Photosensitivity of the isolated pigment epithelium and arachidonic acid metabolism: preliminary results.

The administration of 0.1-0.5% of ethanol produces a slow increase in the transepithelial potential (TEP) of about 2 mV in the bovine pigment epithelium (RPE) under ordinary room lighting. However, virtually no response could be observed when ethanol was administered in the dark. Because of this apparent light sensitivity, the ethanol induced response (EIR) was investigated to determine its spectral response characteristics, temporal interaction with light, and the effects of a variety of metabolic inhibitors as well as pertussis and cholera toxins. The spectral response curve peaked at 520 nm with a narrow half width. The EIR was found to be inhibited by pertussis toxin but not cholera toxin. Inhibition of either phospholipase A2 or lipoxygenase/cyclooxygenase resulted in a marked inhibition of the EIR. The incubating solutions of the apical surface of bovine and cultured chick embryo RPE were analyzed by RP-HPLC under conditions of weak white light and darkness. Two peaks in the chromatogram were observed to vary with these conditions and the presence of nordihydroguaiaretic acid simulated the effects of darkness. The RP-HPLC studies did not involve the employment of ethanol. Two different experimental procedures revealed the photosensitivity of the isolated RPE to weak light and suggest that light initiates or promotes arachidonic acid metabolism. A possible regulatory effect of retinoids was also indicated.