pH-dependent Ca2+ interaction with phospholipids related to phosphatidylethanolamine N-methylation

The interactions of PE and its N-methylated derivatives (PME, PDE AND PC) WITH Ca2+ were examined. PE and the intermediate phospholipids of PE N-methylation (PME and PDE) interacted with Ca2+ in a pH-dependent and reversible manner. When these phospholipids were present in the heptane phase, Ca2+ in the aqueous phase was translocated into the heptane phase at alkaline pH but not at acidic pH. PDE was also effective for the translocation even at around neutral pH, while PC hardly translocated Ca2+ at pH 6.0-9.2. The amounts of Ca2+ interacting with these phospholipids were in the following order: PDE is greater than PME is greater than PE is much greater than PC. P1, phosphatidic acid and PS interacted with Ca2+ in the whole pH range examined. The Ca2+ interactions with P1 and phosphatidic acid were independent of pH, while PS interacted with more Ca2+ at alkaline pH. These phospholipids interacted with Ca2+ most strongly among the cations studied. Liposomes containing PDE also bound the highest amounts Ca2+ among PE and its N-methylated derivatives. Furthermore, mammalian cultured cell membranes, which contain increased amounts of PDE by in vivo modification with N,N'-dimethylethanolamine, bound more Ca2+ than those prepared from choline-treated control cells.