Effects of sodium nitroprusside on cytosolic calcium level in vascular smooth muscle.
The inhibitory effect of sodium nitroprusside on the cytosolic Ca2+ level ([Ca2+]cyt), measured simultaneously with contraction by means of a fluorescence dye, fura-2, and on the 45Ca2+ uptake was tested in the isolated rat aortic smooth muscle. Norepinephrine increased muscle tension, 45Ca2+ uptake and [Ca2+]cyt. In a Ca2+-deficient solution, norepinephrine transiently increased muscle tension and [Ca2+]cyt. Sodium nitroprusside inhibited all changes induced by norepinephrine although the inhibition of [Ca2+]cyt was less than that of muscle contraction. Sodium nitroprusside also inhibited the high K+-induced contraction at concentrations higher than those needed to inhibit norepinephrine-induced contraction. Inhibition of the high K+induced contraction was accompanied by a small decrease in [Ca2+]cyt and a smaller decrease in 45Ca2+ uptake. Methylene blue antagonized, and M&B 22,948 potentiated the inhibitory effect of sodium nitroprusside. These results suggest that sodium nitroprusside has multiple sites of action. At relatively low concentrations, sodium nitroprusside could inhibit the Ca2+ influx and Ca2+ release. At relatively high concentrations, this inhibitor could also augment Ca2+ sequestration and decrease the sensitivity of contractile elements to Ca2+.
Karaki
H
H
Department of Veterinary Pharmacology, Faculty of Agriculture, University of Tokyo, Japan.
Sato
K
K
Ozaki
H
H
Murakami
K
K
D000818:Animals; D001011:Aorta / Q000187:drug effects; D002118:Calcium / Q000032:analysis / Q000378:metabolism* / Q000502:physiology; D003600:Cytosol / Q000378:metabolism; D005292:Ferricyanides / Q000494:pharmacology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009599:Nitroprusside / Q000494:pharmacology*; D009638:Norepinephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013050:Spectrometry, Fluorescence
D005292:Ferricyanides; D009599:Nitroprusside; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine