Glavinović M I
Department of Anaesthesia Research and Physiology, McGill University, Montreal, Canada.
Neuroscience. 1988 Feb;24(2):687-94. doi: 10.1016/0306-4522(88)90361-2.
How much the cleft K+ concentration ([K+]c) is changed by a step-like shift of an endplate membrane potential was estimated from the resulting acceleration of frequency of miniature endplate currents and the dependence of miniature endplate currents frequency on bath K+ concentration ([K+]0). The absolute change in [K+]c is generally constant, and hence relatively more pronounced the lower the [K+]0. It is estimated that in physiological solution [( K+]0 = 2 mM), [K+]c is at least tripled (approximately 6 mM) if the muscle membrane is held at the reversal potential (Vr) for the endplate currents. The same step-like shift in muscle membrane potential leads to an almost instantaneous change of endplate current amplitudes or of their time constants of decay. This indicates that cleft K+ changes have no effect on the voltage dependence of amplitudes and decay phases of endplate currents (and hence on Vr also). The lack of postsynaptic effect of change in [K+]0 from 0.1 to 10 mM and only small influence of [K+]0 changes on nerve-evoked quantal release explain these findings.
