THE INTRACELLULAR CALCIUM AND MECHANISMS
OF ENDOCYTOSIS OF SYNAPTIC VESICLES AT THE FROG NERVE ENDING
A. L. Zefirov,1 M. M. Abdrakhmanov, P. N. Grigoryev, A. M. Petrov
Department of Normal Physiology, Medical State University, Kazan’;
1 e-mail: zefirov@kmu-mf.kcn.ru
In the experiments on frog motor nerve endings of cutaneous pectoris muscle, made by extracellular recording
of synaptic signals, it has been shown that the increase in intracellular calcium ion concentration in the nerve
ending (by enhance of extracellular potassium ion concentration, or by addition of caffeine) leads to an increase
in the miniature end-plate potential frequency, which is preserved over the whole period (about 10 min) of
action of these substrates. The rhythmic stimulation of motor nerve (20 or 100 imp/s) quickly leads to a decrease
in the end plate potentials amplitude. It has been shown by fluorescent microscopy with the use of endocytotic
marker FM 1-43 that in the course of a short time exposition (5 min) in a high potassium solution (40 mM) or
caffeine (5 mM), light spots appeared in the nerve ending. This shows that synaptic vesicles undergo intensive
processes of endocytosis. During a longer exposition (30 min) no light spots were revealed, whereas the nerve
ending width increased. This data allowed to propose that the process of endocytosis was blocked. In the presence
of even lower concentrations of potassium ions and caffeine, and during a long rhythmic stimulation (20 or
100 imp/s) no blocking of endocytosis was revealed. It is concluded that high concentrations of intracellular calcium
in the frog motor nerve ending leads to a reversible block of endocytosis, while exocytosis in synaptic vesicles
is proceeding.
Key words: motor nerve ending, FM 1-43, endocytosis, exocytosis, intracellular calcium, high potassium
solutions, caffeine
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