L-CARNITINE UPTAKE INTO PRIMARY RAT CORTICAL CULTURES - INTERACTION WITH GABA

The ability of the primary rat cortical cells to take up L-carnitine i ncreased with the age of the cultures and plateaued at around day 11 u p to 25 days in vitro (DIV) when a slight decline was evident and by 3 2 DIV there was a major decrease in L-carnitine uptake. The uptake of L-carnitine displayed complex components. Elimination of mitochondrial energy supply by NaCN (1 mM), rotenone (1.25 mu M) and DNP (50 mu M), caused a small but significant decrease in the uptake (21, 11 and 16% , respectively). The uptake was highly dependent on the Na gradient, s ince ouabain (0.5 mM) and Na free buffer (replaced by 250 mM sucrose), reduced uptake by 54 and 63%, respectively. There was competition of L-carnitine uptake by molecules resembling its structure, e.g. gamma-a minobutyric acid (GABA), acetyl-L-carnitine (ALC), D-carnitine, L-amin ocarnitine and L-choline, with GABA being the most potent inhibitor (5 7% at 50 mu M) and L-choline not being significantly active. The Na-de pendent uptake of L-carnitine was saturable with a high K-m (699 mu M) and Vmax (839 pmol/min/mg). This Na-dependent component was not furth er additive with the GABA (500 mu M) or the DNP (50 mu M) inhibitable component, suggesting that it represented the same phenomenon, probabl y the Na gradient dependent transport of L-carnitine. The results indi cate that the uptake of L-carnitine occurs by Na-dependent saturable p rocess as well as non-saturable, Na-independent processes. At least th e former uptake mechanism is potently inhibited by GABA.