Functional Differences in the Acinar Cells of the Murine Major Salivary Glands

Abstract

In humans, approximately 90% of saliva is secreted by the 3 major salivary glands: the parotid (PG), the submandibular (SMG), and the sublingual glands (SLG). Even though it is known that all 3 major salivary glands secrete saliva by a Cl--dependent mechanism, salivary secretion rates differ greatly among these glands. The goal of this study was to gain insight into the properties of the ion-transporting pathways in acinar cells that might account for the differences among the major salivary glands. Pilocarpine-induced saliva was simultaneously collected in vivo from the 3 major salivary glands of mice. When normalized by gland weight, the amount of saliva secreted by the PG was more than 2-fold larger than that obtained from the SMG and SLG. At the cellular level, carbachol induced an increase in the intracellular [Ca2+] that was more than 2-fold larger in PG and SMG than in SLG acinar cells. Carbachol-stimulated Cl- efflux and the protein levels of the Ca2+-activated Cl- channel TMEM16A, the major apical Cl- efflux pathway in salivary acinar cells, were significantly greater in PG compared with SMG and SLG. In addition, we evaluated the transporter activity of the Na+-K+-2Cl- cotransporters (NKCC1) and anion exchangers (AE), the 2 primary basolateral Cl- uptake mechanisms in acinar cells. The SMG NKCC1 activity was about twice that of the PG and more than 12-fold greater than that of the SLG. AE activity was similar in PG and SLG, and both PG and SLG AE activity was about 2-fold larger than that of SMG. In summary, the salivation kinetics of the 3 major glands are distinct, and these differences can be explained by the unique functional properties of each gland related to Cl- movement, including the transporter activities of the Cl- uptake and efflux pathways, and intracellular Ca2+ mobilization.