Transport of L-carnitine in isolated cerebral cortex neurons

The accumulation of carnitine was measured in cerebral cortex neurons isola ted from adult rat brain. This process was found to be lowered by 40% after preincubation with ouabain and with SH-group reagents (N-ethylmaleimide an d mersalyl). The initial velocity of carnitine transport was found to be in hibited by LF-aminobutyrate (GABA) in a competitive way (K-i = 20.9 +/- 2.4 mM). However, of various inhibitors of GABA transporters, only nipecotic a cid and very high concentrations of 1-[2-([(diphenylmethylene) amino] oxy)e thyl] -1,2,5,6-tetrahydro-3 -pyridine-carboxylic acid hydrochloride (NO-711 ) acid decreased carnitine accumulation while betaine, taurine and p-alanin e had no effect. The GABA transporters expressed in Xenopus laevis oocytes did not transport carnitine. Moreover, carnitine was not observed to dimini sh the accumulation of GABA in cerebral cortex neurons, which further exclu ded a possible involvement of the GABA transporter GAT1 in the process of c arnitine accumulation, despite the expression of this protein in the cells under study. The absence of carnitine transporter OCTN2 in rat cerebral cor tex neurons (K. A. Nalecz, D. Dymna, J. E. Mroczkowska, A. Broer, S. Broer M. J. Nalecz and R. Cecchelli, unpublished results), together with the inse nsitivity of carnitine accumulation towards betaines, implies that a novel transporting protein is present in these cells.