Muscarinic receptor subtypes mediating Ca2+ sensitization of intestinal smooth muscle contraction: studies with receptor knockout mice.
In the present study, we have characterized muscarinic receptor subtypes that mediate carbachol-induced Ca2+ sensitization of contraction in intestinal smooth muscle, using mutant mice lacking M(2) or M(3) muscarinic receptors or both receptor subtypes. In alpha-toxin-permeabilized muscle strips from wild-type (WT) mice, isometric tension responses to Ca2+ applied cumulatively (pCa 7.0-5.0) were increased when the muscarinic agonist carbachol (100 microM) was added to the medium, as judged from shifts of pCa-tension curves in both 50% effective concentration (EC(50)) and maximum response (E(max)) of pCa-tension curve. In preparations from M(2)-knockout (KO) mice, pCa-tension curves were also shifted by carbachol (100 microM), and the extents of the EC(50) and E(max) changes resembled those observed in preparations from WT mice. In preparations from M(3)-KO or M(2)/M(3)-double KO mice, however, no significant changes in pCa-tension curves were obtained after carbachol application. The G(q/11)-type G-protein inhibitor YM-254890 (1 microM) completely blocked the Ca2+ sensitization of contraction induced by carbachol in M(2)-KO or WT preparations. The results strongly support the idea that the muscarinic activation of Ca2+ sensitization in intestinal smooth muscles is mediated by the M(3) muscarinic receptor coupled to G(q/11)-type G-proteins, without any significant involvement of the other muscarinic receptor subtypes including M(2).
Suguro
Mayuko
M
Laboratory of Veterinary Pharmacology, Department of Veterinary Medicine, Faculty of Applied Biological Science, Gifu University.
Matsuyama
Hayato
H
Tanahashi
Yasuyuki
Y
Unno
Toshihiro
T
Kitazawa
Takio
T
Yamada
Masahisa
M
Komori
Seiichi
S
D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D002217:Carbachol / Q000494:pharmacology; D005260:Female; D006160:Guanosine Triphosphate / Q000494:pharmacology; D007082:Ileum / Q000187:drug effects / Q000502:physiology*; D007422:Intestines / Q000187:drug effects / Q000502:physiology*; D008297:Male; D051379:Mice; D018345:Mice, Knockout / Q000235:genetics / Q000502:physiology*; D009119:Muscle Contraction / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D010456:Peptides, Cyclic / Q000494:pharmacology; D043585:Receptor, Muscarinic M2 / Q000172:deficiency* / Q000502:physiology; D043587:Receptor, Muscarinic M3 / Q000172:deficiency* / Q000502:physiology; D011976:Receptors, Muscarinic / Q000502:physiology*
D010456:Peptides, Cyclic; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic; C475455:YM-254890; D006160:Guanosine Triphosphate; D002217:Carbachol; D002118:Calcium