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The Journal of General Physiology, Vol 61, 747-766, Copyright © 1973 by The Rockefeller University Press

ARTICLE

Differential Responses of Crab Neuromuscular Synapses to Cesium Ion

H. L. Atwood 1 and Fred Lang 1

1 From the Department of Zoology, University of Toronto, Toronto, Ontario, Canada.

Dr. Lang's present address is Department of Biology, Boston University, Boston, Massachusetts 02215.

Excitatory postsynaptic potentials (EPSP's) generated in crab muscle fibers by a single motor axon, differ in amplitude and facilitation. Some EPSP's are large at low frequencies of stimulation and show little facilitation; others are smaller and show pronounced facilitation. When K+ is replaced by Cs+ in the physiological solution, all EPSP's increase in amplitude, but small EPSP's increase proportionately more than large ones. Quantal content of transmission, determined by external recording at single synaptic regions, undergoes a much larger increase at facilitating synapses. The increase in quantal content of transmission is attributable to prolongation of the nerve terminal action potential in Cs+. After 1–2 h of Cs+ treatment, defacilitation of synaptic potentials occurs at synapses which initially showed facilitation. This indicates that Cs+ treatment drastically increases the fraction of the "immediately available" transmitter store released by each nerve impulse, especially at terminals with facilitating synapses. It is proposed that facilitating synapses normally release less of the "immediately available" store of transmitter than poorly facilitating synapses. Possible reasons for this difference in performance are discussed.

Submitted on November 20, 1972


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A. G. Millar, H. Bradacs, M. P. Charlton, and H. L. Atwood
Inverse Relationship between Release Probability and Readily Releasable Vesicles in Depressing and Facilitating Synapses
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[Abstract] [Full Text] [PDF]


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