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

Abstract

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.

Potassium Currents Activated by Depolarization in Odontoblasts

“…In conclusion, we showed that odontoblasts expressed slow activating voltage-dependent K + currents that are carried by Kv1.1, 1.2, and/or 1.6. Previous reports have shown various Ca 2+ influx/mobilization pathways are mediated by mechano-sensing cation channels, store-operated Ca 2+ channels (SOCs), as well as depolarization-induced Ca 2+ entry (Shibukawa and Suzuki, 2003 ; Son et al, 2009 ; Tsumura et al, 2010 , 2013 ; Kojima et al, 2015 ; Shibukawa et al, 2015 ). Cellular deformation in odontoblasts, which might be elicited by dentinal fluid movement following dentin stimulation, also activates Ca 2+ influx and leads to depolarization.…”

“…Activation of these mechanosensitive ionic channels, as well as ionotropic and metabotropic receptors, increases intracellular free Ca 2+ concentrations, leading to plasma membrane depolarization. Membrane depolarization in odontoblasts is known to activate K + conductance; however, the detailed properties of this process remains to be clarified (Kojima et al, 2015 ).…”