PHOSPHATIDYLSERINE SYNTHESIS IN GLIOMA C6 CELLS IS INHIBITED BY CA2-RETICULUM - EFFECTS OF 2,5-DI-TERT-BUTYLHYDROQUINONE AND THIMEROSAL( DEPLETION FROM THE ENDOPLASMIC)

The effects of 2,5-di-tertbutylhydroquinone (DBHQ) and thimerosal on p hosphatidylserine synthesis by the base exchange reaction and on calci um mobilization in intact glioma C6 cells were compared with that of t hapsigargin, a selective inhibitor of the endoplasmic reticulum Ca2+-A TPase. It has been found that all these agents inhibit phosphatidylser ine synthesis by 70%, but their effectiveness are different. The data show that this inhibition is caused by Ca2+ depletion of the endoplasm ic reticulum, indicating that phosphatidylserine synthesis requires hi gh concentration of Ca2+ within this structure. On this basis and on l iterature data, a new model for the localization of the serine base ex change enzyme in the endoplasmic reticulum membrane is proposed. (C) 1 996 Academic Press, Inc.