Phosphorylation is required for alteration of Kv1.5 K+ channel function bythe Kv beta 1.3 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 i n the activation curve. Here we examine kinase regulation of Kv1.5/ Kv beta 1.3 interaction after coexpression in human embryonic kidney 293 cells. Th e protein kinase C inhibitor calphostin C (3 mu M) removed the fast inactiv ation (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 no t the inactive derivative, blunted both calphostin C effects (V-1/2 = -17.6 +/- 2.2 mV, 38 +/- 1.8% inactivation), consistent with dephosphorylation b eing required for calphostin C action. Calphostin C also removed the fast i nactivation (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 subu nit, which shares only C terminus sequence identity with Kv beta 1.3, In co ntrast, modulation of Kv1.5 by the Kv beta 2.1 subunit was unaffected by ca lphostin C, These data suggest that Kv beta 1.2 and Kv beta 1.3 subunit mod ification of Kv1.5 inactivation and voltage sensitivity require phosphoryla tion by protein kinase C or a related kinase.