Precision Analysis of the ^{136}Xe Two-Neutrino ββ Spectrum in KamLAND-Zen and Its Impact on the Quenching of Nuclear Matrix Elements

We present a precision analysis of the ^{136}Xe two-neutrino ββ electron spectrum above 0.8 MeV, based on high-statistics data obtained with the KamLAND-Zen experiment. An improved formalism for the two-neutrino ββ rate allows us to measure the ratio of the leading and subleading 2νββ nuclear matrix elements (NMEs), ξ_{31}^{2ν}=-0.26_{-0.25}^{+0.31}. Theoretical predictions from the nuclear shell model and the majority of the quasiparticle random-phase approximation (QRPA) calculations are consistent with the experimental limit. However, part of the ξ_{31}^{2ν} range allowed by the QRPA is excluded by the present measurement at the 90% confidence level. Our analysis reveals that predicted ξ_{31}^{2ν} values are sensitive to the quenching of NMEs and the competing contributions from low- and high-energy states in the intermediate nucleus. Because these aspects are also at play in neutrinoless ββ decay, ξ_{31}^{2ν} provides new insights toward reliable neutrinoless ββ NMEs.

Alkaline extracellular conditions promote the proliferation and mineralization of a human cementoblast cell line

AIM

To investigate the proliferation and mineralization of a human cementoblast cell line under alkaline conditions.

METHODOLOGY

A human cementoblast cell line was cultured in alkaline media with several pHs (pH 7.6, 8.0 and 8.4) without CO₂ . Cell numbers, phospho-p44/42 expression, alkaline phosphatase (ALP) activity and mineralization were evaluated. The significance of differences between groups was assessed using two-way analysis of variance 15 (ANOVA) followed by Bonferroni's multiple comparison test (α = 0.01).

RESULTS

Cell numbers increased in a time-dependent manner in the high pH medium groups. Western blot analysis revealed the upregulated expression of phospho-p44/42 under alkaline conditions. ALP activity was also increased at pH 8.0 and 8.4. Alizarin red staining revealed increased mineralization in the high pH medium groups. The incorporation of the transient receptor potential ankyrin subfamily member 1 (TRPA1) antagonist HC030031 markedly negated the effect on proliferation and mineralization.

CONCLUSIONS

Extracellular alkaline conditions promoted the proliferation and mineralization of human cementoblasts in vitro via TRPA1.

Localization of Palatal Area in Human Somatosensory Cortex

To determine the ’hard palate representing’ area in the primary somatosensory cortex, we recorded somatosensory-evoked magnetic fields from the cortex in ten healthy volunteers, using magnetoencephalography. Following electrical stimulation of 3 sites on the hard palate (the first and third transverse palatine ridges, and the greater palatine foramen), magnetic responses showed peak latencies of 15, 65, and 125 ms. Equivalent current dipoles for early magnetic responses were found along the posterior wall of the inferior part of the central sulcus. These dipoles were localized anterior-inferiorly, compared with locations for the hand area in the cortex. However, there were no significant differences in three-dimensional locations among the 3 selected regions for hard palate stimulation. These results demonstrated the precise location of palatal representation in the primary somatosensory cortex, the actual area being small.

Intercellular signal communication among odontoblasts and trigeminal ganglion neurons via glutamate

Various stimuli to the exposed surface of dentin induce changes in the hydrodynamic force inside the dentinal tubules resulting in dentinal pain. Recent evidences indicate that mechano-sensor channels, such as the transient receptor potential channels, in odontoblasts receive these hydrodynamic forces and trigger the release of ATP to the pulpal neurons, to generate dentinal pain. A recent study, however, has shown that odontoblasts also express glutamate receptors (GluRs). This implies that cells in the dental pulp tissue have the ability to release glutamate, which acts as a functional intercellular mediator to establish inter-odontoblast and odontoblast-trigeminal ganglion (TG) neuron signal communication. To investigate the intercellular signal communication, we applied mechanical stimulation to odontoblasts and measured the intracellular free Ca²⁺ concentration ([Ca²⁺]_i). During mechanical stimulation in the presence of extracellular Ca²⁺, we observed a transient [Ca²⁺]_i increase not only in single stimulated odontoblasts, but also in adjacent odontoblasts. We could not observe these responses in the absence of extracellular Ca²⁺. [Ca²⁺]_i increases in the neighboring odontoblasts during mechanical stimulation of single odontoblasts were inhibited by antagonists of metabotropic glutamate receptors (mGluRs) as well as glutamate-permeable anion channels. In the odontoblast-TG neuron coculture, we observed an increase in [Ca²⁺]_i in the stimulated odontoblasts and TG neurons, in response to direct mechanical stimulation of single odontoblasts. These [Ca²⁺]_i increases in the neighboring TG neurons were inhibited by antagonists for mGluRs. The [Ca²⁺]_i increases in the stimulated odontoblasts were also inhibited by mGluRs antagonists. We further confirmed that the odontoblasts express group I, II, and III mGluRs. However, we could not record any currents evoked from odontoblasts near the mechanically stimulated odontoblast, with or without extracellular Mg²⁺, indicating that N-methyl-d-aspartic acid receptor does not contribute to inter-odontoblast signal communication. The results suggest that a mechanically stimulated odontoblast is capable of releasing glutamate into the extracellular space via glutamate-permeable anion channels. The released glutamate activates mGluRs on the odontoblasts in an autocrine/paracrine manner, forming an inter-odontoblasts communication, which drives dentin formation via odontoblast-odontoblast signal communication. Glutamate and mGluRs also mediate neurotransmission between the odontoblasts and neurons in the dental pulp to modulate sensory signal transmission for dentinal sensitivity.

High pH-Sensitive TRPA1 Activation in Odontoblasts Regulates Mineralization

Calcium hydroxide and mineral trioxide aggregate are widely used for indirect and direct pulp capping and root canal filling. Their dissociation into Ca(2+) and OH(-) in dental pulp creates an alkaline environment, which activates reparative/reactionary dentinogenesis. However, the mechanisms by which odontoblasts detect the pH of the extracellular environment remain unclear. We examined the alkali-sensitive intracellular Ca(2+) signaling pathway in rat odontoblasts. In the presence or absence of extracellular Ca(2+), application of alkaline solution increased intracellular Ca(2+) concentration, or [Ca(2+)]i Alkaline solution-induced [Ca(2+)]i increases depended on extracellular pH (8.5 to 10.5) in both the absence and the presence of extracellular Ca(2+) The amplitude was smaller in the absence than in the presence of extracellular Ca(2+) Each increase in [Ca(2+)]i, activated by pH 7.5, 8.5, or 9.5, depended on extracellular Ca(2+) concentration; the equilibrium binding constant for extracellular Ca(2+) concentration decreased as extracellular pH increased (1.04 mM at pH 7.5 to 0.11 mM at pH 9.5). Repeated applications of alkaline solution did not have a desensitizing effect on alkali-induced [Ca(2+)]i increases and inward currents. In the presence of extracellular Ca(2+), alkaline solution-induced [Ca(2+)]i increases were suppressed by application of an antagonist of transient receptor potential ankyrin subfamily member 1 (TRPA1) channels. Ca(2+) exclusion efficiency during alkaline solution-induced [Ca(2+)]i increases was reduced by a Na(+)-Ca(2+) exchanger antagonist. Alizarin red and von Kossa staining revealed increased mineralization levels under repeated high pH stimulation, whereas the TRPA1 antagonist strongly reduced this effect. These findings indicate that alkaline stimuli-such as the alkaline environment inside dental pulp treated with calcium hydroxide or mineral trioxide aggregate-activate Ca(2+) mobilization via Ca(2+) influx mediated by TRPA1 channels and intracellular Ca(2+) release in odontoblasts. High pH-sensing mechanisms in odontoblasts are important for activating dentinogenesis induced by an alkaline environment.

TMJ degeneration in SAMP8 mice is accompanied by deranged Ihh signaling

The temporomandibular joint (TMJ) functions as a load-bearing diarthrodial joint during mastication, and its continuous use and stress can lead to degeneration over age. Using senescence-accelerated (SAMP8) mice that develop early osteoarthritis-like changes in synovial joints at high frequency, we analyzed possible molecular mechanisms of TMJ degeneration and tested whether and how malocclusion may accelerate it. Condylar articular cartilage in young SAMP8 mice displayed early-onset osteoarthritic changes that included reductions in superficial/chondroprogenitor cell number, proteoglycan/collagen content, and Indian hedgehog (Ihh)-expressing chondrocytes. Following malocclusion induced by tooth milling, the SAMP8 condyles became morphologically defective, displayed even lower proteoglycan levels, and underwent abnormal chondrocyte maturation compared with malocclusion-treated condyles in wild-type mice. Malocclusion also induced faster progression of pathologic changes with increasing age in SAMP8 condyles as indicated by decreased PCNA-positive proliferating chondroprogenitors and increased TUNEL-positive apoptotic cells. These changes were accompanied by steeper reductions in Ihh signaling and by expression of matrix metalloproteinase 13 at the chondro-osseous junction in SAMP8 articular cartilage. In sum, we show for the first time that precocious TMJ degeneration in SAMP8 mice is accompanied by--and possibly attributable to--altered Ihh signaling and that occlusal dysfunction accelerates progression toward degenerative TMJ disease in this model.

Muenke syndrome mutation, FgfR3P²⁴⁴R, causes TMJ defects

Muenke syndrome is characterized by various craniofacial deformities and is caused by an autosomal-dominant activating mutation in fibroblast growth factor receptor 3 (FGFR3(P250R) ). Here, using mice carrying a corresponding mutation (FgfR3(P244R) ), we determined whether the mutation affects temporomandibular joint (TMJ) development and growth. In situ hybridization showed that FgfR3 was expressed in condylar chondroprogenitors and maturing chondrocytes that also expressed the Indian hedgehog (Ihh) receptor and transcriptional target Patched 1(Ptch1). In FgfR3(P244R) mutants, the condyles displayed reduced levels of Ihh expression, H4C-positive proliferating chondroprogenitors, and collagen type II- and type X-expressing chondrocytes. Primary bone spongiosa formation was also disturbed and was accompanied by increased osteoclastic activity and reduced trabecular bone formation. Treatment of wild-type condylar explants with recombinant FGF2/FGF9 decreased Ptch1 and PTHrP expression in superficial/polymorphic layers and proliferation in chondroprogenitors. We also observed early degenerative changes of condylar articular cartilage, abnormal development of the articular eminence/glenoid fossa in the TMJ, and fusion of the articular disc. Analysis of our data indicates that the activating FgfR3(P244R) mutation disturbs TMJ developmental processes, likely by reducing hedgehog signaling and endochondral ossification. We suggest that a balance between FGF and hedgehog signaling pathways is critical for the integrity of TMJ development and for the maintenance of cellular organization.

TMJ development and growth require primary cilia function

Primary cilia regulate limb and axial skeletal formation and hedgehog signaling, but their roles in temporomandibular joint (TMJ) development are unknown. Thus, we created conditional mouse mutants deficient in ciliary transport protein Kif3a in cartilage. In post-natal wild-type mice, primary cilia were occasionally observed on the superior, inferior, or lateral side of condylar cells. Cilia were barely detectable in mutant chondrocytes but were evident in surrounding tissues, attesting to the specificity of chondrocyte Kif3a ablation. Mutant condyles from 3-month-old mice were narrow and flat along their antero-posterior and medio-lateral axes, were often fused with the articular disc, and displayed an irregular bony surface. The polymorphic layer in P15 mutants contained fewer Sox9-expressing chondroprogenitor cells because of reduced mitotic activity, and newly differentiated chondrocytes underwent precocious hypertrophic enlargement accompanied by early activation of Indian hedgehog (Ihh). Interestingly, there was excessive intramembranous ossification along the perichondrium, accompanied by local expression of the hedgehog receptor Patched-1 and up-regulation of Osterix and Collagen I. In summary, Kif3a and primary cilia are required for coordination of chondrocyte maturation, intramembranous bone formation, and chondrogenic condylar growth. Defects in these processes in Kif3a condylar cartilage are likely to reflect abnormal hedgehog signaling topography and dysfunction.

Ihh signaling regulates mandibular symphysis development and growth

Symphyseal secondary cartilage is important for mandibular development, but the molecular mechanisms underlying its formation remain largely unknown. Here we asked whether Indian hedgehog (Ihh) regulates symphyseal cartilage development and growth. By embryonic days 16.5 to 18.5, Sox9-expressing chondrocytes formed within condensed Tgfβ-1/Runx2-expressing mesenchymal cells at the prospective symphyseal joint site, and established a growth-plate-like structure with distinct Ihh, collagen X, and osteopontin expression patterns. In post-natal life, mesenchymal cells expressing the Ihh receptor Patched1 were present anterior to the Ihh-expressing secondary cartilage, proliferated, differentiated into chondrocytes, and contributed to anterior growth of alveolar bone. In Ihh-null mice, however, symphyseal development was defective, mainly because of enhanced chondrocyte maturation and reduced proliferation of chondroprogenitor cells. Proliferation was partially restored in dual Ihh;Gli3 mutants, suggesting that Gli3 is normally a negative regulator of symphyseal development. Thus, Ihh signaling is essential for symphyseal cartilage development and anterior mandibular growth.

Sulfotransferase Ndst1 is needed for mandibular and TMJ development

Heparan sulfate proteoglycans (HS-PGs) regulate several developmental processes, but their possible roles in mandibular and TMJ formation are largely unclear. To uncover such roles, we generated mice lacking Golgi-associated N-sulfotransferase 1 (Ndst1) that catalyzes sulfation of HS-PG glycosaminoglycan chains. Ndst1-null mouse embryos exhibited different degrees of phenotypic penetrance. Severely affected mutants lacked the temporomandibular joint and condyle, but had a mandibular remnant that displayed abnormal tooth germs, substandard angiogenesis, and enhanced apoptosis. In mildly affected mutants, the condylar growth plate was dysfunctional and exhibited thicker superficial and polymorphic cell zones, a much wider distribution of Indian hedgehog signaling activity, and ectopic ossification along its lateral border. Interestingly, mildly affected mutants also exhibited facial asymmetry resembling that seen in individuals with hemifacial microsomia. Our findings indicate that Ndst1-dependent HS sulfation is critical for mandibular and TMJ development and allows HS-PGs to exert their roles via regulation of Ihh signaling topography and action.

Indian hedgehog roles in post-natal TMJ development and organization

Indian hedgehog (Ihh) is essential for embryonic mandibular condylar growth and disc primordium formation. To determine whether it regulates those processes during post-natal life, we ablated Ihh in cartilage of neonatal mice and assessed the consequences on temporomandibular joint (TMJ) growth and organization over age. Ihh deficiency caused condylar disorganization and growth retardation and reduced polymorphic cell layer proliferation. Expression of Sox9, Runx2, and Osterix was low, as was that of collagen II, collagen I, and aggrecan, thus altering the fibrocartilaginous nature of the condyle. Though a disc formed, it exhibited morphological defects, partial fusion with the glenoid bone surface, reduced synovial cavity space, and, unexpectedly, higher lubricin expression. Analysis of the data shows, for the first time, that continuous Ihh action is required for completion of post-natal TMJ growth and organization. Lubricin overexpression in mutants may represent a compensatory response to sustain TMJ movement and function.

Odontoblast TRP Channels and Thermo/Mechanical Transmission

Odontoblasts function as mechanosensory receptors because of the expression of mechanosensitive channels in these cells. However, it is unclear if odontoblasts direct the signal transmission evoked by heat/cold or osmotic changes. This study investigated the effects of heat/cold or osmotic changes on calcium signaling and the functional expression of the thermo/mechanosensitive transient receptor potential (TRP) channels in primary cultured mouse odontoblastic cells, with the use of RT-PCR, fluorometric calcium imaging, and electrophysiology. TRPV1, TRPV2, TRPV3, TRPV4, and TRPM3 mRNA was expressed, but TRPM8 and TRPA1 mRNA was not. The receptor-specific stimulation of TRPV1-3 (heat-sensing receptors) and TRPV4/ TRPM3 (mechanic receptors) caused increases in the intracellular calcium concentration. Moreover, the channel activities of TRPV1-4 and TRPM3 were confirmed by a whole-cell patch-clamp technique. These results suggest that primary cultured mouse odontoblasts express heat/mechanosensitive TRP channels and play a role in the underlying mechanisms of thermo/mechanosensitive sensory transmission.

Cortical representation area of human dental pulp

To elucidate the dental pulp-representing area in the human primary somatosensory cortex and the presence of A-beta fibers in dental pulp, we recorded somatosensory-evoked magnetic fields from the cortex in seven healthy persons using magnetoencephalography. Following non-painful electrical stimulation of the right maxillary first premolar dental pulp, short latency (27 ms) cortical responses on the magnetic waveforms were observed. However, no response was seen when stimulation was applied to pulpless teeth, such as devitalized teeth. The current source generating the early component of the magnetic fields was located anterior-inferiorly compared with the locations for the hand area in the primary somatosensory cortex. These results demonstrate the dental pulp representation area in the primary somatosensory cortex, and that it receives input from intradental A-beta neurons, providing a detailed organizational map of the orofacial area, by adding dental pulp to the classic "sensory homunculus".

Structure-function relationships of the NCKX2 Na+/Ca2+-K+ exchanger

K+-dependent Na+/Ca2+ exchangers (NCKX) have been shown to play important roles in physiological processes as diverse as phototransduction in rod photoreceptors, motor learning and memory in mice, and skin pigmentation in humans. Most structure-function studies on NCKX proteins have been carried out on the NCKX2 isoform, but sequence similarity suggests that the results obtained with the NCKX2 isoform are likely to apply to all NCKX1-5 members of the human SLC24 gene family. Here we review our recent work on the NCKX2 protein concerning the topological arrangement of transmembrane segments carrying out cation transport, and concerning residues important for transport function and cation binding.

K+ currents regulate the resting membrane potential, proliferation, and contractile responses in ventricular fibroblasts and myofibroblasts

Despite the important roles played by ventricular fibroblasts and myofibroblasts in the formation and maintenance of the extracellular matrix, neither the ionic basis for membrane potential nor the effect of modulating membrane potential on function has been analyzed in detail. In this study, whole cell patch-clamp experiments were done using ventricular fibroblasts and myofibroblasts. Time- and voltage-dependent outward K+ currents were recorded at depolarized potentials, and an inwardly rectifying K+ (Kir) current was recorded near the resting membrane potential (RMP) and at more hyperpolarized potentials. The apparent reversal potential of Kir currents shifted to more positive potentials as the external K+ concentration ([K+]o) was raised, and this Kir current was blocked by 100–300 μM Ba2+. RT-PCR measurements showed that mRNA for Kir2.1 was expressed. Accordingly, we conclude that Kir current is a primary determinant of RMP in both fibroblasts and myofibroblasts. Changes in [K+]o influenced fibroblast membrane potential as well as proliferation and contractile functions. Recordings made with a voltage-sensitive dye, DiBAC3(4), showed that 1.5 mM [K+]o resulted in a hyperpolarization, whereas 20 mM [K+]o produced a depolarization. Low [K+]o (1.5 mM) enhanced myofibroblast number relative to control (5.4 mM [K+]o). In contrast, 20 mM [K+]o resulted in a significant reduction in myofibroblast number. In separate assays, 20 mM [K+]o significantly enhanced contraction of collagen I gels seeded with myofibroblasts compared with control mechanical activity in 5.4 mM [K+]o. In combination, these results show that ventricular fibroblasts and myofibroblasts express a variety of K+ channel α-subunits and demonstrate that Kir current can modulate RMP and alter essential physiological functions.

Cortical neuromagnetic fields preceding voluntary jaw movements

Slow cortical potentials (readiness potentials, RPs) reflecting the central programming of voluntary jaw movements were reported to appear preceding the movements. However, the current source producing the RP has not yet been localized. This study aimed to determine the cortical regions involved in the central programming of bilaterally symmetrical voluntary jaw movements, by locating the current source of the neuromagnetic counterpart of the RP (readiness field, RF). The RFs were found in the fronto-lateral region bilaterally, starting around 860 and 600 ms prior to the onset of masseter and digastric electromyograms (EMGs), respectively, and gradually increasing in magnitude to the peak within 100 ms before the EMG onset. Thus, the RFs appeared long before the reported onset of the excitability increase of pyramidal tract neurons. The current sources producing the RFs were located in the precentral gyrus bilaterally, with no bilateral differences in strength. We conclude that the primary motor cortex is involved bilaterally in central programming as well as in execution of bilaterally symmetrical voluntary jaw movements.

A voltage-dependent transient K(+) current in rat dental pulp cells

We characterized a voltage-dependent transient K(+) current in dental pulp fibroblasts on dental pulp slice preparations by using a nystatin perforated-patch recording configuration. The mean resting membrane potential of dental pulp fibroblasts was -53 mV. Depolarizing voltage steps to +60 mV from a holding potential of -80 mV evoked transient outward currents that are activated rapidly and subsequently inactivated during pulses. The activation threshold of the transient outward current was -40 mV. The reversal potential of the current closely followed the K(+) equilibrium potential, indicating that the current was selective for K(+). The steady-state inactivation of the peak outward K(+) currents described by a Boltzmann function with half-inactivation occurred at -47 mV. The K(+) current exhibited rapid activation, and the time to peak amplitude of the current was dependent on the membrane potentials. The inactivation process of the current was well fitted with a single exponential function, and the current exhibited slow inactivating kinetics (the time constants of decay ranged from 353 ms at -20 mV to 217 ms at +60 mV). The K(+) current was sensitive to intracellular Cs(+) and to extracellular 4-aminopyridine in a concentration-dependent manner, but it was not sensitive to tetraethylammonium, mast cell degranulating peptide, and dendrotoxin-I. The blood depressing substance-I failed to block the K(+) current. These results indicated that dental pulp fibroblasts expressed a slow-inactivating transient K(+) current.

Overexpression of N-acetylglucosaminyltransferase III enhances the epidermal growth factor-induced phosphorylation of ERK in HeLaS3 cells by up-regulation of the internalization rate of the receptors

N-Acetylglucosaminyltransferase III (GnT-III) is a key enzyme that inhibits the extension of N-glycans by introducing a bisecting N-acetylglucosamine residue. In this study we investigated the effect of GnT-III on epidermal growth factor (EGF) signaling in HeLaS3 cells. Although the binding of EGF to the epidermal growth factor receptor (EGFR) was decreased in GnT-III transfectants to a level of about 60% of control cells, the EGF-induced activation of extracellular signal-regulated kinase (ERK) in GnT-III transfectants was enhanced to approximately 1.4-fold that of the control cells. A binding analysis revealed that only low affinity binding of EGF was decreased in the GnT-III transfectants, whereas high affinity binding, which is considered to be responsible for the downstream signaling, was not altered. EGF-induced autophosphorylation and dimerization of the EGFR in the GnT-III transfectants were the same levels as found in the controls. The internalization rate of EGFR was, however, enhanced in the GnT-III transfectants as judged by the uptake of (125)I-EGF and Oregon Green-labeled EGF. When the EGFR internalization was delayed by dansylcadaverine, the up-regulation of ERK phosphorylation in GnT-III transfectants was completely suppressed to the same level as control cells. These results suggest that GnT-III overexpression in HeLaS3 cells resulted in an enhancement of EGF-induced ERK phosphorylation at least in part by the up-regulation of the endocytosis of EGFR.

A small-conductance Ca(2+)-activated K+ current and Cl- current in rat dental pulp cells

We characterized a voltage-dependent ionic current in dental pulp cells on dental pulp slices using a nystatin perforated-patch recording configuration. The outward currents in dental pulp cells were inhibited by the following channel blockers: 1) Ca(2+)-free extracellular solution containing 10 mM Ba2+, 2) extracellular 400 nM apamin and 3) extracellular 300 nM 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS). On the other hand, 15 mM tetraethylammonium (TEA) did not inhibit the outward currents. The inhibitory effects of Ca(2+)-free extracellular solution, apamin and DIDS had voltage-dependency. These results indicated that dental pulp cells expressed a small-conductance Ca(2+)-activated K+ current (SK current) and a DIDS-sensitive Cl- current. The functional significance of these channels is discussed.

Epidermal growth factor receptor is modulated by redox through multiple mechanisms. Effects of reductants and H2O2

The cellular redox state has been shown to play an essential role in cellular signaling systems. Here we investigate the effects of reductants and H2O2 on the signaling of epidermal growth factor (EGF) in cells. H2O2 induced the phosphorylation of the EGF receptor and the formation of a receptor complex comprising Shc, Grb2, Sos, and the EGF receptor. Dimerization or oligomerization of the EGF receptor was not induced by H2O2. Protein tyrosine phosphatase (PTP) assay showed that H2O2 suppressed dephosphorylation of the EGF receptor in cell lysates, suggesting that inactivation of PTP was involved in H2O2-induced activation of the EGF receptor. In contrast, the reductants N-acetyl-L-cysteine [Cys(Ac)] and dithiothreitol markedly suppressed EGF-induced dimerization and activation of the EGF receptor in cells. In accordance with suppression of the EGF receptor, Cys(Ac) suppressed EGF-induced activation of Ras, phosphatidylinositol 3-kinase and mitogen-activated protein kinase. Dithiothreitol completely inhibited EGF binding and kinase activation of the EGF receptor both in vitro and in vivo. In contrast, Cys(Ac) suppressed high-affinity EGF-binding sites on the cells, but had no effect on low-affinity binding sites. Furthermore, Cys(Ac) did not suppress EGF-induced kinase activation or dimerization of the EGF receptor in vitro, indicating that it suppressed the EGF receptor through a redox-sensitive cellular process or processes. Thus, the EGF receptor is regulated by redox through multiple steps including dephosphorylation by PTP, ligand binding, and a Cys(Ac)-sensitive cellular process or processes.

Characteristics of event related potentials elicited by trains of teeth clenching in humans

Event related potentials were recorded on the human scalp during a foot pedal task, a hand gripping task, and a teeth clenching task. These were carried by targeting four trains of clicks, each at an interval of 1 sec, which were repeated 20 times at random frequencies. The brain potentials were recorded from midline-frontal (Fz), -central (Cz) and -parietal (Pz) sites using surface electrodes. Positive potentials like P3 were elicited predominantly at the frontal site (Fz); those for the clenching task were slower and smaller. The magnitudes of the P3 potentials showed rough facilitation with trains of movement of the tasks. If it is assumed that the observed potentials involve an inhibition or reset of motor neurons referring to the tasks, the facilitation might be expedient for the neurons to recover the potential condition more quickly, which is important in preparing for the next action.

Measurements of cytosolic free Ca2+ concentrations in odontoblasts

To investigate the responsiveness of odontoblasts to electrical and mechanical stimuli, the concentrations of cytosolic free Ca2+ ([Ca2+]i) were measured using fura-2 microfluorometry in slice preparations of rat dental pulp. [Ca2+]i under resting conditions (basal [Ca2+]i) were 258.0 +/- 37.7 nM (mean +/- S.E., n = 113). The basal [Ca2+]i of the odontoblasts with remarkably active responses to stimuli were 221.0 +/- 81.1 nM (mean +/- S.E., range: 16-685 nM). Depolarization by high extracellular K+ concentration ([K+]o) caused a rapid increase in [Ca2+]i. The depolarization-induced increase in [Ca2+]i was enhanced by caffeine. The intense depolarization elicited [Ca2+]i oscillation in odontoblasts, which was enhanced by caffeine and suppressed by dantrolene. Hypotonic stimulation also induced an increase in [Ca2+]i of odontoblasts. The results indicate that the odontoblast possesses voltage-dependent Ca2+ channels, caffeine-sensitive Ca2+ stores and mechanosensitive cation channels.

Responses of peri-implant tissues to undisturbed plaque formation in dogs: clinical, radiographic, and microbiological findings

The present investigation evaluated the clinical and microbiological effects of long-term undisturbed plaque formation on peri-implant tissues. Four mongrel dogs were used in the study. The mandibular 3rd and 4th premolars were extracted. Three months later, four Brånemark implants (BR, n = 8) or Integral implants (IN, n = 8) were placed in the edentulous area of each dog. After another 3 months, an abutment connection was performed. Plaque control regiment was maintained for 30 days until the superstructure was placed (Day 0: baseline). Then the plaque control program was terminated to allow gross plaque accumulation. Clinical, radiographical and microbiological data were recorded at the baseline, and at 90 and 180 days after the termination of the plaque control. Values for the clinical indices such as probing depth, plaque index and bleeding on probing increased at day 90 on both the implant and tooth sites, and remained unchanged at day 180. Significantly more implant sites showed bleeding on probing than did tooth sites. Neither implants nor tooth sites showed clinically significant changes in mobility. No distinct bone resorption was observed over time by radiography. In microscopic morphological observations, cocci dominated at the baseline, and decreased by day 180, while the proportion of motile bacteria increased. In a culture study, black-pigmented anaerobic rods, which consisted predominantly of Porphyromonas gingivalis-like bacteria, were consistently found from the baseline to day 180. No Actinobacillus actinomycetemcomitans-like organisms were isolated. These results indicate that, although the long-term plaque accumulation did not cause marked periodontal destruction, the peri-implant tissue may be more susceptible to plaque accumulation than the periodontal tissue, and that teeth may serve as a reservoir for the bacterial colonization of the implant sulcus.