Phosphorylation is required for alteration of Kv1.5 K+ channel function by the Kvβ1.3 subunit

The Kv1.5 K+ channel is functionally altered by coassembly with the Kv beta 1.3 subunit, which induces fast inactivation and a hyperpolarizing shift in the activation curve. Here we examine kinase regulation of Kv1.5/ Kv beta 1.3 interaction after coexpression in human embryonic kidney 293 cells. The protein kinase C inhibitor calphostin C (3 mu M) removed the fast inactivation (66 +/- 1.9 versus 11 +/- 0.25%, steady state/peak current) and the P-induced hyperpolarizing voltage shift in the activation midpoint (V-1/2) (-21.9 +/- 1.4 versus -4.3 +/- 2.0 mV), Calphostin C had no effect on Kv1.5 alone with respect to inactivation kinetics and V-1/2. Okadaic acid, but not the inactive derivative, blunted both calphostin C effects (V-1/2 = -17.6 +/- 2.2 mV, 38 +/- 1.8% inactivation), consistent with dephosphorylation being required for calphostin C action. Calphostin C also removed the fast inactivation (57 +/- 2.6 versus 16 +/- 0.6%) and the shift in V-1/2 (-22.1 +/- 1.4 versus -2.1 +/- 2.0 mV) conferred onto Kv1.5 by the Kv beta 1.2 subunit, which shares only C terminus sequence identity with Kv beta 1.3, In contrast, modulation of Kv1.5 by the Kv beta 2.1 subunit was unaffected by calphostin C, These data suggest that Kv beta 1.2 and Kv beta 1.3 subunit modification of Kv1.5 inactivation and voltage sensitivity require phosphorylation by protein kinase C or a related kinase.