Phospholipase Cγ1 in Bovine Rod Outer Segments: Immunolocalization and Light‐Dependent Binding to Membranes

: We have investigated the isozymes of a phosphoinositide‐specific phospholipase C (PLC) in bovine retina using several monoclonal antisera to PLCβ1, γ1, and δ1. Immunoblot analysis showed that all three isozymes were present in the retina. Immunocytochemical localization in frozen bovine retina sections showed that PLCγ1 was present in the photoreceptor cell layer, outer plexiform cell layer, inner plexiform cell layer, and ganglion cell layer. Immunoreaction within the photoreceptor cell layer was dependent on dark/light adaptation state of retinas. Immunoblot analysis of rod outer segments (ROS) with monoclonal or polyclonal antibodies to PLCγ1 showed the presence of an immunoreactive band of 140 kDa. ROS prepared from retinas light‐adapted in vitro had more PLCγ1 on immunoblots than ROS from dark‐adapted retinas. PLC enzyme activity in ROS from light‐adapted retinas was 69 and 46% higher than ROS from dark‐adapted retinas, when assayed in the presence and absence of ATP, respectively. This increase in enzyme activity was observed at [Ca2+]free between 0.32 and 100 µM. These results demonstrate the presence of PLCγ1 in bovine ROS and show that ROS prepared from light‐adapted retinas are enriched in this isozyme, suggesting that light may promote the binding of this isozyme to bleached ROS membranes.