Intracellular chloride activity in corneal endothelial cells

Abstract

Purpose: Current models of hydration control by the corneal endothelium suggest that HCO−3 movement across the cell is driven by the energy contained in the re‐entry of NA+ into the cell down its electrochemical gradient. The nature of the coupling between HCO−3 and Na+ is not yet fully resolved. One suggestion is that the Na+/K+/2Cl− co‐transporter drives Cl− into the cell which then exits the same membrane via a HCO−3/Cl− exchanger. This would drive HCO−3 into the cell from where it could exit down its own electrochemical gradient into the aqueous. Such a system would also raise Cl− above its electrochemical equilibrium. The purpose of this study was to determine if Cl− is passively distributed across the plasma membrane or elevated above its electrochemical equilibrium.Method: To determine if this situation was present in rabbit corneal endothelial cells, we measured [Cl−]i directly using potential sensing and Cl− selective microelectrodes. To make the Cl− selective microelectrodes, filamented glass capillaries were silanized and back‐filled with Cl− ionophore (Corning or WPI) immediately before use. Electrode sensitivity was determined using the fixed interference method.Results: Endothelial membrane potential (PDm) in this series was similar to that in previous studies, 29 ± 0.9 mV (mean ± SEM, n = 22). Chloride potential (PDCl) was used to calculate [Cl−]i, which was 53 ± 2.0 mM (mean ± SEM, n = 22).Conclusions: The [Cl−]i measurement is significantly higher (P < 0.001) than that predicted from the measured PDm (39 ± 0.9 mM) and suggests that Cl− is not passively distributed in corneal endothelial cells.