Ionotropic P2X ATP Receptor Channels Mediate Purinergic Signaling in Mouse Odontoblasts

ATP modulates various functions in the dental pulp cells, such as intercellular communication and neurotransmission between odontoblasts and neurons, proliferation of dental pulp cells, and odontoblast differentiation. However, functional expression patterns and their biophysical properties of ionotropic ATP (P2X) receptors (P2X(1)–P2X(7)) in odontoblasts were still unclear. We examined these properties of P2X receptors in mouse odontoblasts by patch-clamp recordings. K(+)-ATP, nonselective P2X receptor agonist, induced inward currents in odontoblasts in a concentration-dependent manner. K(+)-ATP-induced currents were inhibited by P2X(4) and P2X(7) selective inhibitors (5-BDBD and KN62, respectively), while P2X(1) and P2X(3) inhibitors had no effects. P2X(7) selective agonist (BzATP) induced inward currents dose-dependently. We could not observe P2X(1, 2/3, 3) selective agonist (αβ-MeATP) induced currents. Amplitudes of K(+)-ATP-induced current were increased in solution without extracellular Ca(2+), but decreased in Na(+)-free extracellular solution. In the absence of both of extracellular Na(+) and Ca(2+), K(+)-ATP-induced currents were completely abolished. K(+)-ATP-induced Na(+) currents were inhibited by P2X(7) inhibitor, while the Ca(2+) currents were sensitive to P2X(4) inhibitor. These results indicated that odontoblasts functionally expressed P2X(4) and P2X(7) receptors, which might play an important role in detecting extracellular ATP following local dental pulp injury.