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).

Gong et al. Arthritis Research & Therapy 2014 16:R121   doi:10.1186/ar4577
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