External Dentin Stimulation Induces ATP Release in Human Teeth

Abstract

ATP is involved in neurosensory processing, including nociceptive transduction. Thus, ATP signaling may participate in dentin hypersensitivity and dental pain. In this study, we investigated whether pannexins, which can form mechanosensitive ATP-permeable channels, are present in human dental pulp. We also assessed the existence and functional activity of ecto-ATPase for extracellular ATP degradation. We further tested if ATP is released from dental pulp upon dentin mechanical or thermal stimulation that induces dentin hypersensitivity and dental pain and if pannexin or pannexin/gap junction channel blockers reduce stimulation-dependent ATP release. Using immunofluorescence staining, we demonstrated immunoreactivity of pannexin 1 and 2 in odontoblasts and their processes extending into the dentin tubules. Using enzymatic histochemistry staining, we also demonstrated functional ecto-ATPase activity within the odontoblast layer, subodontoblast layer, dental pulp nerve bundles, and blood vessels. Using an ATP bioluminescence assay, we found that mechanical or cold stimulation to the exposed dentin induced ATP release in an in vitro human tooth perfusion model. We further demonstrated that blocking pannexin/gap junction channels with probenecid or carbenoxolone significantly reduced external dentin stimulation-induced ATP release. Our results provide evidence for the existence of functional machinery required for ATP release and degradation in human dental pulp and that pannexin channels are involved in external dentin stimulation-induced ATP release. These findings support a plausible role for ATP signaling in dentin hypersensitivity and dental pain.

Purinergic Signaling and Dental Orofacial Pain

“…The existence of autocrine/ paracrine mechanisms for ATP-involved purinergic signaling in cultured odontoblast-like stem cells is also confirmed [73]. Furthermore, external mechanical and thermal stimulation that mimics dentin hypersensitivity induces ATP release in a tooth perfusion model, while pharmacological blocking connexin and pannexin channels abolished external stimulation-induced ATP release in dental pulp [66]. Based on the above observations, we proposed that, as illustrated in Figure 2, external stimulation-induced mechanosensitive responses and ATP release from odontoblasts and subsequently activation of purinergic receptors in dental pulpal nerves may represent a novel explanation as to how odontoblasts participate in a mechanosensory mechanism leading to the pain transduction in DHS [60,74].…”

“…For the past decades, chemo-, mechano-, and or thermo-sensitive channels such as connexin, pannexin, TRPV1-4, TRPM3, KCa, TREK-1, beta-ENa(+) C, and ASIC2 channels have been identified in odontoblasts [60,[65][66][67][68][69][70]. Activation of these channels depolarizes the membrane potential that induces ATP release via vesicles release or channel opening in odontoblasts.…”

“…Interestingly, mechanicas well as depolarization-sensitive ATP permeable channel such as connexin 43 and pannexins had been detected in odontoblastic processes inserting into dentinal tubules [60,64]. Indeed it has been shown that mechanical and or thermal stimulation that mimics dentin hypersensitivity in clinic induces ATP release from odontoblasts [65,66,71]. Besides, mechanical stimulation-induced ATP release and ATP-mediated signal transmission from odontoblasts to trigeminal neurons have been demonstrated in vitro using co-culture models comprising of odontoblasts and trigeminal neurons [68,72].…”

Ionotropic P2X ATP Receptor Channels Mediate Purinergic Signaling in Mouse Odontoblasts

“…The value of EC 50 of K + -ATP in this study was in line with that for EC 50 of ATP for P2X 7 receptor activation (100 μM: Khakh et al, 2001). Recently, the concentration of released ATP by external dentin cold-stimulation has been reported to be “nM” range in an in vitro human tooth perfusion model (Egbuniwe et al, 2014; Liu et al, 2015). Based on our results, P2X receptor subtypes expressed in odontoblasts need ~1000 times as high of a concentration of extracellular ATP to be activated (ca.…”

Comparative Desensitization Effect of Vital Abutments Realized by Different Methods

“…Three theories on dentinal sensitivity were formulated. The nerve theory postulates the direct stimulation of dentinal tubules and pulpar nerve terminals; the hydrodynamic theory of dentin hypersensitivity consider that external stimuli determine movements in the fluid of dentinal tubules, which induce nociceptive transduction in adjacent pulpal nerve fibers; the odontoblastic theory postulates direct stimulation of odontoblast, and is based on the expression of several ion channels by these cells [6,7]. The theories are not mutually exclusive and cannot be considered separately because of the presence of nerves and odontoblast processes within the dentinal tubules, bathing in the dentinal fluid, and the close apposition of the odontoblasts to the dentinal or basal nerves terminals (fig.…”