Purines,a new class of agonists in salivary glands?

The response of rat submandibular glands to extracellular purines was tested. In crude cellular suspensions, ATP increased the [Ca²⁺]_i mostly by promoting uptake of extracellular calcium. ATP caused the pH_i to drop, a response blocked by chloride channel inhibitors. ATP also inhibited the basal and isoproterenol-stimulated activity of the Na⁺-K⁺-2Cl-cotransporter. These effects were reproduced by benzoyl-ATP, an agonist of ionotropic purinoceptors. In pure ductal suspensions, ATP activated a metabotropic P2Y₁ purinergic receptor coupled to phospholipase C and opened a non-specific cation channel coupled to a P2X₇ receptor. Activation of these receptors stimulated a Ca²⁺-dependent and a Ca²⁺-independent phospholipase A₂, the latter resulting in kallikrein secretion.We conclude that purinergic agonists can modulate the activity of both acinar and ductal phases of secretion. Activation of metabotropic receptors coupled to phospholipase C could lead to responses resembling those to muscarinic or adrenergic agonists. Activation of ionotropic receptors could stimulate new intracellular responses also involved in secretory function.     

Application of a direct pulp capping cement containing S-PRG filler

Objectives

To evaluate new pulp capping cements containing surface pre-reacted glass ionomer (S-PRG) filler and to investigate ion release kinetics and pH shift of eluates from the cement.

Materials and methods

Molars of Wistar rats were directly pulp capped using three kinds of cement containing S-PRG filler and mineral tri-oxide aggregate (MTA) was used as a control. After 1, 2, or 4 weeks, histological evaluation was performed and differences of tertiary dentin formation were analyzed. Release of Sr²⁺, BO₃³⁻, SiO₃²⁻, Na⁺, and Al³⁺ ions was determined by inductively coupled plasma-atomic emission spectrometry, and F⁻ ion release was measured using a fluoride ion selective electrode. The pH of the eluate from each cement after mixing was measured with a pH electrode.

Results

One of S-PRG cements promoted tertiary dentin formation to the same extent as the control (p > 0.05) and it showed a tendency of less inflammatory response. This cement released more BO₃³⁻ and SiO₃²⁻, but less Sr²⁺, Na⁺, and F⁻ than other S-PRG specimens. Each cement recovered nearly neutral compared with glass ionomer cement.

Conclusions

S-PRG cement induced tertiary dentin formation based on multiple ion releases, suggesting that it is suitable as a pulp capping material.

Clinical relevance

This new material can be an alternative pulp capping agent to MTA.

     

Interfacial Characterization of Dentin Conditioned with Chitosan Hydroxyapatite Precursor Nanocomplexes Using Time-of-flight Secondary Ion Mass Spectrometry

IntroductionThe purpose of this study was to evaluate the effect of chitosan-hydroxyapatite precursor (C-HA) nanocomplex conditioning on the chemical modifications at the tricalcium silicate sealer-dentin interface using time-of-flight secondary ion mass spectrometry.MethodsDentin slabs from human premolar root dentin were prepared, demineralized, and randomly distributed between control and C-HA nanocomplex conditioned groups. Tricalcium silicate sealer was applied, and the slabs were allowed to set in 100% humidity for 10 days. The cross-sectional area was exposed, and the sealer-dentin interface was characterized for chemical/ultrastructural evaluation with time-of-flight secondary ion mass spectrometry and transmission electron microscopy, respectively.ResultsChemical analysis revealed the presence of an ion-rich layer constituted of abundant phosphates (PO₂⁻, PO₃⁻, and PO₄⁻), hydroxide (OH⁻), and chitosan fragments (C₂H₄NO⁻, C₃H₄NO₂^−, C₂H₅O₂⁺, C₂H₆NO⁺, C₄H₆NO₂⁺, C₅H₆NO⁺, and C₅H₅O₂⁺) on the dentin surface at the sealer-dentin interface and subsurface dentin after conditioning with C-HA nanocomplexes. In contrast, a decreased interfacial presence of calcium (Ca⁺) and calcium phosphates (CaPO₂⁺, CaPO₃⁺, CaPO₄⁺, and Ca₂PO₃⁺) and the absence of phosphate fragments in the control were noted. Ultrastructural evaluation showed an interfacial layer (<1 μm) with interrupted mineral aggregates in the controls as opposed to a continuous (5 μm) mineral layer formation on the conditioned dentin.ConclusionsC-HA nanocomplex conditioning of dentin before tricalcium silicate sealer application resulted in a chemically modified dentin substrate with an ion-rich layer consisting of phosphate, calcium, calcium phosphates, and chitosan that chemically modified the dentin surface/subsurface.     

Submandibular secretion in the dog after intraluminal injections of amiloride

The effects of amiloride on flow rate, osmolarity, Na⁺, K⁺ and Cl^? concentrations were studied in the submandibular glands of dogs. The drug was injected in a retrograde fashion into the duct system of the gland, which was subsequently stimulated to secrete with pilocarpine. In concentrations of 10^?4 and 10^?3 M, amiloride increased the Na⁺ concentration but did not significantly alter the K⁺ concentration of saliva. A slight decrease in Cl^? concentration was observed at high flow rates after 10^?4 M amiloride, but otherwise the drug did not significantly affect the Cl^? concentration of stimulated salivary secretion. The diuretic has a measurable mucosal (luminal) effect on Na⁺ transport in dog submandibular gland, which is similar to that reported in amphibian epithelia. Its lack of effect on K⁺ excretion differs from findings reported in other epithelial structures, where it has a marked K⁺-sparing effect. The drug increased the salivary osmolarity in a fashion similar to Na⁺, a finding that suggests a dissociation between Na⁺ and water transport in salivary duct epithelium.     

Electrochemical oxidation in different media of bis(p-phenylene crown ether) as a symmetrical molecule bearing two identical redox centers

The oxidation of the long chain polyether p-disubstituted benzene derivative (BO5O5) and the related macrocyclic paracyclophane (BBO5O5) have been investigated by cyclic voltammetry at different concentrations (10⁻³–3×10⁻² M) and potential scan rates (0.05–250 V s⁻¹). At about 10⁻³ M in CH₃CN or CH₂Cl₂ containing a perchlorate salt as the supporting electrolyte, BO5O5 was oxidized reversibly into moderately stable radical cations. The formal potential E°′ corresponding to this first oxidation step was found to be shifted towards more positive values when the cation was changed from Bu₄N⁺ to Na⁺, and this variation may be ascribed to the coordination of the alkali cation by the polyether chains. At higher concentrations of the reactant and in a thoroughly dried medium, no deposit of a polymeric material onto the electrode surface was electrogenerated. At low scan rates and under the same conditions, the oxidation of BBO5O5 gave rise to two closely spaced, irreversible processes. The radical cations involved in each step were thought to be highly reactive towards nucleophilic species present in solution. At high scan rates, a single reversible one-electron transfer was observed, the formal potential of which varied with the nature of the electrolyte cation in the same way as for BO5O5. The heterogeneous charge-transfer rate constants estimated for BO5O5 and BBO5O5 were compared with the values predicted by the Marcus theory. As for BO5O5, attempts to electropolymerize BBO5O5 were unsuccessful.     

Effect of extracellular K+ on saliva secretion by isolated,perfused rat submandibular glands

Changes in perfusate K⁺ concentration altered the secretory response of the glands to 10^?6 M acetylcholine. Lack of extracellular K⁺ caused a transient fluid secretory response lasting less than 10 min, and a 91 per cent reduction in the overall volume of saliva secreted in 60 min; it inhibited the response to acetylcholine even when the perfusate was changed to K⁺-containing solutions after 30 min. Absence of K⁺ in the perfusate resulted in increased Na⁺ and decreased K⁺ and Cl^? concentrations in saliva. An increase in the perfusate K⁺ concentration to 50 mM/l caused a reduced but more sustained secretory response, although the volume of saliva secreted in 60 min was still reduced by 76 per cent compared to that obtained when the perfusate contained 4.6 m-equiv./l K⁺. Acetylcholine release induced by the high K seemed mostly responsible as the response was inhibited by atropine. However, in the presence of excess of exogenous acetylcholine, perfusion with high K⁺ medium resulted in reduced Na⁺ and elevated K⁺ and Cl^? concentrations in saliva. It seems that a physiological (4–5 m-equiv./l) extracellular K⁺ concentration is required for acinar fluid secretion and for transductal electrolyte transport in the rat glands; lack of external K⁺ hyperpolarizes salivary cells and, although allowing an initial increase in Na⁺ conductance capable of causing secretion, prevents the further influx of this ion required to sustain saliva secretion. It also inhibits K⁺secretion and Na⁺ re-absorption in salivary ducts, probably by inhibiting the Na⁺, K⁺ pump in duct cells; high external K⁺ depolarizes acinar cells and may reduce Na⁺ conductance. It also enhances K⁺ secretion and Na⁺ re-absorption in salivary ducts; the effects of K⁺ omission and of high K⁺ on fluid secretion are likely to be the result of changes in the transmembrane K⁺ gradient in acinar cells and of the way they affect the opening of Na⁺ conductance pathways; perfusion with K⁺-free or high K⁺ solutions reveals a dissociation in ductal reabsorption of Na⁺ and Cl^? and unmasks the presence of independent transport mechanisms for these two ions in salivary ducts.     

Caries-preventive effect of anti-erosive and nano-hydroxyapatite-containing toothpastes in vitro

Objectives

The aim of the study was to investigate the caries-preventive effect of newly developed fluoride and fluoride-free toothpastes specially designed for erosion prevention. The hypothesis was that these products might also show superior caries-inhibiting effect than regular fluoride toothpastes, since they were designed for stronger erosive acid challenges.

Materials and methods

Enamel specimens were obtained from bovine teeth and pre-demineralized (pH = 4.95/21 days) to create artificial caries lesions. Baseline mineral loss (ΔZ_B) and lesion depth (LD_B) were determined using transversal microradiography (TMR). Ninety specimens with a median ΔZ_B (SD) of 6027 ± 1546 vol% × μm were selected and randomly allocated to five groups (n = 18). Treatments during pH-cycling (14 days, 4 × 60 min demineralization/day) were brushing 2×/day with AmF (1400 ppm F⁻, anti-caries [AC]); AmF/NaF/SnCl₂/Chitosan (700 ppm F⁻/700 ppm F⁻/3500 ppm Sn²⁺, anti-erosion [AE1]); NaF/KNO₃ (1400 ppm F⁻, anti-erosion [AE2]); nano-hydroxyapatite-containing (0 ppm F⁻, [nHA]); and fluoride-free toothpastes (0 ppm F⁻, negative control [NC]). Toothpaste slurries were prepared with mineral salt solution (1:3 wt/wt). After pH-cycling specimens presenting lesion, surface loss (mainly by NC and nHA) were discarded. For the remaining 77 specimens, new TMR analyses (ΔZ_E/LD_E) were performed. Changes in mineral loss (ΔΔZ = ΔZ_B − ΔZ_E) and lesion depth (ΔLD = LD_B − LD_E) were calculated.

Results

All toothpastes caused significantly less demineralization (lower ΔΔZ) than NC (p < 0.05, ANOVA) except for nHA. The fluoride toothpastes did not differ significantly regarding ΔΔZ and ΔLD (p > 0.05, ANOVA).

Conclusion/clinical relevance

While both anti-erosive and anti-caries toothpastes reduced mineral loss to a similar extent, the fluoride-free nano-hydroxyapatite-containing toothpaste seemed not to be suitable for inhibition of caries demineralization in vitro.

     

Regeneration of dentin-pulp complex: Effect of calcium-based materials on hDPSCs differentiation and gene expression

ObjectiveDentin-pulp complex is object of interest in the regenerative endodontic field as well as the natural function of human dental pulp stem cells (hDPSCs) that may differentiate into specific cells able to repair and/or regenerate both hard and soft dental structures. The aim of the present study was to evaluate the capacity of hDPSCs to differentiate in odontoblastic-like cells by evaluating the expression of specific odontogenic-related genes and to prove the ability of treatment with calcium-based materials such as calcium carbonate (CaCO3), calcium hydroxide (Ca(OH)₂), and mineral trioxide aggregate (MTA).MethodshDPSCs were obtained and isolated from a third molar of a young patient. Odontogenic-related gene expression was assessed unti1 28 days of culture as well as alkaline phosphatase activity (ALP). hDPSCs were cultured in odontoblastic-induction medium used as control, and in presence of different concentrations of CaCO_3, Ca(OH)₂, and MTA.ResultsThe results demonstrated an upregulation in odontoblastic cell-related genes, in particular of the early differentiation marker known as matrix extracellular phosphoglycoprotein (MEPE), as well as increased ALP activity and the presence of calcium deposits, mainly by stimulation with calcium derivatives. In this regard, treatment of pulp tissue with CaCO₃, Ca(OH)₂ and even better with MTA seemed to be effective for dentinogenesis.SignificanceThe ease of isolation of hDPSCs from discarded or extracted teeth offers a promising source of autologous cells that may be applied for regenerative purpose in combination with selected bioactive materials. However, further investigations should be conducted to confirm the obtained results.     

Preparation,characterization, and electrocatalytic properties of copper hexacyanoferrate film and bilayer film modified electrodes

Copper(II)hexacyanoferrate films have been prepared from various electrolyte aqueous solutions using consecutive cyclic voltammetry. The cyclic voltammograms recorded the direct deposition of copper(II)hexacyanoferrate films from the mixing of Cu²⁺ and Fe(CN)₆^3? ions from solutions of ten cations: Li⁺, Na⁺, K⁺, Rb⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, H⁺ and Al³⁺. An electrochemical quartz crystal microbalance (EQCM) and cyclic voltammetry were used to study the in situ growth of the copper(II)hexacyanoferrate films. The copper(II)hexacyanoferrate film showed a single redox couple that exhibited a cation effect (Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺) and an anion effect (F^?, Cl^? and Br^?) in the cyclic voltammograms and formal potential of the redox couple. The electrochemical and EQCM properties of the film indicate that the redox process was confined to the immobilized copper(II)hexacyanoferrate, and the interaction between the copper(II)hexacyanoferrate film with K⁺ (monovalent cation) and Ca²⁺ (divalent cation). The electrocatalytic oxidation properties of NADH, NH₂OH, N₂H₄, SO₃^2? and S₂O₃^2? were also determined. The electrocatalytic reduction properties of SO₅^2? and S₂O₈^2? by monolayered iron, nickel, and cobalt hexacyanoferrate films, and by bilayered metal–copper hexacyanoferrate films were determined. Two-layered modified electrodes and hybrid films composed of a copper(II)hexacyanoferrate film with iron(II)hexacyanoferrate, cobalt(II)hexacyanoferrate, or nickel(II)hexacyanoferrate film were prepared, and these films caused the electrocatalytic reduction of SO₅^2? and S₂O₈^2?.     

Temperature dependence of the electric properties of molten ternary chlorides by MD simulation

The electric properties are simulated in the temperature region of 800–1100 K for molten ternary mixtures (Li, Na, Cs)Cl of various compositions by molecular dynamics simulation in order to investigate the temperature dependence of the Chemla crossing points and the limit of the degree of enrichment of Cs. In addition, the self-diffusion coefficient, self-exchange velocity and the electric conductivities were calculated in molten LiCl–NaCl eutectic mixtures containing CsCl. From the results, it is concluded that the self-diffusion coefficients and self-exchange velocities of Li⁺, Na⁺, and Cs⁺ with reference to Cl^? show very similar tendencies with increasing temperature for each composition and the most appropriate temperature of Cs is 800–900 K for enrichment up to x_Cs=0.5–0.6 in molten LiCl–NaCl eutectic.     

Cholinergic autoantibodies from primary Sjögren’s syndrome modulate submandibular gland Na+/K+‐ATPase activity via prostaglandin E2 and cyclic AMP

Passafaro D, Reina S, Sterin‐Borda L, Borda E. Cholinergic autoantibodies from primary Sjögren’s syndrome modulate submandibular gland Na ⁺ /K ⁺ ‐ATPase activity via prostaglandin E ₂ and cyclic AMP. Eur J Oral Sci 2010; 118: 131–138. © 2010 The Authors. Journal compilation © 2010 Eur J Oral Sci We demonstrate that patients with primary Sjögren’s syndrome (pSS) produce functional IgG autoantibodies that interact with the glandular M₃ muscarinic acetylcholine receptors (mAChRs). These autoantibodies act as a partial muscarinic agonist, increasing prostaglandin E₂ (PGE₂) and cyclic AMP production through modifying Na⁺/K⁺‐ATPase activity, but also interfere with the secretory effect of the parasympathetic neurotransmitter. The IgG from patients with pSS has two effects on the submandibular gland. On the one hand, it may act as an inducer of the proinflammatory molecule (PGE₂) that, in turn, inhibits Na⁺/K⁺‐ATPase activity. On the other hand, it plays a role in the pathogenesis of dry mouth, abolishing the Na⁺/K⁺‐ATPase inhibition and the net K⁺ efflux stimulation of the salivary gland in response to the authentic agonist pilocarpine, decreasing salivary fluid production.     

Characterization of a microsomal fraction from rabbit parotid gland: Partial separation of alkaline phosphatase from Na,K-ATPase

Subfractionation of the 140,000 g_max pellet from the rabbit parotid gland revealed 3 fractions. Both linear and discontinuous sucrose-density gradients were used to separate a region of high-density particles with considerable mitochondria, a middle region rich in Na⁺,K⁺-ATPase (sodium-potassium activated adenosine triphosphatase) and a low-density (top) region with elevated alkaline phosphatase. The top and middle fractions appeared to represent subfractions of plasma-membrane enriched membranes. Treatment of these 2 gradient fractions with low concentrations of sodium dodecyl sulphate confirmed that the middle fraction was preferentially enriched in Na⁺,K⁺-ATPase. Thus, alkaline phosphatase-enriched membranes are at least partially separable from Na⁺,K⁺-ATPase-enriched membranes. Separation of alkaline phosphatase from Na⁺,K⁺-ATPase may be an important purification step in future work involving isolation of plasma membranes of secretory cells, as both alkaline phosphatase and Na⁺,K⁺-ATPase have been used as plasma-membrane markers in the parotid gland. The present findings demonstrate that considerable caution should be exercised in defining the purity of plasma-membrane fractions from the parotid gland in view of the heterogeneity of the plasma-membrane enriched fraction.     

Comparative analysis of alkali and alkaline-earth cation transfer assisted by monensin across the water ∣ 1,2-dichloroethane interface

In the first part of this paper the electrochemical transfer of alkali cations (M⁺) assisted by monensin (HX) across the water ∣ 1,2-dichloroethane (DCE) interface at pH<5, combined with a chemical exchange reaction at 5<pH<9, is proposed as the only mechanism responsible for the transfer of these cations. At pH>9 the current is voltammetrically negligible. An equation for the dependence of Δ_o^wφ_1/2 on pH and Na⁺ concentration is developed. In the second part of the paper the transfer of alkaline earth cations assisted by the same ionophore is studied. The electrochemical reactions (Me_(w)²⁺+HX_(o)?MeHX²⁺_(o)) and (Me_(w)²⁺+X^?_(o)?MeX⁺_(o)) are responsible for the peaks observed at pH<5.0 and at pH>9.0, respectively. As expected, in both cases ΔE_p=0.030 V while at intermediate pH the electrochemical exchange reaction (Me²⁺_(w)+HX_(o)?MeX⁺_(o)+H⁺_(w)) is proposed. The net charge transfer of +1 at the interface accounts for ΔE_p=0.060 V for the peak observed ΔE_p in agreement with the hyper-Nernstian slope of 60 mV found for Ca²⁺ and Ba²⁺ ISE based on antibiotics with carboxylic groups at intermediate pH values. The higher selectivity for Ba²⁺ and the tendency in selectivity at alkaline pH found in the ISEs are also observed and thus explained according to the mechanism proposed.     

The Electrolyte and Water Secretion Mechanism

The currently accepted salivary gland secretion model describes the process of fluid secretion as the coordinated action of water and ion channels and transporters. The secretion of electrolytes and water by salivary glands is thought to be activated by an agonist-induced increase in the intracellular free [Ca²⁺] and to be driven by transepithelial chloride movement. The Cl^- transport is supported by upregulation of several ion transporters, K⁺ and Cl^- channels, and the Na⁺/K⁺-ATPase. This review will focus on the details of the transport mechanisms as well as recent developments in confirming the molecular identities of the involved transporter and channel proteins.     

On the facilitating effect of neutral macrocyclic ligands on the ion transfer across the interface between aqueous and organic solutions: Part III. Competitive facilitated ion-transfer

A theoretical equation of the reversible current–potential curves is derived for the competitive ion-transfer of two kinds of cations present in an aqueous (w) phase simultaneously facilitated by a macrocyclic ligand (L) present in an organic (o) phase. Especially, for the two limiting cases, i.e. case (A): c*_Mj (j=1, 2)?c*_L and case (B): c*_L?c*_Mj (where c*_Mj and c*_L denote the bulk concentrations of cation M_j in the w-phase and of L in the o-phase, respectively), simple explicit expressions are derived and a method analyzing the facilitated waves is presented. Furthermore, the main part of the theoretical predictions obtained is verified experimentally at 25 °C by using the ion-transfer-polarographic method with the electrolyte dropping electrode, for the following four combinations: (i) competitive cations: protonated alanine and H⁺, L: benzo-18-crown-6 ether; (ii) Na⁺ and Li⁺, benzo-15-crown-5 ether; (iii) K⁺ and Na⁺, dibenzo-18-crown-6 ether; and (iv) Na⁺ and Ba²⁺, dibenzo-24-crown-8 ether.     

Cation effects on the voltammetric behavior of α-Keggin-type [SiMo12O40]4− and [PMo12O40]3− complexes in CH3COCH3 and CH3CN

The effect of small cations such as H⁺, Li⁺ and Na⁺ on the voltammetric behavior of α-Keggin-type [SiMo₁₂O₄₀]^4? and [PMo₁₂O₄₀]^3? complexes was investigated in CH₃COCH₃ and CH₃CN. For the [SiMo₁₂O₄₀]^4? complex, the presence of Li⁺ or Na⁺ caused the one-electron waves to be converted into a two-electron wave at ca. 0.3 V more positive than the first one-electron wave. In the presence of Li⁺ or Na⁺, the [PMo₁₂O₄₀]^3? complex underwent a two-electron reduction at the same potential as the original first one-electron wave in CH₃COCH₃, whereas it exhibited only successive one-electron waves in CH₃CN. The addition of a trace amount of H⁺ produced new two-electron waves at more positive potentials. These findings give a clue to the understanding of the reactivity of polyoxometalates as redox catalysts.     

DFT calculations of the interaction of alkali ions with copper and silver

The interaction of alkali ions with the Cu(100) and Ag(100) surfaces is studied using the DFT method. The results of the B3LYP calculations performed for five cations, Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺, adsorbed on the surface of the M₁₂(6,6) cluster (M=Cu, Ag) are presented. On both metals the interaction is found to be strongest for the Li⁺ ion and weakest for the Cs⁺ ion. Three sites were tested for the adsorption of ions on the (100) surface: top, bridge and hollow. For the two smaller ions, Li⁺ and Na⁺, the hollow site is found to be the most stable. For the three larger ions the top position is more attractive. Nevertheless, the energy value at the different sites for a given ion in most cases, differs by less than 5 kJ mol^?1. For all ions the interaction with silver is stronger than the interaction with copper.     

Solvent-effect on the interconversion among one-, two- and four-electron reduction waves for the 18-molybdodiphosphate complex, [(P2O7)Mo18O54]4−

For the [(P₂O₇)Mo₁₈O₅₄]^4? complex, the presence of small cations such as H⁺, Li⁺ and Na⁺ caused one-electron waves to be converted into four- and two-electron waves in a complex manner. With the addition of a trace amount of H⁺, a four-electron reduction wave was obtained in solvents of weaker basicity like acetone, acetonitrile and propylene carbonate (PC); the relative permittivity did not affect the appearance of the four-electron wave. On the other hand, two-electron waves were obtained in solvents of stronger basicity like N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), and N-methylpyrrolidinone (NMP). With the addition of Li⁺ or Na⁺, the one-electron waves were converted into two-electron waves only in acetone, indicating that the conversion can occur in solvents of both weak basicity and low relative permittivity.