Evidence for functional role of εPKC isozyme in the regulation of cardiac Ca2+ channels

Abstract

Limited information is available regarding the effects of protein kinase C (PKC) isozyme(s) in the regulation of L-type Ca2+ channels due to lack of isozyme-selective modulators. To dissect the role of individual PKC isozymes in the regulation of cardiac Ca2+ channels, we used the recently developed novel peptide activator of the εPKC, εV1–7, to assess the role of εPKC in the modulation of L-type Ca2+ current ( I Ca,L). Whole cell I Ca,L was recorded using patch-clamp technique from rat ventricular myocytes. Intracellular application of εV1–7 (0.1 μM) resulted in a significant inhibition of I Ca,L by 27.9 ± 2.2% ( P< 0.01, n = 8) in a voltage-independent manner. The inhibitory effect of εV1–7 on I Ca,L was completely prevented by the peptide inhibitor of εPKC, εV1–2 [5.2 ± 1.7%, not significant (NS), n = 5] but not by the peptide inhibitors of cPKC, αC2–4 (31.3 ± 2.9%, P < 0.01, n = 6) or βC2–2 plus βC2–4 (26.1 ± 2.9%, P< 0.01, n = 5). In addition, the use of a general inhibitor (GF-109203X, 10 μM) of the catalytic activity of PKC also prevented the inhibitory effect of εV1–7 on I Ca,L (7.5 ± 2.1%, NS, n= 6). In conclusion, we show that selective activation of εPKC inhibits the L-type Ca channel in the heart.