Functional modulation of sarcolemmal K channels by atrial natriuretic peptide-elicited intracellular signaling in adult rabbit ventricular cardiomyocytes.

ATP-sensitive potassium (K) channels couple cell metabolic status to membrane excitability and are crucial for stress adaptation and cytoprotection in the heart. Atrial natriuretic peptide (ANP), a cardiac peptide important for cardiovascular homeostasis, also exhibits cytoprotective features including protection against myocardial ischemia-reperfusion injuries. However, how ANP modulates cardiac K channels is largely unknown. In the present study we sought to address this issue by investigating the role of ANP signaling in functional modulation of sarcolemmal K (sarcK) channels in ventricular myocytes freshly isolated from adult rabbit hearts. Single-channel recordings were performed in combination with pharmacological approaches in the cell-attached patch configuration. Bath application of ANP markedly potentiated sarcK channel activities induced by metabolic inhibition with sodium azide, whereas the K-stimulating effect of ANP was abrogated by selective inhibition of the natriuretic peptide receptor type A (NPR-A), cGMP-dependent protein kinase (PKG), reactive oxygen species (ROS), extracellular signal-regulated protein kinase (ERK)1/2, Ca/calmodulin-dependent protein kinase II (CaMKII), or the ryanodine receptor (RyR). Blockade of RyRs also nullified hydrogen peroxide (HO)-induced stimulation of sarcK channels in intact cells. Furthermore, single-channel kinetic analyses revealed that ANP enhanced the function of ventricular sarcK channels through destabilizing the long closures and facilitating the opening transitions, without affecting the single-channel conductance. In conclusion, here we report that ANP positively modulates the activity of ventricular sarcK channels via an intracellular signaling mechanism consisting of NPR-A, PKG, ROS, ERK1/2, CaMKII, and RyR2. This novel mechanism may regulate cardiac excitability and contribute to cytoprotection, in part, by opening myocardial K channels.