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Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata 1900, Argentina
Angiotensin II (ANG II) evokes positive inotropic
responses in various species. However, the effects of this peptide on
L-type Ca2+ currents (ICa) are still
controversial. We report in this study that the effects of ANG II on
ICa differ depending on the mode of patch-clamp
technique used, standard whole cell (WC) or perforated patch (PP). No
significant effects of ANG II (0.5 µM) were observed when WC in cells
dialyzed with high EGTA was used. However, when the intracellular
milieu was preserved using PP, ANG II induced a significant 77 ± 6% increase in ICa (
2.2 ± 0.3 in
control and
3.9 ± 0.6 pA/pF in ANG II, n = 8, P < 0.05). When WC was used in cells dialyzed with low
Ca2+ buffer capacity (EGTA 0.1 mM), ANG II was able to
induce an increase in ICa (
3.5 ± 0.3 in
control vs.
4.8 ± 0.4 pA/pF in ANG II, n = 13, P < 0.05). This increase was prevented when the cells were also dialyzed with the protein kinase C (PKC) inhibitor
chelerythrine (50 µM) or calphostin C (1 µM). The above results
allow us to conclude that strong intracellular Ca2+
buffering prevents the physiological actions of ANG II on cardiac ICa, which are also dependent on activation of PKC.
cardiac myocytes; perforated patch
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