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Calcium responses induced by acetylcholine in submucosal arterioles of the guinea‐pig small intestine
Author(s) -
Fukuta Hiroyasu,
Hashitani Hikaru,
Yamamoto Yoshimichi,
Suzuki Hikaru
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.489ac.x
Subject(s) - acetylcholine , apamin , calcium , charybdotoxin , chemistry , endocrinology , medicine , stimulation , guinea pig , biology
1 Calcium responses induced by brief stimulation with acetylcholine (ACh) were assessed from the fluorescence changes in fura‐2 loaded submucosal arterioles of the guinea‐pig small intestine. 2 Initially, 1–1.5 h after loading with fura‐2 (fresh tissues), ACh increased [Ca 2+ ] i in a concentration‐dependent manner. This response diminished with time, and finally disappeared in 2–3 h (old tissues). 3 Ba 2+ elevated [Ca 2+ ] i to a similar extent in both fresh and old tissues. ACh further increased the Ba 2+ ‐elevated [Ca 2+ ] i in fresh tissues, but reduced it in old tissues. Responses were not affected by either indomethacin or nitroarginine. 4 In fresh mesenteric arteries, mechanical removal of endothelial cells abolished the ACh‐induced increase in [Ca 2+ ] i , with no alteration of [Ca 2+ ] i at rest and during elevation with Ba 2+ . 5 In the presence of indomethacin and nitroarginine, high‐K + solution elevated [Ca 2+ ] i in both fresh and old tissues. Subsequent addition of ACh further increased [Ca 2+ ] i in fresh tissues without changing it in old tissues. 6 Proadifen, an inhibitor of the enzyme cytochrome P450 mono‐oxygenase, inhibited the ACh‐induced changes in [Ca 2+ ] i in both fresh and Ba 2+ ‐stimulated old tissues. It also inhibited the ACh‐induced hyperpolarization. 7 In fresh tissues, the ACh‐induced Ca 2+ response was not changed by apamin, charybdotoxin (CTX), 4‐aminopyridine (4‐AP) or glibenclamide. In old tissues in which [Ca 2+ ] i had previously been elevated with Ba 2+ , the ACh‐induced Ca 2+ response was inhibited by CTX but not by apamin, 4‐AP or glibenclamide. 8 It is concluded that in submucosal arterioles, ACh elevates endothelial [Ca 2+ ] i and reduces muscular [Ca 2+ ] i , probably through the hyperpolarization of endothelial or smooth muscle membrane by activating CTX‐sensitive K + channels.