Calcification of Liposomes and Red Cell Ghosts In Vitro and In Vivo

·To study the role of membranous phospholipids in calcification , liposomes made of phosphatidylserine and red blood cell ghosts (RBCG) prepared from rat and canine blood were incubated in minimal essential medium (MEM) with 2 .5 mM (mmol/l) calcium and 1.3 mM phosphate, pH 7.4 (MEM-2.5), and homologous (rat) or autologous (canine) plasma filtrate (serum) at 37 °C for up to 1 week. Calcification was determined by electron probe microanalysis , electron diffraction, and depletions of calcium and phosphate from MEM-2.5 and sera. Liposomes and rat-RBCG incubated in MEM-2 .5 and serum calcified in a week, whereas isolated collagen and elastin did not. Liposomes and rat-RBCG implanted in rat peritoneal cavities calcified in 4 weeks. Calcification of both liposomes and RBCG under identical conditions suggests that phospholipids in membrane may play a role in calcification. Canine RBCG incubated in MEM-2.5 and serum began to calcify on day one and grew heavier with further incubations . Calcification of.RBCG in autologous serum indicates that calcification is prevented by normal red cells. The capacity to prevent calcification by red cells is apparently abolished by removal, during RBCG preparation, of the cytoplasmic content.