Cultured chick retinal pigment epithelial cells phagocytosed polystyrene latex particles. The phagocytosis was inhibited very specifically by melatonin, which attained 50% inhibition at about 10^––16M. Other indole compounds such as 5-methoxytryptophol, 5-hydroxytryptophol, 6-hydroxymelatonin, N-acetylserotonin, 5-methoxytryptamine and serotonin were also inhibitory although their effects were less than 1/10,000 that of melatonin. Possible retinal neurotransmitters, acetylcholine, γ-aminobutyric acid, glycine, dopamine, aspartic acid and glutamic acid, had no or only a minimum inhibitory effect, and was also the case for prostaglandin D₂, E₂, F₂α, and I₂. Taurine was not inhibitory at all. Among nucleotides, cyclic AMP specifically inhibited phagocytosis, giving 50% inhibition at about 10^––11M. Melatonin inhibition was increased by copresence of isobutylmethylxanthine. Inhibition by either melatonin or cyclic AMP was reversed by dibutyryl cyclic GMP. The reversal was observed also with compounds which were expected to increase intracellular cyclic GMP. Prostaglandin D₂ reversed inhibition in both cases, but its effect was incomplete and per se it had an inhibitory effect. Melatonin derivatives reversed inhibition by melatonin alone but not inhibition by cyclic AMP. Taurine efficiently reversed both kinds of inhibition. Other possible neurotransmitters were ineffective. Taurine was thus the most effective of these compounds. We suggest the following hypothetic control mechanism of phagocytic activity of the pigment epithelial cells: melatonin and cyclic AMP are intercellular and intracellular signals, respectively, of stopping phagocytosis, while taurine and cyclic GMP are intercellular and intracellular signals, respectively of cancelling this stop signal. Phagocytic activity of chick retinal pigment epithelial cells might be regulated by the concentration ratio of melatonin to taurine in the interphotoreceptor space.

A posterior fundus examination around the macula was performed for the patients diagnosed spontaneous posterior vitreous separation. Of 898 eyes, 358 eyes had epiretinal membranes. The presence of membranes did not correlate to sex. The 2-fold greater incidence was observed in the aged group and emmetropic patients. For the progression, age, sex or refractive error alone was not significant, while aged, emmetropic patients showed greater incidence. The longer duration of the membrane existence also indicated the greater progression.

Argon laser photocoagulation was placed on the confluent monolayer of cultured chick retinal pigment epithelial cells as a model of the regeneration process of retinal pigment epithelium after laser burn. The intense fibrillar net immunofluorescent pattern of fibronectin appeared on the burnt area from 2 h after the laser application, before the beginning of tissue reconstruction. Fibronectin was observed for several days, then became undetectable before the complete regeneration of retinal pigment epithelial cells. This indicates that fibronectin is involved in the early regeneration process of retinal pigment epithelium.

Phenothiazines (chlorpromazine, trifluoperazine, prochlorperazine, and fluphenazine) showed dose-dependent inhibition of phagocytosis of latex particles by cultured chick retinal pigment epithelial cells at concentrations of 10^-5–10^-14 mol/1. Calmodulin antagonists (W-5, W-7, W-12, and W-13) showed similar effects as phenothiazines at concentrations of 10^-5–10^-14 mol/1. These reactions were partially reversible at a concentration of 10^-9 mol/1. Cells cultured for 3 days in the presence of 10^-5 mol/1 chlorpromazine or 10^-5 mol/1 W-7 demonstrated morphologic alterations in their microvilli which were similar to those seen after cytochalasin B treatment, i.e., thinning and elongation of the microvilli with honeycomb-like changes.

Antichick fibronectin antiserum, noncross-reactive to bovine fibronectin, was prepared to determine the production of fibronectin by cultured chick retinal pigment epithelial cells which were grown in the presence of fetal bovine serum. The typical fibrillary net pattern of fibronectin was observed by an indirect immunofluorescent technique when this specific antiserum reacted with cultured chick retinal pigment epithelial cells. Cultured chick retinal pigment epithelial cells were shown to produce fibronectin.