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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.

In glands such as the liver and pancreas, gap junctions containing connexin 26 and 32 (Cx26 and Cx32, respectively) couple the secretory cells. Uncoupling these junctions compromises the secretory function of these glands. Lacrimal glands also contain extensive arrays of gap junctions consisting of Cx26 and Cx32. We wanted to determine the role of these junctions in fluid secretion. In Cx32-deficient mice, immunocytochemistry showed that, in the male lacrimal gland, the remaining Cx26 was found evenly distributed in the membrane whereas there was little in the membranes of female glands. Western blot analysis of Cx26 showed that female Cx32-deficient mice expressed Cx26. Patch-clamp analyses of acinar cell coupling showed that the cell pairs from male glands were coupled whereas those from female glands were not. Stimulated fluid production by the glands from Cx32-deficient mice was abnormally low in female glands compared with controls at low topical doses of carbachol. The protein secretory response to different doses of carbachol was the same in all animals. These data suggest that gap junctions are essential for optimal fluid secretion in lacrimal glands.

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. [ABSTRACT FROM AUTHOR]

Purpose. The fluid secretory impairment of lacrimal and salivaryglands in Sjögren's syndrome (SS) is thought to be related to theextent of lymphocytic infiltration (LI) and subsequent loss of glandular tissue.In this study, we examine the correlation between the extent of tear flowreduction and the extent of LI of lacrimal glands in the NZB/W mouse, a modelof SS. Methods. We stimulated tear production by topical applicationof carbachol onto the gland while fluid was collected from the lacrimal duct.The lacrimal glands were removed after fluid collection for histology. Results. Fluid secretion in response to carbachol was less inthe majority of young NZB/W females compared to C57 control animals and noneof the glands showed LI. Fluid secretion was also impaired in the majorityof old NZB/W females, and the extent of LI was highly variable. Some of theold SW females also showed blunted fluid secretory responses and some degreeof focal LI. Young SW females showed no LI and most animals exhibited normalflow responses. Analysis of paired flow and LI measurements showed no correlationbetween LI and flow impairment in any of the groups or in the pooled data.Carbachol-stimulated protein secretion from lacrimal gland slices in vitro were similar in young and old SW and NZB/W mice. Conclusions. These results suggest that LI alone is not sufficientto explain the secretory dysfunction in the NZB/W mouse model of Sjögren'ssyndrome. [ABSTRACT FROM AUTHOR]

Acinar cells in the lacrimal gland are important in tear production. Water movement by osmosis follows solute transport from the serosal side to lumen. The onset of tear secretion is accompanied by cell shrinkage, which reflects a net reduction in cell solute content. Acinar cells also display a regulatory volume increase (RVI) response to exposure to elevated extracellular osmolarity. In both cases, the Na+-K+-2Cl- co-transporter (NKCCl) activity increases which loads Cl- into the cells. To explore the relationship between volume regulation and tear secretion, we developed a mathematical model of ion and water transport in acinar cells. It incorporates conservation of mass and electroneutrality within the cell and the bathing solutions, kinetic models of Na+-K+-ATPase, NKCCl, K+-Cl- co-transporter (KCCl), and passive fluxes of ions, non-electrolytes and water. Cell volume-sensitive reciprocal regulation of the activities of NKCCl and KCCl is represented with two empirical functions that vary with cell volume. The effects of muscarinic stimulation on apical Cl- and K+ permeabilities were also included. The model predicts regulatory volume decrease (RVD) and RVI responses similar to measurements in isolated acinar cells, as well as secretion induced cell shrinkage. In the latter case, the activation of NKCCl supplies K+ and Cl- that balances the apical efflux, resulting in persistent decrease in cell volume. [ABSTRACT FROM AUTHOR]