MUC5AC and cystic fibrosis: Previous studies have shown that CCh-induced mucin granule fusion with the plasma membrane remains intact in CF distal colon tissues, while studies in small intestine organoids from CF mice show that mucus remains within the goblet cells following CCh stimulation, and that stimulation of CF organoids in the presence of high concentrations of bicarbonate can restore the impaired mucus secretory response [12, 20, 28].