INTRACELLULAR CALCIUM-ION MOBILIZATION AND NICOTINIC ACETYLCHOLINE RECEPTOR-MEDIATED SIGNAL TRANSDUCTION IN NEUROSKELETAL MUSCLE SYNAPSE

Intracellular Ca2+ mobilization in neuro-skeletal muscle synapse was studied by measuring Ca2+ aequorin luminescence transients (Ca2+ transients). Ca2+ transients were categorized into three groups as follows: (1) The 1st phase of rapid Ca2+ mobilization was accompained with twitch tension, (2) the 2nd phase of slow Ca2+ was not accompanied with twitch tension, and only observed in the presence of cholinesterase inhibitors, and (3) the 3rd phase was spontaneous Ca2+ 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 (Ca2+ 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 Ca2+ transients are related to T-type n-AChR channel, whereas the 2nd phase Ca2+ transients are related to S-type n-AChR channel and its mediated signal transduction.