Urine-induced currents shifted reversal potential with changes in extracellular Cl⁻, but not with changes in extracellular Na⁺. (A) In a representative VSN, changes in extracellular [Cl⁻] altered the current response pattern measured by whole cell patch clamp. Ringer's, [Cl⁻] = 151 mM; low Cl⁻ Ringer's with chloride replaced by gluconate, [Cl⁻] = 40 mM. (B) Using whole cell patch clamp, the urine response for a VSN was recorded in Ringer's ([Na⁺] = 138 mM) and low Na⁺ Ringer's with sodium replaced by choline ([Na⁺] = 20 mM) at voltage steps from −80 to +80 mV (20-mV increments). (C and D) The I-V at the dashed line in A and B. Currents were measured by subtracting the baseline before urine was applied with that measured at the dashed line. The reversal potential for urine stimulation did not change when extracellular sodium concentration was decreased, but had a positive shift when extracellular chloride concentration was decreased. Potassium currents were blocked by Cs⁺ in the pipette solution. Whole cell patch clamp pipette solution contained (in mM): 140 CsCl, 10 HEPES, 5 EGTA, 1 ATP, and 0.5 GTP, pH 7.4, and 285 mmol/kg (glucose). DU, 1:500 dilute urine.