Increase in Ca2+(Mg2+)-ATPase activity induced by a molsidomine derivative (SIN-1A) and nitroglycerin in microsomal fraction of guinea-pig thoracic aorta.

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Abstract
The amount of phosphoric acid liberated from ATP by Ca2+(Mg2+)-ATPase in microsomal fraction of guinea pig thoracic aorta decreased with decreasing concentrations of Ca2+ from 20.0 to 2.5 mM in the mixture of the enzyme and substrate. When CaCl2 (2.5 mM) and MgCl2 (5.0 mM) were present in the substrate, both nitroglycerin (0.1-1.0 mM) and SIN-1A (a molsidomine derivative, 0.05-1.0 mM) increased the liberated phosphoric acid in a concentration-dependent manner. The contractile tension of smooth muscle prepared from guinea-pig thoracic aorta, which was previously increased by the pretreatment with prostaglandin F2.alpha. (5.0 .mu.M), was relaxed by both nitroglycerin and SIN-1A (0.01-100 .mu.M each) in a concentration-dependent manner. Evidently, the stimulation of Ca2+(Mg2+)-ATPase [Ca2+-pump ATPase] activity induced by nitroglycerin and SIN-1A in the microsome of thoracic aorta takes part in the relaxation of contractile tension in the tissue.