EFFECT OF THE IONOPHORE-A23187, THAPSIGARGIN, CAFFEINE AND HEPARIN ON PHOSPHATIDYLSERINE SYNTHESIS IN RAT-LIVER MICROSOMAL FRACTION

It has been shown that the incorporation of [14C]serine into phosphatidylserine in rat liver microsomal fractions is distinctly stimulated by ATP and Mg2+ at low (10 μM) Ca2+ concentration.This stimulation occurred in untreated microsomes, but did not occur in fully disrupted microsomal vesicles. The stimulatory effect of ATP and Mg2+ on phosphatidylserine synthesis was reduced by calcium ionophore A23187 and by thapsigargin, which is a specific blocker of Ca2+-ATPase. It was also diminished by caffeine and enhanced by heparin, agents known to modulate Ca2+ release by receptor channels. It is therefore postulated that the synthesis of phosphatidylserine occurs on the luminal side of the endoplasmic reticulum and can be regulated by events responsible for Ca2+ release and entry into the structures. © 1993 Academic Press, Inc.