EFFECTS OF BICARBONATE ION ON CHICK RETINAL-PIGMENT EPITHELIUM - MEMBRANE-POTENTIALS AND LIGHT-EVOKED RESPONSES

The purpose of this study was to determine how changes in [HCO3-] alte r the electrical properties of the retinal pigment epithelium (RPE). E xperiments were conducted on the isolated chick retina-RPE-choroid pre paration. The chamber holding the preparation allowed independent perf usion of the retinal and the choroidal surfaces. The light-evoked tran s-tissue potential (TTP), the trans-epithelial potential (TEP), the tr ans-retinal potentials, and the intracellularly-recorded apical and ba sal membrane potentials were studied. Increasing the [HCO3-] in the ch oroidal bath from 25 to 40 mEq/l led to an increase in the TTP and TEP . The same change in the retinal bath decreased the TTP because of a b iphasic change of the RPE membrane potentials. There was also an incre ase in the amplitudes of the TEP, the c-wave and the slow PIII. The li ght-evoked subretinal K+ decrease was greater which is consistent with an increase in the photoreceptor light response. These observations i ndicated that the decrease of TTP resulted from a basal membrane hyper polarization followed by an apical membrane depolarization induced by an increase in retinal [HCO3-](0). The relationship of these potential changes to the human bicarbonate responses is discussed. (C) 1998 Els evier Science Ltd. All rights reserved.