Does the motor nerve impulse evoke 'non-quantal' transmitter release?
Previous experiments have indicated that there is a continuous leakage of acetylcholine (ACh) from resting motor nerve terminals which can produce a small depolarization in anti-esterase treated endplates (Katz & Miledi 1977; Vyskocil & Illés 1978). This leakage might be expected to be intensified during the presynaptic action potential and also lead to a very small non-quantal endplate response. This hypothesis was examined, in frog and mammalian endplates, by stimulating the motor nerve in a calcium-deprived medium and recording the summated average response to several hundred stimuli. The result was completely negative; no trace of a non-quantal endplate potential was ever observed, with the limit of detection being always less than 10 microV, and sometimes as low as 2 microV. These experiments suggest that the leakage of ACh either does not originate predominantly from the synaptic region of the axon terminal, or that it occurs by a mechanism that is not directly influenced by the membrane potential.
D000109:Acetylcholine / Q000378:metabolism*; D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D008564:Membrane Potentials; D051379:Mice; D009045:Motor Endplate / Q000187:drug effects / Q000502:physiology*; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D009469:Neuromuscular Junction / Q000502:physiology*; D011898:Ranidae; D051381:Rats; D013569:Synapses / Q000502:physiology
D000109:Acetylcholine; D002118:Calcium