Photic regulation of L-arginine uptake in the golden hamster retina.

SAENZ, D; CYMERYNG, CORA BEATRIZ; DE NICHILO, A; SACCA, G; KELLER SARMIENTO, MI; ROSENSTEIN, RE

JOURNAL OF NEUROCHEMISTRY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2002 vol. 80 p. 512 - 519

0022-3042

One of the limiting steps in the regulation of nitric oxide (NO) synthesis is the availability of its precursor, L-arginine, which depends on the presence of a specific uptake system. A characterization of the L-arginine uptake mechanism in the golden hamster retina was performed. This mechanism was stereospecific, saturable, and monophasic, with an apparent Km of 56.1 . 2.0 lM and a maximum velocity of 36.0 . 2.8 pmol/mg prot/min. The basic amino acids L-lysine and L-ornithine but not D-arginine or the nitric oxide synthase inhibitors, Nx-nitro-L-arginine methyl ester and Nx-nitro-Larginine impaired L-arginine influx. Preincubation with L-lysine for 1 h prior to the transport assay significantly stimulated L-arginine uptake. Saturation studies of L-arginine uptake performed at 12.00 and 24.00 h indicated a higher value of Vmax at midnight than at midday. When the hamsters were placed under constant darkness or constant light for 48 h and killed at equivalent time points, representing subjective day and subjective night, the differences in L-arginine influx disappeared. Semiquantitative RT-PCR analysis showed that the levels of mRNAs for both CAT-1 and CAT-2B were significantly higher at midnight than at midday. L-Arginine significantly increased cGMP accumulation in a time-dependent manner, with maximal effects during the night. Based on these results, it might be presumed that hamster retinal L-arginine uptake is regulated by the photic stimulus. Keywords: L-arginine uptake, CAT, golden hamster, photic regulation, retina. J. Neurochem. (2002) 80, 512±519.