Adenosine effects upon transmitter release parameters in the Mg2+-paralyzed neuro-muscular junction of frog

The influence of adenosine upon the process of transmitter release was investigated in Mg2+-paralyzed frog neuromuscular junction by using conventional microelectrophysiological techniques and binomial statistical analysis. The statistical parameters used were: m (mean number of quanta released per impulse), p (the probability of quantal release) and n (store of quanta available for release). Adenosine decreased the mean quantal content (m) by reducing n. This effect appeared to be dependent upon the free intracellular Ca2+. The nucleoside competed with the transmitter releasing effects of ouabain and increased the amount of effective Ca2+ necessary for quantal release. It did not change the slope of release parameters modification during low-frequency facilitation. The data are discussed in terms of a physical model of release.