[Immunocytochemical identification of synaptotagmin 1, syntaxin 1, N-type Ca(2+)-channel and nicotinic cholinoreceptor in motor neuromuscular junctions of earthworm somatic muscle Lumbricus terrestris].

The somatic muscle of earthworm contains myoneural synapses forming clusters of "synaptic buttons". In these "buttons", the proteins syntaxin 1, synaptotagmin 1 and alpha 1B subunit of the Ca(2+)-channel of N-type were identified. We suppose that "synaptic buttons" contain a limited number of active zones due to their small size (1-2 microm) and the pattern of distribution of proteins of exo-endocytotic cycle. The postsynaptic membrane of cholinetgic synapses contains nicotinic acetylcholine receptors capable to bind alpha-bungarotoxin. The area of location of receptors on postsynaptic membrane is strictly limited to the region of synaptic contact.