Activators of the PKA and PKG pathways attenuate RhoA-mediated suppression of the KDR current in cerebral arteries

This study tested whether activation of protein kinase A (PKA) and G (PKG) pathways would attenuate the ability of RhoA to suppress the delayed rectifier K(+) (K(DR)) current and limit agonist-induced depolarization and constriction. Smooth muscle cells from rat cerebral arteries were enzymatically isolated, and whole cell K(DR) currents were monitored with conventional patch-clamp electrophysiology. The K(DR) current averaged 21.2 +/- 2.3 pA/pF (mean +/- SE) at +40 mV and was potently inhibited by UTP. Current suppression was eliminated in the presence of C3 exoenzyme, confirming that this modulation is dependent on RhoA. Activation of PKA (dibutyryl-cAMP, forskolin) or PKG (dibutyryl-cGMP, sodium nitroprusside, nitric oxide) similarly abolished the ability of UTP to suppress K(DR) and did so without effect on baseline current. Using pressure myography techniques, we stripped cerebral arteries of endothelium and preconstricted them with UTP; these were subsequently shown to hyperpolarize and dilate to both forskolin and sodium nitroprusside. An increase in K(V) channel activity was found to partly underlie these associated changes, as constriction to 4-aminopyridine (K(DR) channel blocker) was greater after PKA or PKG activation. We conclude from our electrophysiological and functional observations that the PKA and PKG pathways attenuate the ability of UTP to depolarize and constrict cerebral arteries in part by minimizing the RhoA-mediated suppression of the K(DR) current.