Fig. 5.

Acidic pH potentiates the 5-HT-induced, transport-associated current. A, 5-HT-induced current recorded in Na⁺ Ringer’s solutions with various pH values. Solution changes are indicated by arrows above the current trace. 5-HT (5 μm) applications are indicated bybars under the current trace. Holding potential, −40 mV. B, 5-HT (5 μm) does not induce the transport-associated current, but rather inhibits the H⁺leakage current in the absence of Na⁺ (NMDG substitution). Holding potential, −40 mV. Base solution, NMDG Ringer’s, pH 7.5.C, Dose–response relationship for the total transport-associated current. The H⁺leakage current and the 5-HT-induced current at each pH value were combined. This combined current was normalized to the maximal current obtained after a nonlinear regression fitting to the Hill equation (dashed line). EC₅₀ = 7.8 ± 1.4 μmH⁺, pH 5.1 ± 0.1, Hill coefficientn = 1.1 ± 0.1 (mean ± SD).Vertical lines indicate the SD (n = 4 oocytes).