Localization of 2′,3′-cyclic nucleotide-3′-phosphohydrolase within the vertebrate retina

Histochemical and immunochemical techniques are used to locate 2′,3′-cyclic nucleotide-3′-phosphohydrolase (2′,3′-cNMP-3′ase) within cells of the vertebrate retina. A new histochemical method is described which links the hydrolysis of 2′,3′-cNADP to the formation of a reduced, insoluble tetrazolium formazan. Photoreceptors from fish, bovine, and rat retinas are stained by this procedure. The reaction is blocked by 2′-AMP, a known inhibitor of 2′,3′-cNMP-3′ase. Rabbit antibodies prepared against 2′,3′-cNMP-3′ase from bovine brain are found to cross-react with bovine and rat retinal enzymes. Peroxidase-labeled antibody shows by light microscopy the greatest staining along the inner segments of the photoreceptors. Electron microscopy of the same preparations confirm binding to the plasma membrane of the inner segments of both rods and cones. Retinal 2′,3′-cNMP-3′ase is thus predominantly associated with the photoreceptors, suggesting some role for 2′,3′-cyclic nucleotides as substrates in visual function.