Topography and Affinity of Calcium Sensors of Exo- and Endocytosis in Motor Nerve Terminals
Zefirov, A. L. | Grigor'ev, P. N.
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 highaffinity Ca-site in Ca-macrodomain. Endocytosis of vesicles is probably initiated by Camicrodomain during activation of low-affinity Ca-site in the immediate proximity to the Ca channel.Show more [+] Less [-]