Characterization of muscarinic receptor-mediated cationic currents in longitudinal smooth muscle cells of mouse small intestine.
In mouse intestinal smooth muscle cells held at -50 mV, carbachol evoked an atropine-sensitive inward current in the intracellular presence of Cs(+). The current response consisted of an initial peak followed by a smaller plateau component on which oscillatory currents frequently arose. Results from various experimental procedures indicated that the inward current is a muscarinic receptor-operated cationic current (mI(cat)) sensitive to cytosolic Ca(2+) concentration ([Ca(2+)](i)) and that the initial peak and oscillatory components are contaminated by Ca(2+)-activated Cl(-) currents. Under conditions of [Ca(2+)](i) buffered to 100 nM, the mI(cat) response to cumulative carbachol applications was inhibited competitively by an M(2)-selective antagonist but non-competitively by an M(3)-selective one. Also it was severely reduced by pertussis toxin (PTX) treatment or a phospholipase C (PLC) inhibitor. Comparative analysis of mI(cat) in mouse and guinea-pig intestinal myocytes indicated that the underlying channels resemble between those myocytes in agonist sensitivity, current-voltage relationship, and unitary conductance. The results suggest that in mouse intestinal myocytes, mI(cat) arises mainly via an M(2)/M(3) synergistic mechanism involving PTX-sensitive G-proteins and PLC activity in the absence of current modulation by [Ca(2+)](i) changes, as described for guinea-pig ileal mI(cat). The channels underlying mI(cat) are also indistinguishable in gating properties between both types of myocytes.
Department of Pathogenic Veterinary Science, United Graduate School of Veterinary Science, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan.
Takashi
T
Sakamoto
Toshihiro
T
Unno
Hayato
H
Matsuyama
Mai
M
Uchiyama
Mitsunobu
M
Hattori
Masakazu
M
Nishimura
Seiichi
S
Komori
D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D002412:Cations / Q000378:metabolism; D018679:Cholinergic Agonists / Q000494:pharmacology; D003959:Diamines / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004963:Estrenes / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007421:Intestine, Small / Q000187:drug effects / Q000378:metabolism; D015640:Ion Channel Gating; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials; D051379:Mice; D018727:Muscarinic Antagonists / Q000494:pharmacology; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism*; D037342:Pertussis Toxin / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D011760:Pyrrolidinones / Q000494:pharmacology; D043585:Receptor, Muscarinic M2 / Q000187:drug effects / Q000378:metabolism*; D043587:Receptor, Muscarinic M3 / Q000187:drug effects / Q000378:metabolism*; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism
D002412:Cations; D018679:Cholinergic Agonists; D003959:Diamines; D004791:Enzyme Inhibitors; D004963:Estrenes; D007473:Ion Channels; D018727:Muscarinic Antagonists; D010880:Piperidines; D011760:Pyrrolidinones; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; C042375:4-diphenylacetoxy-1,1-dimethylpiperidinium; D002217:Carbachol; D037342:Pertussis Toxin; D010738:Type C Phospholipases; C054938:methoctramine