AN ELECTROPHYSIOLOGICAL ANALYSIS OF THE EFFECT OF Ca IONS ON NEUROMUSCULAR TRANSMISSION IN THE MOUSE VAS DEFERENS

Abstract

1 A study has been made of the effects of changing the external calcium concentration [Ca] ₀ and the external magnesium concentration [Mg] ₀ on the synaptic potential due to noradrenaline release. 2 When [Ca] ₀ was varied in the range 0.7 to 1.8 mM, the synaptic potential increased as about the second power of [Ca] ₀. 3 Increasing [Mg] ₀ depressed the synaptic potential; however, variation of [Ca] ₀ in the presence of high [Mg] ₀ did not significantly change the power relationship between the synaptic potential and [Ca] ₀. 4 The facilitated increase in the synaptic potential during short trains of impulses at different frequencies was quantitatively predicted on the assumption that each impulse leaves residual Ca ions bound to release receptors in the nerve terminal.