Abstract

The effects of 5-methyl-6-(4-pyridyl)-2H-1,4-thiazin-3(4H)-one (ZSY-27), a positive inotropic agent with a vasodilatory action, on a concentration-response curve of CaCl2 in the KCl-depolarized rabbit thoracic aorta and Ca-uptake by the microsomal fraction from the rabbit artery were tested. ZSY-27 (10(-5) - 10(-4) M) inhibited noncompetitively a concentration-response curve of CaCl2 in the KCl-depolarized preparation. Furthermore, ZSY-27 (10(-5) M) stimulated significantly Ca-uptake by the microsomal fraction in the presence of oxalate, as an indicator for Ca-uptake by the internal membrane, in every incubation time. However, it inhibited significantly that in the absence of oxalate, as an indicator for Ca-uptake by the plasma membrane-derived vesicle, after 6 min of incubation time. These results suggest that ZSY-27 stimulates Ca-uptake by the internal membranes and inhibits Ca-uptake by the plasma membrane-derived vesicles. Therefore, these effects of ZSY-27 are considered to be related to relaxation of vascular smooth muscle.

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