Frog muscle endplates were explored with an extracellular microelectrode. An intracellular microelectrode nearby simultaneously monitored invasion of the endplate by a spike directly evoked by a third microelectrode placed away from the endplate in the same fiber. External positivities were seen only at sites generating miniature endplate potentials. The external positivity reached a maximum prior to the internally recorded potential and was followed by a small late negativity. Small movements away from active synaptic sites resulted in positive-negative-positive potential sequences characteristic of activity and propagation. Since the external potential is a function of membrane current, the absence of negativity associated with the rising phase of the spike indicates the absence of inward current at synaptic sites. Thus, the synaptic membrane appears not to be excited by a depolarization of the magnitude of an action potential. In an Appendix it is shown that the late negativity and earlier maximum of the external potential can be accounted for by capacitative current through passive membrane.
Article| January 01 1963
Electrical Inexcitability of the Frog Neuromuscular Synapse
From the Department of Neurology, Columbia University, New York.
The author's present address is the Institute of Psychiatric Research, Indiana University Medical School, Indianapolis
Received: May 21 1962
Online Issn: 1540-7748
Print Issn: 0022-1295
Copyright ©, 1963, by The Rockefeller Institute Press
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Robert Werman; Electrical Inexcitability of the Frog Neuromuscular Synapse . J Gen Physiol 1 January 1963; 46 (3): 517–531. doi: https://doi.org/10.1085/jgp.46.3.517
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