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At least 19 recordsLinked to original sources
PubMed1998

Distribution of P2X3 receptors in the rat trigeminal ganglion after inferior alveolar nerve injury.

The ATP-gated cation channel receptor P2X3 is associated with nociceptive primary sensory neurons. We have, using immunohistochemistry, examined the expression of P2X3 in rat trigeminal ganglia 4-22 days after ligation/section or chronic constriction of the mandibular inferior alveolar nerve. In the normal trigeminal ganglion the anti-P2X3 receptor antibody labeled 37-58% of all neurons. Double labeling demonstrated that about 70-95% of the small neurons that bind the isolectin I-B4 displayed P2X3-immunoreactivity, and that about 40% of larger RT97-positive nerve cells were P2X3 receptor-immunoreactive. At 4 and 10 days after inferior alveolar nerve injury, the proportion of P2X3-immunoreactive neurons had increased to about 65% (range 52-78%). Examinations at the injury sites showed an intense P2X3 receptor-immunoreactivity in nerve endings. At longer survival stages the proportion of P2X3 receptor-positive sensory neurons had returned to control values. These results show that the P2X3 receptor is transiently upregulated and anterogradely transported in trigeminal primary sensory neurons after nerve injury. Since the receptor is accumulated in injured nerve endings, it may be associated with abnormal impulse propagation from these sites.

Animals↗
PubMed2000

Warm-coding deficits and aberrant inflammatory pain in mice lacking P2X3 receptors.

ATP activates damage-sensing neurons (nociceptors) and can evoke a sensation of pain. The ATP receptor P2X3 is selectively expressed by nociceptors and is one of seven ATP-gated, cation-selective ion channels. Here we demonstrate that ablation of the P2X3 gene results in the loss of rapidly desensitizing ATP-gated cation currents in dorsal root ganglion neurons, and that the responses of nodose ganglion neurons to ATP show altered kinetics and pharmacology resulting from the loss of expression of P2X(2/3) heteromultimers. Null mutants have normal sensorimotor function. Behavioural responses to noxious mechanical and thermal stimuli are also normal, although formalin-induced pain behaviour is reduced. In contrast, deletion of the P2X3 receptor causes enhanced thermal hyperalgesia in chronic inflammation. Notably, although dorsal-horn neuronal responses to mechanical and noxious heat application are normal, P2X3-null mice are unable to code the intensity of non-noxious 'warming' stimuli.

Adenosine Triphosphate↗
PubMed2004

Chronological alterations of P2X3 receptor expression in the trigeminal ganglion after ischaemic insult in the Mongolian gerbil.

P2X receptors play a role in the transduction of sensory signals like pain. Few studies have been undertaken on altered P2X(3) receptor (P2X3) expression in sensory neurones after peripheral nerve injury. In the present study, we investigated chronological alterations in P2X3 immunoreactivity and its protein content in the trigeminal ganglion after ischaemic insult in the Mongolian gerbil. In the sham-operated group, P2X3-immunoreactive neurones were found abundantly in small- and medium-sized neurones. From 1 day after ischaemic insult, the number of P2X3-immunoreactive neurones decreased significantly. At 5 days after ischaemic insult, P2X3 immunoreactivity was observed in few neurones, but its immunoreactivity was weak. However, the number of cresyl violet-positive neurones was unchanged throughout this period in all groups. These results suggest that transient trigeminal ganglion ischaemia may provoke a decrease of P2X3 expression and its protein content, and that this down-regulation of P2X3 may be related to the altered pain and thermal sensation without being associated with a transient ischaemic insult.

Animals↗
PubMed2005

Use-dependent inhibition of P2X3 receptors by nanomolar agonist.

P2X3 receptors desensitize within 100 ms of channel activation, yet recovery from desensitization requires several minutes. The molecular basis for this slow rate of recovery is unknown. We designed experiments to test the hypothesis that this slow recovery is attributable to the high affinity (< 1 nM) of desensitized P2X3 receptors for agonist. We found that agonist binding to the desensitized state provided a mechanism for potent inhibition of P2X3 current. Sustained applications of 0.5 nM ATP inhibited > 50% of current to repetitive applications of P2X3 agonist. Inhibition occurred at 1000-fold lower agonist concentrations than required for channel activation and showed strong use dependence. No inhibition occurred without previous activation and desensitization. Our data are consistent with a model whereby inhibition of P2X3 by nanomolar [agonist] occurs by the rebinding of agonist to desensitized channels before recovery from desensitization. For several ATP analogs, the concentration required to inhibit P2X3 current inversely correlated with the rate of recovery from desensitization. This indicates that the affinity of the desensitized state and recovery rate primarily depend on the rate of agonist unbinding. Consistent with this hypothesis, unbinding of [32P]ATP from desensitized P2X3 receptors mirrored the rate of recovery from desensitization. As expected, disruption of agonist binding by site-directed mutagenesis increased the IC50 for inhibition and increased the rate of recovery.

Adenosine Triphosphate↗
PubMed2004

Up-regulation of P2X3 receptor during stretch of bladder urothelial cells from patients with interstitial cystitis.

PURPOSE: Extracellular adenosine triphosphate (ATP) can act through the purinergic receptor subtype P2X3 to transmit a pain signal to the central nervous system. Bladder urothelial cells (BUCs) from patients with interstitial cystitis (IC) patients have augmented release of ATP during in vitro stretch. We queried whether P2X3 receptor subtype exists on cultured BUCs. Furthermore, we asked whether P2X3 expression can be altered by in vitro stretch and whether there exists a difference in expression between IC and control BUCs. MATERIALS AND METHODS: BUCs from 4 IC and 5 control subjects were cultured according to established cell culture techniques. After cells were grown to confluence they were stretched on an in vitro stretch machine at 20% elongation for up to 96 hours. Cells were harvested at various times, and immunofluorescence and Western blots were performed for P2X3 expression. Band densitometry normalized to the actin band was performed using software. To confirm P2X3 expression in a whole cell preparation flow cytometry and fluorescence activated cell sorter analysis were used. RESULTS: P2X3 was expressed in cultured BUCs. With stretch P2X3 expression increased in IC BUCs more than in control BUCs. Using relative densitometry units normalized for actin expression in the Western blots stretch of IC BUCs resulted in 66% more expression of P2X3 than any other experimental condition (p = 0.003). By fluorescence activated cell sorter analysis stretched IC BUCs had the highest P2X3 fluorescence activity (30%) compared with unstretched IC (2.4%, p = 0.003), stretched control (9.7%, p = 0.009) and unstretched control (2.3%, p = 0.003) BUCs. CONCLUSIONS: These data show that P2X3 subunits expressed by cultured IC BUCs are up-regulated during in vitro stretch. Augmented ATP signaling in the bladder may explain IC symptoms. Furthermore, this study further supports the hypothesis that urothelial cells can phenotypically mimic sensory neurons.

Cells, Cultured↗
PubMed1997

Baculovirus expression provides direct evidence for heteromeric assembly of P2X2 and P2X3 receptors.

P2X2 and P2X3 are subunits of P2X receptors, cation channels opened by binding extracellular ATP. cDNAs encoding P2X2 and P2X3 receptor subunits, each with one of two C-terminal epitope tags, were cloned into baculovirus. Virally infected insect cells (Spodoptera frugiperda) expressed moderate to high levels of the corresponding proteins, as detected by Western blotting, by the specific binding of [35S]ATP and by whole-cell recordings of membrane current evoked by ATP or alphabetamethylene-ATP. In cells infected at the same time with two viruses encoding P2X2 and P2X3 receptors, the two proteins could be cross-immunoprecipitated with antibodies specific for either of the epitope tags. Whole-cell recordings from these cells showed that ATP and alphabetamethylene-ATP evoked currents with agonist sensitivity and desensitization quite distinct from those observed when P2X2 or P2X3 receptors were expressed alone. The results offer a method to express large amounts of P2X receptor protein, and they provide direct evidence that P2X2 and P2X3 subunits assemble to form heteromeric channels having distinct properties from those formed as homomers.

Adenosine Triphosphate↗
PubMed2006

Experimental and modeling studies of desensitization of P2X3 receptors.

The function of ATP-activated P2X3 receptors involved in pain sensation is modulated by desensitization, a phenomenon poorly understood. The present study used patch-clamp recording from cultured rat or mouse sensory neurons and kinetic modeling to clarify the properties of P2X3 receptor desensitization. Two types of desensitization were observed, a fast process (t1/2 = 50 ms; 10 microM ATP) following the inward current evoked by micromolar agonist concentrations, and a slow process (t1/2 = 35 s; 10 nM ATP) that inhibited receptors without activating them. We termed the latter high-affinity desensitization (HAD). Recovery from fast desensitization or HAD was slow and agonist-dependent. When comparing several agonists, there was analogous ranking order for agonist potency, rate of desensitization and HAD effectiveness, with 2-methylthioadenosine triphosphate the strongest and beta,gamma-methylene-ATP the weakest. HAD was less developed with recombinant (ATP IC50 = 390 nM) than native P2X3 receptors (IC50 = 2.3 nM). HAD could also be induced by nanomolar ATP when receptors seemed to be nondesensitized, indicating that resting receptors could express high-affinity binding sites. Desensitization properties were well accounted for by a cyclic model in which receptors could be desensitized from either open or closed states. Recovery was assumed to be a multistate process with distinct kinetics dependent on the agonist-dependent dissociation rate from desensitized receptors. Thus, the combination of agonist-specific mechanisms such as desensitization onset, HAD, and resensitization could shape responsiveness of sensory neurons to P2X3 receptor agonists. By using subthreshold concentrations of an HAD-potent agonist, it might be possible to generate sustained inhibition of P2X3 receptors for controlling chronic pain.

Adenosine Triphosphate↗
PubMed2006

Uterine cervical afferents in thoracolumbar dorsal root ganglia express transient receptor potential vanilloid type 1 channel and calcitonin gene-related peptide, but not P2X3 receptor and somatostatin.

BACKGROUND: Little is known regarding the phenotype of afferents that innervate the uterine cervix. Chronic estrogen sensitizes uterine cervical afferents to mechanical distension, but whether this reflects changes in afferent neurotransmitter or excitatory ion channel expression is unknown. The authors used immunocytochemistry to characterize uterine cervical afferents and the effects of estrogen on them. METHODS: Fluorogold was injected into the uterine cervix of intact rats (n = 7) and those with ovariectomy alone (n = 9) or with estrogen supplementation (n = 8). Bilateral dorsal root ganglia at T12-L2 were removed and immunostained for transient receptor potential vanilloid type 1 (TRPV1), P2X3 receptor, calcitonin gene-related peptide, and somatostatin. The proportion of fluorogold-traced dorsal root ganglion neurons expressing each of these markers was compared with untraced neurons. RESULTS: Most fluorogold-traced cells were found at L1 (> 55%) and were of small diameter (24 microm). TRPV1 expression was similar between traced and untraced cells, except the estrogen treatment increased TRPV1 expression in traced cells. Calcitonin gene-related peptide expression was greater in traced than in untraced cells, with no effect of experimental treatment. No traced cells expressed the P2X3 receptor or somatostatin, although each of these was present in untraced cells. CONCLUSION: Uterine cervical afferents in the hypogastric nerve express TRPV1, an important nociceptive channel, which may play a role in estrogen-induced sensitization of cervical afferents. High expression of calcitonin gene-related peptide suggests a sensory and efferent role for this peptide. In contrast to other viscera, these afferents do not express somatostatin or P2X3 receptor, indicating a unique phenotype of these C fibers.

Animals↗
PubMed2006

Delayed upregulation of ATP P2X3 receptors of trigeminal sensory neurons by calcitonin gene-related peptide.

Recent evidence indicates a key role for the neuropeptide calcitonin gene-related peptide (CGRP) in migraine pain, as demonstrated by the strong analgesic action of CGRP receptor antagonists, although the mechanisms of this effect remain unclear. Most trigeminal nociceptive neurons releasing CGRP also express ATP-activated purinergic P2X3 receptors to transduce pain. To understand whether the CGRP action involves P2X3 receptor modulation, the model of trigeminal nociceptive neurons in culture was used to examine the long-term action of this peptide. Although 79% of CGRP-binding neurons expressed P2X3 receptors, acute application of CGRP did not change P2X3 receptor function. Nevertheless, after 1 h of CGRP treatment, strong enhancement of the amplitude of P2X3 receptor currents was observed together with accelerated recovery from desensitization. Receptor upregulation persisted up to 10 h (despite CGRP washout), was accompanied by increased P2X3 gene transcription, and was fully prevented by the CGRP antagonist CGRP(8-37). Surface biotinylation showed CGRP augmented P2X3 receptor expression, consistent with confocal microscopy data indicating enhanced P2X3 immunoreactivity beneath the neuronal membrane. These results suggest that CGRP stimulated trafficking of P2X3 receptors to the cell-surface membrane. Using pharmacological tools, we demonstrated that this effect of CGRP was dependent on protein kinase A and PKC activation and was prevented by the trafficking inhibitor brefeldin A. Capsaicin-sensitive TRPV1 vanilloid receptors were not upregulated. The present data demonstrate a new form of selective, slow upregulation of nociceptive P2X3 receptors on trigeminal neurons by CGRP. This mechanism might contribute to pain sensitization and represents a model of neuronal plasticity in response to a migraine mediator.

Adenosine Triphosphate↗
PubMed2004

Development of nerves expressing P2X3 receptors in the myenteric plexus of rat stomach.

Development of neurones and fibres expressing P2X3 receptors in the myenteric plexus of rat stomach and coexistence of the P2X3 receptor with calbindin, calretinin and NOS during postnatal development, were investigated with immunostaining methods. Extrinsic nerves expressing P2X3 receptors appeared as early as E12 and were localised in the trunk and branches of the vagus nerve, which extended rapidly onto the whole rat stomach from E12 to E14. Intrinsic neurone cell bodies with P2X3-immunoreactivity in the myenteric ganglia were first demonstrated postnatally at P1, and at P14, when the number of neurones expressing the P2X3 receptor peaked at 45%. P2X3 receptor-immunoreactivity decreased subsequently, and at P60 only about 11% were P2X3-immunoreactive. Intraganglionic laminar nerve endings and intramuscular arrays were first demonstrated postnatally at P1 and P7, respectively. In the early postnatal days, there were many growth cone-like structures with strong P2X3 immunostaining associated with these endings and arrays. Double-immunostaining showed that 9-15% of P2X3-immunoreactive neurones in the gastric myenteric plexus expressed calbindin D-28 k only in the early postnatal days, while 14-21% of neurones from P1 to P60 increasingly expressed calretinin. About 20% of neurones with P2X3 immunoreactivity coexpressed NOS throughout perinatal development.

Animals↗
PubMed2005

P2X2 and P2X3 receptor expression in postnatal and adult rat urinary bladder and lumbosacral spinal cord.

P2X receptors mediate the effects of ATP in micturition and nociception. During postnatal maturation, a spinobulbospinal reflex and voluntary voiding replace primitive voiding reflexes. This may involve changes in neuroactive compounds and receptors in bladder reflex pathways. We examined P2X2 and P2X3 receptors in bladder and spinal cord from postnatal (P0-P36, indicating number of days) and adult Wistar rats. Western blot of whole bladders for P2X2 and P2X3 expression was performed. Immunostaining for P2X2 and P2X3 receptors in urothelium and detrusor smooth muscle whole mounts and spinal cord sections was examined. Western blot demonstrated an age-dependent decrease (R(2) = 0.96, P </= 0.005) in P2X2 receptor expression in bladder, whereas P2X3 receptor expression in bladder peaked (P </= 0.005) during P14-P21. P2X2-immunoreactivity (IR) was present in urothelial cells, suburothelial plexus, detrusor smooth muscle, and serosa at birth, with staining in urothelial cells and serosa being most predominant. With increasing postnatal age, the intensity of P2X2-IR decreased in urothelial cells but increased in suburothelial plexus. P2X3-IR increased in urothelial cells and suburothelial plexus with postnatal age, whereas staining in detrusor and serosa remained relatively constant. At birth, P2X3-IR was present in the dorsal horn, lateral collateral pathway, and dorsal commissure. With increasing age, P2X3-IR was restricted to superficial dorsal horn and lateral collateral pathway. P2X2-IR was present in ependyme cells (S-100-IR) of the central canal as early as P2. These studies demonstrate plastic expression of P2X2 and P2X3 receptors in bladder and spinal cord during early postnatal development at times coincident with appearance of mature voiding patterns.

Aging↗
PubMed2005

Regulation of human recombinant P2X3 receptors by ecto-protein kinase C.

The whole-cell patch-clamp technique was used to record current responses to nucleotides and nucleosides in human embryonic kidney HEK293 cells transfected with the human purinergic P2X3 receptor. When guanosine 5'-O-(3-thiodiphosphate) was included into the pipette solution, UTP at concentrations that did not alter the holding current facilitated the alpha,beta-methylene ATP (alpha,beta-meATP)-induced current. ATP and GTP, but not UDP or uridine, had an effect similar to that of UTP. Compounds known to activate protein kinase C (PKC) acted like the nucleoside triphosphates investigated, whereas various PKC inhibitors invariably reduced the effects of both PKC activators and UTP. The substitution by Ala of Ser/Thr residues situated within PKC consensus sites of the P2X3 receptor ectodomain either abolished (PKC2 and PKC3; T134A, S178A) or did not alter (PKC4 and PKC6; T196A, S269A) the UTP-induced potentiation of the alpha,beta-meATP current. Both the blockade of ecto-protein kinase C activity and the substitution of Thr-134 or Ser-178 by Ala depressed the maximum of the concentration-response curve for alpha,beta-meATP without altering the EC50 values. Molecular simulation of the P2X3 receptor structure indicated no overlap between assumed nucleotide binding domains and the relevant phosphorylation sites PKC2 and PKC3. alpha,beta-meATP-induced currents through native homomeric P2X3 receptors of rat dorsal root ganglia were also facilitated by UTP. In conclusion, it is suggested that low concentrations of endogenous nucleotides in the extracellular space may prime the sensitivity of P2X3 receptors toward the effect of subsequently applied (released) higher agonistic concentrations. The priming effect of nucleotides might be attributable to a phosphorylation of PKC sites at the ectodomain of P2X3 receptors.

Animals↗
PubMed2003

2', 3'-O-(2,4,6,trinitrophenyl)-ATP and A-317491 are competitive antagonists at a slowly desensitizing chimeric human P2X3 receptor.

(1) Rapid desensitization of ligand-gated ion channel receptors can alter the apparent activity of receptor modulators, as well as make detection of fast-channel activation difficult. Investigation of the antagonist pharmacology of ATP-sensitive homomeric P2X3 receptors is limited by agonist-evoked fast-desensitization kinetics. (2) In the present studies, chimeric receptors were created using the coding sequence for the N-terminus and the first transmembrane domain of either the nondesensitizing human P2X2a or fast-desensitizing P2X3 receptor joined to the sequence encoding the extracellular loop, second transmembrane domain, and C-terminus of the other receptor (designated P2X2-3 and P2X3-2, respectively). These clones were stably transfected into 1321N1 astrocytoma cells for biophysical and pharmacological experiments using both electrophysiological and calcium-imaging methods. (3) Chimeric P2X2-3 and P2X3-2 receptors were inwardly rectifying and agonist responses showed desensitization properties similar to the wild-type human P2X2a and P2X3 receptors, respectively. (4) The P2X2-3 chimera displayed an agonist pharmacological profile similar to the P2X3 wild-type receptor being activated by low concentrations of both ATP and alpha,beta-meATP. In contrast, the P2X3-2 chimera had markedly reduced sensitivity to both agonists. (5) The P2X3 receptor antagonists TNP-ATP and A-317491 were shown to be potent, competitive antagonists of the P2X2-3 chimera (Ki=2.2 and 52.1 nm, respectively), supporting the hypothesis that rapid receptor desensitization can mask the competitive antagonism of wild-type homomeric P2X3 receptors.

Adenosine Triphosphate↗
PubMed1998

Ultrastructural localization of P2X3 receptors in rat sensory neurons.

We used isolated IgG antibodies selective for P2X3 receptors to study the ultrastructural distribution of these receptors in rat sensory neurons. In trigeminal ganglia, P2X3 receptor immunoreactivity occurred in small and large nerve cell bodies and their processes. Endoplasmic reticulum and Golgi apparatus were heavily stained; cytoplasmic matrix was faintly to moderately stained. In synaptic glomeruli in lamina II of cervical dorsal horn, P2X3 receptor-immunoreactive core terminals were postsynaptic to unlabelled vesicle-containing dendrites and axons. In the nucleus of the solitary tract, receptor-positive boutons synapsed on dendrites and cell bodies and had complex synaptic relationships with other axon terminals and vesiculated dendrites. These observations identify sites from which ATP could be released to influence sensory signalling within the central nervous system.

Animals↗
PubMed2003

Intraganglionic laminar endings in the rat esophagus contain purinergic P2X2 and P2X3 receptor immunoreactivity.

Intraganglionic laminar endings (IGLEs) represent the most prominent vagal afferent terminal structures throughout the gastrointestinal tract. They are most prominent in the esophagus and stomach, but can be found down to the distal colon. Their role as mechanosensors as proposed on anatomical grounds was recently substantiated in elegant functional experiments. There is evidence that vagal mechanosensors in the esophagus and stomach respond to ATP. Thus, the present study aimed at detecting purinergic receptors on IGLEs. IGLEs in the rat esophagus were identified by immunohistochemistry for calretinin and sections were co-incubated with antibodies directed against P2X2 or P2X3 receptors. Also, double label immunocytochemistry for purinergic receptors and calcitonin gene-related peptide as a marker for spinal afferents was performed. Terminal nerve fibers immunoreactive for P2X2 and P2X3, respectively, were observed between outer and inner layers of the tunica muscularis, covering myenteric ganglia totally or partly. Both P2X2 and P2X3 receptor immunoreactivities were highly co-localized with calretinin positive IGLEs as shown by confocal laser scanning microscopy. Numerous calcitonin gene-related peptide immunostained fibers were found to closely approach and intermingle with P2X immunopositive IGLEs. However, there was never co-staining for either of the purinergic receptors and calcitonin gene-related peptide within the same fibers. P2X3 but not P2X2 immunoreactivity was also observed within nerve fiber arborizations in the mucosa of the pharynx. In the nodose ganglion, 8.9 +/- 1.1% of P2X2 and 7.2 +/- 1.3% of P2X3 immunopositive neurons, respectively, co-stained for calretinin. On the other hand, 63.4 +/- 4.6% and 60.1 +/- 5.3% of calretinin positive cell bodies contained P2X2 and P2X3 receptor immunoreactivity, respectively. These results indicate that IGLEs are equipped with both P2X2 and P2X3 receptors. Thus, they may act as chemosensors or their mechanosensory properties may be modulated by ATP. It is also suggested that spinal afferents innervating the esophagus are equipped with neither P2X2 nor P2X3 purinergic receptors.

Animals↗
PubMed2004

The co-expression of P2X3 receptor with VR1 and VRL-1 in the rat trigeminal ganglion.

The co-expression of P2X3 receptor with the vanilloid receptor subtype I (VR1) and vanilloid receptor 1-like receptor (VRL-1) was examined in the rat trigeminal ganglion (TG) by a double immunofluorescence method. P2X3 receptor-immunoreactive (ir) neurons were predominantly small to medium-sized (range=93.8-1844.4 microm(2), mean+/-S.D.=503.8+/-286.5 microm(2)); 35% and 9% of P2X3 receptor-ir TG neurons were immunoreactive for VR1 and VRL-1, respectively. Small and medium-sized P2X3 receptor-ir neurons contained VR1-immunoreactivity (ir), whereas medium-sized and large P2X3 receptor-ir neurons showed VRL-1-ir. The retrograde tracing and immunohistochemical methods revealed that 30% of the TG neurons retrogradely labeled from the facial skin and tooth pulp exhibited P2X3 receptor-ir. The co-expression of P2X3 receptor and VR1 was detected in 16% of cutaneous TG neurons and 6% of tooth pulp neurons. On the other hand, the co-expression of P2X3 receptor and VRL-1 was common in tooth pulp neurons (23%) and rare in cutaneous TG neurons (8%). In the tooth pulp, 95% of P2X3 receptor-ir TG neurons contained VRL-1-ir. The present study indicates that P2X3 receptor-ir TG neurons, which co-express VR-ir, are abundant in the facial skin. The tooth pulp is probably innervated by TG neurons, which contain both P2X3-and VRL-1-ir.

Animals↗
PubMed2005

Re-organization of P2X3 receptor localization on epidermal nerve fibers in a murine model of cancer pain.

To determine whether ATP and P2X3 receptors contribute to bone-cancer pain in a mouse model, immunohistochemical techniques were used to identify whether changes in the labeling of P2X3 receptors on epidermal nerve fibers (ENFs) occurred during tumor development. C3H mice were injected with osteolytic fibrosarcoma cells in and around the calcaneus bone. These mice exhibited mechanical hyperalgesia by day 10 post-implantation as assessed using von Frey monofilaments. Biopsies of the plantar skin overlying the tumor were obtained at days 10, 14, and 18 post-implantation. Confocal images were analyzed for the number of PGP 9.5, P2X3, and CGRP immunoreactive (ir) ENFs. The overall ENF population (PGP-ir) decreased progressively over time, whereas the subsets of P2X3-ir fibers demonstrated a modest increase and CGRP-ir nerve fibers remained fairly constant. Importantly, the proportion of CGRP-ir fibers that labeled for P2X3 increased from approximately 6% in control animals to nearly 30% at day 14 following tumor cell implantation. These studies demonstrate increased expression of P2X3 receptors on CGRP-ir ENFs during tumor growth and suggest a role for ATP in cancer-related pain.

Animals↗
PubMed1999

Localization of ATP-gated P2X2 and P2X3 receptor immunoreactive nerves in rat taste buds.

P2X receptors have been suggested to play a role in the transduction of sensory signals such as pain and sound. In the present study, polyclonal antibodies against P2X1 to P2X6 receptors were used to localize P2X receptors in circumvallate and fungiform papillae of rats. Nerve fibres innervating the taste buds stained intensely with P2X3 receptor antibodies. P2X3 receptor-positive nerves were observed in the intra- and subgemmal regions. The nerve fibres were also stained with P2X2 receptor antibodies, but the intensity was much lower. The distribution of P2X2 receptor immunoreactivity overlaps with that of P2X3. These results suggest that ATP might be a neurotransmitter in taste reception cells in the taste buds, where it transducts the taste signals to the afferent taste nerves by activating P2X receptors at the synapses. This is the first experiment indicating such a role for ATP, although supplementary functional studies are required.

Adenosine Triphosphate↗