Article date: April 1998
By: Katsuya Dezaki, Ikuko Kimura, in Volume 123, Issue 7, pages 1418-1424
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.
ACh (0.1–3 mm, 20 μl) 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.
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.
Even though ACh release from motor nerve endings was blocked by botulinum toxin (5 μg, bolus i.p. before isolation of the tissue), the generation of both a fast and slow Ca2+ component caused by ACh application was observed.
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.
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.
ACh (0.1–3 mm, 20 μl) 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.
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.
Even though ACh release from motor nerve endings was blocked by botulinum toxin (5 μg, bolus i.p. before isolation of the tissue), the generation of both a fast and slow Ca2+ component caused by ACh application was observed.
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.
British Journal of Pharmacology (1998) 123, 1418–1424; doi:10.1038/sj.bjp.0701725
DOI: 10.1038/sj.bjp.0701725
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