title: Intracellular activities of chloride, potassium and sodium ions in rabbit corneal epithelium.
abstract: The mechanism of ion transport in the epithelium of rabbit cornea was studied by determining the intracellular ion activity of Cl-, Na+ and K+ under various conditions. Ionic activities were measured by means of microelectrodes containing liquid ion-exchangers selective for Cl-, Na+ or K+. The Cl- activity in basal cells of the epithelium in Na+ containing bathing solutions amounts to 28 +/- 2 mM (n = 11). This value is 1.9-times greater than expected on the basis of passive distribution across the tear side membrane. This finding suggests the existence of a Cl- accumulating process. Replacement of Na+ in the aqueous bathing solution by choline or tetraethylammonium results in a reversible decrease in Cl- activity to 22 +/- 1 mM (n = 11, P less than 0.025). The ratio of observed and predicted Cl- activity decreased significantly from 1.9 to 1.4 (P less than 0.05). The decrease in Cl- activity due to Na+ replacement was rather slow. In contrast, after readmittance of Na+ to the aqueous bathing solution, Cl- activity rose to a stable level within 30 min. These results indicate involvement of Na+ in Cl- accumulation into the basal cells of the epithelium. The K+ and Na+ activities of the basal cells of rabbit corneal epithelium in control bathing solutions were 75 +/- 4 mM (n = 13) and 24 +/- 3 mM (n = 12), respectively. The results can be summarized in the following model for Cl- transport across corneal epithelium. Cl- is accumulated in the basal cells across the aqueous side membrane, energized by a favourable Na+ gradient. Cl- will subsequently leak out across the tear side membranes. Na+ is extruded again across the aqueous side membrane of the epithelium by the (Na+ + K+)-ATPase.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D003315:Cornea / Q000378:metabolism*; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D008839:Microelectrodes; D008954:Models, Biological; D011188:Potassium / Q000378:metabolism*; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
chemical_list: D002712:Chlorides; D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium