[Sensitivity of intracellular calcium-binding sites of exo- and endocytosis of synaptic vesicles to Sr, Ba and Mg ions].

In the experiments on frog motor nerve endings made with electrophysiological (intra- and extracellular recording ofpostsynaptic sygnals) and optical (confocal microscopy with usage of fluorescent marker FM 1-43) approaches, transmitter release and exo-endocytosis of synaptic vesicles after replacement ofextracellular Ca ions by other alkaline earth metal ions (Sr, Ba, Mg) were studied. Massive asynchronous exocytosis with high potassium solution and evoked exocytosis with high-frequency rhythmic stimulation of motor nerve were initiated. It has been shown that the site of asynchronous exocytosis was sensitive to Ca, Sr, Ba and Mg ions whereas the site of evoked (synchronous) exocytosis--to Ca and Sr ions only. After stimulation either asynchronous or synchronous exocytosis site of endosytosis was found to be sensitive to Ca, Sr and Ba ions and possess the lowest affinity to Sr ions. It is concluded that there exist different intracellular calcium-binding sites for exocytosis and endocytosis that possess distinct sensitivity to alkaline earth metal ions.