Figure 6.

Citrate potentiates the ASIC1 current by chelating extracellular calcium ions. A, B, HEK293 cells were perfused in a bath solution, pH 7.4, containing 2 mm Ca²⁺ and no citrate, and each stimulus consisted of a 3 s exposure (at 30 s intervals) to a test solution, pH 7.4 or 6.5, with or without citrate (25 mm) and/or Ca²⁺ (2 mm). The results indicate that citrate failed to potentiate the ASIC1-mediated current triggered by a Ca²⁺-free test solution, pH 6.5 (A), and that Ca²⁺ removal failed to further potentiate the ASIC1-mediated current triggered by a test solution containing citrate (25 mm; B). C, Summarized results from A and B; error bars indicate the mean ± SEM; n = 5 independent HEK293 cultures; n.s. p > 0.05, **p < 0.01, two-way repeated measures analysis of variance (matching recordings from the same cell) with a post hoc Tukey's test. n.s., Not significant.