Carnitine transport in rat heart slices: II. The carnitine/deoxycarnitine antiport.

In rat heart slices carnitine transport occurs in an exchange process with deoxycarnitine. This has been demonstrated in double labelling experiments allowing a preloading of either 3H-carnitine or 14C-deoxycarnitine, the immediated precursor of carnitine. The stoichiometry of the carnitine/deoxycarnitine exchange resulted close to one in both directions. The relative kinetics supports the assumption that the process is mediated by a membrane bound protein. The results may rationalize the circumstance that carnitine is taken up by myocardium against a concentration gradient. The meaning of the carnitine/deoxycarnitine exchange is discussed.