Karaki H, Sato K, Ozaki H, Murakami K
Department of Veterinary Pharmacology, Faculty of Agriculture, University of Tokyo, Japan.
Eur J Pharmacol. 1988 Nov 1;156(2):259-66. doi: 10.1016/0014-2999(88)90329-9.
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+.
在离体大鼠主动脉平滑肌中，通过荧光染料fura - 2与收缩同时测定硝普钠对胞质Ca2 +水平（[Ca2 +]cyt）的抑制作用以及对45Ca2 +摄取的抑制作用。去甲肾上腺素增加肌肉张力、45Ca2 +摄取和[Ca2 +]cyt。在缺钙溶液中，去甲肾上腺素短暂增加肌肉张力和[Ca2 +]cyt。硝普钠抑制去甲肾上腺素诱导的所有变化，尽管对[Ca2 +]cyt的抑制小于对肌肉收缩的抑制。硝普钠在高于抑制去甲肾上腺素诱导收缩所需的浓度时，也抑制高钾诱导的收缩。抑制高钾诱导的收缩伴随着[Ca2 +]cyt的小幅下降和45Ca2 +摄取的较小下降。亚甲蓝拮抗，而M&B 22,948增强硝普钠的抑制作用。这些结果表明硝普钠有多个作用位点。在相对较低浓度下，硝普钠可抑制Ca2 +内流和Ca2 +释放。在相对较高浓度下，这种抑制剂还可增强Ca2 +的摄取并降低收缩元件对Ca2 +的敏感性。
