Regional distribution of the Na+ and K+currents around the crystalline lens of rabbit

Abstract

Early studies described asymmetrical electrical properties across the ocular lens in the anterior-to-posterior direction. More recent results obtained with a vibrating probe indicated that currents around the lens surface are not uniform by showing an outwardly directed K+ efflux at the lens equator and Na+ influx at the poles. The latter studies have been used to support theoretical models for fluid recirculation within the avascular lens. However, the existence of a nonuniform current distribution in the lens epithelium from the anterior pole to the equator has never been confirmed. The present work developed a modified short-circuiting technique to examine the net flows of Na+ and K+ across arbitrarily defined lens surface regions. Results indicate that passive inflows of Na+ occur at both the anterior polar region and posterior lens surface, consistent with suggestions derived from the vibrating probe data, whereas K+ efflux plus the Na+-K+ pump-generated current comprise the currents at the equatorial surface and an area anterior to it. Furthermore, Na+-K+ pump activity was absent at the posterior surface and its polar region in all lenses examined, as well as from the anterior polar region in most lenses. The latter unexpected observation suggests that the monolayered epithelium, which is confined to the anterior surface of the lens, does not express an active Na+-K+ pump at its anterior-most aspect. Nevertheless, this report represents the first independent confirmation that positive currents leave the lens around the equator and reenter across the polar and posterior surfaces.