The ultrarapidly activating delayed rectifier current, IKur, is a main determinant of atrial repolarization in humans. IKur and the underlying ion channel complex Kv1.5/Kvβ1.2 are negatively regulated by protein kinase C. However, the exact mode of action is only incompletely understood. We therefore analyzed isoenzyme-specific regulation of the Kv1.5/Kvβ1.2 ion channel complex by PKC. Cloned ion channel subunits were heterologously expressed in Xenopus oocytes, and measurements were performed using the double-electrode voltage-clamp technique. Activation of PKC with phorbol 12-myristate 13-acetate (PMA) resulted in a strong reduction of Kv1.5/Kvβ1.2 current. This effect could be prevented using the PKC inhibitor staurosporine. Using the bisindolylmaleimide Ro-31-8220 as an inhibitor and ingenol as an activator of the conventional PKC isoforms, we were able to show that the Kv1.5/Kvβ1.2 ion channel complex is mainly regulated by conventional isoforms. Whereas pharmacological inhibition of PKCα with HBDDE did not attenuate the PMA-induced effect, current reduction could be prevented using inhibitors of PKCβ. Here, we show the isoform βII plays a central role in the PKC-dependent regulation of Kv1.5/Kvβ1.2 channels. These results add to the current understanding of isoenzyme-selective regulation of cardiac ion channels by protein kinases.
Ultrarapid delayed rectifier current Kv1.5 Protein kinase C Isoenzymes Repolarization Adrenergic regulation
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This work was supported by grants from DFG Zi1177/1-1, Scho1350/1-1, and Scho1350/2-1 (to E.Z. and E.P.S.). F.F. is supported by the The Hartmut Hoffmann-Berling International Graduate School of Molecular and Cellular Biology (HBIGS). The skillful assistance of Christine Jeckel is gratefully acknowledged. H.A.K. and E.Z. were supported by the DZHK (German Centre for Cardiovascular Research).
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