Changes in the synaptic cleft potassium concentration produced by polarizing currents.
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.
Glavinović
M I
MI
Department of Anaesthesia Research and Physiology, McGill University, Montreal, Canada.
D000818:Animals; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008564:Membrane Potentials; D009045:Motor Endplate / Q000378:metabolism / Q000502:physiology*; D009132:Muscles / Q000378:metabolism / Q000502:physiology*; D009469:Neuromuscular Junction / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D011894:Rana pipiens; D013569:Synapses / Q000378:metabolism / Q000502:physiology*
D011188:Potassium