Blockade of ASIC1a with PcTx1 reduces acid-induced elevation of (Ca2+)i level in articular chondrocytes. Cellular confocal micrographs of the same scale showing the changes in the (Ca2+)i concentration, as visualized by Fluo-3-AM in articular chondrocytes. (A,a) acid-induced increase of (Ca2+)i in Ca2+-free extracellular solution; (B,b) acid-induced increase of (Ca2+)i in extracellular Ca2+ solution; (C,c) acid-induced increase of (Ca2+)i in articular chondrocytes pretreated with ASIC1a-specific blocker, PcTx1; (D,d) acid-induced increase of (Ca2+)i in articular chondrocytes pretreated with calcium chelating agent, BAPTA-AM. The amplitude of (Ca2+)i intensity in articular chondrocytes induced by acid treatment was quantified as the maximal rise of (Ca2+)i above basal levels. (i) before exposure to acid solution; (ii) increased Ca2+ intensity when pH was decreased to 6.0; (iii) after exposure to the acid solution for three minutes (n = 8 for each).