Re-engineering primary epithelial cells from rhesus monkey parotid glands for use in developing an artificial salivary gland

There is no satisfactory conventional treatment for patients who experience irreversible salivary gland damage after therapeutic radiation for head and neck cancer or because of Sjögren's syndrome. Additionally, if most parenchyma is lost, these patients also are not candidates for evolving gene transfer strategies. To help such patients, several years ago we began to develop an artificial salivary gland. In the present study, we used a non-human primate tissue source, parotid glands from rhesus monkeys, to obtain potential autologous graft cells for development of a prototype device for in situ testing. Herein, we present 3 major findings. First, we show that primary cultures of rhesus parotid gland (RPG) cells are capable of attaining a polarized orientation, with Na(+)/K(+)-adenosine triphosphatase, zonula occludens-1, and claudin-1 distributed in specific domains appropriate for epithelial cells. Second, we show that RPG cells exhibit 2 essential epithelial functions required for graft cells in an artificial salivary gland device (i.e., an effective barrier to paracellular water flow and the generation of a moderate transepithelial electrical resistance). Third, we show that RPG cells can express functional water channels, capable of mediating directional fluid movement, after transduction by adenoviral and adeno-associated virus type 2 vectors. Together these results demonstrate that it is feasible to individually prepare RPG cells for eventual use in a prototype artificial salivary gland.

Parotid function after selective deep lobe parotidectomy

Selective deep lobe parotidectomy is a demanding technique, but it preserves healthy glandular tissue, improves cosmetic results and minimises the incidence of Frey's syndrome. We have evaluated postoperative function of the superficial lobe of the parotid after selective resection of the deep lobe. Fourteen patients who each had a mass involving the deep lobe of the parotid were selected from 127 patients with tumours of the parotid gland who were seen and treated between January 2001 and March 2004. Of the 14, 12 matched the study criteria. The preoperative diagnosis was made using both computed tomography (CT) and ultrasound or fine needle aspiration cytology, and the diagnosis was confirmed by histological analysis. All cases were treated by the same surgeon. At 6 months follow-up all patients had a House-Brackmann test, iodine starch test, and scintigraphy of both parotid glands. After scintigraphy the maximum uptake value and function of the gland were evaluated with the concentration index (CI) and the CI percentage ratio. The concentration function of the gland in the resected side of the study group had a mean (S.D.) CI index of 5.5 (3.6) and a CI percentage ratio of 84%. Selective deep lobe parotidectomy has the following advantages: it minimises the impact of treatment on the facial contour, it does not increase postoperative morbidity and it preserves the function of the gland.

Parotid masses: face the facts

Parotid masses present both functional and aesthetic consequences due to the proximity of the facial nerve and the glands' alignment with the contours of the mandible. As the largest salivary glands, the parotids participate in providing moisture to the mouth through the production of saliva. This paper presents an overview of the anatomy and physiology of the parotid glands, signs and symptoms of parotid conditions, relevant diagnostic testing, medical and surgical treatment of parotid masses, postoperative recovery, and the role of the otorhinolaryngology (ORL) nurse in the continuum of care and patient education.

Gender difference in unstimulated whole saliva flow rate and salivary gland sizes

OBJECTIVE

A gender difference in the unstimulated whole saliva flow rate (UWSFR) may be due to a difference in the sizes of the salivary glands. In this study, we investigated the relationships among the UWSFR, gland sizes and body sizes of healthy young adult males and females.

DESIGN

Unstimulated whole saliva was collected for 5 min by the spitting method in 50 healthy young adults, and the flow rate of the saliva was measured. Heights and weights were measured, and body mass indices (BMI) were calculated. The sizes of the salivary glands were measured by use of a magnetic resonance imaging technique.

RESULTS

Parotid and submandibular gland sizes and flow rates in females were significantly smaller than those in males, as were also the weights, heights and BMI. In both males and females, there were significant positive correlations between gland sizes and the flow rates, weights and BMI. The variations of the flow rates were reduced by standardizing them with gland sizes, weights and BMI.

CONCLUSIONS

These results suggest that the lower UWSFR in females as compared with males is due to the smaller gland sizes due to the smaller body sizes.

Effects of cevimeline on salivation and thirst in conscious rats

OBJECTIVE

Intraperitoneal injection of a sialogogue, pilocarpine, at high concentrations induces salivation via peripheral pathways and thirst sensation via central pathways. In this study, we report that the effects of another sialagogue, cevimeline, on salivation and water intake in conscious rats differ from those of pilocarpine.

DESIGN

We investigated that effects of peripherally and centrally injected cevimeline on parotid saliva flow rate and water intake in conscious rats. The results were compared with those of pilocarpine.

RESULTS

The intraperitoneal injection of cevimeline induced salivation from the parotid gland, but not water intake. In contrast, the intracerebroventricular injection of cevimeline induced water intake without salivation. The concentration of cevimeline needed to induce salivation by intraperitoneal injection was several 10 times that of pilocarpine, but that needed to induce water intake by intracerebroventricular injection was over a 1000 times greater.

CONCLUSIONS

The finding that intraperitoneally injected cevimeline induces salivation without inducing water intake, suggests that the effects on the thirst center in the brain are weaker than those of pilocarpine.

Parotid-sparing intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma: Preserved parotid function after IMRT on quantitative salivary scintigraphy, and comparison with historical data after conventional radiotherapy

PURPOSE

To evaluate the parotid function after parotid-sparing intensity-modulated radiotherapy (IMRT) in patients with nasopharyngeal carcinoma (NPC).

METHODS AND MATERIALS

From March 2003 to May 2004, 16 patients with nonmetastatic NPC underwent parotid-sparing IMRT. Eight of these patients had Stage III or IV NPC based on the 1997 American Joint Committee on Cancer staging system. The post-IMRT parotid function was evaluated by quantitative salivary scintigraphy and represented by the maximal excretion ratio (MER) of the parotid gland after sialogogue stimulation. The parotid function of 16 NPC patients who were previously treated with conventional radiotherapy was reviewed as the historical control.

RESULTS

In the parotid-sparing IMRT group, all 16 patients were alive and without cancer at the end of follow-up period (median, 24.2 months). The mean parotid MER was 53.5% before radiotherapy, 10.7% at 1 month post-IMRT, and 23.3% at 9 months post-IMRT. In the conventional radiotherapy group, the mean parotid MER was 0.6% at 6 to 12 months postradiotherapy. The difference was statistically significant (23.3% vs. 0.6%, p<0.001, Mann-Whitney test). In the IMRT group, the mean parotid doses ranged from 33.2 Gy to 58.8 Gy (average, 43.9 Gy). The correlation between the mean parotid dose and the percentage decrease of parotid MER at 9 months post-IMRT (dMER) was statically significant (p=0.008, Pearson correlation).

CONCLUSIONS

Although the mean parotid doses are relatively high, the significant preservation of parotid function is achieved with IMRT for NPC patients. The significant correlation between mean parotid dose and parotid dMER demonstrates the dose-function relationship of the parotid gland.

[The relationship between the parotid glands function and the dose-volume effect in nasopharyngeal carcinoma patients with intensity-modulated radiation therapy]

OBJECTIVE

To study the preservation of parotid glands function and relationship between parotid glands function and dose-volume histogram (DVH) in nasopharyngeal carcinoma (NPC) patients treated by intensity modulated radiation therapy (IMRT).

METHODS

From August 2002 to December 2004, the excretion index (EI) and uptake index (UI) of parotids in 48 NPC patients underwent radical IMRT was examined by ECT at the beginning, the end of and the 3 months after radiotherapy. The relationship between parotid function (EI and UI) and DVH were analyzed.

RESULTS

The mean doses to the contralateral parotid and ipsilateral parotid were 22.8 +/- 4.5 Gy and 31.9 +/- 4.1 Gy, respectively. The symptom of xerostomia was mild at the end of radiotherapy. ECT showed EI of contralateral parotid were 0.35 +/- 0.25, 0.31 +/- 0.24 and 0.33 +/- 0.22 at the beginning, the end of and 3 months after radiotherapy (RT), respectively. UI were 7.12 +/- 3.56, 5.81 +/- 2.25 and 5.72 +/- 2.81 at the same intervals. This shows no statistical difference. The EI and UI of ipsilateral parotid at the completion of radiotherapy declined significantly (0.21 +/- 0.16 and 4.87 +/- 2.45, respectively) compared with those of pre-treatment (0.36 +/- 0.27 and 8.02 +/- 3.89, respectively) (P < 0.05). DVH showed: at the end of RT, the EI was significant difference between mean dose < 26 Gy and > or = 26 Gy group (P = 0.009) and decreased significantly in the group of V25 (the percentages of parotid volume irradiated with < 25 Gy) > or = 50% compared with the group of V25 < 50% (P < 0.01). The UIs were no significant difference in two groups (P > 0.05).

CONCLUSION

26 Gy is a threshold dose for the preservation of parotid glands function. There is also a threshold volume irradiated for the preservation of the parotid glands function. Based on the precondition of assuring significant dose to the target volume (PTV), we should reduce the irradiated volume and dose to parotid glands as possible as we can so as to preserve its function.

Dynamic magnetic resonance sialography as a new diagnostic technique for patients with Sjogren's syndrome

OBJECTIVE

To evaluate the clinical utility of dynamic magnetic resonance (MR) sialographic images as a diagnostic tool for patients with Sjögren's syndrome.

METHODS

The morphological findings and various kinds of functional parameters in volunteers on dynamic MR sialographic images were compared with those in five patients with definite Sjögren's syndrome.

RESULTS

On the MR sialographs of all five patients with Sjögren's syndrome, the so-called 'apple-tree appearance' was seen. The difference in two functional parameters using the dynamic MR sialographic data was elucidated between the two groups. The maximum area of the detectable ducts in the group of patients was significantly smaller (P < 0.001) than that in the group of volunteers. The ratio of change in the detectable ducts in the group of patients was significantly lower (P = 0.011) than that in the group of volunteers.

CONCLUSIONS

Our study suggests that dynamic MR sialographic data in addition to MR sialographic images might be useful for the diagnosis of Sjögren's syndrome.

Parasympathetic nerve-evoked protein synthesis, mitotic activity and salivary secretion in the rat parotid gland and the dependence on NO-generation

Incorporation of radiolabelled leucine and thymidine into trichloroacetic acid-insoluble material of the parotid gland was used as indices of protein synthesis and mitotic activity, respectively, following electrical stimulation of the parasympathetic auriculo-temporal nerve for 30 min in pentobarbitone-anaesthetized rats under adrenoceptor blockade (phentolamine and propranolol, 2mg/kg intravenous of each) in the absence or presence of atropine (2mg/kg intravenous) and without or with nitric oxide synthase inhibitors. In atropinized rats, the parasympathetic non-adrenergic, non-cholinergic (NANC) nerve-evoked mean increases in protein synthesis at a frequency of 10 Hz (142%) and 40 Hz (200%) were not affected in a statistically significant way (124 and 275%, respectively) by the neuronal type NO-synthase inhibitor N(w)propyl-l-arginine (N-PLA) (30 mg/kg intravenous). Neither were the increase (175%) in protein synthesis at 10 Hz in non-atropinized animals affected by N-PLA (180%). The increase (65%) in mitotic activity, 19 h after the end of stimulation at 40 Hz, in the presence of atropine, was not affected by N-PLA (55%). Neither were the increase (95%) in gland content of amylase at this point of observation statistically significant affected by N-PLA (144%). The secretion of fluid and output of amylase from the parotid gland upon nerve stimulation was not affected by N-PLA. When examining the non-selective NO-synthase inhibitor l-NAME (30 mg/kg intravenous) in atropinized rats subjected to stimulation at 10 Hz, neither the increase in protein synthesis nor the evoked fluid response or amylase outputs were affected. Hence, in contrast to an NO-dependent sympathetic-induced protein synthesis and mitosis in the parotid gland, involving the activity of the neuronal type NO-synthase, no support for a parasympathetic-induced protein synthesis (and gain in gland amylase) and mitosis, depending on NO-generation, was found. Likewise, the present findings provide no evidence for a role of NO in the parasym pathetic nerve-evoked fluid secretion and amylase output.

The functional evaluation of salivary glands using dynamic MR sialography following citric acid stimulation: a preliminary study

OBJECTIVE

We introduce a new technique for the functional evaluation of the salivary glands using continuous magnetic resonance (MR) sialography before and after citric acid stimulation.

METHODS

In 10 volunteers, the time-dependent changes in the maximum area of the detectable parotid gland ducts on MR sialographic images taken every 30 seconds before and after citric acid stimulation were analyzed. The time period to the occurrence of the maximum duct area poststimulation was noted, and then the time for the area to return to its 50% value pre-citric acid stimulation was also observed. This new technique was clinically applied in 1 patient with an excessive supply impression of saliva and in 1 patient with a short supply impression with saliva.

RESULTS

In all volunteers after citric acid stimulation, the maximum area of the detectable salivary gland ducts first increased and then decreased. A strong relationship was found between the maximum area of the detectable salivary gland ducts before citric acid stimulation and total saliva volume (Pearson r = 0.672, P = .031). Compared with all the volunteers, the ratio of change in the detectable ducts was the highest in the patient with an excessive supply impression of saliva, but lowest in the patient with a short supply impression with saliva.

CONCLUSIONS

This initial study suggests that dynamic MR sialography allows for functional and morphological evaluation of the salivary glands. This technique appears to have many possible applications and further investigation in this field is necessary.

Membrane-delimited inhibition of maxi-K channel activity by the intermediate conductance Ca2+-activated K channel

The complexity of mammalian physiology requires a diverse array of ion channel proteins. This diversity extends even to a single family of channels. For example, the family of Ca²⁺-activated K channels contains three structural subfamilies characterized by small, intermediate, and large single channel conductances. Many cells and tissues, including neurons, vascular smooth muscle, endothelial cells, macrophages, and salivary glands express more than a single class of these channels, raising questions about their specific physiological roles. We demonstrate here a novel interaction between two types of Ca²⁺-activated K channels: maxi-K channels, encoded by the K_Ca1.1 gene, and IK1 channels (K_Ca3.1). In both native parotid acinar cells and in a heterologous expression system, activation of IK1 channels inhibits maxi-K activity. This interaction was independent of the mode of activation of the IK1 channels: direct application of Ca²⁺, muscarinic receptor stimulation, or by direct chemical activation of the IK1 channels. The IK1-induced inhibition of maxi-K activity occurred in small, cell-free membrane patches and was due to a reduction in the maxi-K channel open probability and not to a change in the single channel current level. These data suggest that IK1 channels inhibit maxi-K channel activity via a direct, membrane-delimited interaction between the channel proteins. A quantitative analysis indicates that each maxi-K channel may be surrounded by four IK1 channels and will be inhibited if any one of these IK1 channels opens. This novel, regulated inhibition of maxi-K channels by activation of IK1 adds to the complexity of the properties of these Ca²⁺-activated K channels and likely contributes to the diversity of their functional roles.

Endogenous signalling system involved in parotid gland adenosine A(1) receptor-amylase release

AIM

In this study, we have determined signalling pathways involved in adenosine A(1) receptor (A(1) receptor)-dependent stimulation of amylase release in rat parotid gland.

METHODS

Amylase release, binding and cyclic adenosine monophosphate (cAMP) assays, inositol phosphates (IPs) production and nitric oxide synthase (NOS) activity in the presence of cyclopentyl-1,3-dipropylxanthine (CPA) alone or in the presence of different inhibitory drugs were performed.

RESULTS

The binding parameters of specific A(1) antagonist [(3)H]-cyclopentyl 1,3-dipropilxanthine ([(3)H]-DPCPX) in parotid gland membranes show a population of high affinity sites with K(d) (nm) 0.53 +/- 0.06 and B(max) (fmol mg(-1) protein) 122.6 +/- 10.2. CPA stimulation of A(1) receptor exerts an increase in amylase release, IPs accumulation, cAMP production and NOS activity. All these A(1) agonist effects were blocked by the A(1) receptor antagonist DPCPX. Inhibitors of phospholipase C (PLC), calcium/calmodulin (CaM), protein kinase C (PKC), and adenylate cyclase, but not NOS, activities attenuated the CPA stimulatory effect on amylase release. The effect of CPA on amylase release significantly correlated with its action either on cAMP or on IPs accumulation.

CONCLUSION

These results suggest that CPA activation of parotid gland A(1) receptor induces a stimulatory effect on amylase release associated with increased production of cAMP and IPs accumulation. The mechanism appears to occur secondarily to stimulation of phosphoinositide turnover via PLC activation. This, in turn, triggers cascade reactions involving CaM and PKC. The CPA stimulation of NOS does not appear to participate in amylase release.

Quantitative analysis of the voltage-dependent gating of mouse parotid ClC-2 chloride channel

Various ClC-type voltage-gated chloride channel isoforms display a double barrel topology, and their gating mechanisms are thought to be similar. However, we demonstrate in this work that the nearly ubiquitous ClC-2 shows significant differences in gating when compared with ClC-0 and ClC-1. To delineate the gating of ClC-2 in quantitative terms, we have determined the voltage (V(m)) and time dependence of the protopore (P(f)) and common (P(s)) gates that control the opening and closing of the double barrel. mClC-2 was cloned from mouse salivary glands, expressed in HEK 293 cells, and the resulting chloride currents (I(Cl)) were measured using whole cell patch clamp. WT channels had I(Cl) that showed inward rectification and biexponential time course. Time constants of fast and slow components were approximately 10-fold different at negative V(m) and corresponded to P(f) and P(s), respectively. P(f) and P(s) were approximately 1 at -200 mV, while at V(m) > or = 0 mV, P(f) approximately 0 and P(s) approximately 0.6. Hence, P(f) dominated open kinetics at moderately negative V(m), while at very negative V(m) both gates contributed to gating. At V(m) > or = 0 mV, mClC-2 closes by shutting off P(f). Three- and two-state models described the open-to-closed transitions of P(f) and P(s), respectively. To test these models, we mutated conserved residues that had been previously shown to eliminate or alter P(f) or P(s) in other ClC channels. Based on the time and V(m) dependence of the two gates in WT and mutant channels, we constructed a model to explain the gating of mClC-2. In this model the E213 residue contributes to P(f), the dominant regulator of gating, while the C258 residue alters the V(m) dependence of P(f), probably by interacting with residue E213. These data provide a new perspective on ClC-2 gating, suggesting that the protopore gate contributes to both fast and slow gating and that gating relies strongly on the E213 residue.

[Quantitative and qualitative investigations of salivary gland function in dependence on irradiation dose and volume for reduction of xerostomia in patients with head-and-neck cancer]

BACKGROUND AND PURPOSE

Radiation treatment of head-and-neck tumors mostly leads to a damage to the salivary glands and a consequential permanent loss of saliva. The aim of this investigation was to establish a modern three-dimensional conformal radiotherapy (3D-CRT) to show a decrease in severe xerostomia in contrast to the proven conventional technique (K-RT) with photons and electrons.

PATIENTS AND METHODS

Between April 2002 and September 2003, 32 patients (25 male, seven female, mean age: 58 years) with malignant tumors of the head and neck were included-after surgery or in case of inoperability with curative intent-in a prospective, nonrandomized study. 10/32 patients (31%) received K-RT with photons and electrons, and 22/32 patients (69%) 3D-CRT (six to eight photon portals). The quantity of saliva was measured as stimulated saliva flow rate (ml/5 min) prior to treatment, at the end, and 1, 6, and 12 months after termination of treatment. To find out the resulting mean dose of both parotid glands for every patient in Gray (D(mean) doses), the D(mean) doses of the ipsilateral and the contralateral parotid gland, determined by dose-volume histograms (DVHs), were averaged over. For calculation of the NTCP (normal tissue complication probability), the logistic model was used.

RESULTS

In the trend the stimulated salivary flow rates were higher in the group with 3D-CRT than in the group with K-RT during the whole observation period (at 10 weeks after the start of radiotherapy 3D-CRT vs. K-RT with 1.56 +/- 1.6 vs. 0.82 +/- 1.2 ml/5 min; p < 0.1). The patients treated with the K-RT had, on average, significantly higher averaged D(mean) values than those irradiated with 3D-CRT (p < 0.012). Patients, who were irradiated with 3D-CRT for tumors of the larynx or hypopharynx, showed, on average, significantly lower D(mean) values than patients, who were treated with 3D-DRT because of oral cavity or oropharynx carcinomas or with K-RT irrespective of the primary tumor site (p < 0,003). The resulting dose for 50% complication probability (TD(50)) of the salivary glands was 36.9 Gy (30.9-43.5 Gy; 95% confidence interval). The gradient k of the curve located in point TD(50) was 7.7 (4.8-15.8; 95% confidence interval).

CONCLUSION

Basically, 3D-CRT seems to be suitable as a standard for all patients with carcinomas of the oral cavity, oro- and hypopharynx. Especially in patients with tumors located in the larynx and hypopharynx, averaged D(mean) doses of both parotids during irradiation can be reached, to conserve salivary flow rates, which are similar to baseline flow rates.

Role of VAMP-2, VAMP-7, and VAMP-8 in constitutive exocytosis from HSY cells

We evaluated the role of VAMP-2/synaptobrevin, VAMP-7/TI-VAMP, and VAMP-8/endobrevin in exocytic pathways of HSY cells, a human parotid epithelial cell line, by coexpressing these VAMP proteins tagged with green fluorescent protein (GFP) and human growth hormone (hGH) as a secretory cargo. Exocytosis of hGH was constitutive and the fluorescent signal of hGH-GFP was observed in the Golgi area and small vesicles quickly moving throughout the cytoplasm. The cytoplasmic vesicles containing hGH overlapped well with VAMP-7-GFP, but did so scarcely with VAMP-2-GFP or VAMP-8-GFP. However, when the vesicle transport from the trans-Golgi network to the plasma membrane was arrested by incubation at 20 degrees C for 2 h and then released by warming up to 37 degrees C; VAMP-2-GFP and hGH were clearly colocalized together in small cytoplasmic vesicles. Neither VAMP-7-GFP nor hGH-GFP was colocalized with LAMP-1, a marker for lysosomes and late endosomes. These results suggest that (1) VAMP-2 can be one of the v-SNAREs for constitutive exocytosis; (2) VAMP-7 is involved in the constitutive exocytosis as a slow, minor v-SNARE, but not in the lysosomal transport; and (3) VAMP-8 is unlikely to be a v-SNARE for constitutive exocytosis in HSY cells.

Menkes protein localization in rat parotid acinar cells

The aim was to study the subcellular localization of the Menkes protein (MNK; ATP7A) in the rat parotid acinar cell. MNK protein is a copper transporting P-type ATPase whose absence or dysfunction causes a fatal neurodegenerative disorder, MNK disease. Rat parotid glands were fixed and low-temperature embedded in Lowicryl K4M resin, and ultrathin sections were prepared for immunocytochemical analysis. Immunolocalization of MNK was demonstrated mainly over the trans Golgi network (TGN) area. Immature and mature secretory granules were also labelled, indicating that MNK protein could be involved here in copper secretion from acinar cells into saliva, consistent with a proposed cariostatic role for copper.

Dose-volume modeling of salivary function in patients with head-and-neck cancer receiving radiotherapy

PURPOSE

We investigated the factors that affect salivary function after head-and-neck radiotherapy (RT), including parotid gland dose-volume effects, potential compensation by less-irradiated gland tissue, and functional recovery over time.

METHODS AND MATERIALS

Sixty-five patients with head-and-neck tumors were enrolled in a prospective salivary function study. RT was delivered using intensity-modulated RT (n = 45), forward-planning three-dimensional conformal RT (n = 14), or three-dimensional conformal RT with an intensity-modulated RT boost (n = 6). Whole salivary flow was measured before therapy and at 6 months (n = 61) and 12 months (n = 31) after RT. A wide variety of dose-volume models to predict post-RT salivary function were tested. Xerostomia was defined according to the subjective, objective, management, analytic (SOMA) criteria as occurring when posttreatment salivary function was < 25% of the pretreatment function. Multivariate logistic regression analysis was used to assess the combined effect of dose-volume, patient-, and treatment-related factors.

RESULTS

A significant correlation was observed between the relative quality-of-life scores and relative stimulated saliva values at 6 months after RT (Spearman's correlation coefficient [R(s)] = 0.46, p < 0.001). The dose-volume factors were by far the strongest correlates with stimulated saliva flow, although other factors showed modest significance in multimetric models (chemotherapy, gender, and Karnofsky performance status). Several fitted dose-volume models provided a good mathematical description of the data. Significant noise in the salivary measurements (repeated measurement coefficient of variation was 27% in normal subjects) precluded selection of any one of the models presented solely on the basis of the objective fit criteria. Nevertheless, the mean dose-exponential model, in which each parotid gland's relative salivary gland function equaled exp(-A x mean gland dose), with A equal to 0.054/Gy (68% confidence interval 0.052-0.059), provided a good representation of the data and was incorporated into our multimetric analysis. Using that model, we estimated that a mean parotid dose of 25.8 Gy, on average, was likely to reduce a single parotid gland's flow to 25% of its pretreatment value, regardless of the treatment delivery method. Significant correlations were observed between a logistic multivariate model (incorporating the mean dose-exponential equation, gender, and Karnofsky performance status) and stimulated saliva flow at 6 months (R(s) = 0.73), stimulated saliva flow at 12 months (R(s) = 0.54), and quality-of-life score at 6 months (R(s) = 0.35) after RT.

CONCLUSION

Stimulated parotid salivary gland dose-volume models strongly correlated with both stimulated salivary function and quality-of-life scores at 6 months after RT. The mean stimulated saliva flow rates improved from 6 to 12 months after RT. Salivary function, in each gland, appeared to be lost exponentially at a rate of approximately 5%/1 Gy of mean dose. Additional research is necessary to distinguish among the models for use in treatment planning. The incidence of xerostomia was significantly decreased when the mean dose of at least one parotid gland was kept to < 25.8 Gy with conventional fractionation. However, even lower mean doses imply increased late salivary function.

Identification of AQP5 in lipid rafts and its translocation to apical membranes by activation of M3 mAChRs in interlobular ducts of rat parotid gland

Aquaporin-5 (AQP5), an apical plasma membrane (APM) water channel in salivary glands, lacrimal glands, and airway epithelium, has an important role in fluid secretion. M(3) muscarinic acetylcholine receptor (mAChR)-induced changes in AQP5 localization in rat parotid glands were investigated with immunofluorescence or immunoelectron microscopy, detergent solubility, and gradient density floatation assays. Confocal microscopy revealed AQP5 localization in intracellular vesicles of interlobular duct cells in rat parotid glands and AQP5 trafficking to the APM 10 min after injection of the mAChR agonist cevimeline. Conversely, 60 min after injection, there was a diffuse pattern of AQP5 staining in the cell cytoplasm. The calcium ionophore A-23187 mimicked the effects of cevimeline. Immunoelectron microscopic studies confirmed that cevimeline induced AQP5 trafficking from intracellular structures to APMs in the interlobular duct cells of rat parotid glands. Lipid raft markers flotillin-2 and GM1 colocalized with AQP5 and moved with AQP5 in response to cevimeline. Under control conditions, the majority of AQP5 localized in the Triton X-100-insoluble fraction and floated to the light-density fraction on discontinuous density gradients. After 10-min incubation of parotid tissue slices with cevimeline or A-23187, AQP5 levels decreased in the Triton X-100-insoluble fraction and increased in the Triton X-100-soluble fraction. Thus AQP5 localizes in the intracellular lipid rafts, and M(3) mAChR activation induces AQP5 trafficking to the APM with lipid rafts via intracellular Ca(2+) signaling and induces AQP5 dissociation from lipid rafts to nonrafts on the APM in the interlobular duct cells of rat parotid glands.

Electrophysiological characterization of native Na+-HCO3- cotransporter current in bovine parotid acinar cells

Using patch-clamp and molecular biological techniques, we identified and characterized membrane currents most likely generated by an electrogenic Na+-HCO3- cotransporter (NBCe) in acutely dissociated bovine parotid acinar (BPA) cells. When BPA cells were dialysed with a N-methyl-D-glucamine (NMDG)-glutamate-rich pipette solution, switching a Na-glutamate-rich, nominally HCO3--free bath solution to the one containing 25 mM HCO3-, but not Cl-, elicited a whole-cell current with a linear current-voltage relation. The HCO3- evoked current was abolished by total replacement of extracellular Na+ (Na+o) with NMDG or by 0.5 mM 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid (DIDS), and was only partially supported by Li+o, but not by K+o, Cs+o, and cholineo. The reversal potential shift of DIDS (0.5 mM)-sensitive current induced by a change of [Na+]o corresponded to an apparent coupling ratio of HCO3- to Na+ of 2. RT-PCR analysis showed the presence of transcripts of NBCe1-B, but not NBCe1-A in BPA cells. Electrophysiological and pharmacological properties of whole-cell currents recorded from HEK293 cells transfected with the NBCe1-B, which was cloned from BPA cells resembled those of the native currents. Non-invasive measurements of membrane potential changes in the cell-attached patch configuration indicated that an NBCe activity is present in intact unstimulated BPA cells bathed in a 25 mM HCO3--containing solution. Collectively, these results not only suggest that an NBCe is present, functional and may be mediated, at least in part, by NBCe1-B in BPA cells, but also provide the first electrophysiological characterization of transport properties of NBCe expressed in native exocrine glands.

Spatiotemporal analysis of exocytosis in mouse parotid acinar cells

Exocrine cells of the digestive system are specialized to secrete protein and fluid in response to neuronal and/or hormonal input. Although morphologically similar, parotid and pancreatic acinar cells exhibit important functional divergence in Ca(2+) signaling properties. To address whether there are fundamental differences in exocytotic release of digestive enzyme from exocrine cells of salivary gland versus pancreas, we applied electrophysiological and optical methods to investigate spatial and temporal characteristics of zymogen-containing secretory granule fusion at the single-acinar cell level by direct or agonist-induced Ca(2+) and cAMP elevation. Temporally resolved membrane capacitance measurements revealed that two apparent phases of exocytosis were induced by Ca(2+) elevation: a rapidly activated initial phase that could not be resolved as individual fusion events and a second phase that was activated after a delay, increased in a staircaselike fashion, was augmented by cAMP elevation, and likely reflected both sequential compound and multivesicular fusion of zymogen-containing granules. Optical measurements of exocytosis with time-differential imaging analysis revealed that zymogen granule fusion was induced after a minimum delay of approximately 200 ms, occurred initially at apical and basolateral borders of acinar cells, and under strong stimulation proceeded from apical pole to deeper regions of the cell interior. Zymogen granule fusions appeared to coordinate subsequent fusions and produced persistent structures that generally lasted several minutes. In addition, parotid gland slices were used to assess secretory dynamics in a more physiological context. Parotid acinar cells were shown to exhibit both similar and divergent properties compared with the better-studied pancreatic acinar cell regarding spatial organization and kinetics of exocytotic fusion of zymogen granules.

Regulation of the P2X7 receptor permeability to large molecules by extracellular Cl- and Na+

Upon continuous stimulation, the pore of the monovalent cation-selective P2X7 receptor (P2X7R) expands to accommodate large molecules such as N-methyl-D-glucamine (NMDG+). How the change in P2X7R permeability is regulated is not known. Here we report that extracellular Cl- (Cl-(o)) regulates the outward current, whereas extracellular Na+ (Na+(o)) regulates the inward current of large molecules by P2X7Rs. The P2X7R-mediated current was measured in parotid acinar and duct cells of wild type and P2X7R-/- mice and in HEK293 cells expressing the human or mouse P2X7R isoforms. In symmetrical NaCl, triethylammonium chloride, and NMDG+ chloride solutions, the P2X7R current followed a linear current/voltage relationship. In symmetrical NaCl, removal of Cl-(o) reduced the inward Na+ current by approximately 35% and the outward Na+ current by only 10%. By contrast, in the absence of Na+(i) and the presence of Na+(o) or NMDG+(o), the removal of Cl-(o) reduced the inward Na+ or NMDG+ currents by 35% but the outward NMDG+ current by >95%. The effect of Cl-(o) was half-maximal at approximately 60 mm. Reducing Cl-(i) from 150 to 10 mm did not reproduce the effects of Cl-(o). All currents were eliminated in P2X7R-/- cells and reproduced by expressing the P2X7Rs in HEK cells. These findings suggest that Cl-(o) primarily regulates the outward P2X7R current of large molecules. When cells dialyzed with NMDG+ were stimulated in the presence of Na+(o), subsequent removal of Na+(o) resulted in a strongly outward rectifying NMDG+ current, indicating maintained high selectivity for Na+ over NMDG+. During continuous incubation in Na+-free medium, the permeability of the P2X7Rs to NMDG+ gradually increased. On the other hand, when the cells were incubated in symmetrical NMDG+ and only then stimulated with ATP, the NMDG+ current by P2X7Rs followed a linear current/voltage relationship and did not change with time. These findings suggest that the P2X7R has a "Na+(o) memory" and that Na+(o) regulates the inward permeability of P2X7Rs to large molecules. The novel regulation of P2X7R outward and inward permeability to large molecules by Cl-(o) and Na+(o), respectively, may have an important protective function, particularly in secretory epithelial cells.

Gustatory Stimulation Changes the Apparent Diffusion Coefficient of Salivary Glands: Initial Experience

Echo-planar diffusion-weighted (DW) magnetic resonance (MR) imaging was used to evaluate changes in the parotid glands during gustatory stimulation. The study protocol was approved by the local ethics committee, and informed consent was obtained from all volunteers. Twelve healthy volunteers (five women, seven men) with a median age of 25 years (range, 22-30 years) were examined with a 1.5-T MR unit. A DW MR imaging sequence was performed once at rest and continuously repeated over a mean period of 26 minutes (range, 24-28 minutes) during salivary stimulation with a tablet of ascorbic acid given orally. During the first 5 minutes (range, 1 minute 30 seconds--7 minutes 30 seconds) of salivary stimulation, a decrease in apparent diffusion coefficient (ADC) was observed in both the parotid (P = .0001) and the submandibular (P = .0004) glands in all volunteers. During the following 15 minutes, a steady increase in ADC from the baseline value was noted for the parotid glands (P = .0022), and peak ADC was reached a median of 21 minutes (range, 14-21 minutes) after the start of gustatory stimulation. The ADC of the submandibular glands did not increase significantly after the start of gustatory stimulation compared with the ADC at baseline. In conclusion, DW MR imaging allows physicians to noninvasively demonstrate functional changes in the salivary glands.