Effects of bicarbonate ion on chick retinal pigment epithelium: membrane potentials and light-evoked responses1Presented in part at the annual meeting of the Association for Research in Vision and Opthalmology, Sarasota, Florida, May 6, 1994.1

The purpose of this study was to determine how changes in [HCO3 ] alter the electrical properties of the retinal pigment epithelium (RPE). Experiments were conducted on the isolated chick retina-RPE-choroid preparation. The chamber holding the preparation allowed independent perfusion of the retinal and the choroidal surfaces. The light-evoked trans-tissue potential (TTP), the trans-epithelial potential (TEP), the trans-retinal potentials, and the intracellularly-recorded apical and basal membrane potentials were studied. Increasing the [HCO3 ]0 in the choroidal 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 biphasic change of the RPE membrane potentials. There was also an increase in the amplitudes of the TEP, the c-wave and the slow PIII. The light-evoked subretinal K decrease was greater which is consistent with an increase in the photoreceptor light response. These observations indicated that the decrease of TTP resulted from a basal membrane hyperpolarization 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. © 1998 Elsevier Science Ltd. All rights reserved.