KCNMA1 and rheumatoid arthritis: We tested ChTX, which blocks KCa1.1 channels associated with β1, β2, and β3, but not β4 subunits [21], leading to current block in 100 % of the RA-FLS assayed and thus demonstrating the absence of β4 subunits as components of KCa1.1 at the plasma membrane of these cells.