Transport of L-[3H]arginine in cultured neurons: characteristics and inhibition by nitric oxide synthase inhibitors.

To investigate whether transport of L-arginine into neurons plays an integral role in the metabolism of the novel neuromodulator nitric oxide, the uptake of L-[3H]arginine was characterized in cultured neurons of mouse cerebellum and cerebral cortex (neocortex). The transport of L-[3H]arginine was saturable and monophasic into both types of neurons with an apparent Km of 100 microM and Vmax of 2.6 nmol/min/mg of protein. The transport process was stereospecific, and the pattern of inhibition by basic L-amino acids was consistent with a "y+" transport system. The potencies with regard to inhibition of L-arginine uptake of the two inhibitors of nitric oxide synthase, NG-monomethyl-L-arginine and NG-amino-L-arginine (IC50 values of 120 and 65 microM, respectively), suggest that these nitric oxide synthase inhibitors may also reduce formation of nitric oxide and cyclic GMP via a block of arginine uptake. Overall, these data indicate that uptake of L-arginine could regulate its intracellular concentration and, consequently, its availability for synthesis of nitric oxide.