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 approximately 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 approximately +40 mV to approximately +100 mV) and an increase in the level of the saturation up to approximately 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 (tau o) and closed (tau c) times during a burst depended primarily on the electromotive force (V-Vk) for potassium ions. For different [K+]o, tau o was maximal and tau c was minimal in the region of reversal potentials (Vrev); tau o decreased and tau c increased gradually with deviation of V from Vrev. Therefore we conclude that the gating properties of the ATP-sensitive K channels depend on the ion flux parameters.

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