[Synchronization of secretion of the evoked transmitter quanta as mechanism of the facilitating action of sympathomimetics].

Noradrenaline, isoproterenol, dobutamine were found to modulate kinetics of quanta secretion so as to synchronize the transmitter release. This effect could be prevented with blocking agents of beta-adrenoreceptor (atenolol, propranolol). Activators of beta-adrenoreceptors klonidine and phenylephrine did not change the kinetics of quanta secretion, whereas phentolamine did not affect the synchronizing effect of noradrenaline. The change in the time course of the secretion induced by noradrenaline increased the end-plate current amplitude. There seems to exist a specific presynaptic mechanism involving beta-adrenoreceptors for facilitation of effects of sympathomimetics.