Facilitation and impulse propagation failure at the frog neuromuscular junction
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Exposure of frog neuromuscular junctions to solutions which contain a high concentration of calcium ions produces failure of neuromuscular transmission. This failure of transmission is abrupt and usually complete. However, some terminals produce small end-plate potentials even after the exposure to a high concentration of calcium ions.
A second stimulus to the nerve can overcome the block of neuromuscular transmission if the interval between the stimuli is less than a critical value. The size of the end-plate potential is almost independent of the interstimulus interval if the latter is less than the critical value but more than the refractory period. The depth of this neuromuscular block is affected by temperature, potassium ions, osmotic pressure, cobalt ions, and prior high frequency stimulation of the nerve.
Neuromuscular transmission failure coincides with failure of the nerve action potential (NAP) to invade the terminal. Prior to propagation failure, the second extracellularly recorded NAP is smaller, but is conducted faster than the first NAP.
The relevance of these findings to the facilitation of transmitter release seen in solutions of normal divalent ion content is discussed.
Key wordsFacilitation Calcium Propagation Conduction velocity
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- Barton SB (1977) Facilitation and delayed release of transmitter at the frog neuromuscular junction. D Phil Thesis, University of OxfordGoogle Scholar
- Braun M, Schmidt RF (1966) Potential changes recorded from the frog motor nerve terminal during its activation. Pflügers Arch 287:56–80Google Scholar
- Braun M, Schmidt RF, Zimmerman M (1966) Facilitation at the frog neuromuscular junction during and after repetitive stimulation. Pflügers Arch 287:41–55Google Scholar
- Dodge FA, Miledi R, Rahamimoff R (1969) Strontium and quantal release of transmitter at the neuromuscular junction. J Physiol 200:267–283Google Scholar
- Grossman Y, Parnas I, Spira ME (1979) Differential conduction block in branches of a bifureating axon. J Physiol 295:283–305Google Scholar
- Hagiwara S, Tasaki I (1958) A study of the mechanism of impulse transmission across the giant synapse of the squid. J Physiol 143:114–137Google Scholar
- Huxley AF (1959) Ion movements during nerve activity. Ann NY Acad Sci 81:221–246Google Scholar
- Katz B, Miledi R (1965) Propagation of electric activity in motor nerve terminals. Proc Roy Soc B 161:453–482Google Scholar
- Katz B, Miledi R (1968) The role of calcium in neuromuscular facilitation. J Physiol 195:481–492Google Scholar
- Lloyd DPC (1949) Post-tetanic potentiation of response in monosynaptic reflex pathways of the spinal cord. J Gen Physiol 33:147–170Google Scholar
- Magleby (1973) The effect of repetitive stimulation on facilitation of transmitter release at the frog neuromuscular junction. J Physiol 234:327–352Google Scholar
- Mallart A, Martin AR (1967) An analysis of facilitation of transmitter release at the neuromuscular junction of the frog. J Physiol 193:679–694Google Scholar
- Rahamimoff R, Yaari Y (1973) Delayed release of transmitter at the frog neuromuscular junction. J Physiol 288:241–257Google Scholar
- Smith D (1980) Mechanisms of action potential propagation failure at sites of axon branching in the crayfish. J Physiol 301:243–259Google Scholar
- Stinnakre J, Tauc L (1973) Calcium influx in activeAplysia neurons detected by injected Aequorin. Nature 242:113–115Google Scholar
- Vyskocil F, Magazanik LG (1977) Dual end-plate potentials at the single neuromuscular junction of the adult frog. Pflügers Arch 368:271–273Google Scholar
- Wernig A, Carmody JJ (1977) Deviations from simple binomial predictions of transmitter release at frog neuromuscular junction. Neuro Sci Lett 7:277–280Google Scholar
- Zucker RS (1974) Excitability changes in crayfish motor neurone terminals. J Physiol 241:111–126Google Scholar