Synaptic transmission in the guinea-pig vas deferens: the role of nerve action potentials

To determine how transmitter release is related to presynaptic nerve activities, pre- and postsynaptic electrical events of the vas deferens in the guinea-pig were recorded with a suction electrode. Stimulation of the hypogastric nerve elicited excitatory junction currents and nerve action potentials. Intermittence of excitatory junction currents was observed. In some instances, this was related to the absence of nerve action potentials, suggesting failure of impulse propagation into the nerve terminals. Facilitation of both the nerve action potentials and the excitatory junction currents was also observed. Internal perfusion of the recording electrode with tetrodotoxin blocked the nerve impulse, and the polarity of the excitatory junction current became positive. Similar effects on the polarity of the excitatory junction current were observed with alpha, beta-methylene ATP. Perfusion of the suction pipette with 4-aminopyridine or tetraethylammonium increased the amplitude of the excitatory junction currents and prolonged the nerve action potential duration. These experiments show that: (1) transmission failure in some cases can be related to conduction block into the terminal region: (2) facilitation of excitatory junction currents may be related to facilitation of the nerve action potentials; (3) enhancement of transmitter release by potassium channel blockers may be related to prolongation of the duration of the nerve action potential. It is concluded that transmitter release is intimately related to presynaptic nerve activities.