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

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 epsilon PKC, epsilon V1-7, to assess the role of epsilon PKC in the modulation of L-type Ca2+ current (I-Ca,I- L). Whole cell I-Ca,I- L was recorded using patch-clamp technique from rat ventricular myocytes. Intracellular application of epsilon V1-7 (0.1 muM) resulted in a significant inhibition of I-Ca,I- L by 27.9 +/- 2.2% (P < 0.01, n = 8) in a voltage-independent manner. The inhibitory effect of <epsilon>V1-7 on I-Ca,I- L was completely prevented by the peptide inhibitor of epsilon PKC, epsilon V1-2 [5.2 +/- 1.7%, not significant (NS), n = 5] but not by the peptide inhibitors of cPKC, alpha C2-4 (31.3 +/- 2.9%, P < 0.01, n = 6) or <beta>C2- 2 plus beta C2-4 (26.1 +/- 2.9%, P < 0.01, n = 5). In addition, the use of a general inhibitor (GF-109203X, 10 <mu>M) of the catalytic activity of PKC also prevented the inhibitory effect of epsilon V1-7 on I-Ca,I- L (7.5 +/- 2.1%, NS, n = 6). In conclusion, we show that selective activation of epsilon PKC inhibits the L-type Ca channel in the heart.