Acetylcholine sensitivity of biphasic Ca2+ mobilization induced by nicotinic receptor activation at the mouse skeletal muscle endplate.
1. Acetylcholine (ACh) was locally applied onto the endplate region in a mouse phrenic nerve-diaphragm muscle preparation to measure intracellular free calcium ([Ca2+]i) entry through nicotinic ACh receptors (AChRs) by use of Ca2+-aequorin luminescence. 2. ACh (0.1-3 mM, 20 microl) elicited biphasic elevation of [Ca2+]i (fast and slow Ca2+ mobilization) in muscle cells. The peak amplitude of the slow Ca2+ mobilization (not accompanied by twitch tension) was concentration-dependently increased by ACh, whereas that of the fast component (accompanied by twitch tension) reached a maximum response at a lower concentration (0.1 mM) of applied ACh. 3. A pulse of nicotinic agonists, (-)-nicotine (10 mM) and 1,1-dimethyl-4-phenyl-piperazinium (10 mM), but not a muscarinic agonist pilocarpine (10 mM), also elicited a biphasic Ca2+ signal. 4. Even though ACh release from motor nerve endings was blocked by botulinum toxin (5 microg, bolus i.p. before isolation of the tissue), the generation of both a fast and slow Ca2+ component caused by ACh application was observed. 5. These results strongly suggest that ACh locally applied onto the endplate region of skeletal muscle induces a slow Ca2+ signal reflecting Ca2+ entry through a postsynaptic nicotinic AChR, which has a low sensitivity to transmitter ACh.
Dezaki
K
K
Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Sugitani, Japan.
Kimura
I
I
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D008297:Male; D051379:Mice; D009045:Motor Endplate / Q000187:drug effects* / Q000378:metabolism; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism; D018722:Nicotinic Agonists / Q000494:pharmacology*; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction
D018722:Nicotinic Agonists; D000109:Acetylcholine; D002118:Calcium