The dependence of electrophysiological derangements on accumulation of endogenous long-chain acyl carnitine in hypoxic neonatal rat myocytes.
To determine whether accumulation of long-chain acyl carnitine contributes to electrophysiological abnormalities induced by hypoxia, we characterized effects of normoxic and hypoxic perfusion on the subcellular distribution of endogenous long-chain acyl carnitine and transmembrane potentials of cultured rat neonatal myocytes. Hypoxia increased long-chain acyl carnitine more than 5-fold. Sodium 2-[5-(4-chlorophenyl)-pentyl]-oxirane-2-carboxylate (10 microM), a carnitine acyltransferase inhibitor, precluded accumulation of long-chain acyl carnitine induced by hypoxia. Tissue was processed for electron microscopy by a procedure specifically developed for selective extraction of endogenous short-chain and free carnitine but retention of endogenous long-chain acyl carnitine. In normoxic-perfused cells, long-chain acyl carnitine was concentrated in mitochondria and cytoplasmic membranous components. Only small amounts were present in sarcolemma. Hypoxia increased mitochondrial long-chain acyl carnitine by 10-fold and sarcolemmal long-chain acyl carnitine by 70-fold. After 60 minutes of hypoxia, sarcolemma contained 1.4 X 10(7) long-chain acyl carnitine molecules/micron 3 of membrane volume, a value corresponding to approximately 3.5% of total sarcolemmal phospholipid. Hypoxia also significantly decreased maximum diastolic potential, action potential amplitude and maximum upstroke velocity of phase 0. Sodium 2-[5-(4-chlorophenyl)-pentyl]-oxirane-2-carboxylate inhibited accumulation of long-chain acyl carnitine in each subcellular compartment and prevented the depression of electrophysiological function induced by hypoxia. These results strongly implicate endogenous long-chain acyl carnitine as a mediator of electrophysiological alterations induced by hypoxia.
D000818:Animals; D000831:Animals, Newborn; D001345:Autoradiography; D002331:Carnitine / Q000502:physiology*; D004594:Electrophysiology; D004852:Epoxy Compounds / Q000494:pharmacology; D000860:Hypoxia / Q000473:pathology / Q000503:physiopathology*; D008564:Membrane Potentials / Q000187:drug effects; D009206:Myocardium / Q000473:pathology; D051381:Rats
D004852:Epoxy Compounds; C033891:ethyl 2-(5-(4-chlorophenyl)pentyl)oxiran-2-carboxylate; D002331:Carnitine