Changes of whole-cell currents and intracellular [Ca²⁺]_i under different extracellular pH or ionic conditions in primary principal cells. (A–C) Whole-cell currents of principal cells were inhibited in acidic solution (pH_o 6.4) but were enhanced in alkaline solution (pH_o 8.4) under different ionic conditions. The holding potential was set at 0 or −60 mV. (A) The pipette solution was potassium-gluconate based containing 0.1 mM EGTA, and the bathing fluid was normal PSS (K-0.1 EGTA/normal PSS). The dotted line indicates the zero current levels. *, P < 0.05, one-way ANOVA. (B) The pipette solution was potassium-gluconate based containing 5 mM EGTA, and the K⁺ ions in bathing solution were replaced with Cs⁺ (K-5EGTA/Cs-PSS). (C) The major cation in both the pipette and the bathing solutions was replaced with NMDG, and the K⁺ in bathing fluid was replaced with Cs⁺ (NMDG, 5EGTA/Cs-NMDG PSS). All pipette solutions contained 3–4 mM ATP. (D) Changes in intracellular Ca²⁺ concentration ([Ca²⁺]_i) when isolated rat cauda epididymal cells were loaded with Fluo-3-AM fluorescence dye. Fluorescence intensity was measured using a confocal imaging system. Data were obtained from at least 10 cells in three separate experiments. Error bars represent SEM.