Electrical properties of chloride transport across the Necturus proximal tubule

The chloride conductance of the basolateral cell membrane of the Necturus proximal tubule was studied using conventional and chloride-sensitive liquid ion exchange microelectrodes. Individual apical and basolateral cell membrane and shunt resistances, transepithelial and basolateral, cell membrane potential differences, and electromotive forces were determined in control and after reductions in extracellular Cl^-. When extracellular Cl^- activity is reduced in both apical and basolateral solutions the resistance of the shunt increases about 2.8 times over control without any significant change in cell membrane resistances. This suggests a high Cl^- conductance of the paracellular shunt but a low Cl^- conductance of the cell membranes. Reduction of Cl^- in both bathing solutions or only on the basolateral side hyperpolarizes both the basolateral cell membrane potential difference and electromotive force. Hyperpolarization of the basolateral cell membrane potential difference after low Cl^- perfusion was abolished by exposure to HCO₃^--free solutions and SITS treatment. In control conditions, intracellular Cl^- activity was significantly higher than predicted from the equilibrium distribution across both the apical and basolateral cell membranes. Reducing Cl^- in only the basolateral solution caused a decrease in intracellular Cl^-. From an estimate of the net Cl^- flux across the basolateral cell membrane and the electrochemical driving force, a Cl^- conductance of the basolateral cell membrane was predicted and compared to measured values. It was concluded that the Cl^- conductance of the basolateral cell membrane was not large enough to account for the measured flux of Cl^- by electrodiffusion alone. Therefore these results suggest the presence of an electroneutral mechanism for Cl^- transport across the basolateral cell membrane of the Necturus proximal tubule cell.