A metabolic role for mitochondria in palmitate-induced cardiac myocyte apoptosis

After cardiac ischemia, long-chain fatty acids, such as palmitate, increase in plasma and heart. Palmitate has previously been shown to cause apoptosi s in cardiac myocytes. Cultured neonatal rat cardiac myocytes were studied to assess mitochondrial alterations during apoptosis. Phosphatidylserine tr anslocation and caspase 3-like activity confirmed the apoptotic action of p almitate. Cytosolic cytochrome c was detected at 8 h and plateaued at 12 h. The mitochondrial membrane potential (Delta Psi) in tetramethylrhodamine e thyl ester-loaded cardiac myocytes decreased significantly in individual mi tochondria by 8 h. This loss was heterogeneous, with a few energized mitoch ondria per myocyte remaining at 24 h. Total ATP levels remained high at 16 h. The Delta Psi loss was delayed by cyclosporin A, a mitochondrial permeab ility transition inhibitor. Mitochondrial swelling accompanied changes in D elta Psi. Carnitine palmitoyltransferase I activity fell at 16 h; this decl ine was accompanied by ceramide increases that paralleled decreased complex III activity. We conclude that carnitine palmitoyltransferase I inhibition , ceramide accumulation, and complex III inhibition are downstream events i n cardiac apoptosis mediated by palmitate and occur independent of events l eading to caspase 3-like activation.