Phospholipid reorganization and bilayer destabilization during myocardial ischemia and reperfusion: a hypothesis.

The ultrastructure of myocardial tissue was studied during ischemia and reperfusion and during reperfusion with a calcium-containing solution after a short period of calcium-free perfusion (calcium paradox). After ischemia an aggregation of the sarcolemmal intramembranous particles was observed. Subsequent reperfusion resulted in further aggregation of the intramembranous particles and disruption of the sarcolemma, which was attended with the formation and extrusion of multilamellar, lipidic structures. Similar ultrastructural changes of the sarcolemma were observed during the calcium paradox. Our hypothesis is that these changes are a result of lateral phase separation of the membrane phospholipids and destabilization of the lipid bilayer. This reorganization of phospholipids may be induced by a decrease of the intracellular pH during ischemia, and an increase of the intracellular calcium content during reperfusion after ischemia and during calcium repletion after calcium-free perfusion. These ultrastructural changes of the sarcolemma are, in our view, a consequence of the physiochemical behaviour of the sarcolemmal phospholipids.