Activation of Mechanosensitive Transient Receptor Potential/Piezo Channels in Odontoblasts Generates Action Potentials in Cocultured Isolectin B4-negative Medium-sized Trigeminal Ganglion Neurons.

INTRODUCTION: Various stimuli to the dentin surface elicit dentinal pain by inducing dentinal fluid movement causing cellular deformation in odontoblasts. Although odontoblasts detect deformation by the activation of mechanosensitive ionic channels, it is still unclear whether odontoblasts are capable of establishing neurotransmission with myelinated A delta (Aδ) neurons. Additionally, it is still unclear whether these neurons evoke action potentials by neurotransmitters from odontoblasts to mediate sensory transduction in dentin. Thus, we investigated evoked inward currents and evoked action potentials form trigeminal ganglion (TG) neurons after odontoblast mechanical stimulation. METHODS: We used patch clamp recordings to identify electrophysiological properties and record evoked responses in TG neurons. RESULTS: We classified TG cells into small-sized and medium-sized neurons. In both types of neurons, we observed voltage-dependent inward currents. The currents from medium-sized neurons showed fast inactivation kinetics. When mechanical stimuli were applied to odontoblasts, evoked inward currents were recorded from medium-sized neurons. Antagonists for the ionotropic adenosine triphosphate receptor (P2X3), transient receptor potential channel subfamilies, and Piezo1 channel significantly inhibited these inward currents. Mechanical stimulation to odontoblasts also generated action potentials in the isolectin B4-negative medium-sized neurons. Action potentials in these isolectin B4-negative medium-sized neurons showed a short duration. Overall, electrophysiological properties of neurons indicate that the TG neurons with recorded evoked responses after odontoblast mechanical stimulation were myelinated Aδ neurons. CONCLUSIONS: Odontoblasts established neurotransmission with myelinated Aδ neurons via P2X3 receptor activation. The results also indicated that mechanosensitive TRP/Piezo1 channels were functionally expressed in odontoblasts. The activation of P2X3 receptors induced an action potential in the Aδ neurons, underlying a sensory generation mechanism of dentinal pain.

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.

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.

Low-density lipoprotein particle diameter in normal pregnancy and preeclampsia.

We investigated the changes of low-density lipoprotein (LDL) size and serum lipids during pregnancy and postpartum not only in normal pregnant women but also in preeclampsia. Serum triglyceride (TG) and total cholesterol levels as well as serum high-density lipoprotein (HDL)-cholesterol, apolipoprotein (Apo) A1, B, E and remnant-like particle (RLP)-cholesterol levels were increased in normal pregnant women. The LDL peak particle diameter (PPD) in normal pregnant women was decreased during pregnancy and that at 37 weeks of gestation showed significant decrease compared with the women at 4 weeks after delivery (25.8 +/- 1.0 vs.26.8 +/- 0.7 nm, p < 0.05). The LDL-PPD in the preeclamptic women at admission (mean gestational age: 36 +/- 2.4 weeks) was significantly lower than that in normal pregnancy at 37 weeks of gestation (24.7 +/- 1.2 vs. 25.8 +/- 1.0 nm, p < 0.05). Moreover, the LDL-PPD in the preeclamptic women was significantly higher after delivery compared with the level at admission (27. +/- 0.7 vs. 24.7 +/- 1.2 nm, p < 0.05) accompanied by an improvement in plasma lipids profile. These findings suggest that the predominance of small, dense LDL, a potential contributor to endothelial dysfunction, may be a possible predictor of preeclampsia.

Expression and regulation of 4F2hc and hLAT1 in human trophoblasts.

The neutral amino acid transport system L is a sodium-independent transport system in human placenta and choriocarcinoma cells. Recently, it was found that the heterodimer composed of hLAT1 (a light-chain protein) and 4F2 heavy chain (4F2hc), a type II transmembrane glycoprotein, is responsible for system L amino acid transport. We found that the mRNAs of 4F2hc and hLAT1 were expressed in the human placenta and a human choriocarcinoma cell line. The levels of the 4F2hc and hLAT1 proteins in the human placenta increased at full term compared with those at midtrimester. Immunohistochemical data showed that these proteins were localized mainly in the placental apical membrane. Data from leucine uptake experiments, Northern blot analysis, and immunoblot analysis showed that this transport system was partially regulated by protein kinase C and calcium ionophore in the human choriocarcinoma cell line. Our results suggest that the heterodimer of 4F2hc and hLAT1 may play an important role in placental amino acid transport system L.