Plasma membrane stretch activates transient receptor potential vanilloid and ankyrin channels in Merkel cells from hamster buccal mucosa.

Merkel cells (MCs) have been proposed to form a part of the MC-neurite complex with sensory neurons. Many transient receptor potential (TRP) channels have been identified in mammals; however, the activation properties of these channels in oral mucosal MCs remain to be clarified. We investigated the biophysical and pharmacological properties of TRP vanilloid (TRPV)-1, TRPV2, TRPV4, TRP ankyrin (TRPA)-1, and TRP melastatin (TRPM)-8 channels, which are sensitive to osmotic and mechanical stimuli by measurement of intracellular free Ca(2+) concentration ([Ca(2+)]i) using fura-2. We also analyzed their localization patterns through immunofluorescence. MCs showed immunoreaction for TRPV1, TRPV2, TRPV4, TRPA1, and TRPM8 channels. In the presence of extracellular Ca(2+), the hypotonic test solution evoked Ca(2+) influx. The [Ca(2+)]i increases were inhibited by TRPV1, TRPV2, TRPV4, or TRPA1 channel antagonists, but not by the TRPM8 channel antagonist. Application of TRPV1, TRPV2, TRPV4, TRPA1, or TRPM8 channel selective agonists elicited transient increases in [Ca(2+)]i only in the presence of extracellular Ca(2+). The results indicate that membrane stretching in MCs activates TRPV1, TRPV2, TRPV4, and TRPA1 channels, that it may be involved in synaptic transmission to sensory neurons, and that MCs could contribute to the mechanosensory transduction sequence.

Functional expression of TRPM8 and TRPA1 channels in rat odontoblasts.

Odontoblasts produce dentin during development, throughout life, and in response to pathological conditions by sensing stimulation of exposed dentin. The functional properties and localization patterns of transient receptor potential (TRP) melastatin subfamily member 8 (TRPM8) and ankyrin subfamily member 1 (TRPA1) channels in odontoblasts remain to be clarified. We investigated the localization and the pharmacological, biophysical, and mechano-sensitive properties of TRPM8 and TRPA1 channels in rat odontoblasts. Menthol and icilin increased the intracellular free Ca(2+) concentration ([Ca(2+)]i). Icilin-, WS3-, or WS12-induced [Ca(2+)]i increases were inhibited by capsazepine or 5-benzyloxytriptamine. The increase in [Ca(2+)]i elicited by allyl isothiocyanate (AITC) was inhibited by HC030031. WS12 and AITC exerted a desensitizing effect on [Ca(2+)]i increase. Low-temperature stimuli elicited [Ca(2+)]i increases that are sensitive to both 5-benzyloxytriptamine and HC030031. Hypotonic stimulation-induced membrane stretch increased [Ca(2+)]i; HC030031 but not 5-benzyloxytriptamine inhibited the effect. The results suggest that TRPM8 channels in rat odontoblasts play a role in detecting low-temperature stimulation of the dentin surface and that TRPA1 channels are involved in sensing membrane stretching and low-temperature stimulation. The results also indicate that odontoblasts act as mechanical and thermal receptor cells, detecting the stimulation of exposed dentin to drive multiple cellular functions, such as sensory transduction.

Immunolocalization and distribution of functional temperature-sensitive TRP channels in salivary glands.

Transient receptor potential (TRP) cation channels are unique cellular sensors involved in multiple cellular functions. Their role in salivary secretion remains to be elucidated. The expression and localization of temperature-sensitive TRP channels in salivary (submandibular, sublingual and parotid) glands were analyzed by immunohistochemistry and quantitative real-time reverse transcription plus the polymerase chain reaction (RT-PCR). The effects of various TRP channel agonists on carbachol (CCh)-induced salivary secretion in the submandibular gland and on the intracellular Ca(2+) concentration ([Ca(2+)]i) in a submandibular epithelial cell line were also investigated. Immunohistochemistry revealed the expression of TRP-melastatin subfamily member 8 (TRPM8) and TRP-ankyrin subfamily member 1 (TRPA1) in myoepithelial, acinar and ductal cells in the sublingual, submandibular and parotid glands. In addition, TRP-vanilloid subfamily member 1 (TRPV1), TRPV3 and TRPV4 were also expressed in myoepithelial, acinar and ductal cells in all three types of gland. Quantitative real-time RT-PCR results demonstrated the mRNA expression of TRPV1, TRPV3, TRPV4, TRPM8 and TRPA1 in acinar and ductal cells in these salivary glands. Perfusion of the entire submandibular gland with the TRPV1 agonist capsaicin (1 µM) via the submandibular artery significantly increased CCh-induced salivation, whereas perfusion with TRPM8 and TRPA1 agonists (0.5 µM WS12 and 100 µM allyl isothiocyanate) decreased it. Application of agonists for each of the thermosensitive TRP channels increased [Ca(2+)]i in a submandibular epithelial cell line. These results indicate that temperature-sensitive TRP channels are localized and distributed in acinar, ductal and myoepithelial cells in salivary glands and that they play a functional role in the regulation and/or modulation of salivary secretion.

Sodium-calcium exchangers in rat trigeminal ganglion neurons.

BACKGROUND: Noxious stimulation and nerve injury induce an increase in intracellular Ca(2+) concentration ([Ca(2+)]i) via various receptors or ionic channels. While an increase in [Ca(2+)]i excites neurons, [Ca(2+)]i overload elicits cytotoxicity, resulting in cell death. Intracellular Ca(2+) is essential for many signal transduction mechanisms, and its level is precisely regulated by the Ca(2+) extrusion system in the plasma membrane, which includes the Na(+)-Ca(2+) exchanger (NCX). It has been demonstrated that Ca(2+)-ATPase is the primary mechanism for removing [Ca(2+)]i following excitatory activity in trigeminal ganglion (TG) neurons; however, the role of NCXs in this process has yet to be clarified. The goal of this study was to examine the expression/localization of NCXs in TG neurons and to evaluate their functional properties. RESULTS: NCX isoforms (NCX1, NCX2, and NCX3) were expressed in primary cultured rat TG neurons. All the NCX isoforms were also expressed in A-, peptidergic C-, and non-peptidergic C-neurons, and located not only in the somata, dendrites, axons and perinuclear region, but also in axons innervating the dental pulp. Reverse NCX activity was clearly observed in TG neurons. The inactivation kinetics of voltage-dependent Na(+) channels were prolonged by NCX inhibitors when [Ca(2+)]i in TG neurons was elevated beyond physiological levels. CONCLUSIONS: Our results suggest that NCXs in TG neurons play an important role in regulating Ca(2+)-homeostasis and somatosensory information processing by functionally coupling with voltage-dependent Na+ channels.

Hypotonic-induced stretching of plasma membrane activates transient receptor potential vanilloid channels and sodium-calcium exchangers in mouse odontoblasts.

INTRODUCTION: A number of transient receptor potential (TRP) channels have been identified as membrane-bound sensory proteins in odontoblasts. However, the activation properties of these channels remain to be clarified. The purpose of this study was to investigate hypotonic stimulation-induced Ca(2+) entry via TRP vanilloid subfamily member (TRPV) 1, TRPV2, and TRPV4 channels, which are sensitive to osmotic and mechanical stimuli, and their functional coupling with Na(+)-Ca(2+) exchangers (NCXs) in mouse odontoblast lineage cells. METHODS: We examined TRP channel activity by measuring intracellular-free Ca(2+) concentration by using fura-2 fluorescence and ionic current recordings with whole-cell patch-clamp methods. Protein localization and messenger RNA expression were characterized using immunofluorescence and reverse-transcription polymerase chain reaction analyses. RESULTS: Extracellular hypotonic solution-induced stretching of plasma membrane resulted in the activation of Ca(2+) influx and inward currents. TRPV1, TRPV2, and TRPV4 channel antagonists inhibited the hypotonic stimulation-induced Ca(2+) entry and currents. Their respective agonists activated Ca(2+) entry. Although the increase in the intracellular free Ca(2+) concentration decayed rapidly after the applications of these TRPV channel agonists, NCX inhibitors significantly prolonged the decay time constant. The messenger RNA expression of TRPV1, TRPV2, and TRPV4 channels; NCX isoforms 2 and 3; and dentin sialophosphoprotein were up-regulated after 24 hours of exposure to the hypotonic culture medium. CONCLUSIONS: These results indicate that stretching of the odontoblast membrane activates TRPV1-, TRPV2-, and TRPV4-mediated Ca(2+) entry, and increased intracellular-free Ca(2+) concentration is extruded via NCXs. These results suggest that odontoblasts can act as sensors that detect stimuli applied to exposed dentin and drive a number of cellular functions including dentinogenesis and/or sensory transduction.

Voltage-dependent sodium channels and calcium-activated potassium channels in human odontoblasts in vitro.

INTRODUCTION: Transmembrane ionic signaling regulates many cellular processes in both physiological and pathologic settings. In this study, the biophysical properties of voltage-dependent Na(+) channels in odontoblasts derived from human dental pulp (HOB cells) were investigated together with the effect of bradykinin on intracellular Ca(2+) signaling and expression of Ca(2+)-activated K(+) channels. METHODS: Ionic channel activity was characterized by using whole-cell patch-clamp recording and fura-2 fluorescence. RESULTS: Mean resting membrane potential in the HOB cells was -38 mV. Depolarizing steps from a holding potential of -80 mV activated transient voltage-dependent inward currents with rapid activation/inactivation properties. At a holding potential of -50 mV, no inward current was recorded. Fast-activation kinetics exhibited dependence on membrane potential, whereas fast-inactivation kinetics did not. Steady-state inactivation was described by a Boltzmann function with a half-maximal inactivation potential of -70 mV, indicating that whereas the channels were completely inactivated at physiological resting membrane potential, they could be activated when the cells were hyperpolarized. Inward currents disappeared in Na(+)-free extracellular solution. Bradykinin activated intracellular Ca(2+)-releasing and influx pathways. When the HOB cells were clamped at a holding potential of -50 mV, outward currents were recorded at positive potentials, indicating sensitivity to inhibitors of intermediate-conductance Ca(2+)-activated K(+) channels. CONCLUSIONS: Human odontoblasts expressed voltage-dependent Na(+) channels, bradykinin receptors, and Ca(2+)-activated K(+) channels, which play an important role in driving cellular functions by channel-receptor signal interaction and membrane potential regulation.

TRPV1-mediated calcium signal couples with cannabinoid receptors and sodium-calcium exchangers in rat odontoblasts.

Odontoblasts are involved in the transduction of stimuli applied to exposed dentin. Although expression of thermo/mechano/osmo-sensitive transient receptor potential (TRP) channels has been demonstrated, the properties of TRP vanilloid 1 (TRPV1)-mediated signaling remain to be clarified. We investigated physiological and pharmacological properties of TRPV1 and its functional coupling with cannabinoid (CB) receptors and Na(+)-Ca(2+) exchangers (NCXs) in odontoblasts. Anandamide (AEA), capsaicin (CAP), resiniferatoxin (RF) or low-pH evoked Ca(2+) influx. This influx was inhibited by capsazepine (CPZ). Delay in time-to-activation of TRPV1 channels was observed between application of AEA or CAP and increase in [Ca(2+)](i). In the absence of extracellular Ca(2+), however, an immediate increase in [Ca(2+)](i) was observed on administration of extracellular Ca(2+), followed by activation of TRPV1 channels. Intracellular application of CAP elicited inward current via opening of TRPV1 channels faster than extracellular application. With extracellular RF application, no time delay was observed in either increase in [Ca(2+)](i) or inward current, indicating that agonist binding sites are located on both extra- and intracellular domains. KB-R7943, an NCX inhibitor, yielded an increase in the decay time constant during TRPV1-mediated Ca(2+) entry. Increase in [Ca(2+)](i) by CB receptor agonist, 2-arachidonylglycerol, was inhibited by CB1 receptor antagonist or CPZ, as well as by adenylyl cyclase inhibitor. These results showed that TRPV1-mediated Ca(2+) entry functionally couples with CB1 receptor activation via cAMP signaling. Increased [Ca(2+)](i) by TRPV1 activation was extruded by NCXs. Taken together, this suggests that cAMP-mediated CB1-TRPV1 crosstalk and TRPV1-NCX coupling play an important role in driving cellular functions following transduction of external stimuli to odontoblasts.

Adrenomedullin facilitates calcium channel currents in osteoblasts.

Osteoblasts play a major role in bone formation. Osteoblasts employ intracellular Ca(2+) as a second messenger to modulate hormonal responses and a cofactor for bone mineralization. Adrenomedullin (ADM) promotes osteoblast growth and proliferation, inducing an increase in bone mass. Voltage-dependent Ca(2+) channels (VDCCs) mediate the influx of Ca(2+) in response to membrane depolarization. Voltage-dependent Ca(2+) channels serve as crucial mediators of many Ca(2+)-dependent functions, including growth of bone and regulation of proliferation. The purpose of this study was to investigate the effects of ADM on VDCC currents in osteoblasts using a patch-clamp recording method. To our knowledge, the data presented here demonstrate for the first time that ADM facilitates VDCCs in osteoblasts.

Calcitonin gene-related peptide- and adrenomedullin-induced facilitation of calcium current in submandibular ganglion.

OBJECTIVE: The control of saliva secretion is mainly under parasympathetic control. The submandibular ganglion (SMG) is a parasympathetic ganglion which receives inputs from preganglionic cholinergic neurons, and innervates the submandibular salivary gland to control saliva secretion. The aim of this study was to investigate if adrenomedullin (ADM) and/or calcitonin gene-related peptide (CGRP) modulate voltage-dependent calcium channel (VDCCs) current (I(Ca)) in SMG. DESIGN: The profile of CGRP and ADM actions in SMG was studied using the whole-cell configuration of the patch-clamp technique. RESULTS: Both ADM and CGRP facilitated I(Ca). These facilitations were attenuated by intracellular dialysis of the anti-Gα(s)-protein and pretreatment of SQ22536 (an adenylate cyclase inhibitor). CONCLUSIONS: ADM and CGRP facilitates VDCCs mediated by Gα(s)-protein and adenylate cyclase in SMG.

Ca2+ extrusion via Na+-Ca2+ exchangers in rat odontoblasts.

INTRODUCTION: Intracellular Ca(2+) is essential to many signal transduction pathways, and its level is tightly regulated by the Ca(2+) extrusion system in the plasma membrane, which includes the Na(+)-Ca(2+) exchanger (NCX). Although expression of NCX1 isoforms has been demonstrated in odontoblasts, the detailed properties of NCX remain to be clarified. In this study, we investigated localization and ion-transporting/pharmacologic properties of NCX isoforms in rat odontoblasts. METHODS: We characterized both the reverse and forward modes of NCX activity in odontoblasts in a dental pulp slice preparation. Ca(2+) influx by reverse NCX activity was measured by fura-2 fluorescence. Ca(2+) efflux by forward NCX activity elicited inward Na(+) current as measured by perforated-patch clamp recording. For immunohistochemical analysis, cryostat sections of incisors were incubated with antibodies against NCX. RESULTS: Immunohistochemical observation revealed localization of NCX1 and NCX3 in the distal membrane of odontoblasts. Inward currents by forward NCX activity showed dependence on external Na(+). Fura-2 fluorescence measurement revealed that Ca(2+) influx by reverse NCX activity depended on extracellular Ca(2+) concentration, and that this influx was blocked by NCX inhibitor KB-R7943 in a concentration-dependent manner. However, Ca(2+) influx by NCX showed a slight sensitivity to SEA0400 (a potent NCX1 inhibitor), indicating that expression potencies in odontoblasts were NCX3 > NCX1. CONCLUSIONS: These results suggest that odontoblasts express NCX1 and NCX3 at the distal membrane, and that these isoforms play an important role in the Ca(2+) extrusion system as well as in the directional Ca(2+) transport pathway from the circulation to the dentin-mineralizing front.

Calcitonin gene-related peptide- and adrenomedullin-induced facilitation of calcium current by different signal pathways in nucleus tractus solitarius.

Calcitonin gene-related peptides (CGRP) and adrenomedullin (ADM) belong to the calcitonin family of peptides and are structurally related. Both peptides are found in the neurons of the CNS and play a role in many neuronal functions, including the control of blood pressure. The nucleus tractus solitarius (NTS) is known to play a major role in the regulation of cardiovascular, respiratory, gustatory, hepatic and swallowing functions. Recently, hypotension and bradycardia were observed after CGRP and ADM injection in the NTS. Voltage-dependent Ca(2+) channels (VDCCs) serve as crucial mediators of membrane excitability and Ca(2+)-dependent functions, such as neurotransmitter release, enzyme activity, and gene expression. The purpose of this study is to investigate the effects of CGRP and ADM on VDCC currents (I(Ca)) carried by Ba(2+) (I(Ba)) in the NTS, using patch-clamp recording methods. Application of CGRP and ADM caused facilitation of I(Ba) in a concentration-dependent manner. Intracellular dialysis of the anti-Galpha(s)-protein antibody attenuated CGRP-induced facilitation of I(Ba). Intracellular dialysis of the anti-Galpha(i)-protein antibody attenuated ADM-induced facilitation of I(Ba). Pretreatment with SQ22536 (an adenylate cyclase inhibitor) and intracellular dialysis of PKI(5-24) (a protein kinase A inhibitor) attenuated CGRP-induced facilitation of I(Ba). In contrast, pretreatment with PD98,059 (a mitogen-activated protein kinas inhibitor) attenuated ADM-induced facilitation of I(Ba). Mainly L-type VDCCs were facilitated by both CGRP and ADM. These results indicate that CGRP facilitates L-type VDCCs via Galpha(s)-protein involving adenylate cyclase and protein kinase A. In contrast, ADM facilitates L-type VDCCs via Galpha(i)-protein involving mitogen-activated protein kinase in the NTS.

Topical review. Dental pain and odontoblasts: facts and hypotheses.

Dental pain arises from exposed dentin following bacterial, chemical, or mechanical erosion of enamel and/or recession of gingiva. Thus, dentin tissue and more specifically patent dentinal tubules represent the first structure involved in dentin sensitivity. Interestingly, the architecture of dentin could allow for the transfer of information to the underlying dental pulp via odontoblasts (dentin-forming cells), via their apical extension bathed in the dentinal fluid running in the tubules, or via a dense network of trigeminal sensory axons intimately related to odontoblasts. Therefore, external stimuli causing dentinal fluid movements and odontoblasts and/or nerve complex responses may represent a unique mechanosensory system bringing a new role for odontoblasts as sensor cells. How cells sense signals and how the latter are transmitted to axons represent the main questions to be resolved. However, several lines of evidence have demonstrated that odontoblasts express mechano- and/or thermosensitive transient receptor potential ion channels (TRPV1, TRPV2, TRPV3, TRPV4, TRPM3, KCa, TREK-1) that are likely to sense heat and/or cold or movements of dentinal fluid within tubules. Added to this, voltage-gated sodium channels confer excitable properties of odontoblasts in vitro in response to injection of depolarizing currents. In vivo, sodium channels co-localize with nerve terminals at the apical pole of odontoblasts and correlate with the spatial distribution of stretch-activated KCa channels. This highlights the terminal web as the pivotal zone of the pulp/dentin complex for sensing external stimuli. Crosstalk between odontoblasts and axons may take place by the release of mediators in the gap space between odontoblasts and axons in view of evidence for nociception-transducing receptors on trigeminal afferent fibers and expression of putative effectors by odontoblasts. Finally, how axons are guided to the target cells and which kind of signaling molecules are involved is extensively discussed in this review.

Correlation between a reduction in Frontal Assessment Battery scores and delusional thoughts in patients with Alzheimer's disease.

AIMS: The purpose of the present study was to investigate the relationship between delusional thoughts (delusional ideation or misidentification) and frontal lobe function using the Japanese version of the Frontal Assessment Battery (FAB) bedside screening neuropsychological test in early stage Alzheimer's disease (AD) patients. METHODS: Forty-eight probable AD patients with Mini-Mental State Examination score >or=18 points and a clinical dementia rating score of either 0.5 or 1.0 were divided into two groups based on data obtained from interviews with their caregivers: a delusional thought group (n = 19) and a non-delusional thought group (n = 29). The FAB total and subtest scores were then compared for the two groups. RESULTS: Significant differences were found between the FAB total (P < 0.01) and subtest scores (similarities, motor series, conflicting instructions; P < 0.05) for the two groups. Multiple regression analysis showed that delusional thought was significantly associated with the FAB total score. CONCLUSIONS: In addition to episodic memory disorders, a reduction in the FAB score may reflect frontal lobe dysfunctions, including executive function, in patients with AD, leading to delusional ideation.

Electrophysiological properties of AQP6 in mouse parotid acinar cells.

Salivary gland acinar cells secrete large amounts of water and electrolytes, where aquaporins (AQPs) are thought to be involved in the secretion. In the present study, we investigated expression/localization of AQP6, and the anion transporting properties of AQP6 in mouse parotid acinar cells. RT-PCR, western blotting and immunohistochemical analyses revealed expression of AQP6 in acinar cells, localized in apical membrane. Voltage ramp from -100 mV to +100 mV at a holding potential of -60 mV elicited outwardly-rectifying currents, in the presence of extracellular Cl(-) channel blockers and intracellular solution with 150 mM Cs(+). These outward currents were increased when extracellular Cl(-) was replaced by Br(-), NO(3)(-), I(-), or SCN(-), accompanying a negative shift of reversal potentials. The outward current was enhanced by extracellular Hg(2+). These results were consistent with the biophysical properties of transfected AQP6 oocytes or HEK cells, which indicate that the AQP6 channel is functionally expressed in parotid acinar cells, and suggest that AQP6 contributes to secretion of anions in parotid acinar cells.