[Relationship between temperature and calcium ion concentration in the medium and the effect of imidazole, guanidine and theophylline on mediator release at the frog neuromuscular synapse].

The effect of imidazole, guanidine and theophylline on the spontaneous (frequency of miniature end-plate potentials) and evoked (quantum content of end-plate potentials) release of transmitter was studied in the experiments on isolated frog neuromuscular preparation under different temperature and calcium concentration. All the drugs studied were able to enhance the quantal content and frequency under 20 degrees C and 0.5 mM Ca2+. The potency of drugs for increasing evoked release could be ranked as follows: imidazole approximately guanidine greater than theophylline, but for increasing spontaneous release; theophylline greater than imidazole approximately guanidine. Only the effect of theophylline on the frequency depended on temperature. Imidazole and theophylline were independent on calcium concentrations. The possible differences in the mechanism of drug action on spontaneous and evoked release of transmitter are discussed.