Structural localization of calcium binding sites in the neuromuscular junction after supramaximal stimulation.
Rat motor end plates were supramaxillary stimulated by means of acute systemic inhibition of acetylcholinesterase. Electron micrographs obtained from samples subjected to perfusion with a calcium-containing (5 mM) aldehyde fixative demonstrates profound alterations in the fine structures and localization of calcium binding sites, markedly differring from those prevailing in the resting state and/or under conditions of physiological function. Neither "A" sites at the active zones of the synapse, nor "B" sites within the terminal proper, which are apparent in the resting state, do bind calcium after supramaximal stimulation which is characterized by a conspicuous vacuolization of the sole plate, brought about by destruction of the post-synaptic mitochondria. Calcium binding after supramaximal stimulation is partly postsynaptic (in granules of varying sizes within the sole plate) partly presynaptic (in synaptic vesicles, as well as in the whole extent of the presynaptic membrane). Limited resolving power of light microscopy and artificial translocation of the reaction product of the histochemical reaction may account for the earlier interpretation of exclusively post-synaptic localization of calcium after supramaximal stimulation.
D000110:Acetylcholinesterase / Q000378:metabolism; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D005260:Female; D008297:Male; D009388:Neostigmine / Q000494:pharmacology*; D009469:Neuromuscular Junction / Q000187:drug effects* / Q000648:ultrastructure; D051381:Rats
D009388:Neostigmine; D000110:Acetylcholinesterase; D002118:Calcium