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 (10-5-10-4M) inhibited noncompetitively a concentration-response curve of CaCl2 in the KCl-depolarized preparation. Furthermore, ZSY-27 (10-5M) 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 membrance-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.
