Figure 1. Immunogold labeling of PDE in ROS of rat retina. Light- or dark-adapted retinas were fixed and embedded in LR White resin. Ultrathin sections of the retina were incubated with PDEα antibody followed by donkey anti-rabbit secondary antibody conjugated with 12 nm gold particles. Electron micrographs were captured from dark-adapted (A) or light-adapted (B) retina. The scale bar represents 300 nm. The arrow indicates rim positioned phosphodiesterase (PDE). C: PDE distribution in light- or dark-adapted rod outer segment (ROS) disc membranes were quantified. Dark-adapted and light-adapted retinas were fixed and processed for immunogold labeling with PDEα antibody. The distances of each gold particle to the nearest ROS plasma membrane were measured, and the cumulative distribution profiles were plotted. Open squares represent the average distribution of PDE in light-adapted ROS, and filled squares represent PDE distribution in dark-adapted ROS. Error bars represented the standard error of the mean from four different experiments. Filled small circles with a dotted line represent a simulated random distribution of PDE. The observed distribution of PDE near ROS center in both light and dark-adapted conditions is lower than the given random distribution because the probability of obtaining sections that intersects the longitudinal axis of ROS is low.