The Endocannabinoid System Is Present in Rod Outer Segments from Retina and Is Modulated by Light

Abstract

The aim of the present research was to evaluate if the endocannabinoid system (enzymes and receptors) could bemodulated by light in rod outer segment (ROS) from bovine retina. First, we analyzed endocannabinoid 2-arachidonoylglycerol (2-AG) metabolism in purified ROSobtained from dark-adapted (DROS) or light-adapted(LROS) retinas. To this end, diacylglycerol lipase (DAGL), monoacylglycerol lipase (MAGL), and lysophosphatidatephosphohydrolase (LPAP) enzymatic activities were analyzed using radioactive substrates. The protein content ofthese enzymes and of the receptors to which cannabinoids bind was determined by immunoblotting under lightstimulus. Our results indicate that whereas DAGL and MAGLactivities were stimulated in retinas exposed to light,no changes were observed in LPAP activity. Interestingly, the protein content of the main enzymes involved in 2-AGmetabolism, phospholipase Cβ1(PLCβ1), and DAGLα(synthesis), and MAGL (hydrolysis), was also modified bylight. PLCβ1content was increased, while that of lipases was decreased. On the other hand, light produced anincrease in the cannabinoid receptors CB1 and CB2 and adecrease in GPR55 protein levels. Taken together, ourresults indicate that the endocannabinoid system (enzymes and receptors) depends on the illumination state of theretina, suggesting that proteins related to phototransduction phenomena could be involved in the effects observed.