[Slow Ca2+ (RAMIC) mobilization operated by postsynaptic neuronal nicotinic receptor regulates synaptic function at the mouse neuromuscular junction].
We have found that non-contractile slow Ca2+ mobilization (RAMIC; Receptor-Activity Modulating Intracellular Ca2+) is generated by motor nerve stimulation with anti-cholinesterase at the skeletal muscle, and desensitizes muscle nicotinic receptor (nAChR). To confirm this Ca2+ mobilization without anti-cholinesterase, acetylcholine (ACh) was locally applied by N2-gas pressure onto endplate region at the mouse phrenic nerve-diaphragm muscle preparation. ACh (0.1-3 mM, 20 microliters) elicited bi-phasic elevation of [Ca2+]i (fast and slow Ca2+ mobilization measured as Ca(2+)-aequorin luminescence) in muscle cells. The peak amplitude of slow Ca2+ mobilization (not accompanied by contraction) was increased by ACh concentration-dependently, whereas that of fast component (accompanied by contraction) reached a maximum response at a lower concentration of ACh. The slow Ca2+ mobilization was blocked by lower concentrations of competitive nAChR antagonists which did not affect the fast Ca2+ transients. Moreover, the slow Ca2+ signal was selectively depressed by a neuronal nAChR antagonist methyllycaconitine. Neither Ca2+ channel blockers nor a Na+ channel blocker tetrodotoxin prevented the generation of the slow Ca2+ mobilization. These results suggest that RAMIC is mobilized through postsynaptic neuronal nAChR subtype to desensitize muscle nAChR at the neuromuscular junction.
Dezaki
K
K
Department of Chemical Pharmacology, Toyama Medical and Pharmaceutical University, Japan.
Tsuneki
H
H
Kimura
I
I
D000109:Acetylcholine / Q000494:pharmacology; D000157:Aconitine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D009469:Neuromuscular Junction / Q000502:physiology*; D018733:Nicotinic Antagonists; D011493:Protein Kinase C / Q000502:physiology; D011978:Receptors, Nicotinic / Q000502:physiology*; D015398:Signal Transduction; D013569:Synapses / Q000502:physiology*
D018733:Nicotinic Antagonists; D011978:Receptors, Nicotinic; C054634:methyllycaconitine; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D000109:Acetylcholine; D002118:Calcium; D000157:Aconitine