Muscle carnitine deficiency: fatty acid metabolism in cultured fibroblasts and muscle cells.

L-carnitine, as little as 25nM, greatly increased oxidation of palmitate by carnitine-depleted cultured human skin fibroblasts from normal subjects, and from two patients with muscle carnitine deficiency. Carnitine stimulated oxidation of labeled palmitate by cultured muscle cells from rat, normal humans, or patients with muscle carnitine deficiency. Carnitine reduced incorporation of palmitate into glycerides in normal fibroblasts, and it may thereby counteract cellular accumulation of glycerides in cells. Fibroblasts from patients with muscle carnitine deficiency took up labeled carnitine at a normal rate. Dexamethasone increased palmitate oxidation by normal human fibroblasts and muscle cells of rat, and normal and muscle carnitine-deficient humans. The results parallel the reported effectiveness of carnitine, glucocorticoids, or medium-chain triglycerides in treatment of these patients.