Internal and external K+ help gate the inward rectifier.
Recent investigations have demonstrated substantial reductions in internal [K+] in cardiac Purkinje fibers during myocardial ischemia (Dresdner, K.P., R.P. Kline, and A.L. Wit. 1987, Circ. Res. 60: 122-132). We investigated the possible role these changes in internal K+ might play in abnormal electrical activity by studying the effects of both internal and external [K+] on the gating of the inward rectifier iK1 in isolated Purkinje myocytes with the whole-cell patch-clamp technique. Increasing external [K+] had similar effects on the inward rectifier in the Purkinje myocyte as it does in other preparations: increasing peak conductance and shifting the activation curve in parallel with the potassium reversal potential. A reduction in pipette [K+] from 145 to 25 mM, however, had several dramatic previously unreported effects. It decreased the rate of activation of iK1 at a given voltage by several-fold, reversed the voltage dependence of recovery from deactivation, so that the deactivation rate decreased with depolarization, and caused a positive shift in the midpoint of the activation curve of iK1 that was severalfold smaller than the associated shift of reversal potential. These changes suggest an important role of internal K+ in gating iK1 and may contribute to changes in the electrical properties of the myocardium that occur during ischemia.
Cohen
I S
IS
Department of Physiology and Biophysics, State University of New York, Stony Brook 11794.
DiFrancesco
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D
Mulrine
N K
NK
Pennefather
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D000818:Animals; D004285:Dogs; D006329:Heart Conduction System / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000494:pharmacology / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology*; D011690:Purkinje Fibers / Q000502:physiology*
D015221:Potassium Channels; D011188:Potassium