FIGURE 1.

Extracellular acidification induces an acid-sensitive outwardly rectifying (ASOR) current in C28/I2 cells and primary human chondrocytes. (A) Mean amplitudes ± standard error of the means (SEM) of ASOR currents measured at pH 7.2 (n = 20), 5.5 (n = 4), 5.0 (n = 9), and 4.5 (n = 7). Asterisks indicate significant differences between pH 5.0 and pH 7.2 and between pH 4.5 and pH 7.2 (p < 0.05). Wilcoxon rank sum test. Current–voltage (I–V) relationships of mean ASOR currents ± SEM analyzed at the beginning (I₁—open triangles) and at the end (I₂—closed circles) of voltage pulses (indicated by gray shadings in D and E) in C28/I2 cells (n = 8) (B) and primary chondrocytes (n = 7) (C). Asterisks indicate significant differences between I₁ and I₂ (p < 0.05). Paired t-tests. Examples of ASOR current traces elicited by 500-ms voltage steps from –100 to +100 mV in C28/I2 cells (D) and primary chondrocytes (E). (a) Close-up of the inward current peak at –100 mV indicated in (D).