PHOTORECEPTIVE RETINAL GANGLION CELLS: phototransduction mechanisms

CONTIN MARIA ANA; VERRA DANIELA MARIANA; SALVADOR GABRIELA; ILINCHETA MONICA; GIUSTO NORMA; GUIDO MARIO E

Carlos Paz, Cordoba Argentina

Congreso; Sociedad Argentina de Investigacion en Biologia Molecular y Celular (SAIB); 2008

SAIB

PHOTORECEPTIVE RETINAL GANGLION CELLS: phototransduction mechanisms. Contín, M A1, D.M Verra, Salvador G2,  Ilincheta M2, Giusto NM2 and Guido, ME1. 1CIQUIBIC (CONICET) ? Dpto. Qca Biol., Fac. Cs. Químicas, UNC-Córdoba; 2INIBIBB-UNS, Bahia Blanca mcontin@mail.fcq.unc.edu.ar             In Vertebrates, non-visual photoperception provides a measure of environmental lighting conditions that synchronizes biological clocks through retinal ganglion cells (RGCs) that send photic information to the brain. A subset of RGCs expressing the photopigment melanopsin (Opn4) is intrinsically photosensitive (ipRGC) acting as circadian photoreceptors. Our studies and others showed that the nature of the biochemical events in ipRGC phototransduction may resemble that in rhabdomeric (Rb) photoreceptors involving the phosphoinositide (PIP) cascade. Light activates Gq/11-class G proteins, the activity of phospholipase C with the increase in cytoplasmic Ca+2 and membrane depolarization. However, it remains unknown the complete mechanism of phototransduction and involvement of PIPs in ipRGCs. To investigate this, we measured the formation of inositol-P3 and other inositols (by Dowex chromatography columns) in chicken RGC cultures by anti-Thy-1 immunopanning exposed to cool white light at different times. Then we assessed the activity of DAG Kinase and PIP Kinases (PIK and PIPK) in homogenates from the same conditions. Our results showed a 1.3 fold increase of Inositol-P3 and inhibition of PIK, PIPK and DAGK activities during short light stimuli (1 min). These results indicate that chicken ipRGC phototransduction involves a PIP cascade similar to that in Rb photoreceptors.