Ca2+-dependent recycling of synaptic vesicles at the frog neuromuscular junction.

Open Access
Publisher Website
Google Scholar
Abstract
Frog cutaneous pectoris muscles were treated with low doses of crude black widow spider venom (BWSV) or purified .alpha.-latrotoxin. Neuromuscular transmission, quantal secretion, changes in ultrastructure and uptake of horseradish peroxidase (HRP) were studied. When these agents were applied to muscles bathed in a Ca2+-free solution with 1 mM EGTA [ethyleneglycol-bis(.beta.-aminoethyl ether) N,N,N'',N''-tetraacetic acid] and 4 mM Mg2+, the rate of quantal secretion rose to high levels but quickly subsided; neuromuscular transmission was totally and irreversibly blocked within 1 h. The terminals became swollen and were depleted of vesicles; HRP was not taken up. When BWSV was applied to other muscles bathed in a solution with 1.8 mM Ca2+ and 4 mM Mg2+, the rate of secretion rose to high levels and then declined to intermediate levels that were sustained throughout the hour of exposure. Neuromuscular transmission was blocked in fewer than 50% of these fibers. The ultrastructure of these terminals was normal and they contained large numbers of synaptic vesicles. If HRP had been present, most of the synaptic vesicles were labeled with reaction product. Apparently, Ca2+ plays an important role in endocytosis at the frog neuromuscular junction.

This publication has 27 references indexed in Scilit: