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

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Abstract
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 (τo) and closed (τc) times during a burst depended primarily on the electromotive force (V-V k) for potassium ions. For different [K+]o, τo was maximal and τc was minimal in the region of reversal potentials (V rev); τo decreased and τc 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.