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RE Rosenstein; Photic Regulation of the Nitridergic Pathway in the Golden Hamster Retina . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3611.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Despite the potentially significant role of nitric oxide (NO) in retinal development, physiology, and pathology, little is known about the regulation of the retinal nitridergic pathway by the photic information. In this context, the aim of the present work was to characterize nitric oxide synthase (NOS) activity and L-arginine uptake in the golden hamster retina and to study the photic regulation of these parameters. Methods: NOS activity was assessed through the conversion of L-3H-arginine to L-3H-citrulline in retinal homogenates, whereas L-arginine uptake was determined in a crude synaptosomal fraction. NOS isoforms content was assessed by western blot analysis, while semiquantitative RT-PCR analysis was used to assess the levels of L-arginine transporters mRNAs. Retinal levels of cGMP were measured by radioimmunoassay. These parameters were assessed in the retina of hamsters kept under a light-dark photoperiod as well as in hamsters exposed to constant darkness for 48 h before the experiment. Results: Retinal NOS activity was partially Ca2+ and calmodulin-dependent, required NADPH, and was inhibited by L-arginine analogs. The characteristics of the L-3H-arginine transport indicated that the y+ is the predominant system in the hamster retina. Both NOS activity and L-arginine uptake were significantly higher at midnight than at midday. When the hamster were placed under constant darkness for 48 h, and sacrificed at subjective day and subjective night, the differences in both parameters disappeared. The levels of eNOS and nNOS as well as of both CAT-1 and CAT-2B mRNAs 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. Conclusion: Based on these results, it might be presumed that the nitridergic pathway in the hamster retina is regulated by the photic stimulus. Therefore, present results support the hypothesis that NO is involved in the transduction/transmission of light/dark signals in the retina.
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