Calcium responses induced by acetylcholine in submucosal arterioles of the guinea-pig small intestine.
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 [Ca2+]i in a concentration-dependent manner. This response diminished with time, and finally disappeared in 2-3 h (old tissues). 3. Ba2+ elevated [Ca2+]i to a similar extent in both fresh and old tissues. ACh further increased the Ba2+-elevated [Ca2+]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 [Ca2+]i, with no alteration of [Ca2+]i at rest and during elevation with Ba2+. 5. In the presence of indomethacin and nitroarginine, high-K+ solution elevated [Ca2+]i in both fresh and old tissues. Subsequent addition of ACh further increased [Ca2+]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 [Ca2+]i in both fresh and Ba2+-stimulated old tissues. It also inhibited the ACh-induced hyperpolarization. 7. In fresh tissues, the ACh-induced Ca2+ response was not changed by apamin, charybdotoxin (CTX), 4-aminopyridine (4-AP) or glibenclamide. In old tissues in which [Ca2+]i had previously been elevated with Ba2+, the ACh-induced Ca2+ response was inhibited by CTX but not by apamin, 4-AP or glibenclamide. 8. It is concluded that in submucosal arterioles, ACh elevates endothelial [Ca2+]i and reduces muscular [Ca2+]i, probably through the hyperpolarization of endothelial or smooth muscle membrane by activating CTX-sensitive K+ channels.
Fukuta
H
H
Department of Physiology, Nagoya City University Medical School, Mizuho-ku, Nagoya 467-8601, Japan. hfukuta@med.nagoya-cu.ac.jp
Hashitani
H
H
Yamamoto
Y
Y
Suzuki
H
H
D015761:4-Aminopyridine / Q000494:pharmacology; D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D001160:Arterioles / Q000187:drug effects / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D018999:Charybdotoxin / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2; D006168:Guinea Pigs; D007413:Intestinal Mucosa / Q000098:blood supply*; D007421:Intestine, Small / Q000098:blood supply*; D008297:Male; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009569:Nitric Oxide / Q000037:antagonists & inhibitors; D026902:Potassium Channel Blockers
D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D018727:Muscarinic Antagonists; D026902:Potassium Channel Blockers; D018999:Charybdotoxin; D016718:Arachidonic Acid; D009569:Nitric Oxide; D015761:4-Aminopyridine; D000109:Acetylcholine; D002118:Calcium; D016257:Fura-2