shown to be reexpressed in hypertrophied (3) and dedifferentiated adult ventricular cells in culture (9), suggesting a cell cycle-related expression of this calcium channel (13). The L-type high-voltage-activated calcium current has been uniformly observed in cardiac cells regardless of the stage of development. Its sensitivity to dihydropyridine (DHP) as a pharmacological hallmark was used to characterize its molecular structure and to clone the genes encoding for its multimeric protein components (1). In addition to these two types of calcium current, a DHP-resistant calcium current with some properties different from those of the T-type current was observed in 18-day-old rat fetal cardiomyocytes (32).
In the present study, we provide evidence for the presence in neonatal rat ventricular cardiomyocytes of a component of calcium current, resistant to nifedipine, that has some properties different from those of the T-type and L-type calcium currents. This current, which has been characterized in neonatal ventricular cells in culture, can also be found in freshly dissociated cells at the neonatal stage but then progressively diminishes to the point of being absent in adult cells. We suggest here that this current could be caused by a calcium channel isoform, which is expressed as a function of postnatal development and then as a function of the cell cycle.
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METHODS |
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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Neonatal ventricular cardiomyocyte culture. Single-cell cultures were prepared according to previously described methods (28). Briefly, hearts from 1- to 2-day-old Wistar rats killed by cervical dislocation followed by decapitation were excised and placed in a filter-sterilized Ca2+- and Mg2+-free spinner medium. Ventricles were isolated, cut into small pieces, and incubated at 37°C in a spinner solution containing 0.1% trypsin (Seromed). The dissociated cells were preplated for 90 min in a culture medium containing Ham's F-10 (GIBCO Life Technologies) supplemented with 10% FCS (Boehringer Mannheim), 10% heat-inactivated horse serum (GIBCO-BRL), and 1% antibiotics (100 U/ml penicillin G and 50 U/ml streptomycin; Sigma). This preplating step removes most of the rapidly adhering nonmyocyte cells (2). The suspended cells were subsequently collected and counted and then plated and incubated at a density of 300 cells/mm2 in 35-mm dishes. After 1 day in culture, the growth medium was renewed, with the exception of the FCS, which was omitted.
Freshly isolated neonatal and adult ventricular cardiomyocytes. Neonatal rat ventricles were isolated and dissected as described for the neonatal cell cultures. Small pieces of ventricle were incubated at 37°C for 30 min in spinner solution containing 0.05% collagenase (type II, Worthington) under gentle agitation. The cell suspension was collected and centrifuged (100 g for 5 min), and the resulting pellet was rinsed three times in a Kraftbrühe (KB) solution, gradually resuspended in a normal Tyrode solution, and kept at room temperature until used.
Adult ventricular cardiomyocytes were dissociated as previously described (8). Adult male Wistar rats were injected intraperitoneally with 1,000 IU heparin and anesthetized with ether. The heart was quickly removed via a thoracotomy and transferred to an ice-cold Tyrode solution. The aorta was cannulated, and the heart was mounted on a Langendorff apparatus and successively perfused (at 37°C) with the following oxygenated solutions: 5 min with Tyrode solution, 4 min with a nominally Ca2+-free Tyrode solution, and ~20 min with the same solution supplemented with 0.05% collagenase (type II, Worthington), 0.06 mM CaCl2 and 0.1% BSA. When the heart was flaccid, it was rinsed with KB solution for 2 min. The ventricles were dissected out, cut into small pieces, and gently stirred in KB solution. Isolated cells were filtered, maintained for 1 h in the KB solution, and gradually resuspended in Tyrode solution.Electrophysiological measurements.
Voltage-clamp experiments were performed at room temperature
(20-22°C), using the whole cell patch-clamp technique
(14). Micropipettes (2-4 M
) were pulled on a
two-stage patch pipette puller (PP83, Narishige Scientific Instrument)
connected to the head stage of a patch-clamp amplifier (RK 300, Biologic) and driven by a PC-compatible microcomputer via an A/D-D/A
conversion board (Labmaster TM-40, Scientific Solutions). Membrane
voltage clamping, data acquisition, and analysis were performed using
pCLAMP software (version 6, Axon Instruments, Foster City, CA).
Solutions and procedures. The spinner medium for ventricular neonatal cell dissociation contained (in mM) 116 NaCl, 5.3 KCl, 8 NaH2PO4, 22.6 NaHCO3, 10 HEPES, and 5.6 D-glucose, pH 7.4 with NaOH. Thirty minutes before voltage-clamp experiments, cultured cells were rinsed twice and maintained in Tyrode solution. Calcium currents were recorded in a nominally Na+- and K+-free external solution containing (in mM) 130 N-methyl-D-glucamine (NMG), 20 tetraethylammonium-Cl (TEA-Cl), 5.0 CaCl2 or BaCl2, 2 MgCl2, 10 HEPES, and 10 D-glucose, pH 7.4 with HCl. The pipette solution, from which potassium ions were also omitted, contained (in mM) 110 CsCl, 20 TEA-Cl, 5 MgATP, 0.3 NaGTP, 2 Na2ATP, 5 sodium phosphocreatine, and 5 HEPES, pH 7.2 with Tris.
Membrane capacitance (Cm) was estimated from the capacitative transient elicited by a 10-mV depolarizing step (10-ms duration) from a holding potential (HP) of
90 mV and calculated
according to the equation
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c is the time constant of the membrane
capacitance, I0 is the initial current value,
I
is the amplitude of the steady-state
current and 
Vm is the amplitude of the
voltage step (change in membrane potential). No capacitance or series resistance correction was used.
Calcium currents were generated using a double-pulse protocol to obtain
current-voltage (I-V) curves and steady-state
activation and inactivation curves. From a HP of 80 mV, 1-s
depolarizing pulses to different membrane potentials (10-mV increments,
i.e., the conditioning pulse) were followed by a 5-ms return to 80 mV
and then by a 1-s test pulse to 0 mV, at which the maximum L-type
calcium current (ICa-L) was obtained.
The peak current amplitudes for I-V curves and
steady-state activation curves were measured from the conditioning
pulses. Activation curves were estimated according to the relation
(17)
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![I/I<SUB>max</SUB><IT>=</IT>{<IT>1+</IT>exp[(<IT>V</IT><SUB>m</SUB><IT>−V<SUB>0.5</SUB></IT>)<IT>/k</IT>]}<SUP>−<IT>1</IT></SUP>](/content/vol279/issue5/fulltext/H2259/img003.gif)
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![I=I<SUB>Ca(f)</SUB>[exp(−<IT>t/&tgr;</IT><SUB>f</SUB>)]<IT>+I</IT><SUB>Ca(s)</SUB>[exp(−<IT>t/&tgr;</IT><SUB>s</SUB>)]](/content/vol279/issue5/fulltext/H2259/img004.gif)
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f and s the time constants of the fast
and slow components of calcium current decay, respectively.
Chemicals and drugs.
Nifedipine, PN200-110, diltiazem, and verapamil (all purchased from
Sigma) were each dissolved in DMSO to form 10
3 M stock
solutions, -conotoxin GVIA (Sigma) was dissolved in distilled water
to form a 105 M stock solution, and TTX (Latoxan) was
dissolved in dilute acetic acid for to form 103 M stock
solution. When used, these drugs were added from the stock solutions to
the test solution at the desired final concentration.
Statistical analysis. Data are expressed as means ± SE. Statistical analysis of data was performed using ANOVA followed by a Newman-Keuls test. Values of P < 0.05 were considered statistically significant.
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RESULTS |
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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Evidence for a nifedipine-resistant calcium current in neonatal rat
ventricular cardiomyocytes in culture.
Figure 1A shows calcium
currents elicited in cultured 3-day-old neonatal rat ventricular
cardiomyocytes in response to depolarizations increasing in 10-mV steps
from a HP of 80 mV. I-V curves (Fig. 1B) plotted from these current traces show that the whole
cell calcium currents obtained in a Na+- and
K+- free external medium containing 5 mM Ca2+
exhibited ICa-L properties with potential values
of 40, 0, and +50 mV for activation threshold, peak, and reversal of
the current, respectively. The application of nifedipine (2 µM), a
ICa-L blocker, did not however, completely block
this calcium current (Fig. 1A). That is, the peak of the
residual current at 0 mV (Fig. 1B) represented 27.4 ± 1.9% of the total calcium current density (2.0 ± 0.4 vs. 7.3 ± 0.7 pA/pF, n = 17 cells).
Under these experimental conditions, the density of the
ICa-L blocked by nifedipine (measured by
subtracting residual calcium current from total calcium current) was
5.3 ± 0.5 pA/pF (n = 17 cells).
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4.3 ± 0.6 pA/pF,
n = 21 cells) was higher than that measured with
Ca2+ but represented a similar ratio (32 ± 2.8%,
n = 21 cells) of the total current density (12.8 ± 0.9 pA/pF, n = 21 cells).
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80 and
50 mV, respectively. These results clearly confirm the presence of a
nifedipine-resistant calcium current in newborn rat ventricular
cardiomyocytes in culture. This current component was observed in all
cultured cells up to 3 days of age as well as in those cultured for up
to 6 days.
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Characterization of nifedipine-resistant calcium current.
Figure 4 shows the voltage-dependent
availability of the nifedipine-sensitive ICa-L
and the nifedipine-resistant calcium current (ICa-NR) elicited in 3-day-old cultured
cardiomyocytes. In the presence of Ca2+ as the charge
carrier (Fig. 4A), activation curves for the two experimental conditions could be superimposed. Activation parameters were not significantly different from each other
[V0.5 = 11.1 ± 0.3 and 12.9 ± 0.5 mV and k = 7.2 ± 0.2 and 6.8 ± 0.4 (n = 17 cells) for ICa-L and
ICa-NR, respectively]. However, inactivation curves obtained using the double-pulse protocol described in
METHODS showed that the curve for
ICa-NR was shifted to more negative potentials
(V0.5 = 39.3 ± 0.5 mV,
k = 6.7 ± 0.5; n = 17 cells) compared with that measured for ICa-L
(V0.5 = 23.3 ± 0.2 mV, k = 5.4 ± 0.2; n = 17 cells). In
these conditions, the window current obtained for
ICa-NR was significantly reduced compared with
that observed for ICa-L, which has been shown to
be more prominent at the neonatal than at the adult stage (6,
12). Similar results describing V0.5 and
k for activation of ICa-L and
ICa-NR were obtained when Ca2+ was
replaced by Ba2+ [V0.5 = 17.5 ± 0.1 and 18.4 ± 0.1 mV and k = 5.1 ± 0.1 and 4.9 ± 0.1 for L-type barium current
(IBa-L) and nifedipine-resistant barium current
(IBa-NR), respectively (n = 21 cells); Fig. 4B]. Inactivation parameters similar to those
described above were also found after the replacement of external
Ca2+ with Ba2+
[V0.5 = 23.9 ± 0.8 and 38.4 ± 0.6 mV and k = 7.5 ± 0.7 and 6.8 ± 0.5 (n = 21 cells) for IBa-L and
IBa-NR, respectively]. For concentrations
of nifedipine higher than 1 µM, which blocked L-type calcium current,
Table 1 shows that steady-state
inactivation parameters for the residual current were not significantly
changed. This suggests that the shift observed in the voltage-dependent inactivation is not caused by nifedipine.
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f) and 93.0 ± 4.2 ms for the slow
component (s) n = 16 cells], whereas
only one time constant was required when Ba2+ was used in
the extracellular medium (182.1 ± 8.7 ms; n = 16 cells). Furthermore, the nifedipine-resistant current was best fitted
with two time constants under conditions when Ca2+ was used
in the extracellular medium [12.2 ± 0.9 and 94.3 ± 8.9 ms
for f and s, respectively;
n = 16 cells] as well when Ba2+ was used
(20.3 ± 1.0 and 114.0 ± 10.0 ms for f and
s, respectively; n = 16 cells).
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-conotoxin GVIA (1 µM) (data not
shown).
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Presence of ICa-NR in ventricular cardiomyocytes as a function of development. To test whether the ICa-NR described above could be caused by the conditions under which cardiomyocytes were cultured, the effects of nifedipine were studied on calcium currents (with Ba2+ as the charge carrier) recorded from freshly dissociated ventricular cells obtained from 4-, 10-, and 15-day-old immature rats and from young adult (2-3 mo) rats.
Figure 8A confirms that cell membrane capacitance increased as a function of age in young rats, as previously reported (12, 24). When normalized to the mean values of Cm presented in Fig. 8A, the density of IBa-L increased slightly but not significantly (as previously shown; see Refs. 12, 35) during the developmental phase [6.2 ± 1.1 (n = 11 cells),
6.5 ± 1.2 (n = 11 cells), 7.1 ± 1.0 (n = 13 cells), and 8.9 ± 1.5 (n = 17) pA/pF for 4-, 10-, and 15-day-old rats and
adult rats, respectively; Fig. 8B]. In contrast, although
IBa-NR was clearly expressed at the neonatal stage (Fig.
8B), its density significantly decreased during postnatal development [1.9 ± 0.5 (n = 11 cells),
1.5 ± 0.4 (n = 11 cells), and 0.8 ± 0.3 (n = 13 cells) pA/pF in cardiomyocytes from 4-, 10-, and 15-day-old rats, respectively]. In adult rat hearts, IBa-NR was observed in <10% of the isolated
cells tested, with its mean density being only 0.2 ± 0.07 pA/pF
(n = 7 cells).
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DISCUSSION |
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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Our data show that a component of the slow inward calcium current, not inhibited by nifedipine or any other major calcium channel antagonist, was observed in neonatal rat ventricular cardiomyocytes in culture. This current was also expressed in ventricular cardiomyocytes obtained from newborn rats and progressively disappeared during postnatal development. The main voltage-dependent and pharmacological properties of this current are quite similar to those of the DHP-resistant calcium current found in rat fetal cardiomyocytes (32). Moreover, properties of this nifedipine-resistant current seem also quite comparable to those of the nifedipine-insensitive calcium current recently found in the guinea pig mesenteric artery (26).
The first evidence for the presence of ICa-NR in cultured neonatal rat ventricular cardiomyocytes could be seen on the application of 2 µM nifedipine to the extracellular medium. Although this concentration of nifedipine is usually able to completely block the inward L-type calcium current in cardiac cells, we observed that 28% of the calcium current was not inhibited in cultured 3-day-old cardiomyocytes. Moreover, 20% of the current was still present when the concentration of nifedipine was increased to 50 µM (Fig. 3).
In agreement with the voltage-dependent inhibitory effect of nifedipine
on L-type Ca2+ current (16), the total calcium
current measured here was more effectively inhibited when cells were
voltage-clamped at a HP of 50 mV. However, even under these
conditions, 10% of the current was not inhibited in the presence of 50 µM nifedipine (Fig. 4). In addition, the nifedipine-resistant current
was not further blocked by PN200-110 (2 µM; Fig. 6A), an
L-type calcium current inhibitor known to be more potent than
nifedipine, nor was it blocked by other specific inhibitors
(phenylalkylamines and benzothiazepines) of the L-type calcium current.
An analysis of I-V curves showed that
ICa-NR was activated in a voltage range similar
to that seen for ICa-L, whereas its steady-state
inactivation curve was shifted toward more negative potentials compared
with those of ICa-L (Fig. 4). From this result, the hypothesis that this current component could be a T-type calcium current, as previously observed in ventricular cardiomyocytes obtained
from 2-day-old rats (12), can be ruled out. Evidence to
support this conclusion can be found in the fact that
IBa-NR was not affected by 30 µM nickel (Fig.
6B) and its density was increased when Ba2+ was
substituted for Ca2+ as the major charge carrier (Fig.
5B). Furthermore, the lack of an effect of -conotoxin
GVIA and TTX allows us to exclude the hypothesis of an involvement in
this current of N-type calcium channels or of the passage of
Ca2+ through TTX-sensitive sodium channels. According to
the study of Morita et al. (26), this nifedipine-resistant
current presents properties close to those of the R-type calcium
current. However, these authors have shown by a molecular approach with
RT-PCR that the 1E-subunit mRNA was not detected under
their conditions.
By taking into account the I-V curves obtained here and their dependence on the charge carrier used (Figs. 1, 2, and 5) as well as the susceptibility of the channels to phosphorylation processes (Fig. 7), the nifedipine-resistant current could be suitably compared with the ICa-L. However, differences in the sensitivity of ICa-NR to specific inhibitors of ICa-L, and altered steady-state inactivation and activation decay characteristics, clearly support the notion of ICa-NR as another component of the calcium current and possibly as an isotype of ICa-L.
Cloning and expression studies have outlined the molecular determinants
of Ca2+ channel properties and function (34,
37). Properties such as cation permeation and drug sensitivity
would be attributed to the 1-subunit constituting the
ion-conducting pore of the channel, whereas the current amplitude and
the gating of the channel would be mainly regulated by other
2-, -, -, and -subunits. Concerning the cardiac
L-type calcium channel, recent studies have shown that DHP sensitivity
(38) as well as inactivation properties (30)
could be mainly attributed to the 1-subunit. Therefore,
if the present nifedipine-resistant calcium channel is an isoform of
the L-type channel, it can be speculated that it results from the
expression of an alternative splicing of the 1C-subunit.
However, because it has also been shown that auxiliary subunits could
regulate gating properties, particularly the -subunit (4), possible expression of isoforms of these subunits
cannot be excluded. To test these hypotheses, single-channel studies and a molecular approach will be necessary.
The strong possibility that the present nifedipine-resistant
calcium current arises from the same molecular entity as the DHP-resistant calcium current found in rat fetal cardiomyocytes (32) argues for its developmentally regulated expression,
as has been shown for the T-type LVACC (12, 18, 36, 39). To support such an hypothesis, Diebold et al. (7) showed
that the gene for the 1-subunit of the cardiac calcium
channel in rat heart generates developmentally regulated isoforms. In
this way, variant isoforms of the IVS3 motif were expressed in fetal and newborn rat heart, whereas only a single isoform was predominant in
adult rat heart. Secondly, the postnatal decrease in the expression of
IBa-NR reported here (Fig. 8) is well correlated
with a reduction of the 5-bromo-2'-deoxyuridine labeling index (used to
evaluate the cell proliferative capacity) during the postnatal
development of rat ventricles (5).
It has been demonstrated (13) that expression of the ICa-T at the neonatal stage of development decreases in parallel with the rapid withdrawal of ventricular cardiomyocytes from the cell cycle soon after birth, suggesting a cell cycle-related form of channel expression. This was also proposed in vascular smooth muscle cells (21), in which ICa-T has been shown to increase during cell proliferation in culture and to decrease once cells reach confluence, suggesting that this current is important in cell proliferation (29). Such a physiological role of ICa-NR in cell signaling can also be proposed. However, present data have shown that its density was ~30% of the total calcium current in cultured 3-day-old neonatal cells and >20% in ventricular cardiomyocytes from 4-day-old rats. A physiological role similar to that of the ICa-L, as proposed for vascular smooth muscle cells (26), cannot then be excluded but requires further investigation. In addition, investigations on the presence of this current in other cardiac cells such as atrial cells or in ventricular cells from other species as a function of developmental process would provide further informations about its role.
The expression of this current component at the neonatal stage of development but not in adult ventricular cells provides further evidence for a developmental shift in the expression of calcium channels in cardiac muscle.
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ACKNOWLEDGEMENTS |
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We thank Dr. M. F. Patterson for critically reading the manuscript and for correcting the language.
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FOOTNOTES |
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This work was financially supported by grants from the CNRS (UMR 6558), the University of Poitiers, and the Fondation Langlois.
Address for reprint requests and other correspondence: D. Potreau, Univ. of Poitiers, UMR 6558 LBSC, Faculty of Sciences, 40 Ave. du Recteur Pineau, 86022 Poitiers cedex, France (E-mail: daniel.potreau{at}univ-poitiers.fr).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Received 28 January 2000; accepted in final form 10 May 2000.
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REFERENCES |
|---|
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TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
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|---|
1.
Bers, D,
and
Perez-Reyes E.
Ca channels in cardiac myocytes: structure and function in Ca influx and intracellular Ca release.
Cardiovasc Res
42:
339-360,
1999
2.
Blondel, B,
Roijen I,
and
Cheneval JP.
Heart cells in culture: a simple method for increasing the proportion of myoblasts.
Experientia
27:
356-358,
1971[ISI][Medline].
3.
Boyden, PA,
and
Jeck CD.
Ion channel function in disease.
Cardiovasc Res
29:
312-318,
1995[ISI][Medline].
4.
Cens, T,
Restituito S,
Galas S,
and
Charnet P.
Voltage and calcium use the same molecular determinants to inactivate calcium channels.
J Biol Chem
274:
5483-5490,
1999
5.
Cheng, W,
Reiss K,
Kajstura J,
Kowal K,
Quaini F,
and
Anversa P.
Down-regulation of the IGF-1 system parallels the attenuation in the proliferative capacity of rat ventricular myocytes during postnatal development.
Lab Invest
72:
646-655,
1995[ISI][Medline].
6.
Cohen, NM,
and
Lederer WJ.
Changes in the calcium current of rat heart ventricular myocytes during development.
J Physiol (Lond)
406:
115-146,
1988
7.
Diebold, RJ,
Koch WJ,
Ellinor PT,
Wang JJ,
Muthuchamy M,
Wieczorek DF,
and
Schwartz A.
Mutually exclusive exon splicing of the cardiac calcium channel 1 subunit gene generates developmentally regulated isoforms in the rat heart.
Proc Natl Acad Sci USA
89:
1497-1501,
1992
8.
Fares, N,
Bois P,
Lenfant J,
and
Potreau D.
Characterization of a hyperpolarization-activated current in dedifferentiated adult rat ventricular cells in primary culture.
J Physiol (Lond)
506:
73-82,
1998
9.
Fares, N,
Gomez JP,
and
Potreau D.
T-type calcium current is expressed in dedifferentiated adult rat ventricular cells in primary culture.
C R Acad Sci III
319:
569-576,
1996[Medline].
10.
Glossmann, H,
and
Striessnig J.
Molecular properties of calcium channels.
Rev Physiol Biochem Pharmacol
114:
1-105,
1990[ISI][Medline].
11.
Godfraind, T.
Cardioselectivity of calcium antagonists.
Cardiovasc Drugs Ther
8:
353-364,
1994.
12.
Gomez, JP,
Potreau D,
Branka JE,
and
Raymond G.
Developmental changes in Ca2+ currents from newborn rat cardiomyocytes in primary culture.
Pflügers Arch
428:
241-249,
1994[ISI][Medline].
13.
Guo, W,
Kamiya K,
Kodama I,
and
Toyama J.
Cell cycle-related changes in the voltage-gated Ca2+ currents in cultured newborn rat ventricular myocytes.
J Mol Cell Cardiol
30:
1095-1103,
1998[ISI][Medline].
14.
Hamill, OP,
Marty A,
Neher E,
Sakmann B,
and
Sigworth FJ.
Improved patch clamp techniques for high-resolution current recording from cells and cell-free membrane patches.
Pflügers Arch
391:
85-100,
1981[ISI][Medline].
15.
Haworth, RS,
Yasutake M,
Brooks G,
and
Avkiran M.
Cardiac Na+-H+ exchanger during postnatal development in the rat: changes in mRNA expression and sarcolemmal activity.
J Mol Cell Cardiol
29:
321-332,
1997[ISI][Medline].
16.
Hu, H,
and
Marban E.
Isoform-specific inhibition of L-type calcium channels by dihydropyridines is independent of isoform-specific gating properties.
Mol Pharmacol
53:
902-907,
1998
17.
Isenberg, G,
and
Klöckner U.
Calcium currents of isolated bovine ventricular myocytes are fast and of large amplitude.
Pflügers Arch
395:
30-41,
1982[ISI][Medline].
18.
Kawano, S,
and
De Haan R.
Developmental changes in the calcium currents in embryonic chick ventricular myocytes.
J Membr Biol
120:
17-28,
1991[ISI][Medline].
19.
Koban, MU,
Moorman AFM,
Holtz J,
Yacoub MH,
and
Boeheler KR.
Expressional analysis of the cardiac Na-Ca exchanger in rat development and senescence.
Cardiovasc Res
37:
405-423,
1998
20.
Krizanova, O.
Structural implications in the function of L-type voltage-dependent calcium channels.
Gen Physiol Biophys
15:
79-87,
1996[ISI][Medline].
21.
Kuga, T,
Kobayashi S,
Hirakawa Y,
Kanaide H,
and
Takeshita A.
Cell cycle-dependent expression of L- and T-type Ca2+ currents in rat aortic smooth muscle cells in primary culture.
Circ Res
79:
14-19,
1996
22.
Li, F,
Wang X,
Capasso JM,
and
Gerdes AM.
Rapid transition of cardiac myocytes from hyperplasia to hypertrophy during postnatal development.
J Mol Cell Cardiol
28:
1737-1746,
1996[ISI][Medline].
23.
Lopaschuk, GD,
Collins-Nakai RL,
and
Itoi T.
Developmental changes in energy substrate use by the heart.
Cardiovasc Res
26:
1172-1180,
1992
24.
Masuda, H,
and
Sperelakis N.
Inward rectifying potassium current in rat fetal and neonatal ventricular cardiomyocytes.
Am J Physiol Heart Circ Physiol
265:
H1107-H1111,
1993
25.
McDonald, T,
Pelzer S,
Trautwein W,
and
Pelzer DJ.
Regulation and modulation of calcium channels in cardiac, skeletal, and smooth muscle cells.
Physiol Rev
74:
365-507,
1994
26.
Morita, H,
Cousins H,
Onoue H,
Yushi I,
and
Inoue R.
Predominant distribution of nifedipine-insensitive, high voltage-activated Ca2+ channels in the terminal mesenteric artery of guinea pig.
Circ Res
85:
596-605,
1999
27.
Murphy, AM.
Contractile protein phenotype variation during development.
Cardiovasc Res
31:
25-33,
1996.
28.
Pignier, C,
Fares N,
and
Potreau D.
Effects of adrenergic stimulation on postnatal development and calcium current in newborn rat cardiomyocytes in primary culture.
J Cardiovasc Pharmacol
31:
262-270,
1998[ISI][Medline].
29.
Richard, S,
Neveu D,
Carnac G,
Bodin P,
Travo P,
and
Nargeot J.
Differential expression of voltage gated Ca2+ currents in cultivated aortic myocytes.
Biochim Biophys Acta
1160:
95-104,
1992[Medline].
30.
Soldatov, NM,
Zûhlke RD,
Bouron A,
and
Reuter H.
Molecular structures involved in L-type calcium channel inactivation. Role of the carboxyl-terminal region encoded by exons 40-42 in 1C subunit in the kinetics and Ca2+ dependence of inactivation.
J Biol Chem
272:
3560-3566,
1997
31.
Studer, R,
Reinecke H,
Vetter R,
Holtz J,
and
Drexler H.
Expression and function of the cardiac Na+/Ca2+ exchanger in postnatal development of the rat in experimental-induced cardiac hypertrophy and in the failing human heart.
Basic Res Cardiol
82:
53-58,
1997.
32.
Tohse, N,
Masuda H,
and
Sperelakis N.
Novel isoform of Ca2+ channel in rat fetal cardiomyocytes.
J Physiol (Lond)
451:
295-306,
1992
33.
Van Bilsen, M,
and
Chien KR.
Growth and hypertrophy of the heart: towards an understanding of cardiac specific and inducible gene expression.
Cardiovasc Res
27:
1140-1149,
1993[ISI][Medline].
34.
Varadi, G,
Mori Y,
Mikala G,
and
Schwartz A.
Molecular determinants of Ca2+ channel function and drug action.
Trends Physiol Sci
16:
43-49,
1995.
35.
Vornanen, M.
Excitation-contraction coupling of the developing rat heart.
Mol Cell Biochem
28:
1737-1746,
1993.
36.
Wang, R,
Karpinsky E,
and
Pang PKT
Two types of voltage-dependent calcium channel currents and their modulation by parathyroid hormone in neonatal rat ventricular cells.
J Cardiovasc Pharmacol
17:
990-998,
1991[ISI][Medline].
37.
Wei, X,
Pan S,
Lang W,
Kim H,
Schneider T,
Perez-Reyes E,
and
Birnbaumer L.
Molecular determinants of cardiac Ca2+ channel pharmacology. Subunit requirement for the affinity and allosteric regulation of dihydropyridine binding.
J Biol Chem
270:
27106-27111,
1995
38.
Welling, A,
Ludwig A,
Zimmer S,
Klugbauer N,
Flockerzi V,
and
Hofmann F.
Alternatively spliced IS6 segments of the 1C gene determine the tissue-specific dihydropyridine sensitivity of cardiac and vascular smooth muscle L-type Ca2+ channels.
Circ Res
81:
526-532,
1997
39.
Wetzel, GT,
and
Klitzner TS.
Developmental cardiac electrophysiology: recent advances in cellular physiology.
Cardiovasc Res
31:
52-60,
1996.
40.
Zhou, YY,
Lakatta EG,
and
Xiao RP.
Age-associated alterations in calcium current and its modulation in cardiac myocytes.
Drug and Aging
13:
159-171,
1998[ISI][Medline].
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, total calcium current) and after
exposure to nifedipine (2 µM). Traces of L-type calcium current
inhibited by nifedipine (
) were obtained by subtraction
of nifedipine-resistant current traces (
) from the
total current. B: averaged current-voltage relationships for
total (
) and 
) mV by means of protocol indicated in
inset. Values are means ± SE for number of cells
indicated over points on curve. [nifedipine], Nifedipine
concentration.
, A), nickel (30 µM; 
,
B), and cadmium (500 µM; 
, C)
on nifedipine-resistant current carried by Ba2+
(
P < 0.05; 
P < 0.01 compared with values obtained in cardiomyocytes from 4-day-old
rats.
)-, 10 (