Evidence that M3 muscarinic receptors in rat parotid gland couple to two second messenger systems

Molecular Mechanisms of REM Sleep

Rapid-eye movement (REM) sleep is a paradoxical sleep state characterized by brain activity similar to wakefulness, rapid-eye-movement, and lack of muscle tone. REM sleep is a fundamental brain function, evolutionary conserved across species, including human, mouse, bird, and even reptiles. The physiological importance of REM sleep is highlighted by severe sleep disorders incurred by a failure in REM sleep regulation. Despite the intense interest in the mechanism of REM sleep regulation, the molecular machinery is largely left to be investigated. In models of REM sleep regulation, acetylcholine has been a pivotal component. However, even newly emerged techniques such as pharmacogenetics and optogenetics have not fully clarified the function of acetylcholine either at the cellular level or neural-circuit level. Recently, we discovered that the G_q type muscarinic acetylcholine receptor genes, Chrm1 and Chrm3, are essential for REM sleep. In this review, we develop the perspective of current knowledge on REM sleep from a molecular viewpoint. This should be a starting point to clarify the molecular and cellular machinery underlying REM sleep regulation and will provide insights to explore physiological functions of REM sleep and its pathological roles in REM-sleep-related disorders such as depression, PTSD, and neurodegenerative diseases.

Acetylcholinesterase Inhibitors and Drugs Acting on Muscarinic Receptors- Potential Crosstalk of Cholinergic Mechanisms During Pharmacological Treatment

BACKGROUND

Pharmaceuticals with targets in the cholinergic transmission have been used for decades and are still fundamental treatments in many diseases and conditions today. Both the transmission and the effects of the somatomotoric and the parasympathetic nervous systems may be targeted by such treatments. Irrespective of the knowledge that the effects of neuronal signalling in the nervous systems may include a number of different receptor subtypes of both the nicotinic and the muscarinic receptors, this complexity is generally overlooked when assessing the mechanisms of action of pharmaceuticals.

METHODS

We have search of bibliographic databases for peer-reviewed research literature focused on the cholinergic system. Also, we have taken advantage of our expertise in this field to deduce the conclusions of this study.

RESULTS

Presently, the life cycle of acetylcholine, muscarinic receptors and their effects are reviewed in the major organ systems of the body. Neuronal and non-neuronal sources of acetylcholine are elucidated. Examples of pharmaceuticals, in particular cholinesterase inhibitors, affecting these systems are discussed. The review focuses on salivary glands, the respiratory tract and the lower urinary tract, since the complexity of the interplay of different muscarinic receptor subtypes is of significance for physiological, pharmacological and toxicological effects in these organs.

CONCLUSION

Most pharmaceuticals targeting muscarinic receptors are employed at such large doses that no selectivity can be expected. However, some differences in the adverse effect profile of muscarinic antagonists may still be explained by the variation of expression of muscarinic receptor subtypes in different organs. However, a complex pattern of interactions between muscarinic receptor subtypes occurs and needs to be considered when searching for selective pharmaceuticals. In the development of new entities for the treatment of for instance pesticide intoxication, the muscarinic receptor selectivity needs to be considered. Reactivators generally have a muscarinic M2 receptor acting profile. Such a blockade may engrave the situation since it may enlarge the effect of the muscarinic M3 receptor effect. This may explain why respiratory arrest is the major cause for deaths by esterase blocking.

cAMP-dependent recruitment of acidic organelles for Ca2+ signaling in the salivary gland

Autonomic neural activation of intracellular Ca²⁺ release in parotid acinar cells induces the secretion of the fluid and protein components of primary saliva critical for maintaining overall oral homeostasis. In the current study, we profiled the role of acidic organelles in shaping the Ca²⁺ signals of parotid acini using a variety of imaging and pharmacological approaches. Results demonstrate that zymogen granules predominate as an apically polarized population of acidic organelles that contributes to the initial Ca²⁺ release. Moreover, we provide evidence that indicates a role for the intracellular messenger NAADP in the release of Ca²⁺ from acidic organelles following elevation of cAMP. Our data are consistent with the "trigger" hypothesis where localized release of Ca²⁺ sensitizes canonical intracellular Ca²⁺ channels to enhance signals from the endoplasmic reticulum. Release from acidic stores may be important for initiating saliva secretion at low levels of stimulation and a potential therapeutic target to augment secretory activity in hypofunctioning salivary glands.

Blockade of muscarinic receptors impairs the retrieval of well-trained memory

Acetylcholine (ACh) is known to play an important role in memory functions, and its deficit has been proposed to cause the cognitive decline associated with advanced age and Alzheimer's disease (the cholinergic hypothesis). Although many studies have tested the cholinergic hypothesis for recently acquired memory, only a few have investigated the role of ACh in the retrieval process of well-trained cognitive memory, which describes the memory established from repetition and daily routine. To examine this point, we trained rats to perform a two-alternative forced-choice visual detection task. Each trial was started by having the rats pull upward a central-lever, which triggered the presentation of a visual stimulus to the right or left side of the display monitor, and then pulling upward a stimulus-relevant choice-lever located on both sides. Rats learned the task within 10 days, and the task training was continued for a month. Task performance was measured with or without systemic administration of a muscarinic ACh receptor (mAChR) antagonist, scopolamine (SCOP), prior to the test. After 30 min of SCOP administration, rats stopped manipulating any lever even though they explored the lever and surrounding environment, suggesting a loss of the task-related associative memory. Three hours later, rats were recovered to complete the trial, but the rats selected the levers irrespective of the visual stimulus, suggesting they remembered a series of lever-manipulations in association with a reward, but not association between the reward and visual stimulation. Furthermore, an m1-AChR, but not nicotinic AChR antagonist caused a similar deficit in the task execution. SCOP neither interfered with locomotor activity nor drinking behavior, while it influenced anxiety. These results suggest that the activation of mAChRs at basal ACh levels is essential for the recall of well-trained cognitive memory.

Urban legends series: Sjögren's syndrome

Sjögren's syndrome (SjS) is one of the most common autoimmune rheumatic diseases, clinically characterized by xerostomia and keratoconjunctivitis sicca. We investigated the following controversial topics: (i) Do we have reliable ways of assessing saliva production? (ii) How important are the quantity and quality of saliva? (iii) Are only anti-SSA/Ro and anti-SSB/La relevant for the diagnosis of SjS? (iv) Are the American-European Consensus criteria (AECC) the best way to diagnose SjS? Results from literature searches suggested the following: (i) Despite the fact that numerous tests are available to assess salivation rates, direct comparisons among them are scarce with little evidence to suggest one best test. (ii) Recent developments highlight the importance of investigating the composition of saliva. However, more research is needed to standardize the methods of analysis and collection and refine the quality of the accumulating data. (iii) In addition to anti-Ro/La autoantibodies, anti α-fodrin IgA and anti-MR3 autoantibodies seem to be promising diagnostic markers of SjS, but more studies are warranted to test their sensitivity and specificity. (iv) AECC are classification, not diagnostic criteria. Moreover, recent innovations have not been incorporated into these criteria. Consequently, treatment directed to patients diagnosed using the AECC might exclude a significant proportion of patients with SjS.

Molecular mechanism of pancreatic and salivary gland fluid and HCO3 secretion

Fluid and HCO(3)(-) secretion is a vital function of all epithelia and is required for the survival of the tissue. Aberrant fluid and HCO(3)(-) secretion is associated with many epithelial diseases, such as cystic fibrosis, pancreatitis, Sjögren's syndrome, and other epithelial inflammatory and autoimmune diseases. Significant progress has been made over the last 20 years in our understanding of epithelial fluid and HCO(3)(-) secretion, in particular by secretory glands. Fluid and HCO(3)(-) secretion by secretory glands is a two-step process. Acinar cells secrete isotonic fluid in which the major salt is NaCl. Subsequently, the duct modifies the volume and electrolyte composition of the fluid to absorb the Cl(-) and secrete HCO(3)(-). The relative volume secreted by acinar and duct cells and modification of electrolyte composition of the secreted fluids varies among secretory glands to meet their physiological functions. In the pancreas, acinar cells secrete a small amount of NaCl-rich fluid, while the duct absorbs the Cl(-) and secretes HCO(3)(-) and the bulk of the fluid in the pancreatic juice. Fluid secretion appears to be driven by active HCO(3)(-) secretion. In the salivary glands, acinar cells secrete the bulk of the fluid in the saliva that is driven by active Cl(-) secretion and contains high concentrations of Na(+) and Cl(-). The salivary glands duct absorbs both the Na(+) and Cl(-) and secretes K(+) and HCO(3)(-). In this review, we focus on the molecular mechanism of fluid and HCO(3)(-) secretion by the pancreas and salivary glands, to highlight the similarities of the fundamental mechanisms of acinar and duct cell functions, and to point out the differences to meet gland-specific secretions.

Enhancement of carbachol-induced amylase secretion in parotid glands from rats with experimental periodontitis

OBJECTIVE

In a previous study we observed that parotid glands from rats with experimental periodontitis showed an increase in basal amylase release as a result of an increase in cAMP accumulation induced by PGE(2) production. The aim of this work was to study whether this change in amylase release influences the secretory effect of carbachol.

DESIGN

Experimental periodontitis was induced through placing a black thread around the cervix of the two lower first molars. Experiments were done 22 days after ligature induced periodontitis. Amylase release was evaluated in vitro and determined using a colorimetric method which uses starch as substrate.

RESULTS

The effect of carbachol was increased in parotid glands from periodontitis rats. The effect of 10(-6)M carbachol was inhibited by 4-DAMP (10(-6)M), U-73122 (5 × 10(-6)M) and trifluoperazine (5 × 10(-6)M) in both groups. No changes were observed in the binding sites and affinity in parotid membranes from rats with experimental periodontitis. The inhibition of the adenylyl cyclase and the cyclooxygenase induced a right shift of the carbachol concentration-response curve in periodontitis group whilst the opposite effect was observed in control group in the presence of db-cAMP and PGE(2).

CONCLUSIONS

Parotid glands from rats with experimental periodontitis release more amylase in response to carbachol suggesting an interaction between Ca(2+) and cAMP in the fusion/exocytosis step of secretory vesicles.

Modulation of benzodiazepine receptor, adrenoceptor and muscarinic receptor by diazepam in rat parotid gland

This study investigated the influence of diazepam on the binding characteristics of adrenoceptor, muscarinic and benzodiazepine receptors in rat parotid gland membrane using a radioligand binding assay. At a concentration of >10(-6)M, diazepam competed with [(3)H]dihydroalprenolol for β-adrenoceptor, but not [(3)H]prazosin for α-adrenoceptor or [(3)H]quinuclidinyl benzilate for muscarinic receptor. Continuous administration of diazepam at doses of 0.4mg/kg/day, i.p. for 7days in rat significantly decreased pilocarpine (4.0mg/kg, i.p.)-induced parotid salivary flow. Diazepam also produced a significant increase in the dissociation constant (Kd) value for [(3)H]dihydroalprenolol binding, but no change in the maximal binding capacity (Bmax) value, and a decrease in the Kd value for [(3)H]diazepam binding to benzodiazepine receptors, but no change in the Kd or Bmax values for [(3)H]prazosin or [(3)H]quinuclidinyl benzilate binding. These results suggest that continuous administration of diazepam modifies affinity for β-adrenoceptor and benzodiazepine receptor binding sites in parotid gland membrane and that changes in these binding sites may be closely related to diazepam-induced suppression of salivary secretion.

Abnormal subcellular localization of AQP5 and downregulated AQP5 protein in parotid glands of streptozotocin-induced diabetic rats

BACKGROUND

The mechanisms underlying diabetic xerostomia have not been clarified in relation with aquaporin-5 (AQP5) subcellular localization in salivary glands.

METHODS

Western blotting, real-time PCR, and immunocytochemistry were used to analyse AQP5 protein levels and mRNA expression. AQP5 protein levels were measured in the apical plasma membrane (APM) and detergent-insoluble fraction prepared from streptozotocin-diabetic rat parotid glands.

RESULTS

Despite an increase in AQP5 mRNA, AQP5 protein levels were decreased in diabetic parotid glands compared with controls. Immunohistochemical studies indicated that AQP5, under unstimulated conditions, colocalised with flotillin-2 and GM1 with a diffuse pattern in the apical cytoplasm of acinar and duct cells in both control and diabetic rats. Ten minutes after intravenous injection of muscarinic agonist cevimeline, AQP5 was dramatically increased together with flotillin-2 and GM1 in the APM of parotid acinar and duct cells of control but not diabetic rats. Sixty minutes after injection, AQP5 was located in a diffuse pattern in the apical cytoplasm in both rats. Treatment of the parotid tissues with cevimeline for 10min increased the Triton X-100 solubility of AQP5 in control but not diabetic rats. Administration of insulin to diabetic rats tended to restore the cevimeline-induced translocation of AQP5.

CONCLUSION

Lack of AQP5 translocation in the salivary gland in response to a muscarinic agonist and downregulation of AQP5 protein might lead to diabetic xerostomia.

GENERAL SIGNIFICANCE

Cevimeline is useful to cure diabetic xerostomia under insulin administration.

A comparison of scopolamine and biperiden as a rodent model for cholinergic cognitive impairment

RATIONALE

The nonselective muscarinic antagonist scopolamine hydrobromide (SCOP) is employed as the gold standard for inducing memory impairments in healthy humans and animals. However, its use remains controversial due to the wide spectrum of behavioral effects of this drug.

OBJECTIVE

The present study investigated whether biperiden (BIP), a muscarinic m1 receptor antagonist, is to be preferred over SCOP as a pharmacological model for cholinergic memory deficits in rats. This was done by comparing the effects of SCOP and BIP using a battery of operant tasks: fixed ratio (FR5) and progressive ratio (PR10) schedules of reinforcement, an attention paradigm and delayed nonmatching to position task.

RESULTS

SCOP induced diffuse behavioral disruption, which included sensorimotor responding (FR5, 0.3 and 1 mg/kg), food motivation (PR10, 1 mg/kg), attention (0.3 mg/kg, independent of stimulus duration), and short-term memory (delayed nonmatching to position (DNMTP), 0.1 and 0.3 mg/kg, delay-dependent but also impairment at the zero second delay). BIP induced relatively more selective deficits, as it slowed sensorimotor responding (FR5, 10 mg/kg) and disrupted short-term memory (DNMTP, 3 mg/kg, delay-dependent but no impairment at the zero second delay). BIP had no effect on food motivation (PR10) or attention.

CONCLUSION

Muscarinic m1 antagonists should be considered an interesting alternative for SCOP as a pharmacological model for cholinergic mnemonic deficits in animals.

Isoproterenol and cAMP block ERK phosphorylation and enhance [Ca2+]i increases and oxygen consumption by muscarinic receptor stimulation in rat parotid and submandibular acinar cells

Salivary glands are innervated by sympathetic and parasympathetic neurons, which release neurotransmitters that promote fluid secretion and exocytosis when they bind to muscarinic and beta-adrenergic receptors, respectively. Signaling pathways downstream of these receptors are mainly distinct, but there is cross-talk that affects receptor-dependent events. Here we report that the beta-adrenergic ligand isoproterenol blocks increases in extracellular signal-related kinase (ERK) phosphorylation, a protein kinase C-dependent event promoted by the muscarinic receptor ligand carbachol in freshly dispersed rat parotid acinar cells. The inhibitory action of isoproterenol was reproduced by cAMP stimuli (forskolin) and mimetics (dibutyryl-cAMP, 8-(4-chlorophenylthio)-cAMP), including one highly selective for protein kinase A (N(6)-benzoyl-cAMP). In contrast, Epac (exchange proteins directly activated by cAMP)-selective activators did not mimic the blockade of ERK by isoproterenol, suggesting that inhibition involved protein kinase A. Isoproterenol also blocked ERK downstream of phorbol 12-myristate 13-acetate and the P2X(7) and epidermal growth factor receptors. Isoproterenol and forskolin blocked MEK phosphorylation, reduced RAF phosphorylation on a stimulatory site (Ser-338), and increased RAF phosphorylation on an inhibitory site (Ser-259). Inhibitory effects on ERK were also observed in freshly dispersed rat submandibular acinar cells but not in three immortalized/cancer salivary cell lines (Par-C10, HSY, HSG), indicating significant differences between native cells and cell lines. Notably, in native parotid cells isoproterenol enhanced the carbachol-promoted increases in [Ca(2+)](i) and oxygen consumption, events that initiate and accompany, respectively, the stimulation of fluid secretion by muscarinic ligands. Thus, isoproterenol produces opposite effects on prominent events downstream of the muscarinic receptor second messengers diacylglycerol (decrease in ERK phosphorylation) and inositol trisphosphate (increase in [Ca(2+)](i) and fluid secretion).

Salivation triggered by pilocarpine involves aquaporin-5 in normal rats but not in irradiated rats

1. Using rats, we examined the muscarinic receptor subtype mediating pilocarpine-induced parotid salivary secretion and the contributions of ion transporter systems (effluxes of K+ and Cl(-)) and aquaporin-5 (AQP5) translocation to this response in parotid glands in irradiated-induced xerostomia. 2. Salivary secretion was significantly lower in irradiated compared with sham-irradiated (normal) rats. In xerostomia rats, 0.4 and 0.8 mg/kg pilocarpine significantly increased parotid salivary secretion, although the salivary volume was still significantly less than in normal rats after the same dose of pilocarpine. 3. Pirenzepine (1 x 10(-6) to 1 x 10(-1) mol/L), AF-DX 116 (3 x 10(-6) to 3 x 10(-2) mol/L) and N-2-chloroethyl-4-piperidinyl diphenylacetate (4-DAMP; 1 x 10(-8) to 1 x 10(-2) mol/L) dose-dependently displaced radioligand binding to M(1), M(2) and M(3) receptors, respectively, in parotid membranes from both normal and irradiated rats. In each group of rats, 4-DAMP had the highest binding affinity. Pretreatment with 4-DAMP or pirenzepine dose-dependently inhibited pilocarpine-induced parotid secretion in both normal and irradiated rats, with 4-DAMP being markedly more potent than pirenzepine. 4. Normal and irradiated-rat parotid cells did not differ significantly in terms of pilocarpine-induced changes in [Ca2+](i), [K+](i) and [Cl(-)](i). Pilocarpine markedly increased the amount of AQP5 in the apical plasma membrane of parotid cells isolated from normal but not irradiated rats. 5. Thus, pilocarpine induces parotid salivary secretion mainly via the M(3) receptor subtype in both irradiated and normal rats. The reduction in this pilocarpine-induced secretion seen in irradiated rats is due not to disturbances of intracellular Ca2+ mobilization or ion transporter systems, but rather to a disturbance of AQP5 translocation, which may be involved in the pathogenesis of X-ray irradiation-induced xerostomia.

Distinct pathways of ERK activation by the muscarinic agonists pilocarpine and carbachol in a human salivary cell line

Cholinergic-muscarinic receptor agonists are used to alleviate mouth dryness, although the cellular signals mediating the actions of these agents on salivary glands have not been identified. We examined the activation of ERK1/2 by two muscarinic agonists, pilocarpine and carbachol, in a human salivary cell line (HSY). Immunoblot analysis revealed that both agonists induced transient activation of ERK1/2. Whereas pilocarpine induced phosphorylation of the epidermal growth factor (EGF) receptor, carbachol did not. Moreover, ERK activation by pilocarpine, but not carbachol, was abolished by the EGF receptor inhibitor AG-1478. Downregulation of PKC by prolonged treatment of cells with the phorbol ester PMA diminished carbachol-induced ERK phosphorylation but had no effect on pilocarpine responsiveness. Depletion of intracellular Ca2+ ([Ca2+]i by EGTA did not affect ERK activation by either agent. In contrast to carbachol, pilocarpine did not elicit [Ca2+]i mobilization in HSY cells. Treatment of cells with the muscarinic receptor subtype 3 (M3) antagonist N-(3-chloropropyl)-4-piperidnyl diphenylacetate decreased ERK responsiveness to both agents, whereas the subtype 1 (M1) antagonist pirenzepine reduced only the carbachol response. Stimulation of ERKs by pilocarpine was also decreased by M3, but not M1, receptor small interfering RNA. The Src inhibitor PP2 blocked pilocarpine-induced ERK activation and EGF receptor phosphorylation, without affecting ERK activation by carbachol. Our results demonstrate that the actions of pilocarpine and carbachol in salivary cells are mediated through two distinct signaling mechanisms-pilocarpine acting via M3 receptors and Src-dependent transactivation of EGF receptors, and carbachol via M1/M3 receptors and PKC-converging on the ERK pathway.

Expression of muscarinic receptor subtypes in salivary glands of rats, sheep and man

In rat parotid, submandibular and sublingual glands and in ovine parotid and in human labial glands, the expression of muscarinic receptor subtypes was examined by immunoblotting and immunohistochemistry. Functional correlates were searched for in rat salivary glands. In the rat submandibular and sublingual glandular tissues clear signals of muscarinic M1 and M5 receptors could be detected in the immunoblotting and vague bands for muscarinic M3 and, in particular for, M4 receptors. The rat parotid gland differed. In this gland, the signal was less obvious for the muscarinic M1 receptor, and further, muscarinic M4 receptors appeared more strongly marked than in the submandibular glands. The results from the immunohistochemistry could be interpreted as the muscarinic M4 receptors are located on nerve fibres, since the outer layer of lobuli were densely stained. Intraglandular vessels in the rat submandibular and parotid glands showed expression of M3 receptors. In contrast to the parotid gland, the submandibular vessels also expressed M1 and M2 receptors. Occasionally M5 receptors appeared in the arteries and veins also. The functional studies in the rat confirmed muscarinic M1 receptor mediated secretion in the submandibular gland. Since the M1 receptor blockade did not affect submandibular blood flow, indirect vascular effects could not in total explain the secretory inhibition. Also in the human labial glands, muscarinic M1, M3 and M5 receptors occurred. No or low amounts of muscarinic M2 and M4 receptors could be detected. In patients with Sjögren-like symptoms an up-regulation of M3, M4 and M5 receptors was apparent in the labial glands. In ovine parotid glands all receptors could be detected, but constantly with vague bands for muscarinic M2 receptors. In conclusion, muscarinic M1 receptors seem to be expressed in seromucous/mucous glands. A secretory effect by muscarinic M5 receptors is not to be excluded, since they were expressed in all the glands examined. However, other functions, such as promotion of inflammation, cell growth and proliferation are possible as well.

The efficacy of cevimeline hydrochloride in the treatment of xerostomia in Sjögren's syndrome in southern Chinese patients: a randomised double-blind, placebo-controlled crossover study

Cevimeline hydrochloride, a specific agonist of the M3 muscarinic receptor, is beneficial in the treatment of symptoms of xerostomia and xerophthalmia associated with Sjögren's syndrome (SS). Cevimeline has not been evaluated in southern Chinese patients. Furthermore, the effects of cevimeline on health-related quality of life and oral health status are not known. In this randomised, double-blind, placebo-controlled crossover study, patients received cevimeline 30 mg or matched placebo three times per day over 10 weeks followed by a 4-week washout period before treatment crossover. Participants self-completed the following questionnaires: Xerostomia Inventory (XI), the General Oral Health Assessment Index (GOHAI), the Ocular Surface Disease Index (OSDI) and the Medical Outcomes Short Form (SF-36). Clinical assessments included sialometry, examination of the oral cavity for the degree of xerostomia and dental complications of xerostomia. Fifty patients (22 primary SS and 28 secondary SS) were enrolled in the trial. Forty-four patients completed the study. There was a significant improvement in the XI and GOHAI scores as well as the objective rating of xerostomic signs of the oral cavity after treatment with cevimeline. However, there was no improvement in salivary flow rates and dry eye symptoms. SS patients had lower SF-36 scores, but these did not improve after treatment with cevimeline.

Modified aquaporin 5 expression and distribution in submandibular glands from NOD mice displaying autoimmune exocrinopathy

OBJECTIVE

To investigate the expression and localization of aquaporin 5 (AQP5) in salivary glands and salivary gland function in the NOD mouse.

METHODS

All experiments were performed using NOD and BALB/c mice (ages 8 weeks and 24 weeks). Real-time reverse transcription-polymerase chain reaction, Western blotting, and immunohistochemical analysis were used to study the expression and distribution of AQP5 in salivary glands. In addition, salivary gland function was determined.

RESULTS

Compared with the levels in BALB/c mice, relative AQP5 messenger RNA levels were not significantly modified in the parotid glands from NOD mice of both ages but were significantly increased in the submandibular glands from NOD mice of both ages. Western blot analyses of both salivary gland membranes revealed that the level of AQP5 protein was increased in 24-week-old NOD mice. Important inflammatory infiltrates were observed in the submandibular glands, but not in the parotid glands, from 24-week-old NOD mice. The 8-week-old and 24-week-old BALB/c mice and the 8-week-old NOD mice showed AQP5 primarily at the apical membrane of the salivary gland acinus. In contrast, in acini from the submandibular glands (but not the parotid glands) from 24-week-old NOD mice, AQP5 staining was reduced at the apical membrane but was increased at the basal membrane. A moderately statistically significant decrease in pilocarpine-stimulated salivary flow was observed in 24-week-old NOD mice compared with that in age-matched BALB/c mice.

CONCLUSION

Submandibular glands from 24-week-old NOD mice displayed inflammatory infiltrates, increased AQP5 protein expression, and impaired AQP5 distribution. However, the moderately statistically significant decrease in the salivary flow rate in these mice did not match the extent of AQP5 misdistribution.

Signaling pathways involved in pilocarpine-induced mucin secretion in rat submandibular glands

We have studied the signaling pathways involved in pilocarpine-induced mucin release in rat submandibular slices. Pilocarpine produced a significant increment of PGE2 levels and a positive (r=0.8870) and significant (p=0.0077) correlation between PGE2 production and mucin released was determined. The participation of PGE2 was confirmed by the use of indomethacin (indo) and of acetyl salicylic acid (ASA), cyclooxygenase inhibitors, which inhibited pilocarpine-induced mucin release. The muscarinic receptors involved in the regulation of mucin release were identified as M1 and M4 by the use of the selective acetylcholine receptors (mAChR) antagonists, pirenzepine, AF-DX 116, 4-DAMP and tropicamide. The secretory process was dependent on both, intracellular and extracellular calcium pools since it was inhibited by thapsigargin and verapamil. Cyclic AMP, nitric oxide synthase and PKC also participated in pilocarpine-induced mucin release. It is concluded that pilocarpine, by activation the M1 and M4 mAChR subtypes induces an increase of intracellular Ca2+ concentration ([Ca2+]I) and elevates cAMP levels, which in turn stimulates COX, PKC and NOS and promotes mucin exocytosis. PGE2 released induces cAMP accumulation which, together with PKC are involved in the PGE2 increased Ca2+/cAMP-regulated exocytosis. Thus, cAMP accumulation induced by cholinergic stimulation is, in part, the result of PGE2 production.

An Overview of Autonomic Regulation of Parotid Gland Activity: Influence of Orchiectomy

The parotid gland participates in the digestive process by providing fluid, electrolytes and enzymes that facilitate the onset of digestion. Neurotransmitters, hormones and biologically active peptides regulate its activity. The autonomic system is the main regulatory mechanism of the gland. Sympathetic stimulation induces amylase release through beta(1)-receptor activation and few fluid secretion by alpha(1)-receptor activation. The parasympathetic system controls basal activity of the gland acting on M(1) and M(3) muscarinic acetylcholine receptors and induces the secretion of fluid saliva rich in electrolytes through the modulation of ion channels and the Na(+)-K(+)-ATPase activity. In addition, its activation induces amylase release. The mechanisms involved in amylase secretion by isoproterenol and carbachol, as well as the mechanism of the cholinergic regulation of Na(+)-K(+)-ATPase activity and the changes observed after orchiectomy, are the scope of this review.

Distribution and function of muscarinic receptor subtypes in the ovine submandibular gland

The effects of muscarinic receptor antagonists on responses to electrical stimulation of the chorda-lingual nerve were determined in pentobarbitone-anesthetized sheep and correlated to the morphology of tissue specimens. Stimulation at 2 Hz continuously, or in bursts of 1 s at 20 Hz every 10 s, for 10 min induced similar submandibular fluid responses (19 ± 3 vs. 21 ± 3 μl·min−1·g gland−1), whereas vasodilatation was greater during stimulation in bursts (−52 ± 4 vs. −43 ± 5%; P < 0.01). Continuous stimulation at 8 Hz induced substantially greater responses (66 ± 9 μl·min−1·g gland−1 and −77 ± 3%). While atropine (0.5 mg/kg iv) abolished the secretory response at 2 and 20 Hz (1:10 s), a small response persisted at 8 Hz (<5%). The “M1-selective” antagonist pirenzepine (40 μg/kg iv) reduced the fluid response at all frequencies tested ( P < 0.05–0.01), most conspicuously at 2 Hz (reduced by 69%). Methoctramine (“M2/M4-selective”; 100 μg/kg iv; n = 5) had no effect on fluid or the vascular responses but increased the protein output at 2 (+90%, P < 0.05) and 8 Hz (+45%, P < 0.05). The immunoblotting showed distinct bands for muscarinic M1, M3, M4, and M5 receptors, and immunohistochemistry showed muscarinic M1 and M3 receptors to occur in the parenchyma. Thus muscarinic M1 receptors contribute to the secretory response to parasympathetic stimulation but have little effect on the vasodilatation in the ovine submandibular gland. Increased transmitter release caused by blockade of neuronal inhibitory receptors of the M4 subtype would explain the increase in protein output.

Spatial microenvironment defines Ca2+ entry and Ca2+ release in salivary gland cells

The difference of Ca(2+) mobilization induced by muscarinic receptor activation between parotid acinar and duct cells was examined. Oxotremorine, a muscarinic-cholinergic agonist, induced intracellular Ca(2+) release and extracellular Ca(2+) entry through store-operated Ca(2+) entry (SOC) and non-SOC channels in acinar cells, but it activated only Ca(2+) entry from non-SOC channels in duct cells. RT-PCR experiments showed that both types of cells expressed the same muscarinic receptor, M3. Given that ATP activated the intracellular Ca(2+) stores, the machinery for intracellular Ca(2+) release was intact in the duct cells. By immunocytochemical experiments, IP(3)R2 colocalized with M3 receptors in the plasma membrane area of acinar cells; in duct cells, IP(3)R2 resided in the region on the opposite side of the M3 receptors. On the other hand, purinergic P2Y2 receptors were found in the apical area of duct cells where they colocalized with IP(3)R2. These results suggest that the expression of the IP(3)Rs near G-protein-coupled receptors is necessary for the activation of intracellular Ca(2+) stores. Therefore, the microenvironment probably affects intracellular Ca(2+) release and Ca(2+) entry.

Comparison of agonist-induced Ca2+ responses in rat submandibular acini and ducts

Changes in intracellular Ca(2+) concentration ([Ca(2+)]i) induced by agonists were simultaneously monitored in rat submandibular acini and ducts using a Ca(2+) imaging system. Substance P (SP) elicited marked increases in [Ca(2+)]i in acini but not in ducts. Carbachol (CCh) increased [Ca(2+)]i in both acini and ducts, but the maximal level was higher in acini than in ducts. In contrast, epinephrine (Epi) also induced an increase in [Ca(2+)]i in acini and ducts, but to a greater extent in ducts than in acini. Isoproterenol (ISO) caused a small but significant increase in [Ca(2+)]i in ducts but not acini. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis using total RNA extracted from highly purified acinar and ductal cells showed that substance P receptor mRNA was present in acini at higher levels than in ducts. In contrast, alpha(1a)-adrenoceptor mRNA was more strongly expressed in ducts than in acini. The muscarinic receptors (M(3) and M(5)) and beta-adrenoceptors (beta(1) and beta(2)) were expressed at equivalent levels in both cell types. These results confirm that acini and ducts exhibit significant differences in agonist-induced Ca(2+) responses. Furthermore, substance P- and epinephrine-induced Ca(2+) responses were consistent with receptor mRNA expression in acini and ducts, but carbachol- and isoproterenol-induced [Ca(2+)]i increases were not.

Defects in muscarinic receptor-coupled signal transduction in isolated parotid gland cells after in vivo irradiation: evidence for a non-DNA target of radiation

Radiation-induced dysfunction of normal tissue, an unwanted side effect of radiotherapeutic treatment of cancer, is usually considered to be caused by impaired loss of cell renewal due to sterilisation of stem cells. This implies that the onset of normal tissue damage is usually determined by tissue turnover rate. Salivary glands are a clear exception to this rule: they have slow turnover rates (>60 days), yet develop radiation-induced dysfunction within hours to days. We showed that this could not be explained by a hypersensitivity to radiation-induced apoptosis or necrosis of the differentiated cells. In fact, salivary cells are still capable of amylase secretion shortly after irradiation while at the same time water secretion seems specifically and severely impaired. Here, we demonstrate that salivary gland cells isolated after in vivo irradiation are impaired in their ability to mobilise calcium from intracellular stores (Ca2+ i), the driving force for water secretion, after exposure to muscarinic acetylcholine receptor agonists. Using radioligand-receptor-binding assays it is shown that radiation caused no changes in receptor density, receptor affinity nor in receptor-G-protein coupling. However, muscarinic acetylcholine agonist-induced activation of protein kinase C alpha (PKCalpha), measured as translocation to the plasma membrane, was severely affected in irradiated cells. Also, the phorbol ester PMA could no longer induce PKCalpha translocation in irradiated cells. Our data hence indicate that irradiation specifically interferes with PKCalpha association with membranes, leading to impairment of intracellular signalling. To the best of our knowledge, these data for the first time suggest that, the cells' capacity to respond to a receptor agonist is impaired after irradiation.

Effect of cevimeline on salivary components in patients with Sjögren syndrome

The aim of this study is to clarify the effects of cevimeline on various components in human saliva, such as immunoglobulin A (IgA), lysozyme, alpha-amylase and squamous cell carcinoma (SCC) antigen. Twelve female patients with Sjögren syndrome (SS) and 14 healthy women were enrolled. After the first saliva collection, one capsule (30 mg) of cevimeline was administered to each subject. Saliva was collected again after 90 min. The salivary flow rate and concentration of each component were measured. In both groups the salivary flow rate and amylase concentration were significantly increased by cevimeline. The lysozyme and IgA concentrations did not change significantly in both groups. The SCC antigen concentration did not change significantly in the SS group, but it decreased significantly in the control group. The secretion rates of amylase and IgA showed significant increases in both groups. The secretion rate of lysozyme significantly increased only in the control group, while the secretion rate of SCC significantly increased only in the SS group. Cevimeline augments not only the salivary flow rate but also the secretion rate of some digestive and/or defense factors from infections. It may be beneficial for SS patients to continue taking cevimeline to prevent oral infections, and other serious sequelae.

Selective use of a reserved mechanism for inducing calcium oscillations

Concentration-dependent transformation of hormone- and neurotransmitter-induced calcium oscillation is a common phenomenon in diverse types of cells especially of the secretory type. The rodent submandibular acinar cells are an exception to this rule, which show elevated plateau increase in intracellular calcium under all stimulatory concentrations of both norepinephrine and acetylcholine. However, under depolarized state this cell type could also show a variation of periodic calcium changes. This reserved mechanism of calcium oscillation is jump-started by depolarization only with muscarinic cholinergic stimulation, but not with adrenergic stimulation. This latter effect is attributable to alpha receptor activation, not due to simultaneous activation of alpha and beta receptors, with beta receptor activation only serving to enhance the magnitude. These data suggest that this reserved mechanism for inducing calcium oscillation can be selectively used only by specific receptor-signaling pathways, and may therefore partly explain the long-known differences between secretion induced by sympathetic and parasympathetic stimulation in the submandibular gland.

Cholinergic Stimulation of Salivary Secretion Studied with M1 and M3 Muscarinic Receptor Single- and Double-Knockout Mice

Identification of the specific muscarinic acetylcholine receptor (mAChR) subtypes mediating stimulation of salivary secretion is of considerable clinical interest. Recent pharmacological and molecular genetic studies have yielded somewhat confusing and partially contradictory results regarding the involvement of individual mAChRs in this activity. In the present study, we re-examined the roles of M(1) and M(3) mAChRs in muscarinic agonist-mediated stimulation of salivary secretion by using M(1) and M(3) receptor single-knockout (KO) mice and newly generated M(1)/M(3) receptor double-KO mice. When applied at a low dose (1 mg/kg, s.c.), the muscarinic agonist pilocarpine showed significantly reduced secretory activity in both M(1) and M(3) receptor single-KO mice. However, when applied at higher doses, pilocarpine induced only modestly reduced (5 mg/kg, s.c.) or unchanged (15 mg/kg, s.c.) salivation responses, respectively, in M(1) and M(3) receptor single-KO mice, indicating that the presence of either M(1) or M(3) receptors is sufficient to mediate robust salivary output. Quantitative reverse transcriptase-polymerase chain reaction studies with salivary gland tissue showed that the inactivation of the M(1) or M(3) mAChR genes did not lead to significantly altered mRNA levels of the remaining mAChR subtypes. Strikingly, the sialagogue activity of pilocarpine was abolished in M(1)/M(3) receptor double-KO mice. However, salivary glands from M(1)/M(3) receptor double-KO mice remained responsive to stimulation by the beta-adrenergic receptor agonist, (S)-isoproterenol. Taken together these studies support the concept that a mixture of M(1) and M(3) receptors mediates cholinergic stimulation of salivary flow.

M(3) muscarinic acetylcholine receptor plays a critical role in parasympathetic control of salivation in mice

The M(1) and M(3) subtypes are the major muscarinic acetylcholine receptors in the salivary gland and M(3) is reported to be more abundant. However, despite initial reports of salivation abnormalities in M(3)-knockout (M(3)KO) mice, it is still unclear which subtype is functionally relevant in physiological salivation. In the present study, salivary secretory function was examined using mice lacking specific subtype(s) of muscarinic receptor. The carbachol-induced [Ca(2+)](i) increase was markedly impaired in submandibular gland cells from M(3)KO mice and completely absent in those from M(1)/M(3)KO mice. This demonstrates that M(3) and M(1) play major and minor roles, respectively, in the cholinergically induced [Ca(2+)](i) increase. Two-dimensional Ca(2+)-imaging analysis revealed the patchy distribution of M(1) in submandibular gland acini, in contrast to the ubiquitous distribution of M(3). In vivo administration of a high dose of pilocarpine (10 mg kg(-1), s.c.) to M(3)KO mice caused salivation comparable to that in wild-type mice, while no salivation was induced in M(1)/M(3)KO mice, indicating that salivation in M(3)KO mice is caused by an M(1)-mediated [Ca(2+)](i) increase. In contrast, a lower dose of pilocarpine (1 mg kg(-1), s.c.) failed to induce salivation in M(3)KO mice, but induced abundant salivation in wild-type mice, indicating that M(3)-mediated salivation has a lower threshold than M(1)-mediated salivation. In addition, M(3)KO mice, but not M(1)KO mice, had difficulty in eating dry food, as shown by frequent drinking during feeding, suggesting that salivation during eating is mediated by M(3) and that M(1) plays no practical role in it. These results show that the M(3) subtype is essential for parasympathetic control of salivation and a reasonable target for the drug treatment and gene therapy of xerostomia, including Sjögren's syndrome.

In vitro and in vivo tissue selectivity profile of solifenacin succinate (YM905) for urinary bladder over salivary gland in rats

Solifenacin succinate [YM905; (+)-(1S,3'R)-quinuclidin-3'-yl 1-phenyl-1,2,3,4-tetrahydroisoquinoline-2-carboxylate monosuccinate] is a new muscarinic receptor antagonist developed for the treatment of overactive bladder. The aim of the present study was to evaluate the in vitro and in vivo bladder selectivity profile of solifenacin over salivary gland in the same animal species, and to compare the results with those obtained for tolterodine, oxybutynin, darifenacin and atropine. Solifenacin and the other antimuscarinic drugs inhibited carbachol-induced increases in intracellular Ca(2+) levels in bladder smooth muscle cells and salivary gland cells isolated from rats in a concentration-dependent manner. The inhibitory effect of solifenacin for bladder smooth muscle cells (pK(i)=8.12) was 3.6-fold more potent than that for salivary gland cells (pK(i)=7.57). In contrast, the inhibitory effects of the other antimuscarinic drugs for bladder smooth muscle cells were 1.7- to 2.2-fold more potent than those for salivary gland cells. In anesthetized rats, solifenacin dose-dependently inhibited carbachol-induced intravesical pressure elevation and salivary secretion, and exhibited functional selectivity (3.7- to 6.5-fold) for urinary bladder over salivary gland. Tolterodine was also 2.2- to 2.4-fold more selective in inhibition of bladder response. In contrast, oxybutynin, darifenacin and atropine did not show functional selectivity for urinary bladder. These results indicate that solifenacin exerts greater selectivity for urinary bladder over salivary gland than tolterodine, oxybutynin, darifenacin and atropine, and may consequently provide symptomatic benefit in the treatment of overactive bladder with less dry mouth than currently used antimuscarinic drugs.

Comparison of in vitro selectivity profiles of solifenacin succinate (YM905) and current antimuscarinic drugs in bladder and salivary glands: a Ca2+ mobilization study in monkey cells

We investigated the effects of the new muscarinic receptor antagonist solifenacin succinate [YM905; (+)-(1S,3'R)-quinuclidin-3'-yl 1-phenyl-1,2,3,4-tetrahydroisoquinoline-2-carboxylate monosuccinate] and the current antimuscarinic drugs for the treatment of overactive bladder (oxybutynin, tolterodine and darifenacin) on intracellular Ca(2+) mobilization in response to M(3) muscarinic receptor activation in bladder smooth muscle and submandibular gland cells isolated from Cynomolgus monkeys. Solifenacin concentration-dependently inhibited carbachol-induced Ca(2+) mobilization, with affinity constant values (pKi) of 8.5 +/- 0.053 in bladder smooth muscle cells and 8.2 +/- 0.051 in submandibular gland cells (n = 5). The pKi value of solifenacin was almost equivalent to the values of oxybutynin, tolterodine and darifenacin in bladder smooth muscle cells (8.7, 8.5 and 8.4, respectively), while being lower than those in submandibular gland cells (9.0, 8.7 and 8.8, respectively). The bladder-selectivity index (Ki ratio: submandibular gland/bladder) for solifenacin (2.1) was statistically higher, moreover, than those for oxybutynin, tolterodine and darifenacin (0.51, 0.65 and 0.46, respectively). These findings consequently indicate solifenacin's unique profile in terms of its selectivity for bladder smooth muscle cells over salivary gland cells in non-human primates, relative to oxybutynin, tolterodine and darifenacin. Solifenacin may, therefore, confer a promising therapeutic advantage for reducing adverse effects, such as dry mouth, exhibited by current antimuscarinic therapy for overactive bladder.

Antimuscarinics for treatment of overactive bladder

For many years, antimuscarinic drugs have been the first-line pharmacological treatment for urgency, frequency, and urge incontinence, all symptoms of the disorder termed overactive bladder. Antimuscarinic treatment is not always effective and is associated with side-effects that limit its clinical use. The clinical significance of the effects of antimuscarinic drugs has been questioned lately. In this review, the rationale for the use of these drugs in the management of overactive bladder is re-examined and the results of treatment are discussed. I conclude that these drugs are the only treatment with undisputed effectiveness in the treatment of overactive bladder. They may not be the perfect treatment for all patients with this disorder, but their value for individual patients should not be underestimated. Further clinical trials with improvement in quality of life as the primary endpoint are needed and may give a fair reflection of the clinical value of antimuscarinic drugs.

Age-related decreases in the response of aquaporin-5 to acetylcholine in rat parotid glands

Aquaporin-5 (AQP5) is important in salivary fluid secretion in response to cholinergic and adrenergic stimuli in rat parotid glands. We hypothesized that expression and function of AQP5 might change with age. Acetylcholine and epinephrine induced increases in AQP5 levels in the apical plasma membranes of both young adult and senescent rats. The stimulatory effect of acetylcholine, but not that of epinephrine, on AQP5 levels in the apical plasma membranes of the cells decreased markedly during aging. The quinuclidine derivative, SNI-2011, induced a persistent increase in AQP5 levels in the apical plasma membrane in the cells of both these rats. The amounts of M(3)-muscarinic receptor and Gq proteins did not decrease during aging. The age-related alteration in the responsiveness of AQP5 in the cells to these stimuli might account for the concomitant changes in nitric oxide synthase activity. These results suggest that SNI-2011 might have therapeutic benefit for the treatment of age-related xerostomia.

Castration decreases amylase release associated with muscarinic acetylcholine receptor downregulation in rat parotid gland

1 The mechanism and receptor subtypes involved in carbachol-stimulated amylase release and its changes after castration were studied in parotid slices from male rats. 2 Carbachol induced both amylase release and inositol phosphate (IP) accumulation in parotid slices from control and castrated rats, but castration induced a decrease of carbachol maximal effect. The effect of castration was reverted by testosterone replacement. 3 The selective M(1) and M(3) muscarinic receptor antagonists, pirenzepine and 4-diphenylacetoxy-N-methylpiperidine methiodide, respectively, inhibited carbachol-stimulated amylase release and IP accumulation in a dose-dependent manner in parotid slices from control and castrated rats. 4 A diminution of binding sites of muscarinic receptor in parotid membrane from castrated rats was observed. Competition binding assays showed that both, M(1) and M(3) muscarinic receptor subtypes are expressed in membranes of parotid glands from control and castrated rats, M(3) being the greater population. 5 These results suggest that amylase release induced by carbachol in parotid slices is mediated by phosphoinositide accumulation. This mechanism appears to be triggered by the activation of M(1) and M(3) muscarinic receptor subtypes. Castration induced a decrease of the maximal effect of carbachol evoked amylase release and IP accumulation followed by a diminution in the number of parotid gland muscarinic acetylcholine receptors.

Role of specific muscarinic receptor subtypes in cholinergic parasympathomimetic responses, in vivo phosphoinositide hydrolysis, and pilocarpine-induced seizure activity

Muscarinic agonist-induced parasympathomimetic effects, in vivo phosphoinositide hydrolysis and seizures were evaluated in wild-type and muscarinic M1-M5 receptor knockout mice. The muscarinic agonist oxotremorine induced marked hypothermia in all the knockout mice, but the hypothermia was reduced in M2 and to a lesser extent in M3 knockout mice. Oxotremorine-induced tremor was abolished only in the M2 knockout mice. Muscarinic agonist-induced salivation was reduced to the greatest extent in M3 knockout mice, to a lesser degree in M1 and M4 knockout mice, and was not altered in M2 and M5 knockout mice. Pupil diameter under basal conditions was increased only in the M3 knockout mice. Pilocarpine-induced increases in in vivo phosphoinositide hydrolysis were completely absent in hippocampus and cortex of M1 knockout mice, but in vivo phosphoinositide hydrolysis was unaltered in the M2-M5 knockout mice. A high dose of pilocarpine (300 mg/kg) caused seizures and lethality in wild-type and M2-M5 knockout mice, but produced neither effect in the M1 knockout mice. These data demonstrate a major role for M2 and M3 muscarinic receptor subtypes in mediating parasympathomimetic effects. Muscarinic M1 receptors activate phosphoinositide hydrolysis in cortex and hippocampus of mice, consistent with the role of M1 receptors in cognition. Muscarinic M1 receptors appear to be the only muscarinic receptor subtype mediating seizures.

Presynaptic muscarinic receptor mechanisms and submandibular responses to stimulation of the parasympathetic innervation in bursts in rats

Submandibular secretory responses to electrical stimulation of the parasympathetic innervation at variable frequencies were measured in anaesthetized rats. Selective blockade by pirenzepine and by methoctramine occurred at doses (50 and of 300 nmol kg (-1), i.v., respectively) that did not inhibit the responses to exogenous acetylcholine. In the presence of methoctramine, the nerve-evoked fluid responses were increased by 100% at 1 Hz independently of the total number of impulses (10-300), suggesting that M2 receptor activation inhibits transmitter release. The magnitude of the increase was inversely related to frequency of stimulation. The protein concentrations in the fluid responses were not significantly affected by methoctramine. Pirenzepine had an inhibitory effect on the fluid secretory responses, which was dependent of frequency, as well as of number of impulses, suggesting that M1 receptor activation facilitates transmitter release. At 10 Hz given intermittently (for 1 s at 10-s intervals), pirenzepine reduced the fluid response by 25%. The protein release was substantially and significantly reduced by pirenzepine independent of frequency but only during long periods of stimulation (300 impulses). It is concluded that muscarinic M1 receptor activation normally has a facilitatory effect on transmitter release, and that the facilitation occurs during short, intense stimulation. Muscarinic M1 receptors are, however, likely to regulate protein secretion by other mechanisms. Muscarinic M2 receptors, on the other hand, normally inhibit cholinergic transmission at low frequencies. Similar to findings in the alimentary tract of several species, stimulation in bursts at high frequencies is a more efficient stimulation pattern than continuous low frequency stimulation. This pattern of stimulation thus takes advantage of transient facilitation and avoids the inhibition at less intense neuronal activity.

Regulation of phospholipase D by muscarinic receptors in rat submandibular ductal cells

The muscarinic agonist carbachol stimulated phospholipase D (PLD) in rat submandibular gland (RSMG) ductal cells in a time and concentration-dependent manner. This effect was inhibited by chelation of extracellular calcium with ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA). PLD could also be activated by epinephrine and AlF(4)(-), two polyphosphoinositide-specific phospholipase C (PPI-PLC) activators, and by the phorbol ester o-tetradecanoylphorbol 13-acetate (TPA) which activates protein kinase C (PKC). Ionomycin and thapsigargin only slightly increased PLD activity. Ortho-vanadate, a tyrosine phosphatase inhibitor, also stimulated PLD activity. Both carbachol and o-vanadate increased the formation of inositol phosphates and the tyrosine phosphorylation of at least two proteins (55-60 and 120 kDa). Calphostin C (a PKC inhibitor), U73122 (a PPI-PLC inhibitor) and genistein (a tyrosine kinase inhibitor) blocked the activation of PLD, of PLC and the phosphorylation of tyrosyl residues in response to carbachol and vanadate. Taken together, these results suggest that rat submandibular gland ductal cells express a calcium-dependent PLD activity. This enzyme is regulated by carbachol via a PLC-PKC-tyrosine kinase pathway.

Studies of muscarinic receptor subtypes in salivary gland function in anaesthetized rats

The in vivo study aimed to examine whether muscarinic receptor subtypes other than muscarinic M3 receptors exert exocrine functional roles in the rat salivary glands. The effects of pirenzepine, methoctramine and 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) were examined on secretion from the major salivary glands evoked by acetylcholine (0.001-10 micromol kg(-1) i.v.) in pentobarbitone-anaesthetized rats. Observations were occasionally made on glandular blood flow. 4-DAMP (0.1-100 nmol kg(-1) i.v.) markedly and equipotently inhibited the acetylcholine-evoked fluid responses in all glands. Pirenzepine (0.1 micromol kg(-1) i.v.-10 mmol kg(-1) i.v.) showed significantly lower inhibitory potency than 4-DAMP, most conspicuously in the parotid, while methoctramine (0.1 micromol kg(-1) i.v.-10 mmol kg(-1) i.v.) exerted an even lesser inhibitory effect. Also against acetylcholine-evoked blood flow increases, 4-DAMP showed a conspicuous potency. At 1 and 10 micromol kg(-1) i.v. of pirenzepine, the antagonist reduced the protein concentration in the submandibular saliva, but not in the parotid saliva. While 4-DAMP (1 and 10 nmol kg(-1) i.v.) significantly inhibited acetylcholine-evoked protein secretory responses in the submandibular glands, methoctramine (below 10 micromol kg(-1) i.v.) affected the responses in neither gland. The reduction of the protein concentration in submandibular saliva caused by 4-DAMP and pirenzepine was inhibited by N(omega)-nitro-L-arginine methyl ester (L-NAME; 30 mg kg(-1) i.p.), while L-NAME had no or only minute effects on the parotid protein secretion. Thus, in addition to muscarinic M3 receptors, other muscarinic receptors contribute to in vivo functional responses in rat submandibular and sublingual glands. While these other receptors are muscarinic M1 receptors in the sublingual gland, they may be a different subtype, possibly muscarinic M5 receptors, in the submandibular gland. However, muscarinic M1 receptors may induce indirect effects via nitric oxide in the submandibular gland.

Gene transfer to salivary glands

This article provides a review of the application of gene transfer technology to studies of salivary glands. Salivary glands provide an uncommon target site for gene transfer but offer many experimental situations likely of interest to the cell biologist. The reader is provided with a concise overview of salivary biology, along with a general discussion of the strategies available for gene transfer to any tissue. In particular, adenoviral vectors have been useful for proof of concept studies with salivary glands. Several examples are given, using adenoviral-mediated gene transfer, for addressing both biological and clinical questions. Additionally, benefits and shortcomings affecting the utility of this technology are discussed.

Role of salivary IgA in the pathogenesis of Sjögren syndrome

Saliva IgA autoantibodies against M(3) muscarinic acetylcholine receptors (mAChRs) could be a new marker for the diagnosis for Sjögren syndrome (SS) dry mouth. Saliva IgA from dry mouth primary SS (pSS) or secondary SS patients tested by ELISA recognized membrane parotid gland acinar cell antigens and the synthetic 25-mer peptide corresponding to the second extracellular loop of human M(3) mAChRs. Moreover, the IgA fraction was able to inhibit the [(3)H]QNB binding to parotid acinar membrane mAChRs. In addition, the IgA prevented carbachol stimulation of protein secretion by the parotid gland. As controls, IgA and saliva from women without dry mouth and from normal control subjects gave negative results on ELISA, binding, and biological assays, thus demonstrating the specificity of the reaction. IgA autoantibodies against mAChR may be considered among the immunoglobulin factors implicated in the pathophysiology of the development of pSS dry mouth and could be a new marker for differentiating SS dry mouth from non-SS dry mouth.

Activation of endogenous nitric oxide synthase coupled with methacholine-induced exocytosis in rat parotid acinar cells

Methacholine (MCh) interacted with M(3) muscarinic receptors in rat parotid tissue slices and induced amylase secretion. MCh- and calcimycin-induced exocytosis was completely inhibited by N-[2-(N-(4-chlorocinnamyl)-N-methylaminomethyl)phenyl]-N-[2-hydroxyethyl]-4-methoxybenzenesulfonamide, N(G)-nitro-L-arginine methylester (L-NAME), 1H-(1,2,4)-oxadiazolo[4,3-a]quinoxaline-1-one, and 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide, suggesting that activations of calmodulin (CaM) kinase II, nitric oxide synthase (NOS), and cGMP-dependent protein kinase (PKG) were coupled with the exocytosis. These suggestions were supported by the results that exposure of the slices to MCh induced a rapid increase in these enzyme activities. Western blot analysis showed that neuronal NOS (nNOS) was expressed in isolated parotid acinar cells of rats. To measure nitric oxide (NO) production in response to the stimulation with MCh in real time, the isolated parotid acinar cells had been preloaded with 4,5-diaminofluorescein diacetate and incubated with the agonist. MCh (1 microM) induced a fast increase in 4,5-diaminofluorescein fluorescence, corresponding to an increase in the NO synthesis in the presence of extracellular Ca(2+) but not in the absence of it. When the isolated parotid acinar cells preloaded with L-NAME or 2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis (acetoxymethylester) were treated simultaneously with MCh, the increase in the fluorescence also was not observed. The MCh-induced increase in the fluorescence was not observed in the cells incubated in the absence of extracellular calcium, showing the importance of Ca(2+) entry from extracellular sites for MCh-induced NOS activation. These results indicate that nNOS is endogenously present in rat parotid acinar cells and that the rapid activation of this enzyme together with those of CaM kinase II and PKG contributes to MCh-induced amylase secretion.

A double-blind, randomized, placebo-controlled study of cevimeline in Sjögren's syndrome patients with xerostomia and keratoconjunctivitis sicca

OBJECTIVE

To evaluate the safety and efficacy of 2 dosages of cevimeline for the treatment of xerostomia and keratoconjunctivitis sicca in patients with Sjögren's syndrome.

METHODS

A 12-week double-blind, randomized, placebo-controlled study was performed. Patients were randomly assigned to receive either placebo, 15 mg of cevimeline 3 times daily, or 30 mg of cevimeline 3 times daily. Patients were evaluated at baseline and throughout the study for their global assessment of dryness (mouth, eyes, overall) as well as their subjective assessment of the specific symptoms of dry mouth and dry eyes. Total saliva and tear flow also were measured.

RESULTS

Patients taking 30 mg of cevimeline 3 times daily had statistically significant improvements in their subjective global assessment of dry eyes (P = 0.0453), dry mouth (P = 0.0004), and increased salivary flow (P = 0.007). Patients receiving the 30-mg dosage also showed greater objective improvement (increased salivary and lacrimal flow rates, as measured by Schirmer's test) than did patients receiving placebo. Frequently reported adverse events included headache, increased sweating, abdominal pain, and nausea.

CONCLUSION

Treatment with cevimeline at a dosage of 30 mg 3 times daily resulted in substantive improvement by increasing the rate of saliva and tear flow in patients with Sjögren's syndrome, as well as improving subjective symptoms of dry mouth, dry eyes, and overall dryness. The 15-mg dosage relieved some symptoms, and both dosages were well tolerated.

Functional requirement of aquaporin-5 in plasma membranes of sweat glands

The distribution and function of aquaporins (AQPs) have not previously been defined in sweat glands. In this study, AQP1, AQP3, and AQP5 mRNA were demonstrated in rat paw by reverse transcription (RT)-PCR, but AQP2 and AQP4 were not. AQP1, AQP3, and AQP5 protein were confirmed in these tissues by immunoblotting. AQP1 was identified in capillary endothelial cells by immunohistochemical labeling, but not in sweat glands or epidermis. Abundant AQP3 expression was seen in basal levels of epidermis, but not in sweat glands. AQP2 and AQP4 were not observed in either skin or sweat glands. Immunohistochemical labeling revealed abundant AQP5 in secretory parts of rat and mouse sweat glands, where immunoelectron microscopy demonstrated abundant AQP5 labeling in the apical plasma membrane. AQP5 immunolabeling of human sweat glands yielded a similar pattern. To establish the role of AQP5 in sweat secretion, we tested the response of adult mice to s.c. injection of pilocarpine, as visualized by reaction of secreted amylase with iodine/starch. The number of active sweat glands was dramatically reduced in AQP5-null (-/-) mice compared with heterozygous (+/-) and wild-type (+/+) mice. We conclude that the presence of AQP5 in plasma membranes of sweat glands is essential for secretion, providing potential insight into mechanisms underlying mammalian thermoregulation, tactile sensitivity, and the pathophysiology of hyperhidrosis.