Immunocytochemical localization of phosphatidylinositol-4,5-bisphosphate in dark- and light-adapted rat retinas.

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Abstract
Light-mediated hydrolysis of phosphatidylinositol-4, 5-bis-ph osphate (TPI) to 1, 2-diacylglycerol and D-myo-inositol 1, 4, 5-triphosphate (IP3) has been reported in the visual photoreceptor cells. We have investigated the localization of the TPI antigenic sites in dark-and light-adapted rat retinas using rabbit anti TPI antibodies (Ab). Sprague-Dawley rats were dark-, or light-adapted, or were exposed to a light flash. The eyes were fixed immedi-ately and the tissue sections stained with the rabbit anti TPI Ab. The per-oxidase-antiperoxidase method was used to find the localization of the TPI antigenic site. Image analysis of the sections was performed to obtain optical density profiles of the stain. Dark-adapted retinas showed intense staining of the rod outer segment (OS) layer but much less staining of the rod inner segment layer. Compared with the OS of dark-adapted retinas, those of the flash-bleached retinas were stained much less. The OS of fully bleached retinas showed little or no staining. The anti TPI Ab-protein A-gold conjugate intense-ly stained disks from dark-adapted retina but those from bleached retina much less. Our results suggest that rapid hydrolysis of TPI in rat rod outer segments occurs in vivo in response to light.

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