The accumulation of carnitine was measured in cerebral cortex neurons isolated from adult rat brain. This process was found to be lowered by 40% after preincubation with ouabain and with SH-group reagents (N-ethylmaleimide and mersalyl). The initial velocity of carnitine transport was found to be inhibited by 4-aminobutyrate (GABA) in a competitive way (K i 20.9^2.4 mm). However, of various inhibitors of GABA transporters, only nipecotic acid and very high concentrations of 1-[2-([(diphenylmethylene)amino]oxy)ethyl]-1,2,5,6-tetrahydro-3-pyridinecarboxylic acid hydrochloride (NO-711) acid decreased carnitine accumulation while betaine, taurine and b-alanine had no effect. The GABA transporters expressed in Xenopus laevis oocytes did not transport carnitine. Moreover, carnitine was not observed to diminish the accumulation of GABA in cerebral cortex neurons, which further excluded a possible involvement of the GABA transporter GAT1 in the process of carnitine accumulation, despite the expression of this protein in the cells under study. The absence of carnitine transporter OCTN2 in rat cerebral cortex neurons (K. A. Naøe Îcz, D. Dymna, J. E. Mroczkowska, A. Broe Èr, S. Broe Èr, M. J. Naøe Îcz and R. Cecchelli, unpublished results), together with the insensitivity of carnitine accumulation towards betaines, implies that a novel transporting protein is present in these cells.

Accumulation of palmitoylcarnitine inside the neuroblastoma NB‐2a cells was observed to promote their differentiation. Exposure of these cells to carnitine resulted in an intensive estrification of this compound with palmitate. Accumulation of palmitoylcarnitine inside the cells coincided with an increase of the B‐50 protein. A phorbol ester stimulated phosphorylation of the B‐50 protein and of a coprecipitated 78 kDa band was diminished by 50% in the presence of palmitoylcarnitine. A transfer of B‐50 to the membranes was observed to occur at increased intracellular palmitoylcarnitine (upon treatment with 1 mM carnitine). A role of palmitoylcarnitine, as a protein kinase C modulator and a store of precursor for the process of palmitoylation has been postulated.

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