Possible involvement of PKC anchoring protein in the modulation of voltage-dependent K^+ channels by endothelin

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The effects of endothelin-1 on the transient outward currents by Kv1.4 and Kv4.3 were examined using Xenopus oocyte expression system. Stimulation of endothelin receptor ET_A coexpressed with Kv channels suppressed K^+ currents. The suppression was in part reversed in the presence of 1 μM staurosporine, which suggest that PKC is involved in the suppression of the K^+ currents by Kv1.4 and Kv4.3. Mutants were made in which serine/threonine residues of putative phosphorylation sites by PKC were changed to alanine to examine the role of protein phosphorylation in the suppression of the K^+ current by endothelin-1. We compared the effects of endothelin-1 on wild and mutant channels and identified the PKC phosphorylation sites in Kv1.4 and Kv4.3. As it is known that ET_A couples G_<q/11> and increases intracellular lP_3/DAG, we examined the possibility that the protein kinase activated by Ca^<2+> may be involved in the suppression of Kv1.4 and Kv4.3 currents. From the mutagenesis experiment it was suggested that in Kv1.4 a putative phosphorylation site of CaMKII is in part involved in the suppression of the K^+ current. A synthetic peptide, which has sequence of 13 amino acid corresponding to the N-terminal region of PKC known to bind PKC anchoring protein (RACKs : receptors for activated C kinases), was injected into the oocytes expressing the Kv channels and ET_A receptor. Endothelin exerted similar suppression of the K^+ currents of Kv1.4 and Kv4.3 in the presence of the peptide. It seems unlikely that PKC anchoring protein may be involved in the suppression of the currents. However, there are possibility that different PKC isozymes could be involved in the endothelin-induced suppression of the currents. Further study is needed to clarify these issues.