Phospholipids, calcium binding and arterial smooth muscle membranes

The effects of phosphatidylserine (PS), phosphatidylinositol (PI), and phosphatidylcholine (PC) on 45Ca uptake, binding and efflux in canine aortic microsomes and of PS on 45Ca distribution and tension in rabbit aortic smooth muscle are reviewed. PS potentiated contractile responses to histamine and norepinephrine, and these effects were correlated with PS-induced removal of superficial Ca++ and decreased exchangeability of membrane Ca++. In microsomal preparations, PS and PI (but not PC) increased high affinity 45Ca binding but not 45Ca uptake. Only PI increased low affinity 45Ca uptake, and both PS and PI decreased oxalate-potentiated 45Ca uptake. The Ca++ ionophore A23187 removed membrane Ca++ in contrast to PS and PI. Exogenous negatively-charged PS or PI may enter plasma membranes and increase Ca++ binding levels. The roles of endogenous phospholipids in altered vascular responsiveness and function in disease states may be of critical importance.