title: Relaxing action of sodium nitroprusside independent of membrane potential in the CCh-induced contracture of the guinea pig stomach muscle.
abstract: Carbachol (CCh, 10(-6) M) induced biphasic contraction of longitudinal muscle of the guinea pig stomach, consisting of rapid phasic contraction and contracture. The contracture was almost completely inhibited by sodium nitroprusside (SNP, 10(-6) M) and S-nitroso-N-acetyl penicillamine (SNAP, 10(-6) M). A membrane permeable analogue of cyclic GMP, 8Br-cGMP (10(-4) M), also inhibited the CCh induced contracture. Although a heme site inhibitor of nitric oxide-sensitive guanylyl cyclase, 1-H-[1, 2, 4] oxadiazolo-[4, 3 a]quinoxalin-1-one (ODQ; 10(-6) M), reduced the inhibitory action of SNP, it did not affect the inhibitory action of 8Br-cGMP, indicating that the effect of SNP was developed via cyclic GMP production in the presence of D600. Charybdotoxin (10(-7) M), an inhibitor of Ca2+ activated K+ channel, did not influence on the CCh induced contracture. On the other hand, CCh induced a depolarization of the longitudinal muscle cell membrane (from -60 mV to -45 mV) in the presence of 10(-6) M D600, but SNP did not affect the depolarization. These results suggest that in the presence of D600 SNP induces relaxation of CCh induced contracture of the longitudinal muscle of the guinea pig stomach via cyclic GMP but not membrane potential dependent mechanism.
authors.affiliation: Department of Physiology, School of Medicine, Fukuoka University, Japan. sakamoto@msat.fukuoka-u.ac.jp
authors.forename: Y
authors.initials: Y
authors.lastname: Sakamoto
mesh_terms: D000818:Animals; D002217:Carbachol / Q000494:pharmacology*; D018999:Charybdotoxin / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology*; D006152:Cyclic GMP / Q000378:metabolism / Q000494:pharmacology; D005260:Female; D005711:Gallopamil / Q000494:pharmacology; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects; D003473:Neuromuscular Nondepolarizing Agents / Q000494:pharmacology; D009599:Nitroprusside / Q000378:metabolism / Q000494:pharmacology*; D013270:Stomach / Q000187:drug effects; D014665:Vasodilator Agents / Q000494:pharmacology*
chemical_list: D018679:Cholinergic Agonists; D003473:Neuromuscular Nondepolarizing Agents; D014665:Vasodilator Agents; D018999:Charybdotoxin; D009599:Nitroprusside; D005711:Gallopamil; D002217:Carbachol; D006162:Guanylate Cyclase; D006152:Cyclic GMP