Figure 8.

Proton channels in sour taste cells are open near neutral pH. A) Current evoked in a PKD2L1-YFP taste cell to extracellular acidification (TEA-MA based) from a solution at pH 7.4. The current elicited at pH 6.5 is completely blocked by 1 mM Zn²⁺. B) Current amplitude plotted against H⁺ concentration (n = 4 cells). The relationship is linear at low concentrations of protons, but saturates beyond pH 6.0. The red curve shows the fit to a one site binding curve with a K_d of 1.9 μM. C) Time series of cytosolic pH (pH_i) for PKD2L1 and TRPM5 taste cells loaded with BCECF-AM in Tyrode’s from which resting values of pH_i were measured. High-K⁺ + 20 μM nigericin (pH 6.0 to pH 8.0 in 0.5 pH unit increments) was used to generate a linear calibration curve from which fluorescent intensities were converted to pH_i. D) Scatterplot of resting pH_i in Tyrode’s pH 7.4 determined as in C. ***P < 0.001, 1-tailed Student's t test.