AGGREGATION OF MYOCARDIAL SARCOLEMMAL TRANSMEMBRANE PROTEINS IS NOT HINDERED BY AN INTERACTION WITH THE CYTOSKELETON - POSSIBLE IMPLICATIONS FOR ISCHEMIA AND REPERFUSION

Heart myocytes subjected to ischemia show a clustering of the sarcolem mal proteins. In the erythrocyte membrane, a system in which intramemb ranous particle (IMP) aggregation is extensively studied, it is found that an IMP aggregation can in principle only occur upon removal of th e membrane skeleton of spectrin and actin by rather drastic experiment al conditions. With regard to phospholipid composition and topology th e sarcolemma and the erythrocyte membrane show large similarities and therefore it was proposed that a loss of the interaction of the IMPs a nd the cytoskeleton is also a prerequisite for the sarcolemmal IMP agg regation (Verldeij et al., 1990). Freezing myocardial tissue, both fro m adult and neonatal rat, from temperatures lower than 37 degrees C re sulted in an aggregation of the sarcolemmal IMPs. The aggregation is p roportional to the degree of lowering of the temperature at which the tissue is cryofixed. This in contrast to the erythrocyte membrane, whe re lowering the temperature only induces moderate IMP aggregation, The IMP aggregation in the sarcolemma is reversible upon a subsequent inc rease in incubation temperature, The results clearly demonstrate that the interaction between the sarcolemmal proteins does not hinder aggre gation of the IMPs, as proposed previously, and suggest that loosening of this complex does not have to proceed the aggregation of the sarco lemmal intramembranous particles during ischemia. (C) 1995 Academic Pr ess Limited