Establishment and characterization of a telomerase immortalized human gingival epithelial cell line

BACKGROUND AND OBJECTIVE

Gingival keratinocytes are used in model systems to investigate the interaction between periodontal bacteria and the epithelium in the initial stages of the periodontal disease process. Primary gingival epithelial cells (GECs) have a finite lifespan in culture before they enter senescence and cease to replicate, while epithelial cells immortalized with viral proteins can exhibit chromosomal rearrangements. The aim of this study was to generate a telomerase immortalized human gingival epithelial cell line and compare its in vitro behaviour to that of human GECs.

MATERIAL AND METHODS

Human primary GECs were immortalized with a bmi1/hTERT combination to prevent cell cycle triggers of senescence and telomere shortening. The resultant cell-line, telomerase immortalized gingival keratinocytes (TIGKs), were compared to GECs for cell morphology, karyotype, growth and cytokeratin expression, and further characterized for replicative lifespan, expression of toll-like receptors and invasion by P. gingivalis.

RESULTS

TIGKs showed morphologies, karyotype, proliferation rates and expression of characteristic cytokeratin proteins comparable to GECs. TIGKs underwent 36 passages without signs of senescence and expressed transcripts for toll-like receptors 1-6, 8 and 9. A subpopulation of cells underwent stratification after extended time in culture. The cytokeratin profiles of TIGK monolayers were consistent with basal cells. When allowed to stratify, cytokeratin profiles of TIGKs were consistent with suprabasal cells of the junctional epithelium. Further, TIGKs were comparable to GECs in previously reported levels and kinetics of invasion by wild-type P. gingivalis and an invasion defective ΔserB mutant.

CONCLUSION

Results confirm bmi1/hTERT immortalization of primary GECs generated a robust cell line with similar characteristics to the parental cell type. TIGKs represent a valuable model system for the study of oral bacteria interactions with host gingival cells.

Silver staining of extensively glycosylated proteins on sodium dodecyl sulfate-polyacrylamide gels: enhancement by carbohydrate-binding dyes

Two methods are described for detecting less than 1 microgram of highly glycosylated proteins, such as mucins, on sodium dodecyl sulfate-polyacrylamide gels. They combine commonly employed periodic acid-Schiff (PAS) and Alcian blue dyes with silver stain. Carbohydrate prestaining renders mucins more cationic and favors greater complexation with ionic silver. Comparisons of different mucin samples stained either with PAS-silver or alcian blue-silver indicate differential staining between the two techniques. Such differences may, in part, be due to an affinity of Alcian blue for sulfated glycoproteins. These two staining protocols when used in conjunction with silver staining alone are particularly valuable for assessing sample purity and for detecting contaminating proteins during mucin purification protocols.

Factors influencing the recurrence rate of bladder cancer

A prospective analysis was done on 318 patients with bladder cancer observed during a 4-year period. We examined the predictive value for tumor recurrence of the initial grade, stage, number and size of bladder tumors. None of the observed parameters alone or in combination could predict tumor recurrence. Cystoscopy and cytology, as well as random bladder and tumor biopsies, were part of the diagnostic studies.

Persistence of a perinatal cellular phenotype in submandibular glands of adult rat

In the perinatal submandibular gland (SMG) of the rat, Type I cells secrete protein C (89 KD) and Type III cells secrete B1-immunoreactive proteins (20-30 KD); both cell types secrete protein D (175 KD). After the disappearance of both perinatal cell types from the maturing acini, only cells of the intercalated ducts (ID) show strong reactivity for the perinatal antigens. In adult ID, light and electron microscopic immunocytochemical analysis showed that most cells had either C or B1 reactivity, a few had either C and D or B1 and D reactivities, and some cells were unreactive for all of the perinatal proteins. Occasional clusters of "adult" acini, however, were strongly positive for B1 and for D, and these clusters were negative for a typical adult acinar marker, the glutamine/glutamic acid-rich proteins (GRP). Also seen in some preparations were a few anomalous acini with the histological appearance of sublingual (SLG) acini. These were negative for the perinatal and adult submandibular gland marker proteins but reactive with an antibody against SLG mucin. We suggest that the B1-positive acini in the adult SMG consist of newly differentiated replacement cells that have arisen from the ID, and that the anomalous mucous acini are, phenotypically, SLG acini that have differentiated within the SMG parenchyma.

Light and electron microscopic immunolocalization of rat submandibular gland mucin glycoprotein and glutamine/glutamic acid-rich proteins

We studied the subcellular localization of two major secretory products of adult rat submandibular gland (RSMG), blood group A-reactive mucin glycoprotein and glutamine/glutamic acid-rich protein (GRP), by light and electron microscopic immunocytochemistry. The structure of the major neutral oligosaccharide of the mucin was shown to be: GalNAc alpha 1,3(Fuc alpha 1,2)Gal beta 1,3GalNAc. A mouse monoclonal antibody (1F9) with specificity for blood group A determinants was prepared against the mucin. The antibody recognized a single band of approximately 114 KD on Western blots of RSMG extract. A previously characterized monoclonal antibody (59) against GRP (Mirels et al.: J Biol Chem 262: 7289, 1987) reacted with a doublet of 45-50 KD on Western blots of extraparotid saliva. Immunofluorescence and immunoperoxidase staining of cryostat sections of RSMG with anti-mucin antibodies and anti-GRP antibodies revealed reactivity in acinar cells of the gland. No specific labeling was seen in duct cells of RSMG or in mucous acinar cells of the adjacent sublingual gland. Post-embedding immunogold labeling of thin sections of glutaraldehyde-fixed RSMG with anti-mucin showed strong labeling of the Golgi apparatus and secretory granules of acinar cells. Gold particles were seen mainly over electron-lucent areas of the granules. No labeling occurred over the endoplasmic reticulum. The labeling pattern with the anti-GRP antibodies was similar, except that both electron-dense and -lucent areas of the granules were labeled, and the endoplasmic reticulum was reactive. Double labeling with two different sizes of gold particles showed that both mucin and GRP co-localized in the same granules. Pre-absorption of the antibodies with their respective antigens eliminated immunolabeling of the acinar cells. These antibodies will be useful in studies of cell differentiation in RSMG and of synthesis, processing, and packaging of RSMG secretory products.

A mouse caries model and evaluation of aqp5-/- knockout mice

Current techniques to alter gene expression in mice allow direct analysis of the net role of a host factor in caries development. Towards this goal we first established protocols to induce and score caries in NFS/N mice and determined caries susceptibility in mice with targeted deletion of the gene encoding aquaporin-5 (Aqp5-/-), a water channel involved in the production of saliva. In the NFS/N strain of mice total sulcal caries and severity scores were consistent between experiments, whereas smooth surface caries scores were lower, more variable but distributed fairly evenly among the buccal, lingual and sulcal surfaces. In Black Swiss/129SvJ mice (genetic background of Aqp5-/- mice) caries scores were 50-75% lower compared to NFS/N mice, suggesting strain variation in caries susceptibility under our experimental conditions. In Aqp5-/- mice, in which the volume of total salivary secretion is reduced by 60-65%, there was a significant increase in caries, primarily on the buccal and sulcal surfaces. Results indicate that caries susceptibility increases with a reduced salivary flow that is associated with decreased water content of saliva.

Both M1 and M3 receptors regulate exocrine secretion by mucous acini

We investigated the role of M1 and M3 receptors in regulating exocrine secretion from acini isolated from rat sublingual glands. In secretion experiments, we derived affinity values (KB) from Schild regression analysis for the antagonists pirenzepine (61.0 nM) and 4-diphenylacetoxy-N-methylpiperidine (4-DAMP; 1.06 nM). The KB for 4-DAMP is similar to its affinity value [equilibrium dissociation constant from competition studies (Ki); 1.81 nM] determined from radioligand competition experiments. In contrast, the KB for pirenzepine is between its high-affinity (17.6 nM) and low-affinity (404 nM) Ki values. In separate secretion experiments, we found that the M1 receptor antagonist, M1-toxin, induces a rightward shift in the concentration-response curve to muscarinic agonist and inhibits maximal secretion by 40%. The inhibitory effect of M1-toxin appears specific for M1 receptor blockade, since the toxin abolishes acinar high-affinity pirenzepine-binding sites and does not inhibit secretion induced by nonmuscarinic agents. Additional pharmacological studies indicate muscarinic receptors do not function through putative neural elements within isolated acini. Our combined results are consistent with both M1 and M3 receptors directly regulating mucous acinar exocrine secretion and indicate M3 receptors alone are insufficient to induce a maximal muscarinic response.

The gene encoding mouse Muc19: cDNA, genomic organization and relationship to Smgc

We previously demonstrated expression of full-length transcripts for sublingual mucin apoprotein, Muc19, of approximately 24 kb (Fallon MA, Latchney LR, Hand AR, Johar A, Denny PA, Georgel PT, Denny PC, and Culp DJ. Physiol Genomics 14: 95-106, 2003). We now describe the complete sequence and genomic organization of the apomucin encoded by 43 exons. Southern analyses indicate a central exon of approximately 18 kb containing 36 tandem repeats, each encoding 163 residues rich in serine and threonine. Full-length transcripts are an estimated 22,795 bp in length that span 106 kb of genomic DNA. The transcriptional start site is 24 bp downstream of a TATA box and 42 bp upstream of the conceptual translational start codon. The putative apoprotein has an estimated mass of 693.4 kDa and contains 7,524 amino acids (80% serine, threonine, glycine, alanine, and proline). We present a model for rat Muc19 transcripts and compare the conceptually translated Muc19 proteins for mouse, rat, pig, and the 3' end of human Muc19. Conserved among these apoproteins are a signal peptide, a large tandem repeat region, von Willebrand factor type C and D domains, a trypsin inhibitor-like Cys-rich domain, and a COOH-terminal cystine knot-like domain. Southern blot analyses indicate transcripts for Muc19 and Smgc (submandibular gland protein C) are splice variants of a larger gene, Muc19/Smgc. Comparative Northern analyses between the major salivary glands demonstrate highly selective Muc19 expression in neonatal and adult sublingual glands, whereas Smgc is expressed in neonatal submandibular and sublingual glands. Regulation of Muc19/Smgc gene expression is discussed with respect to alternative splicing and mucous cell cytodifferentiation.

Analysis of bladder tumor recurrence in 178 patients

The identification of bladder tumor characteristics which may affect tumor recurrence has been of interest to the clinician for a long time. Previous attempts to identify predictive factors of recurrence involved comparisons based on the twelve-month recurrence rate in a prospective clinical investigation of bladder tumor patients observed over a five-year period. A statistical regression model known as the proportional hazards model was employed to identify these factors using the disease-free interval as the outcome variable. Prior bladder cancer history, age at admission, initial tumor stage, grade, number, size, shape, and site were examined. The results confirm that a patient's prior history of bladder cancer must be considered in evaluating his likelihood of tumor recurrence. The analysis then focuses on patients with no prior history for predictive factors of recurrence.

Muscarinic cholinergic receptor subtypes in rat sublingual glands

Mucin glycoprotein secretion by rat sublingual glands is regulated primarily by muscarinic cholinergic receptors. Studies were conducted to identify muscarinic receptor subtypes in whole glands as well as in isolated acinar structures. In radioligand binding studies, we used subtype-selective antagonists in competition studies to initially determine receptor subtype heterogeneity. In membranes from whole glands, both pirenzepine and methoctramine displayed two affinity sites (M1 and M3) of nearly equal proportions. In contrast, acinar membranes contained a 1:2 and 2:1 ratio of M1 to M3 sites for pirenzepine and methoctramine, respectively. In all cases, p-fluoro-hexahydro-siladifenidol and 4-diphenylacetoxy-N-methylpiperidine each bound to a single class of binding sites. Northern analysis using oligonucleotide probes specific for the 5' ends of the translated regions of m1 through m5 receptors detected only m1 and m3 subtypes in poly(A)+ RNA from whole glands. We also used antisera specific for each receptor subtype to immunoprecipitate solubilized receptors from membrane preparations. Only m1 (51.7 and 64.9%) and m3 (48.3 and 34.7%) subtypes were found consistently in membranes from whole sublingual glands and isolated acini, respectively. Studies with other exocrine glands generally described the predominance of m3 receptors, and m1 receptors, if present, were presumably associated with contaminating neural structures. Our results therefore demonstrate that mucous acini from rat sublingual glands contain abundant amounts of both m1 and m3 receptors.

Rat sublingual gland as a model to study glandular mucous cell secretion

To study the regulation of mucous cell secretion, we have developed an in vitro cell model consisting of enzymatically dispersed mucous acinar structures (cell aggregates) from rat sublingual glands. Histological and ultrastructural evidence demonstrates that the cell aggregates are highly enriched in mucous cells, retain the morphological and ultrastructural features observed in intact glands, and undergo transition to an extensive secretory state when stimulated by 10 microM carbachol. The secretory responsiveness of the cell aggregates was verified in pharmacological studies. Carbachol stimulated secretion in a dose-dependent manner with high affinity (concentration causing half-maximal response = 0.3 microM) and was completely inhibited by atropine. Secretion was also stimulated by vasoactive intestinal peptide and substance P but not by alpha- or beta-adrenergic agonists. Biochemical characterization of secretion during nonstimulated and carbachol-stimulated conditions (after preincubation in [3H]glucosamine) demonstrated that, in response to carbachol, cell aggregates synthesized and secreted mucins which were similar to mucin glycoproteins isolated from whole glands. Collectively, our results establish that the rat sublingual cell aggregate model is a viable and pharmacologically responsive cell system to study the regulation of mucous cell secretion.

Sulfuric acid aerosol exposure in humans assessed by bronchoalveolar lavage

Epidemiologic and experimental evidence suggests that exposure to acidic aerosols may affect human health. Brief exposures to acidic aerosols alter mucociliary clearance and increase airway responsiveness, but effects on host defense mechanisms at the alveolar level have not been studied in humans. Twelve healthy, nonsmoking volunteers between 20 and 39 yr of age were exposed for 2 h to aerosols of approximately 1,000 micrograms/m3 sulfuric acid (H2SO4) or sodium chloride (NaCl [control]), with intermittent exercise, in a randomized, double-blind fashion. Each subject received both exposures, separated by at least 2 wk. Bronchoalveolar lavage (BAL) was performed 18 h after exposure in order to detect evidence of an inflammatory response, changes in alveolar cell subpopulations, or changes in alveolar macrophage (AM) function, which is important in host defense. When compared with NaCl, exposure to H2SO4 did not increase polymorphonuclear leukocytes in BAL fluid. The percentage of T lymphocytes decreased in association with H2SO4 exposure, but the difference was not statistically significant (14.9% after NaCl, 11.5% after H2SO4; p = 0.14). Antibody-mediated cytotoxicity of AM increased in association with H2SO4 exposure (percent lysis 19.1 after NaCl, 23.6 after H2SO4; p = 0.16). No significant change was seen in release of superoxide anion or inactivation of influenza virus in vitro. Brief exposures to H2SO4 aerosol at 1,000 micrograms/m3 do not cause an influx of inflammatory cells into the alveolar space, and no evidence was found for alteration in antimicrobial defense 18 h after exposure.

G protein coupling to M1 and M3 muscarinic receptors in sublingual glands

Rat sublingual gland M2 and M3 muscarinic receptors each directly activate exocrine secretion. To investigate the functional role of coreceptor expression, we determined receptor-G protein coupling. Although membrane proteins of 40 and 41 kDa are ADP-ribosylated by pertussis toxin (PTX), and 44 kDa proteins by cholera toxin (CTX), both carbachol-stimulated high-affinity GTPase activity and the GTP-induced shift in agonist binding are insensitive to CTX or PTX. Carbachol enhances photoaffinity labeling ([alpha-(32)P]GTP-azidoaniline) of only 42-kDa proteins that are subsequently tractable to immunoprecipitation by antibodies specific for Galpha(q) or Galpha(11) but not Galpha(12) or Galpha(13). Carbachol-stimulated photoaffinity labeling as well as phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis is reduced 55% and 60%, respectively, by M1 receptor blockade with m1-toxin. Galpha(q/11)-specific antibody blocks carbachol-stimulated PIP2 hydrolysis. We also provide estimates of the molar ratios of receptors to Galpha(q) and Galpha(11). Although simultaneous activation of M1 and M3 receptors is required for a maximal response, both receptor subtypes are coupled to Galpha(q) and Galpha(11) to stimulate exocrine secretion via redundant mechanisms.

Longitudinal study of bladder cancer with cytology and biopsy

A study of urinary cytology and selected mucosal biopsies in conjunction with cystoscopy provided additional information of value in the management of 318 patients with bladder cancer. These procedures were especially helpful in patients with no visible lesions on follow-up cystoscopies in assessing the bladder epithelium, the behaviour of which may be unpredictable in that no further tumours may occur, or they may arise at irregular intervals.

Pain and tension are reduced among hospital nurses after on-site massage treatments: a pilot study

Tension and pain are common occupational hazards of modern-day nursing, especially given recent changes to the health care system. The aims of the pilot study were (1) to evaluate the feasibility of carrying out a series of eight 15-minute workplace-based massage treatments, and (2) to determine whether massage therapy reduced pain and stress experienced by nursing staff at a large teaching hospital. Twelve hospital staff (10 registered nurses and 2 nonmedical ward staff) working in a large tertiary care center volunteered to participate. Participants received up to eight, workplace-based, 15-minute Swedish massage treatments provided by registered massage therapists. Pain, tension, relaxation, and the Profile of Mood States were measured before and after each massage session. Pain intensity and tension levels were significantly lower after massage (P < .01). In addition, relaxation levels and overall mood state improved significantly after treatments (P < .01). The results of this pilot study support the feasibility of an eight-session, workplace-based, massage therapy program for pain and tension experienced by nurses working in a large teaching hospital. Further research is warranted to study the efficacy of workplace massage in reducing stress and improving overall mood.

The sld mutation is specific for sublingual salivary mucous cells and disrupts apomucin gene expression

NFS/N-sld mice harbor a spontaneous autosomal recessive mutation, sld (sublingual gland differentiation arrest) and histologically display attenuated mucous cell expression in sublingual glands (Hayashi et al. Am J Pathol 132: 187-191, 1988). Because altered serous demilune cell expression is unknown, we determined the phenotypic expression of this cell type in mutants. Moreover, we evaluated whether absence of glycoconjugate staining in 3-day-old mutant glands is related to disruption in apomucin gene expression and/or to posttranslational glycosylation events. Serous cell differentiation is unaffected, determined morphologically and by serous cell marker expression (PSP, parotid secretory protein; and Dcpp, demilune cell and parotid protein). Conversely, apical granules in "atypical" exocrine cells of mutant glands are PSP and mucin negative, but contain abundant SMGD (mucous granule marker). Age-related appearance of mucous cells is associated with expression of apomucin gene products, whereas SMGD expression is unaltered. "Atypical" cells thus appear specified to a mucous cell fate but do not synthesize mucin glycoproteins unless selectively induced postnatally, indicating the sld mutation disrupts apomucin transcriptional regulation and/or decreases apomucin mRNA stability.

A technique for the isolation of submucosal gland cells from cat trachea

We have developed a procedure to isolate submucosal gland cells from cat trachea. The excised trachea was stripped of surface epithelium by stroking the luminal surface with a nylon brush. The remaining submucosa was scraped free from underlying cartilage and minced into small fragments. To disperse glandular cells from these fragments, we subjected the minced tissue to both enzymatic (collagenase and elastase) and mechanical treatment. In 23 preparations of cells we yielded an average (+/- SE) of 8.4 +/- 0.9 (X 10(6] cells. In eight cell preparations 95 +/- 1% of the cells stained with periodic acid-Schiff stain, suggesting that the cells are of glandular origin. We used the following criteria to assess cell viability. The dye trypan blue was excluded by 92 +/- 1% of the cells (n = 23). Under the electron microscope, cellular membranes and organelles appeared normal. The isolated cells consumed oxygen at an average rate of 1.34 +/- 0.05 microliters O2 X h -1 X (10(6) cell) -1, (n = 65). Oxygen consumption was constant for at least 4 h after cell isolation, was inhibited 21% by 10(-4) M ouabain, and was subsequently stimulated to 135% above basal levels by 4 X 10(-5) M dinitrophenol.

Regulation of mucous acinar exocrine secretion with age

Denny and co-workers (Navazesh et al., 1992) recently reported decreased concentrations of MG1 and MG2 mucins in resting and stimulated whole human saliva with age. The current study was therefore conducted to examine whether there is a corresponding attenuation with age in stimulus secretion coupling regulating mucous cell exocrine secretion. We utilized an in vitro model system, isolated rat sublingual acini, to evaluate the regulation of mucous cell exocrine secretion. Rat sublingual glands are similar to human sublingual and minor mucous glands, both histologically and in terms of their pattern of innervation, which is predominantly parasympathetic. Mucin secretion is thus activated primarily by muscarinic cholinergic agonist and to a lesser extent by vasoactive intestinal peptide (VIP), which is co-localized with acetylcholine in parasympathetic nerve terminals. We isolated sublingual mucous acini from five-month-old and 24-month-old rats and compared the concentration responses for mucin secretion induced by VIP and the muscarinic agonist, arecaidine propargyl ester (APE). Concentration-response curves for VIP were nearly identical for mucous acini from the five-month-old and 24-month-old animals. Values for basal secretion, maximal secretion, and EC50 (approximately equal to 200 nmol/L VIP) were statistically equivalent between both age groups. Concentration-response curves for APE were also very similar between age groups, with no statistically significant difference in basal secretion or EC50 values (approximately equal to 50 nmol/L APE). Maximal secretion was slightly less but statistically different for 24-month-old vs. five-month-old animals, 158% vs. 169% above basal secretion, respectively. Collectively, we found no substantial age-related changes in the secretory responsiveness of salivary mucous cells.

An enriched preparation of basal-lateral plasma membranes from gastric glandular cells

A procedure is described for the preparation of a membrane fraction enriched in basal-lateral plasma membranes from gastric mucosa. Gastric glands isolated from rabbit were employed as starting material, greatly reducing contamination from non-glandular cell types. The distribution of cellular components during the fractionation procedure was monitored with specific marker enzymes. (Na+ + K+)-ATPase, ouabain-sensitive K+-stimulated p-nitrophenyl-phosphatase and histamine-stimulated adenylate cyclase were used as markers for basal-lateral membranes. These three markers were similarly distributed during both differential and equilibrium density gradient centrifugation. The enriched membrane fraction contained more than 30% of the total initial activities of the three basal-lateral membrane markers which were purified better than 11-fold with respect to protein. (Na+ + K+)-ATPase activity was resolved from the activities of acid phosphatase, pepsin, Mg2+-ATPase, cytochrome c oxidase, NADPH-cytochrome c reductase, glucose-6-phosphatase, (K+ + H+)-ATPase, DNA and RNA.

Role of calcium and PKC in salivary mucous cell exocrine secretion

Fluid and exocrine secretion of mucins by salivary mucous glands is regulated predominantly by parasympathetic activation of muscarinic receptors. A direct role for subsequent putative signaling steps, phospholipase C (PLC), increased intracellular calcium ([Ca(2+)](i)), and isoforms of protein kinase C (PKC) in mediating muscarinic exocrine secretion has not been elucidated, and these are potential therapeutic targets to enhance mucin secretion in hyposalivary patients. We found that muscarinic-induced mucin secretion by rat sublingual tubulo-acini was dependent upon PLC activation and the subsequent increase in [Ca(2+)](i), and further identified a transient PKC-independent component of secretion dependent upon Ca(2+) release from intracellular stores, whereas sustained secretion required entry of extracellular Ca(2+). Interactions among carbachol, PKC inhibitors, phorbol 12-myristate 13-acetate, and thapsigargin to modulate [Ca(2+)](i) implicated conventional PKC isoforms in mediating sustained secretion. With increasing times during carbachol perfusion of glands, in situ, PKC-α redistributed across glandular membrane compartments and underwent a rapid and persistent accumulation near the luminal borders of mucous cells. PKC-β1 displayed transient localization near luminal borders, whereas the novel PKCs, PKC-δ or PKC-ε, displayed little or no redistribution in mucous cells. Collective results implicate synergistic interactions between diacylglycerol (DAG) and increasing [Ca(2+)](i) levels to activate cPKCs in mediating sustained muscarinic-induced secretion.

The effect of chronic atropine treatment on salivary composition and caries in rats

Many instances of salivary dysfunction in humans can be traced to the use of medications that have hyposalivary side-effects. In this study, atropine, a cholinergic antagonist, was administered chronically to rats by use of osmotic mini-pumps. Steady-state blood levels, similar to levels obtained in human multiple oral dosing, were thus maintained. Atropine delivered in this manner for 24 days was found to decrease protein concentration of parotid saliva (p less than 0.05) elicited by pilocarpine, and to increase smooth-surface caries scores (p less than 0.05) in rats fed a cariogenic diet. Parotid saliva collected via ductal cannulation from rats subjected to chronic atropine administration (and stimulated to secrete by pilocarpine) exhibited increased levels of two basic proline-rich proteins (Peak A and SP-3), as evaluated by SDS-PAGE, compared with those observed in saliva from controls. Cannulation of sublingual glands in animals receiving high doses of atropine produced no measurable secretion upon pilocarpine stimulation. Carbachol stimulation of dispersed cell aggregates of sublingual glands from sham-operated and high-dose atropine groups indicated that the glands responded similarly once the antagonist was washed from the system, implying that the lack of secretion in vivo was caused by antagonism of the cholinergic receptor by atropine. Our observations suggest that this model system can be exploited for determination of the effects of chronic administration of hyposalivary drugs on salivary composition and caries rates.

Biochemical and immunological studies and assay of rat sublingual mucins

Original studies of rat sublingual mucins raised questions as to the existence of a second mucin species as distinguished by binding to hydroxyapatite. The existence of multiple mucin species is of concern in pharmacological studies of mucous-cell secretion as each species could represent distinct mucous-cell populations that respond differently to secretagogues. Thus a separate hydroxyapatite-bound mucin pool expressed in rat sublingual glands was isolated and characterized. Biochemical comparison of hydroxyapatite-bound mucins to total and hydroxyapatite-unbound sublingual mucins demonstrated no substantial differences in either amino acid and carbohydrate contents or in size distributions. In addition, a radioimmunoassay was developed using antisera prepared previously against unbound mucins. The three mucin pools exhibited equal specificities in displacement of radiolabelled unbound mucin tracer in the radioimmunoassay. Thus, bound and unbound mucins are indistinguishable, both immunologically and in biochemical composition. The radioimmunoassay was then evaluated for use in pharmacological studies of acinar mucous-cell secretion. Measurement by radioimmunoassay of secretion from isolated acini in response to carbachol was concentration-dependent (EC50 approx. 0.3 microM and maximal stimulation at 1 microM carbachol). In immunolocalization studies the antiserum was highly selective for mucous cells, recognized all mucous cells within histological sections, and was localized subcellularly to mucous-cell secretion granules and trans-Golgi, further validating the radioimmunoassay as a method to detect exocrine secretion from the entire pool of acinar mucous cells. Moreover, the radioimmunoassay was compared and found equivalent to an acid-precipitation method to assess relative secretion, suggesting the acid-precipitation method is also valid for pharmacological studies of isolated acini.

Characterization of muscarinic cholinergic receptors in cat tracheal gland cells

Studies of airway glands indicate a muscarinic cholinergic regulation of secretion. Because of the cellular complexity of the airways, receptor characterization in whole tissue is unfeasible. Therefore, we utilized homogenates of disaggregated gland cells isolated from cat trachea and the muscarinic antagonist [1-3H]quinuclidinyl benzilate ([3H]QNB) to characterize glandular muscarinic receptors. Receptors of isolated cells were functionally intact as assessed by carbachol (10(-4) M) stimulation of O2 consumption 86 +/- 6% (+/- SE, n = 20). Stimulation was dose dependent (mean effective concentration = 3.5 microM), inhibited by atropine [dissociation constant (KD) = 4.2 nM] but not phentolamine nor propranolol. Specific binding of [3H]QNB to cell homogenates was saturable, of high affinity (KD = 36 pM) and to a single population of receptors. Maximum binding was 58 fmol/10(6) cells or about 35,000 receptors per cell. Estimated affinities for muscarinic agents were in the micromolar range for agonists and nanomolar range for antagonists. Histamine, alpha-adrenergic, and beta-adrenergic agonists and antagonists did not inhibit specific binding. These results suggest that muscarinic receptors on tracheal gland cells are of high affinity and density.

Influenza virus infection of tracheal gland cells in culture

Influenza virus-induced tracheobronchitis causes limited epithelial deciliation but markedly decreased mucociliary transport. This suggests that virus-induced alterations in airway mucus play a role in decreased mucociliary transport. Airway submucosal glands are a primary source of mucus. Therefore, we examined virus-gland cell interactions by exposing primary cultures of isolated feline tracheal gland cells to influenza A/Scotland/840/74 H3N2 virus for 1 h at a multiplicity of infection of 0.1. Virus production and release into the culture medium first occurred between 8 and 12 h postinfection and eventually reached a steady state that continued for at least 8 days. Virus which was produced and released by infected cells infected other monolayers, resulting in viral production similar to that after infection with stock virus. Hemadsorption assays conducted 24 h after infection demonstrated that most of the cells in a monolayer became infected. The infection was nonlytic according to cell morphology, trypan blue dye exclusion, and release of lactate dehydrogenase. Because lysis of a cell subpopulation could have been masked by subsequent cell division, we compared the uptake of [3H]thymidine by infected and control monolayers. There was no increase in uptake by infected monolayers. These results demonstrate that feline tracheal gland cells in primary culture undergo productive and nonlytic infection with influenza A virus. This model provides a unique system for the study of virus-gland interactions isolated from the influence of other tissues.