Virmani M A, Conti R, Spadoni A, Rossi S, Arrigoni-Martelli E
Brain Res Mol Brain Res. 1994 Aug;25(1-2):105-12. doi: 10.1016/0169-328x(94)90284-4.
The ability of the primary rat cortical cells to take up L-carnitine increased with the age of the cultures and plateaued at around day 11 up to 25 days in vitro (DIV) when a slight decline was evident and by 32 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 microM) and DNP (50 microM), caused a small but significant decrease in the uptake (21, 11 and 16%, respectively). The uptake was highly dependent on the Na gradient, since 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-aminobutyric acid (GABA), acetyl-L-carnitine (ALC), D-carnitine, L-aminocarnitine and L-choline, with GABA being the most potent inhibitor (57% at 50 microM) and L-choline not being significantly active. The Na-dependent uptake of L-carnitine was saturable with a high Km (692 microM) and Vmax (839 pmol/min/mg). This Na-dependent component was not further additive with the GABA (500 microM) or the DNP (50 microM) inhibitable component, suggesting that it represented the same phenomenon, probably the Na gradient dependent transport of L-carnitine. The results indicate that the uptake of L-carnitine occurs by Na-dependent saturable process as well as non-saturable, Na-independent processes. At least the former uptake mechanism is potently inhibited by GABA.
原代大鼠皮质细胞摄取左旋肉碱的能力随培养时间增加，在体外培养11天左右至25天达到平台期，此时略有下降，到32天体外培养时，左旋肉碱摄取量大幅下降。左旋肉碱的摄取表现出复杂的成分。用氰化钠（1 mM）、鱼藤酮（1.25 microM）和二硝基苯酚（50 microM）消除线粒体能量供应，导致摄取量有小幅但显著的下降（分别为21%、11%和16%）。摄取高度依赖于钠梯度，因为哇巴因（0.5 mM）和无钠缓冲液（用250 mM蔗糖替代）分别使摄取量降低了54%和63%。与左旋肉碱结构相似的分子，如γ-氨基丁酸（GABA）、乙酰左旋肉碱（ALC）、D-肉碱、L-氨基肉碱和L-胆碱，对左旋肉碱摄取存在竞争，其中GABA是最有效的抑制剂（50 microM时抑制率为57%），而L-胆碱无明显活性。左旋肉碱的钠依赖性摄取具有高Km（692 microM）和Vmax（839 pmol/min/mg）的饱和性。这种钠依赖性成分与GABA（500 microM）或二硝基苯酚（50 microM）可抑制成分不再具有加和性，表明它们代表相同的现象，可能是左旋肉碱的钠梯度依赖性转运。结果表明，左旋肉碱的摄取通过钠依赖性饱和过程以及非饱和、非钠依赖性过程发生。至少前一种摄取机制受到GABA的强烈抑制。
