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 co-transporters 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 approximately 30%. Isolated cells exposed to a hypertonic shock shrank by approximately 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 approximately 10% in the presence of carbachol. Blocking NKCC1 with furosemide reduced the amount of shrinkage by approximately 50%. These data suggest that NKCC1 plays an important role in fluid secretion by the exorbital gland of mice.

Defining epithelial cell dynamics and lineage relationships in the developing lacrimal gland

“…2B) (Bouwens et al, 1994). Slc12a2 (also known as Nkcc1), a sodium/ potassium chloride co-transporter important for fluid secretion that is enriched in the ducts of the adult lacrimal gland (Evans et al, 2000;Walcott et al, 2005), was dynamically expressed during early stages of lacrimal gland development (Fig. 2B).…”

Mechanisms of secretion-associated shrinkage and volume recovery in cultured rabbit parietal cells

“…We hypothesized that the observed volume loss after stimulation may occur via K ϩ and/or Cl Ϫ channels, which have been implicated in water and electrolyte efflux during stimulated secretion in various epithelia (3,7,23,34,35). K ϩ channels are present in the apical and basolateral membranes of the parietal cell (12,14,18,32) and could potentially play a role in stimulation-associated cell shrinkage in both locations, which makes it important to differentiate between constitutively active and secretagogue-activated conductances.…”

Diverse Mediators Modulate the Chloride Ion Fluxes That Drive Lacrimal Fluid Production

“…They depend on H 2 O transport proteins (aquaporins [AQPs]) [25][26][27] and ion transport proteins [28][29][30][31][32] arrayed in the cells' apical-and basallateral plasma membranes. The ion transport proteins in the acini include Na þ /H þ exchangers (NHE), 29 Cl À /HCO 3 À exchangers (AE), 30 and Na þ -K þ -2Cl À cotransporters (NKCC1) 31 which function in the basal-lateral plasma membranes, Cl À selective channels (ClC3 and CFTR) 32,33 -which function in the apical membranes, 34 and Na þ /K þ exchange pumps (Na,KATPase), which some evidence indicates function in both the apical-and the basal-lateral membranes. 28 The mechanism in the acini secretes Cl À ions into the lumens, thereby generating a negative transepithelial voltage difference; the voltage difference presumably drives Na þ ions into the lumens via the zonulae occludens and zonulae adherens that link adjacent epithelial cells, 35 and the osmotic imbalance that results from the net secretion of Cl À and Na þ draws H 2 O through the epithelium.…”