Anoctamins are a family of Ca2+ activated Cl− channels

Abstract

Anoctamin 1 (Ano1; TMEM16A) and anoctamin 2 (Ano2; TMEM16B) are novel Cl− channels transiently activated by increase in intracellular Ca2+. These channels are essential for epithelial Cl− secretion, smooth muscle peristalsis and olfactory signal transduction. They are central to inherited diseases and cancer and can act as heat sensors. Surprisingly, another member of this protein-family, Ano6, operates as a Ca2+ activated phospholipid scramblase, while others were reported as intracellular proteins. It is therefore unclear whether anoctamins constitute a family of Ca2+ activated Cl− channels, or reflect proteins with heterogeneous functions. Using whole cell patch clamping we demonstrate that Ano 4–10 are all able to produce transient Ca2+ activated Cl− currents, when expressed in HEK293 cells. While some anoctamins (Ano1,2,4,6,7) were found to be well expressed in the plasma membrane, others (Ano8,9,10) show rather poor membrane expression and were mostly retained in the cytosol. The transient nature of the Cl− currents was demonstrated to be independent of intracellular Ca2+ levels. We show that inactivation of Ano1 currents occurs in the continuous presence of elevated Ca2+ concentrations, possibly by calmodulin-dependent kinase. The present results demonstrate that anoctamins are a family of Ca2+ activated Cl− channels, which also induce permeability for cations. They may operate as Cl− channels located in the plasma membrane or in intracellular compartments. These results will support our understanding of the physiological significance of anoctamins and their role in disease.