CELLULAR UNCOUPLING INDUCED BY ACCUMULATION OF LONG-CHAIN ACYLCARNITINE DURING ISCHEMIA

Long-chain acylcarnitines (LCACs) increase rapidly within minutes afte r the onset of ischemia in vivo or hypoxia in vitro and produce a time -dependent reversible reduction in gap junctional conductance in isola ted myocyte pairs. The present study was performed to assess whether L CACs contribute to cellular uncoupling in response to ischemia in isol ated blood-perfused rabbit papillary muscles by use of simultaneous me asurements of transmembrane action potentials, extracellular electrogr ams, extracellular K+, and tissue LCACs and ATP. LCACs increased three fold in response to 20 minutes of no-flow ischemia from 127 +/- 5 to 3 97 +/- 113 pmol/mg protein (P<.01), concomitant with the onset of cell ular uncoupling, extracellular K+ accumulation, and a marked reduction in conduction velocity and action potential duration. To assess wheth er inhibition of the accumulation of LCACs modified the electrophysiol ogical alterations during ischemia, muscles were pretreated with eithe r sodium 2-(5-(4-chlorophenyl)-pentyl)oxirane-2-carboxylate (POCA, 10 mu mol/L) or oxfenicine (100 mu mol/L), inhibitors of carnitine acyltr ansferase I. Both POCA and oxfenicine completely prevented the increas e in LCACs even with 40 minutes of ischemia (138 +/- 37 and 56 +/- 4 p mol/mg protein, respectively), associated with a marked delay in the o nset and progression of cellular uncoupling and ischemic contracture. Although POCA and oxfenicine did not affect either the initial early r ise in extracellular K+ or the initial fall in conduction velocity, bo th agents markedly delayed the secondary rise in extracellular K+ as w ell as the secondary fall in conduction velocity, independent of the l evel of tissue ATP. Thus, LCACs accumulate during myocardial ischemia and contribute substantially to the initiation of cell-to-cell uncoupl ing. Inhibition of carnitine acyltransferase I and prevention of the i ncrease in LCACs markedly delays cellular uncoupling and development o f ischemic contracture in response to ischemia.