Fig. 4

The calcium-activated potassium channel KCa1.1 β3 subunit is expressed by CD44^high fibroblast-like synoviocytes from patients with rheumatoid arthritis (RA-FLS), whereas the β1 subunit is expressed by CD44^low RA-FLS and fibroblast-like synoviocytes from patients with osteoarthritis (OA-FLS). a Representative flow cytometry histograms showing expression of KCa1.1α by CD44^high and CD44^low RA-FLS. Gray shading represents control staining; black lines represent CD44 (left) or KCa1.1α (middle and right) staining. b Invasiveness of unsorted RA-FLS and RA-FLS from the same donors sorted by flow cytometry into CD44^low and CD44^high populations. Mean ± SEM; n = 3 RA-FLS donors. The line for the error bar for the control was thickened compared with other plots to make it visible. c Representative flow cytometry histograms showing expression of podoplanin, cadherin-11, and matrix metalloproteinase (MMP)-2 by CD44^high (green) and CD44^low (gray) RA-FLS. In the left panel, gray shading represents control staining and black lines represent CD44 staining. d Individual RA-FLS stained for CD44. The patch-clamp pipette’s shadow is visible on the right of each image. e K⁺ current density elicited at 140 mV in CD44^high RA-FLS, CD44^low RA-FLS, and OA-FLS. Mean ± SEM; n = 5 RA-FLS donors and 4 OA-FLS donors. f Activation kinetics (τ_Act) of K⁺ currents elicited at 140 mV in CD44^high RA-FLS, CD44^low RA-FLS, and OA-FLS. Mean ± SEM; n = 5 RA-FLS donors and 4 OA-FLS donors. g K⁺ current density after treatment of CD44^high RA-FLS, CD44^low RA-FLS, and OA-FLS with 75 μM lithocholic acid (LCA) or 30 μM arachidonic acid (AA) and normalized to current densities before treatment (horizontal dashed line). Mean ± SEM; n = 5 RA-FLS donors and 4 OA-FLS donors. *p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001