The effects of myocardial ischemia and nisoldipine pretreatment on the asymmetric distribution of phosphatidylethanolamine in a canine heart sarcolemmal preparation.

We examined the distribution of phosphatidylethanolamine (PE) in the membrane bilayer of sarcolemmal preparation isolated from the ischemic and nonischemic areas of dog ventricles. The membrane preparation, isolated by the Reeves and Sutko's method, was purified ninefold over homogenates as judged from the results of measurements of (Na+K+)-ATPase and K+-p-nitrophenylphosphatase activities, sialic acid, and cholesterol. Sealed vesicles were comprised of 60% inside-out-oriented and 40% rightside-out-oriented vesicles; 30% of the total were unsealed vesicles. The results obtained from the incubation of the membrane preparation with 2,4,6-trinitrobenzenesulfonic acid (TNBS) and cycloheptaamylose-fluorescamine complex, both of which served as nonpermeable chemical probes, indicated that 80% of the total PE was accessible from the outside. By contrast, it was possible to label up to 98% of the PE by using a permeable probe, 1-fluoro-2,4-dinitrobenzene. These results suggest that PE is predominantly localized in the cytosolic side of the sarcolemmal membrane bilayer in the dog heart. Ischemic lesion was produced in the dog heart by the occlusion of a branch of the left anterior descending coronary artery for 1.5 hr followed by 3 hr of reflow. The concentrations of both total phospholipid and phosphatidylcholine and PE in the sarcolemmal fraction prepared from the ischemic area of the myocardium were significantly decreased as compared to those from the nonischemic area. The magnitude of labeling sarcolemmal PE by TNBS was reduced in the preparation from the ischemic area as compared to that from the nonischemic area. This difference was abolished when the dog received nisoldipine (an iv injection of 5 micrograms/kg twice) or chlorpromazine (infusion at a rate of 10 micrograms/kg X min plus an iv injection of 400 micrograms/kg twice). These results suggest that ischemia decreased primarily the membrane PE existing at the cytosolic side of the sarcolemmal membrane and that pharmacological intervention can prevent the change in membrane lipids induced by ischemia.