Study of the vesicular cycle in nerve structures in somatic muscle of earthworm (Lumbricus terrestris)
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In the muscle wall of the earthworm Lumbricus terrestris, with the aid of fluorescent endocytotic dyes FM1-43, FM2-10, and FM4-64, there are revealed fluorescent spots 1–2 μm in diameter that represent clusters of “synaptic boutons.” Application takes place onto ganglia of the abdominal nerve chain of the Dil membrane probe capable of translocation by axoplasmic transport; the subsequent (next day) staining of nerve structures with the endocytotic marker FM4-64 showed the complete superposition of fluorescence of these dyes fluorescing in different specter areas. The fluorescent marker DiBAC4(3) revealed an enhancement of fluorescence of nerve elements with increase of K+ concentration in the extracellular medium. Use of FM2-10 showed that, the higher the K+ content in solution and, accordingly, the nerve cell depolarization, the faster the release of the marker and, on the contrary, the slower the process in the absence of K+ in the medium. In the Ca2+-free solution and in the presence of the Ca2+ chelator BAPTA or BAPTA-AM, there uptake and release of FM2-10 are blocked, but only after preliminary 40-min incubation in such solution. In clusters of synaptic boutons, exo- and endocytosis processes take place that are also preserved under conditions of rest. This vesicular cycle depends on the membrane potential of nerve structures and on the content of K+ and Ca2+ in the medium, the calcium sensor working most likely by the “all or nothing” principle.
Keywordsearthworm fluorescent markers “synaptic boutons,” vesicular cycle
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