Relaxing Action of Sodium Nitroprusside Independent of Membrane Potential in the CCh-induced Contracture of the Guinea Pig Stomach Muscle

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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 Ca^<2+>-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.
日本平滑筋学会の論文