Chloride transport across the basolateral cell membrane of theNecturus proximal tubule: Dependence on bicarbonate and sodium

Abstract

The transport of chloride across theNecturus proximal tubule cell was studied in the doubly-perfused kidney using conventional, chloride-sensitive and pH-sensitive microelectrodes. Lowering chloride activity in the basolateral solution results in a reduction in intracellular Cl⁻ activity (a _Cl ⁱ ). This reduction ina _Cl ⁱ is inhibited by removing either HCO ₃ ⁻ or Na⁺ from the perfusion solution, indicating that both HCO ₃ ⁻ and Na⁺ are required for Cl⁻ movement across the basolateral cell membrane. Reducing either HCO ₃ ⁻ or Na⁺ in the basolateral solution causes an increase ina _Cl ⁱ . Thus changes in either Na⁺ or HCO ₃ ⁻ chemical gradients across the basolateral cell membrane significantly affect chloride movement. Changing intracellular pH by means of NH₄Cl exposure results in an increase ina _Cl ⁱ followed by a sharp decrease when NH₄Cl is removed. These changes in intracellular chloride do not occur in the absence of HCO ₃ ⁻ . Likewise, the decrease ina _Cl ⁱ following NH₄Cl treatment requires the presence of Na⁺ in the basolateral solution. We conclude that chloride is transported across the basolateral cell membrane in exchange for both Na⁺ and HCO ₃ ⁻ . Our results also support the presence of a Na⁺/Cl⁻ contransport mechanism on the apical cell membrane.