The intracellular chloride activity of rat kidney proximal tubular cells

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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.