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 (Ad) 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 Piezol channel significantly inhibited these inward currents. Mechanical stimulation to odontoblasts also generated action potentials in the isolectin B-4-negative medium-sized neurons. Action potentials in these isolectin B-4-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 A delta neurons. Conclusions: Odontoblasts established neurotransmission with myelinated Ad neurons via P2X(3) receptor activation. The results also indicated that mechanosensitive TRP/Piezol channels were functionally expressed in odontoblasts. The activation of P2X(3) receptors induced an action potential in the Ad neurons, underlying a sensory generation mechanism of dentinal pain.