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PRESYNAPTIC ACTION OF HEMICHOLINIUM AT THE NEUROMUSCULAR JUNCTION,
LUND UNIV (SWEDEN) DEPT OF PHARMACOLOGY
By the use of intracellular electrodes a presynaptic effect of HC-3, hemicholinium no. 3, was shown at the mammalian neuromuscular junction. This effect was demonstrable only when the transmitter was released from the motor nerve terminals at a high rate and consisted of a progressive decline in the size of the miniature end-plate potentials and in the quantal components of the end-plate potentials as the transmitter was released. Releasing the transmitter by nerve stimulation or by increased potassium ion concentration were equally effective in eliciting the phenomenon. Post-synaptic chemosensitivity as measured by bath application of carbachol was the same before and after the quantal units had become small as a consequence of stimulation of transmitter release in the presence of HC-3. The effect is attributed to an inhibition of ACh synthesis by HC-3, the quanta becoming smaller in size as the presynaptic stores of ACh become depleted. It is suggested that the amount of releasable ACh in the motor nerve terminals can be estimated from the sum of all endplate potentials andor miniature end-plate potentials that can be elicited after blockade of ACh synthesis. Author
Pub. in Journal of Physiol. v177 p463-82 1965 (Copies available only to DDC users).
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