Abstract
ATP-sensitive potassium (K(ATP)) 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(ATP) 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(ATP) (sarcK(ATP)) 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(ATP) channel activities induced by metabolic inhibition with sodium azide, whereas the K(ATP)-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(2+)/calmodulin-dependent protein kinase II (CaMKII), or the ryanodine receptor (RyR). Blockade of RyRs also nullified hydrogen peroxide (H(2)O(2))-induced stimulation of sarcK(ATP) channels in intact cells. Furthermore, single-channel kinetic analyses revealed that ANP enhanced the function of ventricular sarcK(ATP) 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(ATP) 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(ATP) channels.