The effect of calcium ions on the binomial statistic parameters that control acetylcholine release at preganglionic nerve terminals.

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Abstract
A study has been made of the effects of changing [Ca2+].permill. [extracellular Ca2+ concentration] and [Mg2+].permill. were studied on the binomial statistic parameters p and n that control the average quantal content (.hivin.m) of the excitatory post-synaptic potential (EPSP) due to acetylcholine release at preganglionic nerve terminals in the guinea pig. When [Ca2+].permill. was increased in the range from 0.2-0.5 mM, p increased as the 1st power of [Ca2+].permill., whereas n increased as the 0.5 power of [Ca2+.permill.; when [Mg2+].permill. was increased in the range from 5-20 mM, p decreased as the 1st power of [Mg2+], whereas n decreased as the 0.5 power of [Mg2+].permill.. The increase in quantal release of a test impulse following a conditioning impulse was primarily due to an increase in n; the increase in quantal content of successive EPSP in a short train was due to an increase in n and p, and the increase in n was quantitatively described in terms of the accumulation of a Ca2+-receptor complex in the nerve terminal. The decrease in quantal content of successive EPSP during long trains of impulses over several minutes was primarily due to a decrease in n. The physical basis of n and p in the release process is discussed.