DECREASE IN CARDIAC PHOSPHATIDYLGLYCEROL IN STREPTOZOTOCIN-INDUCED DIABETIC RATS DOES NOT AFFECT CARDIOLIPIN BIOSYNTHESIS - EVIDENCE FOR DISTINCT POOLS OF PHOSPHATIDYLGLYCEROL IN THE HEART

Biosynthesis of phosphatidylglycerol (PG) and cardiolipin (CL) were in vestigated in perfused hearts of diabetic rats 4 days or 28 days after streptozotocin injection. Sham-injected and insulin-treated diabetic rats were used as controls. In addition, another group of rats fasted for 54 h was examined. Isolated rat hearts from these groups were perf used for 30 min with [P-32]P-i, and the radioactivity incorporated int o PG and CL and their pool sizes were determined in heart ventricles. There was no difference in the amount of radioactivity incorporated in to CL, PG or other phospholipids between all groups. In addition, the pool sizes of CL and other phospholipids were unaltered. However, a st riking decrease in the pool size of PG was observed in both diabetic a nd fasted rats compared to sham- and insulin-treated controls at 4 day s after streptozotocin injection. The decrease in PG mass in diabetic rats was rapid (within 24-48 h) and was localized to cardiac membranes . Diabetes did not affect the activity of the enzymes of PG and CL bio synthesis in the mitochondrial fraction, or phospholipase A activity i n subcellular fractions prepared from rat heart homogenates. In additi on, pulse-chase experiments confirmed that diabetes did not affect the rate of new PG or CL biosynthesis. Since radioactivity associated wit h PG was unaltered in continuous-pulse perfusion experiments, a calcul ated 1.8-fold increase in the specific radioactivity of cardiac PG was observed in the hearts of acute diabetic rats compared with controls. Since the radioactivity incorporated into PG and CL, and the rate of CL biosynthesis, were unaltered in diabetic-rat hearts compared with c ontrols, new CL was probably synthesized from newly synthesized PG. We postulate the existence of distinct pools of PG in the heart, and tha t the pool of newly synthesized PG used for CL biosynthesis does not a ppear to mix immediately with the pre-existing pool of PG in the isola ted intact rat heart.