Voltage Dependency of Neurotransmitter Release at the Crayfish Neuromuscular Junction

Abstract

To test the new hypothesis that a calcium independent mechanism is required for neurotransmitter release, we measured excitatory post-synaptic potentials (EPSPs) at the neuromuscular junction of the crayfish tail extensor muscle. Stimulation of the nerve was accomplished with a suction electrode and measurements were made with a micropipette placed in a post-synaptic muscle cell. The tail was bathed in Co²⁺ to effectively eliminate EPSPs. Next, the calcium ionophore A23187 was added to raise the intracellular concentration of Ca²⁺. Upon addition of A23187 a small recovery of EPSP was observed in dilute cobalt concentrations but this was reversed using a higher concentration of Co²⁺. Our results neither confirm nor deny either theory.