Phorbol ester and light-induced endogenous phosphorylation of rat retinal rod outer segment (ROS) proteins

The authors have previously described the presence of a C-kinase in bovine ROS and its in vitro activation by light in crude rat ROS. In this study, they have labelled the retinas with 33Pi by intravitreal injection and compared the phosphorylation pattern of ROS proteins induced by light and activators of the C-kinase phosphorylation system. Except for light treatment, all procedures were carried out in complete darkness using an infrared image converter. Incubation of 33P-labelled retinas in light for 5 minutes resulted in the phosphorylation of rhodopsin, 80,65,47,44, and 15kd proteins of crude ROS. Incubation of 33P-labelled retinas with 5μM 12-0-tetradecanoylphorbol-13-acetate (TPA) resulted in the phosphorylation of 80,65,47,44,33, and 15 kd proteins of crude ROS. The complete darkness control did not exhibit any phosphorylation or proteins whereas the red light control exhibited variable low phosphorylation of 80,47,44, and 15kd proteins. 1-oleoyl-2-acetyl-glycerol (OAG) at 500μg/ml caused the phosphorylation of the same proteins as observed with TPA. TPA (0.5-500μM) and OAG (150-500μg/ml) did not induce rhodopsin phosphorylation. Since light, TPA and OAG exhibit similarities in the phosphorylation patterns of proteins (except for rhodopsin), these results suggest at least a partial linkage of light and C-kinase effects in vivo