Identification of alternate transcripts of neuronal nitric oxide synthase in the mouse retina

Nitric oxide (NO) is a major signaling molecule in the retina and CNS, with physiological roles in every cell type in the retina. Previous work shows that neuronal nitric oxide synthase (nNOS) is an important source of NO in the vertebrate retina. There are distinct, active alternative transcripts of nNOS observed in many tissues, including testes and brain, that may differ in both localization and enzyme kinetics. The present study characterized nNOS and the NO production from nNOS in the mouse retina in terms of its alternate transcripts, namely, nNOSα, nNOSβ, and nNOSγ. We examined both basal and light‐stimulated NO production as imaged using the NO‐sensitive dye 4‐amino‐5‐methylamino‐2′,7′‐difluorofluorescein diacetate‐FM (DAF‐FM), and we compared the NO production with the immunocytochemical localization of nNOS using antisera that recognize nNOSα/β or nNOSα/β/γ. Western blots suggested the presence of NOSα/γ protein in retina, but not nNOSβ, and we confirmed this at the message level by using a combination of RT‐PCR and quantitative real‐time PCR. Our findings indicated that the primary source of NO in the mammalian retina is nNOSα and that nNOSγ may contribute to NO production as well. © 2009 Wiley‐Liss, Inc.