Phospholipid composition and Ca2+ uptake properties of plasma membrane isolated from canine stomach smooth muscle.

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Ito, T. and Sakai, Y. Phospholipid composition and Ca2+ uptake properties of plasma membrane isolated from canine stomach smooth muscle. Japanese Journal of Smooth Muscle Research, 22 (1), 11-19.-The Ca2+ uptake and phospholipids influencing it in plasma membrane isolated from canine stomach smooth muscle was investigated. The major phospholipids in plasma membrane were phosphatidylethanolamine (PE, 26%), phosphatidylcholine (PC, 20%) and phosphatidylserine + phosphatidylinositol (PS +PI, 15%). The cholesterol/phospholipid ratio in the membrane was 0.64. ATP-dependent Ca2+ uptake was inhibited by exogenous PE, PC and PS, but increased by PI. Saponin and phospholipase C inhibited ATP-dependent Ca2+ uptake and accelerated release of Ca2+ from actively loaded plasma membrane vesicles. In the absence of ATP, PE slightly and PI significantly increased Ca2+ uptake, but PC and PS did not affect the Ca2+ uptake. Release of Ca2+ from actively loaded vesicles was 5 times greater in the presence of PI than in its absence. Results suggest PI to be the most active of the tested phospholipids in influencing Ca2+movement across plasma membrane.