Functional Communication Between Cardiac ATPSensitive K+ Channel and Na/K ATPase

K_ATP Channel and Na/K ATPase. Introduction: Functional interaction between K_ATP channel and Na/K ATPase was studied in single guinea pig ventricular myocytes because both membrane molecules are known to he involved in ischemic episodes. Methods and Results: K_ATP channel currents were recorded at 36°C by using whole cell, cell attached, inside-out, and open cell-attached modes of patch clamp techniques on enzymatically isolated ventricular myocytes. In the whole cell mode, ouabain (1 μM) reversibly inhibited the K_ATP currents induced by metabolic stress (ATP-free pipette solution and 1 mM NaCN), but not those activated by cromakalim (100 μM), a K_ATP channel opener. In the cell-attached mode, ouabain concentration dependently inhibited K_ATP, channel opening induced by metabolic suppression (5.5 μM 2-deoxyglucose and 1 mM CN). Half-inhibition concentration for ouabain was 21.0 ± 5.5 nM and the Hill coefficient was 0.8 ± 0.1 (n = 26). However, ouabain did not have an effect on the channel activity induced by cromakalim (100 μM). In the inside-out mode, ouabain applied to the internal side of membrane did not affect the channel. In the open cell-attached mode made by preincubation with streptolysin-0 (0.08 U/mL), the K_ATP channels were not activated by the metabolic inhibitors but were by reducing extracellular ATP concentrations, because subsarcolenimal ATP concentration could he controlled through tiny membrane holes. The channels thus activated were not suppressed by ouabain. Conclusion: The inhibition of Na/K ATPase by ouahain appeared to block the K_ATP channels by accumulating subsarcolemmal ATP caused by a decrease of the transition from ATP to ADP. In the presence of ischemic episodes, the administration of digitalis compounds may affect the opening of K_ATP channels, which is primarily protective against the development of irreversible myocardial damage.