Tmem16A encodes the Ca²⁺-activated Cl^- channel in mouse submandibular salivary gland acinar cells

Activation of an apical Ca²⁺-dependent Cl^- channel (CaCC) is the rate-limiting step for fluid secretion in many exocrine tissues. Here, we compared the properties of native CaCC in mouse submandibular salivary gland acinar cells to the Ca²⁺-gated Cl^- currents generated by Tmem16A and Best2, members from two distinct families of Ca ²⁺-activated Cl^- channels found in salivary glands. Heterologous expression of Tmem16A and Best2 transcripts in HEK293 cells produced Ca²⁺-activated Cl^- currents with time and voltage dependence and inhibitor sensitivity that resembled the Ca²⁺- activated Cl^- current found in native salivary acinar cells. Best2^-/- and Tmem16A^-/- mice were used to further characterize the role of these channels in the exocrine salivary gland. The amplitude and the biophysical footprint of the Ca²⁺-activated Cl ^- current in submandibular gland acinar cells from Best2-deficient mice were the same as in wild type cells. Consistent with this observation, the fluid secretion rate in Best2 null mice was comparable with that in wild type mice. In contrast, submandibular gland acinar cells from Tmem16A^-/- mice lacked a Ca²⁺-activated Cl^- current and a Ca ²⁺-mobilizing agonist failed to stimulate Cl^- efflux, requirements for fluid secretion. Furthermore, saliva secretion was abolished by the CaCC inhibitor niflumic acid in wild type and Best2^-/- mice. Our results demonstrate that both Tmem16A and Best2 generate Ca²⁺- activated Cl^- current in vitro with similar properties to those expressed in native cells, yet only Tmem16A appears to be a critical component of the acinar Ca²⁺-activated Cl^- channel complex that is essential for saliva production by the submandibular gland.