Distribution of acetylcholine-sensitive currents around the rabbit crystalline lens

The relative distribution of acetylcholine (ACh) receptors on the surface of the isolated ocular lens of the rabbit was determined from induced changes in translens short-circuit current (I(SC)) and the translenticular resistance (R(t)) at seven delineated, parallel zones from the anterior to the posterior pole. For this, one O-ring (from among several having different diameters) was used to separate two zones in a vertically arranged Ussing-type chamber. Different O-rings separated different zone pairs. Earlier experiments from this laboratory used a conventional divided chamber, which occluded the equatorial surface, to demonstrate that anterior applications of ACh transiently decreased the I(SC) due to an intracellular Ca(2+) release and inhibition of anteriorly located K(+) channels. Measurements obtained with the newly designed zonal arrangement determined that the entire epithelial surface from its anterior-most aspect to the equatorial region responds electrically to ACh exposure, while the posterior-most region does not. Furthermore, lens-mounting positions that resulted in separation of the epithelium so that portions of its surface were present in each hemichamber resulted in inverse current changes upon bilateral ACh addition to the bathing solutions. Reductions in outward cationic current across the anterior surface into the anterior bath upon ACh treatment were accompanied by an increase in translens resistance consistent with a closure of basolateral K(+) channels. Overall, these results suggest that the posterior fiber cells may lack ACh receptors, which are clearly present in the lens epithelium that covers about two-thirds of the rabbit lens surface area, and indicate that an ACh-evoked Ca(2+) signal does not spread throughout the epithelial layer. A functional role for lens acetylcholine receptors remains to be determined.