[The intracellular calcium and mechanisms of endocytosis of synaptic vesicles at the frog nerve ending].
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.
A L
AL
Zefirov
M M
MM
Abdrakhmanov
P N
PN
Grigor'ev
A M
AM
Petrov
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D004594:Electrophysiology; D004705:Endocytosis / Q000502:physiology*; D005089:Exocytosis; D009046:Motor Neurons / Q000378:metabolism / Q000502:physiology; D018482:Muscle, Skeletal; D009473:Neuronal Plasticity; D011188:Potassium / Q000494:pharmacology; D011895:Rana ridibunda; D013569:Synapses / Q000502:physiology*; D013572:Synaptic Vesicles / Q000502:physiology
D002110:Caffeine; D011188:Potassium; D002118:Calcium