Photoreceptive retinal ganglion cells: Involvement of a Phosphoinositide cycle in Phototransduction Mechanisms

CONTÍN, M A, VERRA DM, SALVADOR G, ILINCHETA M, GIUSTO NM AND GUIDO M.E

Fort Lauderdale, EEUU

Congreso; Annual meeting Association for Research in Vision and Ophthalmology (ARVO),; 2009

Association for Research in Vision and Ophthalmology (ARVO)

PHOTORECEPTIVE RETINAL GANGLION CELLS: Involvement of Phosphoinositide cycle in Phototransduction Mechanisms

Contín, M A¹, Verra DM¹, 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

Purpose: 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. Light activates Gq/11-class G proteins, which increase phospholipase C activity leading to the enhancement of Ca⁺², and membrane depolarization. However, it remains unknown the complete mechanism of phototransduction and involvement of PIPs in ipRGCs. To achieve this goal we examined in chick RGCs primary culture model, exposed to cool white light at different times: a) the calcium levels, b) the formation of inositol-P₃ and other inositols and c) the activity of Diacyl Glicerol kinase, Phosphatidil inositol Kinase and Phosphatidil inositol phosphate Kinase (DAGK, PIK and PIPK respectively).

Methods: Primary cultures of chicken RGCs were obtained at embryonic day 8 (E8) by anti-Thy-1 immunopanning and synchronized at time 0 by medium exchange. At the third day the cells were exposed to bright light (1200 lux) during 5, 30, 60, 90, 300 and 600 second. Then we measure calcium by microscopy with Fura-2, inositol-P₃ by Dowex chromatography columns and kinases activity in homogenates cell samples.

Results: our results show a significant increment of calcium levels in concordance whit a higher levels of Inositol-P₃ (1.3 fold) and an activation of PIK, PIPK and DAGK activities during short light stimuli (5 sec).

Conclusion: These results indicate that chicken ipRGC phototransduction involves a PIP cascade with higher activity of phosphoinositide cycle enzyme during the first 5 seconds of stimulation, suggesting the involvement of phosphoinositide cycle like phototransduction mechanism in rhabdomeric photoreceptor cells.