Figure 1

Ca²⁺ imaging determines the responses of (Ca2+) _i to acidic pH in fibroblast-like synoviocytes (FLS). (Ca2+)_i intensity was calculated for each pH over a 150-s application and normalized as a percent change to the response to pH 7.4. (A) (Ca2+)_i intensity normalized to pH 7.4 for decreasing pH concentrations in wild-type (WT) and acid-sensing ion channel (ASIC3-/-) FLS. Notice a progressive increase in (Ca2+)_i intensity with decreasing doses of pH. (Ca2+)_i intensity from ASIC3-/- run simultaneously showed reduced (Ca2+)_i intensity with acidic pH. (B) (Ca2+)_i intensity normalized to pH 7.4 for decreasing pH concentrations in WT and ASIC1-/- FLS. (Ca2+)_i intensity from ASIC1-/- FLS run simultaneously showed reduced (Ca2+)_i intensity with acidic pH. (C) Data for ASIC3-/- and ASIC1-/- were normalized to the (Ca2+)_i of WT cells at pH 5.0 to control for variability between cells and between days. A dose-dependent increase in (Ca2+)_i occurred in both WT, ASIC3-/- and ASIC1-/- FLS. However, when compared to WT FLS, ASIC3-/- and ASIC1-/- FLS showed significantly reduced (Ca2+)_i at all pH’s tested when compared to WT FLS (*P <0.05). (D) In WT FLS, replacement of the extracellular bath with a Ca²⁺-free medium had no effect on the increases in (Ca2+)_i to acidic-pH. Blockade of (Ca2+)_i stores with cyclopiazonic acid (CPA) (30 μM) completely abolished the (Ca2+)_i increases produced by acidic pH (*P <0.05). (E) (Ca2+)_i in FLS from people with rheumatoid arthritis show an increase in response to pH 6.0 when compared to responses at pH 7.4 (RA control). This increase in (Ca2+)_i response to pH 6.0 is significantly reduced by the non-specific ASIC blocker amiloride (500 μM) (P <0.05).