[Evaluation of the tonic and phasic effects of endogenous adenosine on the transmitter secretion in the neuromuscular junction].

Exogenous adenosine reduced the amplitude of multiquantal end-plate currents due to a depressant action on transmitter release. Theophylline did not change the amplitude of end-plate currents under low-rate motor nerve stimulation. The findings suggest a possibility of both tonic and phasic inhibitory actions of endogenous adenosine on transmitter release when utilization of this purine in synaptic cleft is inactivated.