The potentiating effects of ethanol on the blue light depolarization of the retinal pigment epithelium

The retinal pigment epithelium (RPE) is the site of two major effects of ethanol. In humans, ethanol produces a slow damped oscillation in the steady electrical potential of the eye, which is generated primarily by the RPE. It has also been shown that ethanol potentiates the reversible, depolarizing effect of blue light on the transepithelial potential (TEP) of the isolated RPE. The present study demonstrates that in addition to the depolarizing effect of blue light on the TEP, a secondary, compensatory potential arises, which functions to maintain the TEP. The magnitude of the secondary response varies somewhat among preparations. It appears that ethanol eliminates or reduces the secondary, compensatory potential change which results in a large depolarization of the TEP when the RPE is irradiated with blue light. Microelectrode studies reveal that ethanol hyperpolarizes both the apical and basal membranes of the RPE with a greater effect noted in the apical membrane. This would account for the corneal positive potential elicited by ethanol in the human eye. Brief exposures (2-3 min) of blue light, after administration of 0.5% ethanol, results in a large (25-30 mV) depolarization of both membrane potentials as compared with 3 to 5 mV in untreated tissue. On the basis of our observations, it is hypothesized that some of the potentiating effects of ethanol in combination with other agents may result from an interference with a cellular adaptive response to impaired respiration rather than an additive effect on a common mechanism.