Intracellular Ca
2+ mobilization in neuro-skeletal muscle synapse was studied by measuring Ca
2+-aequorin luminescence transients (Ca
2+ transients). Ca
2+ transients were categorized into three groups as follows : (1) The 1st phase of rapid Ca
2+ mobilization was accompanied with twitch tension, (2) the 2nd phase of slow Ca
2+ mobilization was not accompanied with twitch tension, and only observed in the presence of cholinesterase inhibitors, and (3) the 3rd phase was spontaneous Ca
2+ mobilization which was rather related to contracture. The caffeine effects were composed of 1st phase-potentiation (cyclic AMP increase?), 2nd phase-inhibition (n-acetylcholine receptor (AChR) closely related), and the increase of 3rd phase (Ca
2+ release from salcoplasmic reticulum). d-Tubocurarine showed much higher potency for the inhibition of the 2nd phase than for that of the 1st phase. These results suggest that the 1st phase Ca
2+ transients are related to T-type n-AChR channel, whereas the 2nd phase Ca
2+ transients are related to S-type n-AChR channel and its mediated signal transduction.
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