Effect of ouabain and alterations in potassium concentration on relaxation induced by sodium nitroprusside.
Relaxation of the rat thoracic aorta induced by sodium nitroprusside, 8-bromo-cyclic GMP and cyclic nucleotide phosphodiesterase inhibitor M & B 22,948 was inhibited by exposure to K+-free solution and ouabain in a concentration-dependent manner. Relaxation occurring with the change in potassium concentration in media from 1 to 2 to 10 mM was increased by sodium nitroprusside, 8-bromo-cyclic GMP and M & B 22,948. Thus, agents and procedures known to decrease and increase the activity of the Na+,K+-pump, and presumably alter the membrane potential, inhibited and enhanced relaxation, respectively. Exposure to 1 mM K+ solution increased the relaxation to low concentrations of sodium nitroprusside, but had no effect on relaxation induced by 8-bromo-cyclic GMP or M & B 22,948. Thus, another procedure which inhibits the Na+,K+-pump enhanced the effect of low concentrations of sodium nitroprusside on relaxation. Ouabain had no effect on sodium nitroprusside-induced accumulation of cyclic GMP. These results suggest that sodium nitroprusside may induce relaxation through cyclic GMP formation, effects on the Na+,K+-pump and/or hyperpolarization of the smooth muscle cell membrane.
D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000494:pharmacology; D005292:Ferricyanides / Q000494:pharmacology*; D007473:Ion Channels / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects*; D009599:Nitroprusside / Q000494:pharmacology*; D010042:Ouabain / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains
D005292:Ferricyanides; D007473:Ion Channels; D009599:Nitroprusside; C016276:8-bromocyclic GMP; D010042:Ouabain; D006152:Cyclic GMP