Muscarinic cation current and suppression of Ca2+ current in guinea pig ileal smooth muscle cells.
Cationic current (Icat) and inhibition of the voltage-dependent Ca2+ current (ICa) evoked by muscarinic receptor activation with carbachol were studied using whole-cell patch clamp technique in smooth muscle cells isolated from longitudinal muscle of guinea pig small intestine. With low buffering of [Ca2+]i (0.1 mM BAPTA [1,2-bis-(2-aminophenoxy)-ethane-N,N, N', N'-tetraacetic acid] in pipette solution) Icat and ICa inhibitory responses had a rapid onset to an initial peak followed by a sustained phase. The sustained phase of ICa suppression was bigger than in the case when [Ca2+]i was clamped to 100 nM, but decreased with repeated stimulation. Upon repeated stimulation with 50 microM carbachol in cells where [Ca2+]i was clamped to 100 nM and when GTP was absent, Icat amplitude decreased strongly and more substantially compared to ICa inhibition, but both responses declined only slightly when 1 mM GTP was present in the pipette solution. GDP-betaS (1 or 5 mM) in pipette solution or pre-treatment of cells with pertussis toxin (6 microg/ml, for 4 h or longer) blocked Icat more than ICa suppression by carbachol, whereas L-NAME (N-omega-nitro-L-arginine methyl ester hydrochloride) (100 microM in pipette solution) affected neither of them significantly. We conclude that the cationic current and the suppression of the voltage-dependent Ca2+ current evoked by muscarinic receptor activation are mediated by pertussis toxin-sensitive G-protein(s) but the latter response was less sensitive to blockade by GDP-betaS and to GTP deficiency in the cell.
Pucovský
V
V
Institute of Experimental Pharmacology, Slovak Academy of Sciences, Bratislava, Slovak Republic.
Zholos
A V
AV
Bolton
T B
TB
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002412:Cations / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000494:pharmacology; D006168:Guinea Pigs; D007082:Ileum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects; D008297:Male; D018721:Muscarinic Agonists / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D037342:Pertussis Toxin; D011976:Receptors, Muscarinic / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002412:Cations; D004791:Enzyme Inhibitors; D007473:Ion Channels; D018721:Muscarinic Agonists; D011976:Receptors, Muscarinic; D010566:Virulence Factors, Bordetella; D006160:Guanosine Triphosphate; D002217:Carbachol; D019001:Nitric Oxide Synthase; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D019331:NG-Nitroarginine Methyl Ester