Calcium ion-dependent diacylglycerol accumulation in erythrocytes is associated with microvesiculation but not with efflux of potassium ions

Abstract

Erythrocytes from several different species were exposed to Ca2+ and the bivalent-cation ionophore A23187. The lipid composition, morphology and K+ permeability of the treated cells were investigated. Erythrocytes from human, rat, guinea pig and rabbit (a) showed an increased concentration of 1,2-diacyl-sn-glycerol and enhanced labelling of phosphatidate with 32P, (b) underwent echinocytosis and outward vesiculation, and (c) rapidly released much of their intracellular K+. Pig cells showed only the K+ loss, and ox and sheep (high-K+) cells showed none of these Ca2+-evoked effects. All of the cells underwent stomatocytosis and inward vesiculation when treated externally with Clostridium perfringens phospholipase C. These results support the idea that there is a correlation between the asymmetric insertion of diacylglycerol (or ceramide) into the membrane and the shape-changes leading to microvesiculation, but they indicate that Ca2+-triggered K+ efflux and diacylglycerol production are unrelated events. Erythrocytes of chicken and turkey showed no Ca2+-stimulated K+ efflux. They showed slight ionophore A23187-stimulated vesiculation, but this appeared to be associated with the appearance in the membrane of ceramide rather than of diacylglycerol. Phospholipase C treatment caused very similar changes in morphology and phosphatidate labelling to those seen in mammalian erythrocytes.