Gating kinetics of ATP-sensitive single potassium channels in myocardial cells depends on electromotive force

ATP-sensitive single-channel potassium currents were studied in the membrane of rat ventricular myocytes. With an internal K⁺ concentration of [K⁺]_i=140 mM, the outwardly directed currents saturated at 1.8 pA in the region of positive potentials independently of the external K⁺ concentration [K⁺]_o, whereas an increase in [K⁺]_i of up to 300 mM caused a positive shift in the region of current saturation (from +40 mV to +100 mV) and an increase in the level of the saturation up to 4 pA. The openings of the channels appeared in bursts. Gating kinetics within the bursts were investigated. It was shown that the channel mean open (_o) and closed (_c) times during a burst depended primarily on the electromotive force (V-V_k) for potassium ions. For different [K⁺]_o, _o was maximal and _c was minimal in the region of reversal potentials (V_rev); _o decreased and _c increased gradually with deviation ofV fromV_rev. Therefore we conclude that the gating properties of the ATP-sensitive K channels depend on the ion flux parameters.