Mammalian photo receptors express IP3 receptor type I and phospholipase c-β4

Purpose. Previous studies in vertebrate pholoreceptors showed that light stimulâtes phosphatidylinositol 4,5-bisphosphate ( 'IP2) hydrolysis and inositol 1.4,5trisphosphate (IP3) production. Thus, phospholipase C (PLC) and IP3 receptor could he present in photoreceptors. We studied the expression patterns of PLCβ4 and 1P3 recepior type I (IP3RI) in sever il mammalian retina. Methods. Western blotting, RT-PCR, and immunocytoche nistry at the light and electron microscope (EM) levels. Results. IP3RI: The mRN A for IP3RI, amplified from rat retina total RNA by RT-PCR using specific primer., appeared at the appropriate size. On Western blois. two antibodies raised against different domains of IP3RI recognized a single band at 260 KD. In rat. cat, and monkey, immunostaining for IP3RI was strong in cone outer segments and weaker in rod outer segments. EM study showed that the receptor was localized to both cisk and plasma membranes. In monkey, double labeling for IP3RI and different jpsins revealed that IP3RI was expressed exclusively in red and green cones but i ot in blue cones. PLCβ4: In rodents, staining for PLCβ4 u as stronger in con ; outer segments than in rod outer segments. This staining wa restricted to the plasma membrane. Conclusion. Apparently, PLCβ4 and IP3 receptor type I are expr:ssed in photoreceptor outer segments and might mobilize C'a 'in response to light The stronger expression in red and green cones suggests that these proteins may t ontribute to the fast recovery of cone light responses.