Cold Stimulus Activates Ionic Channels in Freshly Isolated Human Odontoblasts

Objectives: The hydrodynamic theory is widely accepted for explaining dentinal pain. Dissected single pulpal nerve fibers can be activated by the terminal deformation due to probing, air-blast, warm and cold stimuli applied to exposed dentin. These stimuli cause sharp pain in human. But the contribution of odontoblasts to pulpal sensory transduction mechanism is still controversial. In this study, we tried to elucidate the influence of cold stimulation applied to freshly isolated odontoblast cell membrane on the electrical behaviour of ionic channels.
Methods: Six freshly extracted premolars for an orthodontic reason from informed patients (14y, n=2; 16y, n=1; 17y, n=1; 18y, n=1) were used. The cells were used for electrophysiology within 3 h after plating. Temperature of extracellular solution was precisely controlled in both a water pool and a cell plating medium with two thermometers incorporating automatic regulations. Electrophysiological recording was made from odontoblasts using single-channel and nystatin perforated patch clamp configurations.
Results: (1) Symmetric intercellular conductance was obtained from aligned odontoblast pairs.
(2) Cold stimulation of a single odontoblast resulted in a current influx of the cell membrane.
(3) This current electricity was clearly observed when the temperature of the extracellular solution was lowered from 26 to 16 degrees centigrade, and blocked by a TRPM8 receptor antagonist.
Conclusions: The present results support an idea that ionic channels of odontoblast cell membrane play an essential role in sensory transduction and propagation mechanism of innocuous cold stimulation applied to dental pulp.