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1 Department of Medicine, The transient
outward K+ current
(Ito) in the
heart is responsible for the initial phase of repolarization and for
setting the plateau voltage of the ventricular action potential.
Recently, Kv4.3 has emerged as the leading candidate
potassium channel; Kv4.2; Kv4.3; Xenopus oocytes; heterologous
expression; fluorescence in situ hybridization; chromosome 1
THE CARDIAC ACTION POTENTIAL is generated by the
composite activity of many ion channels, pumps, and transporters.
Voltage-dependent K+ channels are
particularly prominent in repolarization of cardiac myocytes.
K+ channels exhibit extreme
physiological diversity, which arises from the large number of
K+ channel genes, alternative RNA
splicing, heteromultimeric assembly of channel proteins, and the
existence of accessory subunits (for review see Ref. 3). The
determination of the molecular basis of
K+ currents resident in excitable
tissue is complicated by the diversity of
K+ channel genes.
The transient outward K+ channel
(Ito) is
especially important in the early phase of repolarization in many
species, including human (5, 10, 14, 17, 21, 23-25, 31, 37, 40,
41). Recently, the gene encoding a
K+ channel subunit that underlies
the calcium-independent
Ito has been
described. On the basis of analysis of mRNA transcripts in mammalian
ventricles (12) and correlation of the mRNA level with that of
Ito current
density in human ventricular myocytes (20), Kv4.3 has emerged as the
leading candidate K+ channel gene
encoding the cardiac
Ito in large
mammals such as dogs and humans.
Physiological and pathophysiological stimuli can alter the level of
expression of K+ channel genes,
protein, and current (16, 20, 32, 36, 38). The first step in
understanding the molecular basis of the regulation of
K+ currents in response to
biological stimuli is the cloning of the cDNA and genomic DNA encoding
relevant K+ channel genes. We
describe the cloning, functional expression, and chromosomal location
of the human Kv4.3 (hKv4.3) K+
channel. The hKv4.3 gene has two alternatively spliced forms, with the
long version containing a 19-amino acid insert after the S6
membrane-spanning region. Both variants are present in human atrial and
ventricular myocardium.
Cloning of human Kv4.3 cDNA and genomic DNA.
Standard hybridization screening of a random primed human cDNA library
in
ABSTRACT
Top
Abstract
Introduction
Methods
Results
Discussion
References
-subunit gene
that underlies
Ito in larger
mammals such as dogs and humans. We have cloned the human Kv4.3 homolog
and describe a carboxyl-terminal splice variant that inserts 19 amino
acids with a consensus protein kinase C (PKC) phosphorylation site into
the protein after the last membrane-spanning segment. The coding region
of Kv4.3 is comprised of at least five exons and is located on
chromosome 1p13.3. In the basal state the basic biophysical properties
of both of the splice variants are identical.
INTRODUCTION
Top
Abstract
Introduction
Methods
Results
Discussion
References
METHODS
Top
Abstract
Introduction
Methods
Results
Discussion
References
-Zap (Uni-Zap, Stratagene) was performed to obtain partial cDNAs
encoding hKv4.3. Degenerate oligonucleotide primers designed to the
Shal (Kv4) family of
K+ channels were used in the
polymerase chain reaction with reverse transcribed cDNA (RT-PCR) from
total human ventricular RNA as a template (12). A 290-bp fragment of
the hKv4.3 channel in the amino terminus immediately preceding the
first membrane-spanning segment was amplified. This fragment was used
to screen the cardiac library, and four identical clones 5 kb in length
without the 3'-end of hKv4.3 cDNA were identified. This 5-kb cDNA
was subcloned into pBluescript II SK (Stratagene). The 3'-end of
the coding region was obtained by RT-PCR of human cardiac RNA using
rat-specific primers. The upstream primer located at the S2
transmembrane segment had the sequence
5'-CCTTCTTCTGCCTGGACAC-3' encoding the amino acid sequence
FFCLD. The downstream primer encodes the last seven amino acids of the
rat channel protein (VVKVSVL) with the nucleotide sequence
5'-CAAGACAGAGACCTTGACAAC-3'. The 3'-RT-PCR fragment
was cloned into pGEM-T (Promega). The sequence of the 3'-end of
the cDNA was confirmed by sequencing the corresponding human genomic DNA.
) (Invitrogen). The pIRES-GFP-hKv4.3 expression vector was
constructed by digesting pcDNA3.1()-hKv4.3 with
Apa I and
EcoR V. The 2-kb
Apa
I-EcoR V fragment was cloned into
pIRES-GFP (Clontech, Palo Alto, CA) digested with
Apa I and Sma I. The entire cDNA was sequenced
on both strands with an ABI310 Sequencer (Perkin-Elmer).
Northern and Southern blots, ribonuclease protection assay, and PCR. Human ventricular myocardium was obtained from explanted failing hearts or donor hearts unsuitable for transplantation. The tissue was excised from the left ventricular free wall between the left anterior descending and left circumflex coronary arteries. The samples used for RNA isolation were transventricular including both the epicardium and endocardium.
The tissue was quick frozen in liquid N2 within 10-15 min after tissue harvesting and stored at80°C until further
processing. Total RNA for RT-PCR was prepared either by using TRIzol
reagent (GIBCO BRL) according to the manufacturer's instructions or by centrifugation through a CsCl cushion (34). The integrity of all RNA
samples was confirmed by analysis on a denaturing agarose gel and
quantified by optical density measurements at 260 nm.
A multiple human tissue Northern blot was obtained from Invitrogen
(catalog no. D1101-01). The blot was probed with a 480-bp fragment of
hKv4.3 from nucleotides 1,485 to 1,965, corresponding to amino acids
P496-L655. The blot was developed on a storage phosphor screen and
then scanned on a phosphoimager (Molecular Dynamics).
RT-PCR was performed on 5 µg of total RNA isolated from the left
ventricular free wall. RT was performed with a poly-dT primer and
Superscript II RT (GIBCO BRL) according to the manufacturer's instructions. The primers 5'-CTCTGGAGCTGACCGGCACCC-3' (F1)
and 5'-GGGAGCAGCAGGTGGTGGTGAGG-3' (R) span the insert and
were used to amplify the short and long variants of hKv4.3. These
primers generate PCR products of 231 and 288 bp in length. In addition, a forward primer in the insert,
5'-CCCCTGTTGTCTGTACGAACCTCC-3' (Fins) and the reverse primer
were used to generate a 160-bp RT-PCR product.
Ribonuclease protection assays (RPA) were performed as described
previously (11, 12, 20). All probes contained regions of plasmid
sequence at one or both ends of the transcript, permitting easy
distinction between any remaining undigested probe and the shorter,
specifically protected region of the probe. Ten micrograms of yeast
tRNA were used as a negative control to test for the presence of probe
self-protection. For each sample point, 10 µg of total RNA were used
in the assay. Determinations were performed in duplicate for each
sample. Steady-state mRNA levels were quantified by exposing the gels
on a storage phosphor screen and then scanning on a phosphoimager
(Molecular Dynamics).
Genomic DNA was prepared from white blood cells using a standard
protocol (34). Genomic and p54 DNA were cut with
EcoR I, BamH I, and
Bgl II, separated on 1% agarose, and
transferred to nitrocellulose. The same fragment that was used to
screen the cDNA library was used to probe the Southern blot.
Chromosomal localization. Fluorescence in situ hybridization was employed to confirm the chromosomal location of hKv4.3. One microgram of the p54 clone containing the genomic sequence was labeled with digoxigenin (Boehringer Mannheim) in a nick-translation reaction (GIBCO BRL), used as a probe, and hybridized to metaphase spreads from peripheral blood lymphocytes (29). Two hundred nanograms of labeled probe were precipitated with 5 µg of Cot-1 DNA; resuspended in 70% formamide, 2× SSC (1× SSC is 0.15 M NaCl and 0.015 M sodium citrate), 10% dextran sulfate, pH 7.0; denatured for 5 min at 75°C; and preannealed for 1 h at 37°C. Slides were prepared from phytohemagglutinin-stimulated human blood by standard methods and denatured in 70% formamide for 5 min at 75°C before hybridization at 37°C for 18 h. The slides were washed twice in 50% formamide-2× SSC and then twice in 2× SSC at 42°C. The probe was detected with rhodamine-labeled anti-digoxigenin according to the manufacturer's instructions (Oncor). Chromosomes were counterstained with the A-T binding fluorophore 4',6-diamidino-2-phenylindole (DAPI) and viewed with a Zeiss Axioskop equipped with a SenSys cooled charge-coupled device camera (Photometrics) and Smart Capture imaging software (Vysis).
Heterologous expression and electrophysiology.
Full-length cDNAs encoding both splice variants of hKv4.3 were cloned
into the pIRES-GFP vector for bicistronic expression of the channel and
green fluorescence protein driven by the human cytomegalovirus (CMV)
major immediate-early promoter/enhancer in cultured mammalian cells.
The expression cassette contains the hKv4.3 cDNA with an artificial
intron upstream from the encephalomyocarditis that permits the
translation of two proteins from a single mRNA. Mouse
Ltk
fibroblasts were used
for channel expression. The culture and transfection conditions were as
previously described (44). Transient transfection was performed by
calcium phosphate precipitation for 6-12 h with 2.5 µg of the
hKv4.3-containing expression plasmids per 35-mm dish.
when filled
with the internal solution containing (in mM) 110 KCl, 1 MgCl2, 2 MgATP, 1 EGTA, and 10 HEPES, pH 7.2 (final K+
concentration ~112 mM). Cell capacitance was estimated by integrating the area under an uncompensated 10-mV depolarizing voltage step from 80 mV; the cell capacitance was 8.6 ± 0.7 pF
(n = 17). Series resistance was
compensated as much as possible (generally 80-90%) such that the
maximal uncompensated voltage error was <5 mV. Currents were low-pass
filtered at 2 kHz and digitized at 10 kHz through a Digidata 1200 analog-to-digital interface (Axon Instruments) for off-line analysis.
Currents were corrected for small (<5 mV) liquid junction potentials
(Axoscope, Axon Instruments) (4).
Pooled data are presented as means ± SE. Statistical comparisons
were made using an ANOVA with P < 0.05 considered to be significant.
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RESULTS |
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Top
Abstract
Introduction
Methods
Results
Discussion
References
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Isolation of Kv4.2 and Kv4.3 cDNA and genomic clones. The full-length cDNAs encoding hKv4.3 were obtained by a combination of screening of a cardiac cDNA library and RT-PCR of human ventricular RNA. The cDNA contains an open reading frame of 1,911 nucleotides encoding a 637-amino acid channel protein. The human Kv4.3 is highly homologous to the rat homolog (92 and 99% at the nucleotide and amino acid levels, respectively). The hKv4.3 shares 95% amino acid identity in the transmembrane regions and overall 76% identity with the related hKv4.2 channel (unpublished data). RT-PCR of the carboxyl terminus of hKv4.3 reproducibly produced two bands that differed in size by 57 bp (Fig. 1A). Cloning and sequencing the PCR products from the carboxyl-terminal end revealed a short product that was homologous to the previously described rat Kv4.3 cDNA and a longer product containing a 19-amino acid insert after S6 (1,968 nucleotides encoding a 656-amino acid protein). This insert contains a consensus protein kinase C (PKC) phosphorylation site of the form RXXT*XK, where T* is the phosphorylated amino acid (28). The relative location and sequence of the splice insert are shown in a schematic of the predicted transmembrane topology (Fig. 1B).
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Gene structure and chromosomal location of Kv4.3. We used the full-length rat Kv4.2 cDNA to screen a human genomic PAC library and obtained three unique clones. The clones designated p54 and p56 contain the genes encoding hKv4.3 and hKv4.2, respectively. The genomic clone p54 contains the 5'-untranslated region and the coding region in the first exon of hKv4.3. There is an apparent splice donor site in the predicted P-region of the channel at the first glycine of the GYGD K+ channel signature motif (Fig. 2A). The long 5'-untranslated region is consistent with the size of the mRNA on the Northern blot (Fig. 1C). Analysis of human genomic DNA by PCR and sequencing demonstrates at least four exons that encode the carboxyl terminus of the channel. The size of the second and third coding region-containing exons is uncertain. There are two large introns between the first and second exons and the second and third exons. PCR was used to define the downstream structure of hKv4.3. A 2.4-kb product was amplified using human genomic DNA, a forward primer that recognizes the sequence encoding the 19-amino acid insert, and a reverse primer that was complementary to the carboxyl terminus of the channel. This product contained the third through the fifth exons, which are separated by introns of 1,162 and 746 bp in length (Fig. 2A). A Southern blot of the genomic clone p54 and human genomic DNA reveals identical banding patterns with an hKv4.3 fragment from the 5'-end of the cDNA used as a probe (Fig. 2B).
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Functional expression of hKv4.3 splice variants.
We cloned both splice variants of hKv4.3 into the expression vector
pIRES-GFP, which drives bicistronic expression of the channel and
reporter GFP genes by the CMV promoter/enhancer. Transient transfection
into mouse Ltk cells
results in the robust expression of inactivating
K+-selective currents. The whole
cell currents elicited by a family of depolarizing voltage steps are
shown in Fig. 4,
A and
B. The current activates rapidly and
decays to a steady-state level within 400 ms. The current-voltage
relationships for each of the splice variants demonstrate that the
currents activate over the same voltage range, between 40 and
30 mV, and monotonically increase in size at more positive
voltages (Fig. 4C). The time course
of inactivation was determined by fitting the decay of the whole cell
current to a single exponential. The rate of inactivation was voltage
dependent at less positive voltages and essentially voltage independent
at test potentials above +10 mV (Fig.
4D). The long and short splice
variants do not differ in either their voltage dependence or
inactivation kinetics in the basal state.
|
120
to +60 mV after a test pulse to +60 mV was determined over a range of
external K+ concentration
([K+]o).
The reversal potential as a function of
[K+]o
is plotted in Fig. 4E. The dotted line
is the reversal potential predicted by the Nernst equation. The solid
line is the best fit of the data to the Goldman-Hodgkin-Katz voltage
equation (19) with a relative permeability of
Na+ to
K+ of 0.01.
Sensitivity to block by 4-aminopyridine (4-AP) is a hallmark of the
Ca2+-independent
Ito (9, 19). The
short and long splice variants of hKv4.3 exhibit a similar sensitivity
to 4-AP; currents through both splice variants are ~50% blocked by 1 mM 4-AP. The dose-response curves are shown in Fig.
4F. The
IC50 values determined by fitting the data to a single binding site function are 1.3 ± 0.3 and 1.4 ± 0.3 mM for the short and long splice variants, respectively [P = not significant
(NS)].
The steady-state availability was determined using 1-s conditioning
pulses to voltages between 100 and +20 mV in increments of 10 mV.
The currents are half-maximally available at 42.6 ± 5.1 and
43.1 ± 6.4 mV with slope factors of 6.3 ± 1.3 and 6.3 ± 0.6 mV for the short and long splice variants, respectively (P = NS; Fig.
5A).
|
100
mV. The recovery curves were fit by single exponentials with time
constants of 73.4 ± 32 and 75.1 ± 23 ms for the short and long
splice variants, respectively (P = NS;
Fig. 5B). The current is completely
recovered by 300 ms at room temperature.
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DISCUSSION |
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Top
Abstract
Introduction
Methods
Results
Discussion
References
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The transient outward K+ current
is a critical component of the normal action potential of atrial and
ventricular myocytes of most species. In human ventricle, Kv4.3 is the
gene that encodes the -subunit of the
K+ channel that underlies
Ito (12). The
density of Ito is
reduced in failing human ventricles (25), and this may be caused by altered transcription (20). We describe the cloning, genomic structure,
and chromosomal localization of hKv4.3. Two alternatively spliced cDNAs
are present in the ventricle; the long splice variant has a 19-amino
acid insert that contains a consensus PKC phosphorylation site. Similar
splice variants have been described in the rat ventricle (27, 36). Each
of the hKv4.3 splice variants encode
K+-selective currents similar to
native Ito when
expressed in mammalian tissue culture cells.
The hKv4.3 cDNAs are 8.5-9.0 kb with a large 5'- and smaller 3'-untranslated region. The hKv4.3 gene spans at least 40 kb of the genome. Analysis of the genomic structure of hKv4.3 reveals the presence of five exons in the coding region; one splice site occurs at the K+ channel signature sequence. Another pair of alternatively utilized exons determines the hKv4.3 variant. The gene is located on the short arm of chromosome 1 at 1p13.3. Notably, the human K+ channel Shaker homolog KCNA3 (Kv1.3) (15) and the Shab homolog KCNC4 (Kv3.4) (33) have been localized to human chromosome 1p21, the Giemsa-positive band just distal to p13.3.
The voltage dependence of the hKv4.3 splice variants expressed in
Ltk fibroblasts resembles
that of native
Ito in human
ventricular myocytes recorded under similar conditions (1, 6, 25, 26,
40, 41). The activation voltage range is similar in both native
currents and expressed channels; in both cases, activation occurs at
test potentials greater than 40 mV and the half-maximal activation voltage is approximately +10 mV (1, 6, 25, 26, 40, 41).
Steady-state inactivation characteristics of the expressed hKv4.3
channels are similar to native cardiac
Ito (25, 26, 40,
41).
Regional differences in the biophysical characteristics of the cardiac Ito have been described. In cells isolated from the subepicardium or mid left ventricular wall, Ito recovers rapidly from inactivation (25, 26, 40, 41). In contrast, Ito from endocardium recovers from inactivation slowly (26, 41). Recovery from inactivation is no different in the two hKv4.3 splice variants; thus it is unlikely that differences in the expression of the splice variants mediates the regional differences in recovery in the basal state (Fig. 5B). It is conceivable that phosphorylation could differentially modulate the rate of recovery of the hKv4.3 splice variants.
Heteromultimerization of K+ channel subunits can significantly change the electrophysiological features of the resulting current (e.g., see Ref. 30). Regional differences in recovery from inactivation of Ito are not likely to be the result of heteromultimerization of hKv4.3 with hKv4.2 because heterologously expressed hKv4.2 also recovers rapidly (data not shown) and is not expressed in the human ventricle (Fig. 1D). It may be that a more slowly recovering transient K+ channel such as hKv1.4 underlies human endocardial Ito (7); however, it is uncertain whether hKv1.4 is expressed in adult human cardiomyocytes. Other explanations for the slowly recovering subendocardial Ito include differences in posttranslational modification or differences in regional expression of ancillary subunits or other modifying proteins.
The addition of a PKC phosphorylation site in the long splice variant
raises the possibility of isoform-specific regulation of hKv4.3 by
phosphorylation. Stimulation of -adrenergic receptors enhances
cardiac contractility largely because of prolongation of the action
potential duration that results from reduction of repolarizing
K+ currents (13). The transient
outward current is modulated by second messenger systems. Prominently,
stimulation of
1-adrenoreceptors has been
shown to reduce
Ito current
density (2, 8). In some preparations, activation of PKC mimics the
effect of 1-adrenergic stimulation (2), whereas in others, different second messenger systems
appear to mediate the effect of
1-stimulation (8). The role of
PKC in 1-adrenergic regulation
of the human cardiac Ito has not been
defined; however, in cultured human atrial myocytes, Ito is inhibited
by the PKC inhibitor staurosporine (18).
Transient outward current expression in the mammalian heart is dynamic. For example, the density and, in some cases, the kinetics of Ito change with development (22, 39, 43) and exposure to thyroid hormone (35, 42) in the rat ventricle. The changes in the action potential and outward current profile have suggested to some investigators an isoform switch from Kv1.4 to Kv4 channels during development and treatment with triiodothyronine (42). In the human ventricle there is also a reduction in the current density of Ito that accompanies heart failure (6, 25, 41). The molecular basis of this change in current density is uncertain, but we have observed a reduction in the steady-state level of hKv4.3 mRNA that correlates with current density in the same hearts (20). As a first step to try and understand the basis of changes in the expression of human Ito, we describe the cloning, genomic structure, and functional expression of the splice variants of hKv4.3. Understanding the regulation of expression of this gene may have important implications for changes in expression of this and other ion channels and transport proteins in human heart failure.
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ACKNOWLEDGEMENTS |
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We thank Drs. Jeffrey Balser and Brian O'Rourke for critical review of the manuscript, Dr. Maggie Zheng and Colleen McCormack for excellent technical support, and Dr. Clara Moore for help with Fig. 3. We gratefully acknowledge Drs. Stefan Kääb, Michael Näbauer (University of Munich), Dirk Beucklemann (University of Cologne), and our cardiothoracic surgical colleagues at the Johns Hopkins Hospital for access to human ventricular tissue.
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FOOTNOTES |
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The hKv4.3 splice variant sequences have been submitted to GenBank with the accession numbers AF048712 and AF048713.
This work was supported by National Heart, Lung, and Blood Institute Grant P50 HL-52768, American Heart Association Fellowship Grant (to W. Kong), and National Heart, Lung, and Blood Institute Training Grant HL-07227 (to S. Po).
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. §1734 solely to indicate this fact.
Address for reprint requests: G. F. Tomaselli, Dept. of Medicine, Div. of Cardiology, Johns Hopkins School of Medicine, Ross 844, 720 N. Rutland Ave., Baltimore, MD 21205.
Received 4 June 1998; accepted in final form 19 August 1998.
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REFERENCES |
|---|
|
Top
Abstract
Introduction
Methods
Results
Discussion
References
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1.
Amos, G. J.,
E. Wettwer,
F. Metzger,
Q. Li,
H. M. Himmel,
and
U. Ravens.
Differences between outward currents of human atrial and subepicardial ventricular myocytes.
J. Physiol. (Lond.)
491:
31-50,
1996
2.
Apkon, M.,
and
J. M. Nerbonne.
Alpha 1-adrenergic agonists selectively suppress voltage-dependent K+ current in rat ventricular myocytes.
Proc. Natl. Acad. Sci. USA
85:
8756-8760,
1988
3.
Barry, D. M.,
and
J. M. Nerbonne.
Myocardial potassium channels: electrophysiological and molecular diversity.
Annu. Rev. Physiol.
58:
363-394,
1996[Medline].
4.
Barry, P. H.
JPCalc, a software package for calculating liquid junction potential corrections in patch-clamp, intracellular, epithelial, and bilayer measurements and for correcting junction potential measurements.
J. Neurosci. Methods
5:
107-116,
1994.
5.
Berger, F.,
U. Borchard,
and
D. Hafner.
Effects of (+)- and (+/)-sotalol on repolarizing outward currents and pacemaker current in sheep cardiac Purkinje fibres.
Naunyn Schmiedebergs Arch. Pharmacol.
340:
696-704,
1989[Medline].
6.
Beuckelmann, D. J.,
M. Näbauer,
and
E. Erdmann.
Alterations of K+ currents in isolated human ventricular myocytes from patients with terminal heart failure.
Circ. Res.
73:
379-385,
1993
7.
Brahmajothi, M. V.,
M. J. Morales,
D. L. Campbell,
R. L. Rassmusson,
S. Wang,
S. Liu,
J. S. Trimmer,
and
H. C. Strauss.
Distribution of fast-inactivating K+ channel subunits in ferret epicardial and endocardial left ventricular myocytes (Abstract).
Circulation
96:
I-498,
1997.
8.
Braun, A. P.,
D. Fedida,
R. B. Clark,
and
W. R. Giles.
Intracellular mechanisms for alpha 1-adrenergic regulation of the transient outward current in rabbit atrial myocytes.
J. Physiol. (Lond.)
431:
689-712,
1990
9.
Coraboeuf, E.,
and
E. Carmeliet.
Existence of two transient outward currents in sheep cardiac Purkinje fibers.
Pflügers Arch.
392:
352-359,
1982[Medline].
10.
Crumb, W. J. J.,
J. D. Pigott,
and
C. W. Clarkson.
Comparison of Ito in young and adult human atrial myocytes: evidence for developmental changes.
Am. J. Physiol.
268 (Heart Circ. Physiol. 37):
H1335-H1342,
1995
11.
Dixon, J. E.,
and
D. McKinnon.
Quantitative analysis of potassium channel mRNA expression in atrial and ventricular muscle of rats.
Circ. Res.
75:
252-260,
1994
12.
Dixon, J. E.,
W. Shi,
H. S. Wang,
C. McDonald,
H. Yu,
R. S. Wymore,
I. S. Cohen,
and
D. McKinnon.
Role of the Kv4.3 K+ channel in ventricular muscle. A molecular correlate for the transient outward current.
Circ. Res.
79:
659-668,
1996
13.
Fedida, D.,
and
R. A. Bouchard.
Mechanisms for the positive inotropic effect of alpha 1-adrenoceptor stimulation in rat cardiac myocytes.
Circ. Res.
71:
673-688,
1992
14.
Firek, L.,
and
W. R. Giles.
Outward currents underlying repolarization in human atrial myocytes.
Cardiovasc. Res.
30:
31-38,
1995[Medline].
15.
Folander, K.,
J. Douglass,
and
R. Swanson.
Confirmation of the assignment of the gene encoding Kv1.3, a voltage-gated potassium channel (KCNA3) to the proximal short arm of chromosome 1.
Genomics
23:
295-296,
1994[Medline].
16.
Gidh-Jain, M.,
B. Huang,
P. Jain,
and
N. el-Sherif.
Differential expression of voltage-gated K+ channel genes in left ventricular remodeled myocardium after experimental myocardial infarction.
Circ. Res.
79:
669-675,
1996
17.
Gross, G. J.,
R. P. Burke,
and
N. A. Castle.
Characterisation of transient outward current in young human atrial myocytes.
Cardiovasc. Res.
29:
112-117,
1995[Medline].
18.
Hatem, S. N.,
A. Benardeau,
C. Rucker-Martin,
J. L. Samuel,
E. Coraboeuf,
and
J. J. Mercadier.
Differential regulation of voltage-activated potassium currents in cultured human atrial myocytes.
Am. J. Physiol.
271 (Heart Circ. Physiol. 40):
H1609-H1619,
1996
19.
Hille, B.
Ionic Channels of Excitable Membranes. Sunderland, MA: Sinauer, 1992.
20.
Kääb, S., J. Dixon, J. Duc, M. D. Ashen, M. Näbauer, D. J. Beuckelmann, G. Steinbeck, D. McKinnon,
and G. F. Tomaselli. Molecular basis of transient
outward current down-regulation in human heart failure.
Circulation. In press.
21.
Kääb, S.,
H. B. Nuss,
N. Chiamvimonvat,
B. O'Rourke,
P. H. Pak,
D. A. Kass,
E. Marban,
and
G. F. Tomaselli.
Ionic mechanism of action potential prolongation in ventricular myocytes from dogs with pacing-induced heart failure.
Circ. Res.
78:
262-273,
1996
22.
Kilborn, M. J.,
and
D. Fedida.
A study of the developmental changes in outward currents of rat ventricular myocytes.
J. Physiol. (Lond.)
430:
37-60,
1990
23.
Le Grand, B. L.,
S. Hatem,
E. Deroubaix,
J. P. Couetil,
and
E. Coraboeuf.
Depressed transient outward and calcium currents in dilated human atria.
Cardiovasc. Res.
28:
548-556,
1994[Medline].
24.
Mansourati, J.,
and
B. Le Grand.
Transient outward current in young and adult diseased human atria.
Am. J. Physiol.
265 (Heart Circ. Physiol. 34):
H1466-H1470,
1993
25.
Näbauer, M.,
D. J. Beuckelmann,
and
E. Erdmann.
Characteristics of transient outward current in human ventricular myocytes from patients with terminal heart failure.
Circ. Res.
73:
386-394,
1993
26.
Näbauer, M.,
D. J. Beuckelmann,
P. Überfuhr,
and
G. Steinbeck.
Regional differences in current density and rate-dependent properties of the transient outward current in subepicardial and subendocardial myocytes of human left ventricle.
Circulation
93:
168-177,
1996
27.
Ohya, S.,
M. Tanaka,
T. Oku,
Y. Asai,
M. Watanabe,
W. Giles,
and
Y. Imaizumi.
Molecular cloning and tissue distribution of an alternatively spliced variant of an A-type K channel alpha-subunit, Kv4.3 in the rat.
FEBS Lett.
420:
47-53,
1997[Medline].
28.
Pearson, R. B.,
and
B. E. Kemp.
Protein kinase phosphorylation site sequences and consensus specificity motifs: tabulations.
In: Methods in Enzymology. Protein Phosphorylation. Part A, edited by T. Hunter,
and B. M. Sefton. San Diego, CA: Academic, 1991, vol. 200, p. 62-81.
29.
Pinkel, D.,
T. Straume,
and
J. W. Gray.
Cytogenetic analysis using quantitative, high sensitivity, fluorescence hybridization.
Proc. Natl. Acad. Sci. USA
83:
2934-2938,
1986
30.
Po, S.,
S. Roberds,
D. J. Snyders,
M. M. Tamkun,
and
P. B. Bennett.
Heteromultimeric assembly of human potassium channels. Molecular basis of a transient outward current?
Circ. Res.
72:
1326-1336,
1993
31.
Qi, A.,
J. A. Yeung-Lai-Wah,
J. Xiao,
and
C. R. Kerr.
Regional differences in rabbit atrial repolarization: importance of transient outward current.
Am. J. Physiol.
266 (Heart Circ. Physiol. 35):
H643-H649,
1994
32.
Qin, D.,
Z. H. Zhang,
E. B. Caref,
M. Boutjdir,
P. Jain,
and
N. el-Sherif.
Cellular and ionic basis of arrhythmias in postinfarction remodeled ventricular myocardium.
Circ. Res.
79:
461-473,
1996
33.
Rudy, B.,
K. Sen,
E. Vega-Saenz de Meiera,
D. Lau,
T. Ried,
and
D. C. Ward.
Cloning of a human cDNA expressing a high voltage-activating TEA-sensitive, type-A K+ channel which maps to chromosome 1 band p21.
J. Neurosci. Res.
29:
401-412,
1991[Medline].
34.
Sambrook, J.,
E. F. Fritsch,
and
T. Manniatis.
Molecular Cloning: A Laboratory Manual. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press, 1989.
35.
Shimoni, Y.,
C. Fiset,
R. B. Clark,
J. E. Dixon,
D. McKinnon,
and
W. R. Giles.
Thyroid hormone regulates postnatal expression of transient K+ channel isoforms in rat ventricle.
J. Physiol. (Lond.)
500:
65-73,
1997
36.
Takimoto, K.,
D. Li,
K. M. Hershman,
P. Li,
E. K. Jackson,
and
E. S. Levitan.
Decreased expression of Kv4.2 and novel Kv4.3 K+ channel subunit mRNAs in ventricles of renovascular hypertensive rats.
Circ. Res.
81:
533-539,
1997
37.
Thuringer, D.,
A. Coulombe,
E. Deroubaix,
E. Coraboeuf,
and
J. J. Mercadier.
Depressed transient outward current density in ventricular myocytes from cardiomyopathic Syrian hamsters of different ages.
J. Mol. Cell. Cardiol.
28:
387-401,
1996[Medline].
38.
Van Wagoner, D. R.,
A. L. Pond,
P. M. McCarthy,
J. S. Trimmer,
and
J. M. Nerbonne.
Outward K+ current densities and Kv1.5 expression are reduced in chronic human atrial fibrillation.
Circ. Res.
80:
772-781,
1997
39.
Wahler, G. M.,
S. J. Dollinger,
J. M. Smith,
and
K. L. Flemal.
Time course of postnatal changes in rat heart action potential and in transient outward current is different.
Am. J. Physiol.
267 (Heart Circ. Physiol. 36):
H1157-H1166,
1994
40.
Wettwer, E.,
G. Amos,
J. Gath,
H. R. Zerkowski,
J. C. Reidemeister,
and
U. Ravens.
Transient outward current in human and rat ventricular myocytes.
Cardiovasc. Res.
27:
1662-1669,
1993
41.
Wettwer, E.,
G. J. Amos,
H. Posival,
and
U. Ravens.
Transient outward current in human ventricular myocytes of subepicardial and subendocardial origin.
Circ. Res.
75:
473-482,
1994
42.
Wickenden, A. D.,
R. Kaprielian,
T. G. Parker,
O. T. Jones,
and
P. H. Backx.
Effects of development and thyroid hormone on K+ currents and K+ channel gene expression in rat ventricle.
J. Physiol. (Lond.)
504:
271-286,
1997
43.
Xu, H.,
J. E. Dixon,
D. M. Barry,
J. S. Trimmer,
J. P. Merlie,
D. McKinnon,
and
J. M. Nerbonne.
Developmental analysis reveals mismatches in the expression of K+ channel alpha subunits and voltage-gated K+ channel currents in rat ventricular myocytes.
J. Gen. Physiol.
108:
405-419,
1996
44.
Yamagishi, T.,
M. Janecki,
E. Marban,
and
G. F. Tomaselli.
Topology of the P segments in the sodium channel pore revealed by cysteine mutagenesis.
Biophys. J.
73:
195-204,
1997[Medline].
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and solid line;
hKv4.3-2, 
and dashed line) are similar with currents activating and
increasing monotonically at voltages greater than 
h) is determined by a single
exponential fit to decaying phase of whole cell current.
