p38 Mitogen-activated protein kinase modulates exocrine secretion in rabbit lacrimal gland.

The lacrimal gland (LG) is an exocrine gland important for secretion of the tear film. The kinase p38 has important signal transduction functions, e.g.

Adenosine A2 receptor presence and synergy with cholinergic stimulation in rabbit lacrimal gland.

Purpose: Secretion from the lacrimal gland is an important part of the well-being of the eye, and a central part in the search for treatment of dry eye syndrome. Adenosine has stimulatory effects on the lacrimal gland, and can potentiate the effect of the cholinergic agonist carbachol (Cch). The aim of the present study is to investigate the presence of the adenosine A(2) receptor subtypes A(2A) and A(2B) in the rabbit lacrimal gland, and to characterize their role in regulated acinar cell secretion.

Functional expression of the adenosine A1 receptor in rabbit lacrimal gland.

It has become increasingly clear that purine compounds play a mediator role in exocrine secretion. Therefore, the present study was aimed at examining the presence of the adenosine A1 receptor in rabbit lacrimal gland and to evaluate the role of the A1 receptor in regulated secretion. The expression of the A1 receptor was investigated with reverse transcriptase PCR, cyto- and histochemistry as well as with pharmacological methods.

Characterization of beta-hexosaminidase secretion in rabbit lacrimal gland.

The present study was aimed at validating the use of the lysosomal enzyme beta-hexosaminidase as a marker of secretory function in cultured rabbit lacrimal gland acinar cells. The secretory response and morphological characteristics of isolated acinar cells cultured in a serum-free medium supplemented with an extracellular matrix extract were monitored over time as part of optimization of our culturing protocol. Secreted beta-hexosaminidase activity was analyzed and compared with that of another lysosomal enzyme, cathepsin B, as well as protein secreted into the media, w or w/o the presence of secretagogues or protein kinase C activators and inhibitors.

Integrin adhesion in regulation of lacrimal gland acinar cell secretion.

The extracellular microenvironment regulates lacrimal gland acinar cell secretion. Culturing isolated rabbit lacrimal gland acinar cells on different extracellular matrix proteins revealed that laminin enhances carbachol-stimulated secretion to a greater extent than other extracellular matrix proteins investigated. Furthermore, immunofluorescence indicated that integrin subunits, potentially functioning as laminin receptors are present in acinar cells.

Sequencing, expression, and enzymatic characterization of beta-hexosaminidase in rabbit lacrimal gland and primary cultured acinar cells.

The lysosomal enzyme, beta-hexosaminidase, exists as two major isoforms; HexA and HexB. HexA is an alpha beta-subunit heterodimer and HexB a beta-subunit homodimer. Both isoforms can remove nonreducing beta-N-acetyl-D-glucosamine residues, whereas HexA hydrolyzes charged substrates as G(M2) gangliosides as well.

Purification of rabbit lacrimal gland plasma membranes by aqueous two-phase affinity partitioning.

We describe the purification of lacrimal gland plasma membranes by affinity partitioning using a two-phase system containing polyethylene glycol and dextran in which wheat germ agglutinin conjugated to dextran is used as affinity ligand. When partitioning a microsomal fraction, the plasma membrane marker 5'-nucleotidase was obtained in the affinity ligand-containing bottom phase, whereas the endoplasmic reticulum marker NADH-ferricyanide reductase remained in the top phase. The affinity partitioning behaviour of components involved in exocytosis and cellular signalling was also examined.

Prolactin and prolactin receptors in the lacrimal gland.

Light and electron microscopic immunocytochemistry, in situ hybridization and Dot Blot analysis revealed intracellular localization of prolactin-like molecules and prolactin mRNA in epithelial cells of the lacrimal glands of rabbits. There was also positive immunostaining for prolactin receptors on acinar cells and some interstitial cells. On Western blots of homogenates of whole lacrimal gland, isolated lacrimal acinar cells, isolated lacrimal interstitial cells and peripheral blood lymphocytes, prolactin antibody consistently labeled protein bands migrating at approximately 36 and 50 kD.

Sjögren's autoimmunity: how perturbation of recognition in endomembrane traffic may provoke pathological recognition at the cell surface.

CD4 T cell antigen recognition requires presentation by major histocompatibility complex Class II molecules (MHC II). B cell surface immunoglobulins recognize antigens independently of MHC II, but activation typically requires CD4 cell cytokines as accessory signals. Plasma membrane-endomembrane traffic in lacrimal gland acinar cells, targets of autoimmune activity in Sjögren's syndrome, may satisfy both requirements.

Cholinergic stimulation of lacrimal acinar cells promotes redistribution of membrane-associated kinesin and the secretory protein, beta-hexosaminidase, and increases kinesin motor activity.

The role of the microtubule-based motor, kinesin, in membrane trafficking has been investigated in resting and stimulated acinar cells from rabbit lacrimal gland, a cholinergically controlled secretory tissue. Microtubule-dependent motors from extracts of control and carbachol-treated acini were isolated by microtubule-affinity purification and their activity was determined using a video-enhanced differential interference contrast microscopy assay for microtubule gliding. The observation that carbachol treatment resulted in a 2.

Na-K-ATPase in lacrimal gland acinar cell endosomal system: correcting a case of mistaken identity.

Na-K-ATPase is associated with a variety of membrane populations in lacrimal acinar cells. Acinus-like structures formed by rabbit acinar cells in primary culture were incubated with horseradish peroxidase (HRP) to label basolateral and endosomal membranes and then analyzed by electron microscopy cytochemistry with the 3-3'-diaminobenzidine reaction or by fractionation and measurement of marker catalytic activities or immunoreactivities. HRP adsorbed to basolateral membranes at 4 degrees C.

Fluid phase endocytosis by isolated rabbit lacrimal gland acinar cells.

It is well known that lacrimal gland acinar cells retrieve secretory vesicle membrane constituents from their apical plasma membranes after stimulated exocytosis of secretory proteins. There have also been indications of a recycling traffic involving the basal-lateral plasma membranes. In an effort to document this traffic, determine how it is regulated, and discern whether it involves more than one intracellular compartment, we studied internalization of the fluid phase marker, Lucifer Yellow, and its relationship to protein release in acinar cells isolated from rabbit lacrimal glands.

Traffic of major histocompatibility complex class II molecules in rabbit lacrimal gland acinar cells.

Purpose: It has been suggested that lacrimal gland acinar cells, which have been induced to express major histocompatibility complex class II (MHC II) molecules, might initiate local autoimmunity by using mechanisms similar to those operating in the specialized antigen-presenting cells to process and present autoantigens. Surface-labeling experiments indicate that constituents of the acinar cell plasma membrane participate in a rapid recycling traffic. The authors have surveyed the subcellular distribution of MHC II molecules and have evaluated their participation in the traffic between plasma membranes and intracellular compartments.

Rabbit lacrimal acinar cells in primary culture: morphology and acute responses to cholinergic stimulation.

Purpose: The rabbit lacrimal gland yields large numbers of viable acinar cells that, when exposed to carbachol, respond with accelerated protein release, fluid phase endocytosis (Lucifer yellow uptake), and Na/H antiport activation. The current study was undertaken to determine whether such cells exhibit similar responses after having been maintained in primary culture.

Methods: Cells were isolated from 2-kg, juvenile male New Zealand White rabbits and maintained in a supplemented DMEM/Ham's F-12 medium for up to 72 hours.

Plasma membrane internalization and recycling in rabbit lacrimal acinar cells.

Purpose: The purpose of this study was to examine internalization and recycling of plasma membrane constituents in lacrimal gland acinar cells.

Methods: Acinar cells were isolated from rabbit lacrimal glands. Surface-expressed reactive groups were biotinylated at 4 degrees C with sulfo-N-hydroxysuccinimidyl-biotin.