Calcium uptake, release and Mg-ATPase activity of sarcoplasmic reticulum from arterial smooth muscle

Sarcoplasmic reticulum (SR) isolated from rat aorta exhibited ATP dependent Ca2+ uptake in the presence of Mg2+. The maximum capacity and apparent binding constant were 23n moles/mg and 1.8 X 10(4) M (-1), respectively. The energy source of this active Ca2+ accumulation would be Mg-ATPase associated with the membrane. Ca2+ which was taken up inside of sarcoplasmic reticulum was released rapidly by washout with the medium containing no Ca2+. These facts suggest that sarcoplasmic reticulum in vascular smooth muscle cell may play and important role in the regulation of intracellular Ca2+ concentration.