Fluid secretion and the Na+-K+-2Cl−cotransporter in mouse exorbital lacrimal gland

Abstract

We have previously suggested that fluid flow in the mouse exorbital lacrimal gland is driven by the opening of apical Cl−and K+channels. These ions move into the lumen of the gland and water follows by osmosis. In many tissues, the Na+-K+-2Cl−cotransporter (NKCC1) replaces the Cl−and K+ions that move into the lumen. We hypothesize that mouse exorbital lacrimal glands would have NKCC1 cotransporters and that they would be important in fluid transport by this gland. We used immunocytochemistry to localize NKCC1-like immunoreactivity to the membranes of the acinar cells as well as to the basolateral membranes of the duct cells. We developed a method to measure tear flow and its composition from mouse glands in situ. Stimulation with the acetylcholine agonist carbachol produced a peak flow followed by a plateau. Ion concentration measurements of this stimulated fluid showed it was high in K+and Cl−. Treatment of the gland with furosemide, a blocker of the NKCC1 cotransporter, reduced the plateau phase of fluid flow by ∼30%. Isolated cells exposed to a hypertonic shock shrank by ∼20% and then showed a regulatory volume increase (RVI). Both the RVI and swelling were blocked by treatment with furosemide. Cells isolated from these glands shrink by ∼10% in the presence of carbachol. Blocking NKCC1 with furosemide reduced the amount of shrinkage by ∼50%. These data suggest that NKCC1 plays an important role in fluid secretion by the exorbital gland of mice.