SMAD2 and atrial fibrillation: To conversely test if SMAD2/3 phosphorylation in 293 cells in response to AF could be suppressed by the addition of recombinant sol- BG, we added 1 ng/mL (average of sBG concentration within the patient AF samples (Fig. 6H), to the AF with the lowest sol-BG levels (Suppl.