INTRACELLULAR POTASSIUM ACTIVITY OF ISOLATED HUMAN AND RABBIT CORNEAL EPITHELIUM

Single-barrelled open tip microelectrodes containing a potassium-selective liquid ion exchanger (Corning 477 317) were used to determine intracellular K-activity aKi in squamous and basal cells of isolated rabbit and human corneal epithelium. The intracellular potassium activity aKi during the five hours of incubation in Ringer solution was 114·3±23·6 mmol/l and 107·6±26·2 mmol/l for the basal cell layer of rabbit and human epithelia respectively. The corresponding values for the squamous cells of the superficial cell layer were 41·2±14·2 mmol/l and 50·2±11·1 mmol/l. Based on intracellular chemical concentrations of potassium cKi an apparent activity coefficient could be calculated that is close to that of a dilute solution of the same ionic strength. This indicates that intracellular potassium is essentially free in both epithelia. Ouabain (5 × 10-5 mol/l) added to the bathing solution of the rabbit cornea lowered the transmembranal voltage ΨM as well as the intracellular K-activities of squamous and basal cells. Three hours after application of ouabain aKi of the basal cells had decreased to about one third of its initial value. Under all experimental conditions the potassium equilibrium potential EK considerably exceeded ΨM. Our data indicate: (1) The high absolute values for aKi imply that almost no potassium is bound or sequestered within the epithelial cells. (2) An active potassium uptake is necessary to explain the high K-activity in relation to the transmembranal voltage ΨM. (3) There is an intraepithelial gradient of aKi within the corneal epithelia. © 1979.