Anoctamins, or TMEM16 proteins (TMEM16A to K), are a family of Ca2+- activated chloride channels (CaCC) and phospholipid scramblases. TMEM16A was identified in 2008 as the bona fideCaCC in airways and a number of epithelial tissues. It has been shown to tether the cortical endoplasmic reticulum (ER) to the plasma membrane. The presence of TMEM16A and TMEM16F augments Ca2+store release upon stimulation of G-protein coupled receptors (GPCRs) detected by Pl-G-CaMP2, whereas others TMEM16 proteins (D, H, I) largely reduced Ca2+signals. We found a pronounced inhibition of ATP-induced Ca2+signals after siRNA knockdown of endogenous TMEM16F and TMEM16K and, inversely, a strong augmentation of Ca2+signals in TMEM16F and TMEM16K overexpressing cells. The role of TMEM16A in intestinal epithelial cells has been previously shown (Schreiber, R. et al, 2014). In addition we observed that lack of expression of TMEM16K in TMEM16K -/- mice, inhibits Ca2+release (n=6, males and females). Recent results suggested that TMEM16A and TMEM16F control membrane exocytosis by setting Ca2+levels near the plasma membrane, and/or by controlling the intracellular Cl- concentration. Generation of TMEM16A tissue specific knock out mice in both airways and intestine allowed us to study the role of TMEM16A in exocytosis in vivo. Airway-ciliated and intestinal epithelial-specific knockout of TMEM16A leads to accumulation of mucus in airway secretory cells and intestinal goblet cells, respectively.Acute ATP-induced mucus secretion in airway club cells is inhibited when TMEM16A is knocked out in ciliated cells, possibly as a result of compromised release of prosecretory cytokines (n=16, males and females). In contrast, cholinergic stimulated mucus secretion was independent of TMEM16A (n=23, males and females). The data demonstrate a previously unrecognized role of TMEM16A for membrane exocytosis and describe a novel, ATP-driven pathway for intestinal mucus secretion (Benedetto et al, 2019).