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. 1977 Oct;271(3):673–698. doi: 10.1113/jphysiol.1977.sp012020

The effect of calcium ions on the binomial parameters that control acetylcholine release during trains of nerve impulses at amphibian neuromuscular synapses

M R Bennett, C Fisher
PMCID: PMC1353627  PMID: 411920

Abstract

1. A study has been made of the effects of changing the external calcium concentration [Ca]o on the binomial parameters p and n that control the average quantal content (m̄) of the end-plate potential (e.p.p.) during trains of nerve impulses at synapses in amphibian striated muscle.

2. In high external calcium concentrations (0·4 mM ≤ [Ca]o < 1·0 mM) the increase in m̄ of a test impulse following a conditioning impulse at different intervals (< 100 msec) was due to an increase in the number of quanta available for release, n; the increase in m̄ of successive e.p.p.s in a short high frequency train was primarily due to an increase in n.

3. In high external calcium concentrations (1·0 mM ≤ [Ca]o < 10 mM) there was a decrease in m̄ of a test impulse following a short high frequency conditioning train (4-5 impulses, 20-100 Hz) at different intervals (200 msec < 5 sec) and this was due to a decrease in the number of quanta available for release, n; in a long high frequency train (20 impulses, 20-100 Hz) there was an increase in m̄ for the first few successive e.p.p.s followed by a depression of m̄ which eventually reached a steady state and these changes in m̄ were due to changes in n; the higher the frequency the greater was the depression in n during the steady-state period.

4. In high calcium concentrations, the steady-state m̄ reached in the first 20 impulses during continual stimulation at high frequency gave way to a decline in m̄ over several minutes until a new depressed steady-state value of m̄ was reached and this was maintained during the longest periods of stimulation (30 min); this decline in m̄ was primarily due to a decline in the number of quanta available for release.

5. These changes in the number of quanta available for release during trains of impulses are predicted in terms of a hypothesis in which facilitation is due to the accumulation of a residual calcium-receptor complex in the nerve terminal that determines the fraction of a pool of quanta which contributes to n, and depression is due to a decrease in the number of quanta in this pool.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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