AJP - Heart and Circulatory Physiology, Vol 242, Issue 4 585-H592, Copyright © 1982 by American Physiological Society

ARTICLES

Characterization of carnitine transport in isolated perfused adult rat hearts

T. C. Vary and J. R. Neely

Carnitine transport was characterized in isolated perfused adult rat hearts. Carnitine uptake consisted of both a saturable (carrier-mediated) and nonsaturable (diffusion) component. Perfusion with 0.05 mM mersalyl acid, a sulfhydryl binding agent, inhibited the carrier-mediated transport but did not inhibit diffusion. The saturable transport system exhibited Michaelis-Menten kinetics with a maximum velocity of 154 nmol . g dry wt-1 . h-1 and an apparent Michaelis constant of 24 microM. D-carnitine competitively inhibited L-carnitine transport with an apparent inhibitor dissociation constant of 500 microM. Anoxia and K+ arrest resulted in only a slight inhibition of the saturable transport, suggesting that transport is not adenosine 5'-triphosphate (ATP) dependent. At physiological concentrations of extracellular carnitine (44 microM), total carnitine uptake rate was about 100 nmol . g dry wt-1 . h-1, 80% of which was by carrier-mediated transport. This rate of uptake would require about 60 h to replace the total cellular carnitine. Loss of tissue carnitine also appeared to be a slow process. These results suggest that carnitine is transported across the sarcolemma by both diffusion and carrier-mediated transport.