Intracellular activities of chloride, potassium and sodium ions in rabbit corneal epithelium.
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.
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
D002712:Chlorides; D013757:Tetraethylammonium Compounds; D019789:Tetraethylammonium; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium