Figure 5.

Citrate potentiates ASIC1 current only when applied concurrently with each stimulus. A, HEK293 cells were initially perfused in a bath solution, pH 7.4, without 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). Thereafter, the cells were perfused in a bath solution, pH 7.4, that contained citrate (25 mm); after the citrate bath, the same set of test solutions now produce smaller inward currents. The result indicates that ASIC1-mediated current was potentiated by the concurrent presence of citrate during the pH drop (B₁ vs C₁ or B₂ vs C₂) but was depressed (as indicated by arrows) by a preexposure to citrate before the pH drop (B₁ vs B₂ or C₁ vs C₂). B, C, Summarized results from A, comparing current amplitudes of B₁ to B₂ (B) and C₁ to C₂ (C); error bars indicate the mean ± SEM; n = 6 independent HEK293 cultures. ***p < 0.001, two-tailed Student's t test.