Yuki Kojima

Intercellular Odontoblast Communication via ATP Mediated by Pannexin-1 Channel and Phospholipase C-coupled Receptor Activation

Extracellular ATP released via pannexin-1 channels, in response to the activation of mechanosensitive-TRP channels during odontoblast mechanical stimulation, mediates intercellular communication among odontoblasts in dental pulp slice preparation dissected from rat incisor. Recently, odontoblast cell lines, such as mouse odontoblast lineage cells, have been widely used to investigate physiological/pathological cellular functions. To clarify whether the odontoblast cell lines also communicate with each other by diffusible chemical substance(s), we investigated the chemical intercellular communication among cells from mouse odontoblast cell lines following mechanical stimulation. A single cell was stimulated using a glass pipette filled with standard extracellular solution. We measured intracellular free Ca2+ concentration ([Ca2+]i) by fura-2 in stimulated cells, as well as in cells located nearby. Direct mechanical stimulation to a single odontoblast increased [Ca2+]i, which showed sensitivity to capsazepine. In addition, we observed increases in [Ca2+]i not only in the mechanically stimulated odontoblast, but also in nearby odontoblasts. We could observe mechanical stimulation-induced increase in [Ca2+]i in a stimulated human embryo kidney (HEK) 293 cell, but not in nearby HEK293 cells. The increase in [Ca2+]i in nearby odontoblasts, but not in the stimulated odontoblast, was inhibited by adenosine triphosphate (ATP) release channel (pannexin-1) inhibitor in a concentration- and spatial-dependent manner. Moreover, in the presence of phospholipase C (PLC) inhibitor, the increase in [Ca2+]i in nearby odontoblasts, following mechanical stimulation of a single odontoblast, was abolished. We could record some inward currents evoked from odontoblasts near the stimulated odontoblast, but the currents were observed in only 4.8% of the recorded odontoblasts. The results of this study showed that ATP is released via pannexin-1, from a mechanically stimulated odontoblast, which transmits a signal to nearby odontoblasts by predominant activation of PLC-coupled nucleotide receptors.

Potassium Currents Activated by Depolarization in Odontoblasts

Increased intracellular free Ca2+ concentrations elicit plasma membrane depolarization, which leads to the activation of K+ currents. However, the precise properties of K+ currents activated by depolarization in odontoblasts remain to be elucidated. The present study identified biophysical and pharmacological characteristics of time-dependent and voltage-activated K+ currents in freshly dissociated rat odontoblasts using patch-clamp recordings in a whole-cell configuration. Using a holding potential of −70 mV, outwardly rectifying time- and voltage-dependent currents were activated by depolarizing voltage. To record pure K+ conductance, we substituted Cl− in both the extracellular and intracellular solutions with gluconate−. Under these conditions, observation of K+ concentration changes in the extracellular solution showed that reversal potentials of tail currents shifted according to the K+ equilibrium potential. The activation kinetics of outward K+ currents were relatively slow and depended on the membrane potential. Kinetics of steady-state inactivation were fitted by a Boltzmann function. The half-maximal inactivation potential was −38 mV. Tetraethylammonium chloride, 4-aminopyridine, and α-dendrotoxin inhibited outward currents in odontoblasts in a concentration-dependent manner, suggesting that rat odontoblasts express the α-subunit of the time- and voltage-dependent K+ channel (Kv) subtypes Kv1.1, 1.2, and/or 1.6. We further examined the effects of Kv activity on mineralization by alizarin red and von Kossa staining. Continuous application of tetraethylammonium chloride to human odontoblasts grown in a mineralization medium over a 21-day period exhibited a dose-dependent decrease in mineralization efficiency compared to cells without tetraethylammonium chloride. This suggests that odontoblasts functionally express voltage-dependent K+ channels that play important roles in dentin formation.

Depolarization-induced Intracellular Free Calcium Concentration Increases Show No Desensitizing Effect in Rat Odontoblasts.

Odontoblasts play an important role in the transduction of the sensory signals underlying dentinal pain. Transmembrane voltage-independent Ca(2+) influx in odontoblasts has been well described. Voltage-dependent Ca(2+) influx has also been reported, but its biophysical properties remain unclear. The aim of the present study was to investigate the desensitizing effect of voltage-dependent Ca(2+) influx in rat odontoblasts by measuring depolarization-induced intracellular free Ca(2+) concentrations ([Ca(2+) ]i ). Odontoblasts on dental pulp slices from newborn rats were acutely isolated and [Ca(2+) ]i measured by using fura-2 fluorescence. Repeated application of extracellular high-K(+) solution (50 mM), which induces membrane depolarization-elicited repeated and transient increases in [Ca(2+) ]i in the presence of extracellular Ca(2+). Increases in depolarization-induced [Ca(2+) ]i showed no significant desensitizing effect (p >0.05; Friedman test). These results suggest that odontoblasts express a voltage-dependent Ca(2+) influx pathway with no desensitizing properties.

Dental Treatment Effect on Deep Brain Stimulation System in Parkinson’s Disease

Parkinsons disease (PD) is a highly prevalent, long-term neurodegenerative disorder that is sometimes treated by deep brain stimulation (DBS), which significantly reduces the need for dopaminergic drug therapy and improves quality of life. Such patients are cautioned, however, that dental instruments such as a dental turbine or ultrasonic scaler may adversely affect the functioning of such a system. Here, we report dental treatment for right maxillary tooth pain in a 65-year-old woman undergoing DBS for PD. The diagnosis was occlusal trauma. After verification with occluding paper each time, treatment comprised milling of the high contact points of tooth #17, followed by scaling with an ultrasonic scaler. This treatment was spread out over 3 visits, and its course was uneventful. To our knowledge, there are no previous reports on the interaction between dental instruments and DBS systems. Although no interference with the DBS system was observed here, we believe that the dentist should be aware of the potential for such, especially with the use of devices used to measure root canal length, dental lasers, and electrical scalpels.

Intracellular Ca 2+ mobilization pathway via bradykinin B 1 receptor activation in rat trigeminal ganglion neurons

Bradykinin (BK) and its receptors, B1 and B2, in trigeminal ganglion (TG) neurons are involved in the regulation of pain. Recent studies have revealed that B1 receptors are expressed in neonatal rat TG neurons; however, the intracellular signaling pathway following B1 receptor activation remains to be elucidated. To investigate the mechanism by which B1 receptor activation leads to intracellular Ca2+ mobilization, we measured the intracellular free Ca2+ concentration ([Ca2+]i) in primary-cultured TG neurons. The application of Lys-[Des-Arg9]BK (B1 receptor agonist) increased the [Ca2+]i in these TG neurons even in the absence of extracellular Ca2+. Pretreatment with inhibitors of ryanodine receptors or sarco/endoplasmic reticulum Ca2+-ATPase suppressed the increase in Lys-[Des-Arg9]BK-induced [Ca2+]i. The Lys-[Des-Arg9]BK-induced [Ca2+]i increase was unaffected by phospholipase-C inhibitor. B1 receptor activation-induced [Ca2+]i increase was suppressed by phosphodiesterase inhibitor and enhanced by adenylyl cyclase inhibitor. These results suggest that B1 receptor activation suppresses intracellular cAMP production via adenylyl cyclase inhibition and mobilizes intracellular Ca2+ via ryanodine receptors that access intracellular Ca2+ stores.

A case of mandibular osteomyelitis in a patient with chronic myelomonocytic leukaemia

We report a case of chronic myelomonocytic leukaemia (CMMoL) in a 68-year-old man who developed osteomyelitis of the mandible. At the initial visit, he reported uncontrolled gingival bleeding, despite self-administered haemostasis. He complained of severe pain in the socket, despite potent opioid analgesia. After consultation with the internal medicine specialists, we undertook a surgical anti-inflammatory approach that included sequestrectomy with massive blood transfusion. His physical condition was ameliorated after the surgical procedure, and he was discharged from the hospital. However, 3 months later, he died because of cardiac arrest after haemorrhagic shock and cardiovascular failure because his CMMoL had developed to an acute blastic crisis. This experience demonstrates that the most important goal in such cases is to alleviate a patients discomfort by applying minimally invasive actions to eliminate infection and improve the quality of life without causing deterioration in the CMMoL status.

A Case of Buccal Abscess from an Impacted Wisdom Tooth in an Elderly Person with Malnutrition

We report a case of buccal abscess caused by an impacted wisdom tooth in an extremely elderly person with malnutrition. The patient was a 94-year-old man, who complained that he had found it hard to open his mouth and that his cheek had been swollen for the previous 2 weeks. He had a shallow oral wound caused by an improperly fitting denture; however, the wound became infected. We performed incisional drainage of the abscess under local anesthesia. The swelling disappeared and he was able to open his mouth 55 mm. The elderly have a high risk of healing failure of injuries and it has been reported that infection in a host in a compromised state is severely intractable. This elderly patient was in a compromised state because of malnutrition. Cases such as this one will increase as the elderly population increases. Dentists need to consider the quality of life of patients with a longer life expectancy and should offer patients several treatment options before their general condition deteriorates.

Transient Receptor Potential Cation Channel Subfamily Vanilloid Member 3 is not Involved in Plasma Membrane Stretch-induced Intracellular Calcium Signaling in Merkel Cells.

Merkel cells (MCs), which form part of the MC-neurite complex, making contact with sensory afferents to drive mechanosensory transduction mechanisms, express transient receptor potential (TRP) cation channel subfamily vanilloid (V) members 1, 2, and 4, as well as ankyrin subfamily member 1. While these proteins are involved in sensing plasma membrane stretch, less is known about the functional properties of TRPV subfamily member 3 (TRPV3) during membrane stretch in MCs. The aim of this study was to determine whether TRPV3 channels were involved in mechanosensory activity by measuring intracellular free Ca(2+) concentrations ([Ca(2+)]i) in MCs isolated from hamster buccal mucosa. Application of a hypotonic extracellular solution to quinacrine-positive MCs elicited a transient increase in [Ca(2+)]i. When TRPV3 channel antagonist 2,2-diphenyltetrahydrofuran was added to the hypotonic extracellular solution, however, no effect was observed on hypotonic stimulation-induced increase in [Ca(2+)]i. These results suggest that TRPV3 channels are not involved in the mechanosensory mechanism during membrane stretch in MCs.

Buccal mucosa tumour around the parotid papilla

We present a case of a 50-year-old male patient with a lump around the right parotid papilla. A 25×20 mm soft pendulous lump was identified around the right parotid duct. After obtaining non-malignant results from a tissue biopsy, we resected the tumour to preserve the right parotid duct under local anaesthesia. The patient had an uncomplicated postoperative course and maintained normal salivary secretion function. Based on the histopathological features, the lump was thought to have developed secondary to being repeatedly bitten. Several cases of parotid duct disease have been reported, but a literature search revealed that the present case is rare.