Figure 4.

Citrate targets the extracellular site of ASIC1 to potentiate acid-induced currents. A, B, Extracellular citrate increased efficacy of ASIC1 currents in HEK293 cells. The cells were perfused in a bath solution, pH 7.4, containing no citrate, and each stimulus consisted of a 3 s exposure (at 30 s intervals) to a test solution, pH 6.0–7.4, with or without citrate (25 mm). In A, after changing to an acid bath solution, pH 6.5, inward current can no longer be triggered by the same set of test solutions. In B, bath pH was maintained at pH 7.4; n = 6 independent HEK293 cultures. C, Similar to B, except that the intracellular solution was preloaded with 25 mm citrate before recording; n = 8 independent HEK293 cultures. In B and C, error bars indicate the mean ± SEM.