Topography and affinity of calcium sensors of exo- and endocytosis in motor nerve terminals.
Measurements with extracellular microelectrode technique showed that depolarization of motor nerve terminals in frog cutaneous pectoris muscle with high-potassium solution (40 mM K(+)) increased frequency of miniature end-plate currents. Both fast intracellular calcium chelator BAPTA-AM and slow chelator EGTA-AM equally moderated the increase in the frequency of miniature end-plate currents. Intravital fluorescent microscopy with FM 1-43 dye showed that under conditions of stimulation of neurotransmitter exocytosis and secretion with high-potassium solution, internalization of the dye into newly-formed endocytotic synaptic vesicles proceeded both in the control and in the presence of EGTA-AM. In contrast, internalization of the dye was not observed in the presence of BAPTA-AM. It was concluded that asynchronous exocytosis of synaptic vesicles goes on in the active zones enriched with Ca-channels due to activation of high-affinity Ca-site in Ca-macrodomain. Endocytosis of vesicles is probably initiated by Ca-microdomain during activation of low-affinity Ca-site in the immediate proximity to the Ca channel.
Zefirov
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AL
Department of Normal Physiology, Kazan State Medical University, Tatarstan, Russia. zefiroval@rambler.ru
Grigor'ev
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PN
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002614:Chelating Agents; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology*; D005089:Exocytosis / Q000502:physiology*; D066298:In Vitro Techniques; D009046:Motor Neurons / Q000378:metabolism*; D009132:Muscles / Q000378:metabolism / Q000502:physiology; D011726:Pyridinium Compounds / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D011895:Rana ridibunda; D013572:Synaptic Vesicles / Q000378:metabolism*
D002614:Chelating Agents; C073804:FM1 43; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; C046770:EGTA acetoxymethyl ester; D002118:Calcium