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

Investigation of the role of individual protein kinase C (PKC) isozymes in the regulation of Na+ channels has been largely limited by the lack of isozyme-selective modulators. Here we used a novel peptide-specific activator (epsilon V1-7) of epsilon PKC and other peptide isozyme-specific inhibitors in addition to the general PKC activator phorbol 12-myristate 13-acetate (PMA) to dissect the role of individual PKCs in the regulation of the human cardiac Na+ channel hH1, heterologously expressed in Xenopus oocytes. Peptides were injected individually or in combination into the oocyte. Whole cell Na+ current (I-Na) was recorded using two-electrode voltage clamp. epsilon V1-7 (100 nM) and PMA (100 nM) inhibited I-Na by 31 +/- 5% and 44 +/- 8% (at -20 mV), respectively. These effects were not seen with the scrambled peptide for epsilon V1-7 (100 nM) or the PMA analog 4 alpha -phorbol 12,13-didecanoate (100 nM). However, epsilon V1-7- and PMA-induced I-Na inhibition was abolished by epsilon V1-2, a peptide-specific antagonist of epsilon PKC. Furthermore, PMA-induced I-Na inhibition was not altered by 100 nM peptide-specific inhibitors for alpha-, beta-, delta-, or eta PKC. PMA and epsilon V1-7 induced translocation of ePKC from soluble to particulate fraction in Xenopus oocytes. This translocation was antagonized by epsilon V1-2. In native rat ventricular myocytes, PMA and epsilon V1-7 also inhibited I-Na; this inhibition was antagonized by epsilon V1-2. In conclusion, the results provide evidence for selective regulation of cardiac Na+ channels by epsilon PKC isozyme.