Modulation of ATP-sensitive potassium channels by cGMP-dependent protein kinase in rabbit ventricular myocytes

This investigation used a patch clamp technique to test the hypothesis that protein kinase G (PKG) contributes to the phosphorylation and activation o f ATP-sensitive K+ (K-ATP) channels in rabbit ventricular myocytes. Nitric oxide donors and PKG; activators facilitated pinacidil-induced K-ATP channe l activities in a concentration-dependent manner, and a selective PKG inhib itor abrogated these effects. In contrast, neither a selective protein kina se A (PKA) activator nor inhibitor had any effect on K-ATP channels at conc entrations up to 100 and 10 muM, respectively. Exogenous PKG, in the presen ce of both cGMP and ATP, increased channel activity, while the catalytic su bunit of PKA had no effect. PKG activity was prevented by heat inactivation , replacing ATP with adenosine 5 ' -O-(thiotriphosphate) (a nonhydrolyzable analog of ATP), removing Mg2+ from the internal solution, applying a PKG i nhibitor, or by adding exogenous protein phosphatase 2A The effects of cGMP analogs and PKG were observed under conditions in which PKA was repressed by a selective PKA inhibitor. The results suggest that K-ATP channels are r egulated by a PKG-signaling pathway that acts via PKG-dependent phosphoryla tion. This mechanism may, at least in part, contribute to a signaling pathw ay that induces ischemic preconditioning in rabbit ventricular myocytes.