title: The effect of reduced calcium on quantal unit current and release at the crayfish neuromuscular junction.
abstract: Excitatory postsynaptic currents (EPSCs) were recorded extracellularly from large muscle fibers by means of 'patch clamp' electrodes. Compared to usual extracellular recordings, better signal/noise ratio and temporal stability were achieved. In the range of extracellular calcium concentrations [Ca]0 between 2.7 and 13.5 mmol/l (normal), the average amplitude of the EPSC increased more than proportional to [Ca]0. The unit quantum current, C1, and the average release rate, m, were determined from EPSCs and also from spontaneous sEPSCs, using both Poisson and binomial statistics. The main effect of [Ca]0 was on m: at different synaptic sites m depended on the second to fourth power of [Ca]0. In terms of binomial parameters, the release probability p is the [Ca]0-dependent one. In addition, reduction of [Ca]0 from 13.5 to 2.7 mmol/l decreased the unit quantum C1 consistently to 60%; simultaneously the rise and decay of EPSCs and sEPSCs were shortened by 10-20%. [Ca]0 thus has strong presynaptic effects on the release probability, but in addition smaller ones on the postsynaptic channel characteristics.
mesh_terms: D000818:Animals; D003400:Astacoidea / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D004594:Electrophysiology; D005110:Extracellular Space / Q000502:physiology; D008433:Mathematics; D009469:Neuromuscular Junction / Q000502:physiology*; D009435:Synaptic Transmission; D013997:Time Factors
chemical_list: D002118:Calcium