Abstract
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 (P2X1–P2X7) 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 P2X4 and P2X7 selective inhibitors (5-BDBD and KN62, respectively), while P2X1 and P2X3 inhibitors had no effects. P2X7 selective agonist (BzATP) induced inward currents dose-dependently. We could not observe P2X1, 2/3, 3 selective agonist (αβ-MeATP) induced currents. Amplitudes of K+-ATP-induced current were increased in solution without extracellular Ca2+, but decreased in Na+-free extracellular solution. In the absence of both of extracellular Na+ and Ca2+, K+-ATP-induced currents were completely abolished. K+-ATP-induced Na+ currents were inhibited by P2X7 inhibitor, while the Ca2+ currents were sensitive to P2X4 inhibitor. These results indicated that odontoblasts functionally expressed P2X4 and P2X7 receptors, which might play an important role in detecting extracellular ATP following local dental pulp injury.
Highlights
Extracellular adenosine triphosphate (ATP) and other nucleotides play important roles in various cellular physiological and pathological functions, which are limited to purinergic neurotransmission for dentinal sensitivity (Shibukawa et al, 2015) or tastes (Taruno et al, 2013) and diseases in the immune and neural systems as well as inflammatory response and pain (Burnstock, 2013), by activating plasma membrane purinergic receptors
The odontoblast lineage cells (OLCs) used in this study are positive for various odontoblastrepresentative transcripts such as dentin sialophosphoprotein, dentin matrix protein-1, and nestin (Arany et al, 2006; Sato et al, 2013)
BzATP-induced currents and K+-ATP-induced currents were sensitive to KN62, a selective antagonist for P2X7 receptors
Summary
Extracellular adenosine triphosphate (ATP) and other nucleotides play important roles in various cellular physiological and pathological functions, which are limited to purinergic neurotransmission for dentinal sensitivity (Shibukawa et al, 2015) or tastes (Taruno et al, 2013) and diseases in the immune and neural systems as well as inflammatory response and pain (Burnstock, 2013), by activating plasma membrane purinergic receptors. Ionic Conductance of P2X Receptor in Odontoblasts are ATP-gated cation channels, whereas P2Y receptor subtypes are preferentially activated by nucleotides other than ATP (Abbracchio et al, 2006). All P2X receptors are cation-selective channels with almost equal permeability to Na+, K+, and significant permeability to Ca2+ (Jarvis and Khakh, 2009; Samways et al, 2014). It has been reported that nociceptive tooth-pulp afferent (trigeminal ganglion neurons) express P2X3 receptors (Cook et al, 1997) and are sufficient to elicit nociceptive behavioral responses (Adachi et al, 2010)
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