Phospholipid phosphorylation in erythrocyte of spontaneously hypertensive rats

The rapid turnover of phosphoinositides within membranes suggests that these lipids play an important role in membrane function. Since various abnormalities have been described in the erythrocyte membrane of the spontaneously hypertensive rat (SHR) we have studied the turnover of phosphoinositides in the erythrocyte of SHR and age-matched normotensive Wistar-Kyoto rat (WKY). This was achieved by measuring the incorporation of 32P into inositol lipids after incubation of 1) intact erythrocytes with [32P]orthophosphate and 2) isolated ghost membranes with [gamma-32P]ATP. In both series of experiments more than 99% of the radioactivity incorporated into lipids was into the polyphosphoinositides diphosphoinositide (DPI) and triphosphoinositide (TPI). In both intact erythrocytes and ghost membranes, the levels of 32P incorporated into DPI and TPI were significantly different in SHR than in WKY. Further analysis of factors known to influence the labeling of DPI and TPI indicated that this could be ascribed to decreased activities of phosphatidylinositol kinase and/or DPI kinase, with respect to ATP as substrate. Moreover comparison of data obtained in intact cells with those obtained with ghost membranes suggests that within the SHR erythrocyte, membrane-cytosol interactions may occur that could also be responsible for the alteration of phosphoinositide labeling observed in hypertensive animals. Since phosphoinositides have been reported to be involved in the Ca2+-gating system of membrane, our findings could be associated with the abnormal Ca2+ binding and transport recently described in SHR erythrocyte.