Light-activation of the Phosphoinositide Cycle in Intrinsically Photosensitive Chicken Retinal Ganglion Cells

MARIA ANA CONTÍN, DANIELA M. VERRA, GABRIELA SALVADOR, MONICA ILINCHETA, NORMA M. GIUSTO AND MARIO E. GUIDO.

INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE

ASSOC RESEARCH VISION OPHTHALMOLOGY INC

Año: 2010 vol. 51 p. 5491 - 5498

0146-0404

PURPOSE. In vertebrates, intrinsically photosensitive retinal gan-glion cells (ipRGCs) acting as nonvisual photoreceptors transmitenvironmental illumination information to the brain, regulatingdiverse non–image-forming tasks. The phototransduction cascadein chicken ipRGCs has been shown to resemble that of rhabdo-meric photoreceptors and involves phospholipase C (PLC) acti-vation. The current work was an investigation of the participationof the phosphoinositide (PIP) cycle in this mechanism and ofwhether changes in activities of inositol 1,4,5-trisphosphate (IP3)and PIP kinase are triggered by light.METHODS. Primary cultures of Thy-1 immunopurified chickenembryonic RGCs were exposed to bright light pulses or kept inthe dark, to assess intracellular Ca2 mobilization by Fluo-3 AMfluorescence microscopy, IP3 levels, and enzymatic activities ofdiacylglycerol, phosphatidylinositol, and phosphatidylinositolphosphate kinases (DAGK, PIK, and PIPK, respectively), byradioactive assays. The presence of different melanopsins(Opn4m and Opn4x) and other photopigments was deter-mined by RT-PCR and immunochemistry.RESULTS. Cultured RGCs expressing different nonvisual pho-topigments displayed a significant and rapid increase in IP3levels (1.3-fold) and Ca2 mobilization by light, which wasreversed by administration of the PLC inhibitor U73122 (5M). Brief light pulses also caused a very rapid and transientactivation of DAGK, PIK, and PIPK compared with that in thedark control.CONCLUSIONS. The results indicate for the first time that lightstimulation of chicken RGC cultures activates the PIP cycle,causing an increase in intracellular levels of IP3, changes inlevels of phosphatidic acid, PIP, and PIP2; and mobilization of Ca.