Effect of Extracellular Calcium Concentration on Facilitation in the Crayfish Neuromuscular Junction

Abstract

The influx of calcium into the presynaptic cell is the primary mechanism by which the release of neurotransmitter into the synaptic cleft is achieved. This release of neurotransmitter is essential in the transmission of action potentials between neurons. The concentration of calcium outside the cell influences the amount of calcium that passes into the presynaptic cell, which subsequently influences the amount of neurotransmitter released and the intensity of excitatory postsynaptic potentials. Residual calcium from recently fired EPSPs also serves to increase the amount of calcium in the presynaptic cell and facilitate neurotransmitter release. We measured the level of facilitation between a first and second EPSP, triggered by paired pulse stimulation, in varying concentrations of extracellular calcium, to determine the role of calcium concentration in cooperativity and facilitation. The results demonstrated differences in the level of facilitation across concentrations, with the highest facilitation occurring between 3.38 mM Ca and 6.75 mM Ca outside the cell. This supports previous research on the nature of cooperativity in calcium dependence.