The intracellular chloride activity of rat kidney proximal tubular cells

Abstract

The intracellular Cl⁻ activity was determined in rat kidney proximal tubular cells in vivo, using single-barreled Cl⁻ sensitive microelectrodes filled with Corning no. 477913 liquid ion exchanger resin to measureV _Cl and using — in separate experiments — conventional KCl-filled microelectrodes to measure the membrane potential,V _m. After correction for interference from other anions onV _Cl the intracellular Cl⁻ activity averaged 13.1 mmol·l⁻¹ SD±4.5 mmol·l⁻¹ (n=96). This value is approximately two-fold higher than the intracellular equilibrium activity which can be calculated from the extracellular Cl⁻ activity of 90–103 mmol·l⁻¹ andV _m of −71.2 mV, SD±4.9 mV (n=23) to amount to 6.3 to 6.7 mmol·l⁻¹. Since both cell membranes are permeable for Cl⁻ ions, as concluded from luminal and/or peritubular Cl⁻ substitution experiments, we conclude that the cellular Cl⁻ accumulation above equilibrium results from transcellular active Cl⁻ transport, the detailed mechanism of which is presently not known. From the slow decline of intracellular Cl⁻ concentration after substitution of luminal Cl⁻ by gluconate, however, we deduce that transcellular Cl⁻ absorption is of minor importance in surface tubules of rat kidney under free flow and that the major part of transtubular Cl⁻ flux is passive and paracellular.