A C-terminal motif found in the beta2-adrenergic receptor, P2Y1 receptor and cystic fibrosis transmembrane conductance regulator determines binding to the Na+/H+ exchanger regulatory factor family of PDZ proteins.

The Na+/H+ exchanger regulatory factor (NHERF) binds to the tail of the beta2-adrenergic receptor and plays a role in adrenergic regulation of Na+/H+ exchange. NHERF contains two PDZ domains, the first of which is required for its interaction with the beta2 receptor. Mutagenesis studies of the beta2 receptor tail revealed that the optimal C-terminal motif for binding to the first PDZ domain of NHERF is D-S/T-x-L, a motif distinct from those recognized by other PDZ domains. The first PDZ domain of NHERF-2, a protein that is 52% identical to NHERF and also known as E3KARP, SIP-1, and TKA-1, exhibits binding preferences very similar to those of the first PDZ domain of NHERF. The delineation of the preferred binding motif for the first PDZ domain of the NHERF family of proteins allows for predictions for other proteins that may interact with NHERF or NHERF-2. For example, as would be predicted from the beta2 receptor tail mutagenesis studies, NHERF binds to the tail of the purinergic P2Y1 receptor, a seven-transmembrane receptor with an intracellular C-terminal tail ending in D-T-S-L. NHERF also binds to the tail of the cystic fibrosis transmembrane conductance regulator, which ends in D-T-R-L. Because the preferred binding motif of the first PDZ domain of the NHERF family of proteins is found at the C termini of a variety of intracellular proteins, NHERF and NHERF-2 may be multifunctional adaptor proteins involved in many previously unsuspected aspects of intracellular signaling.

Purinergic mechanisms of lateral parabrachial nucleus facilitate sodium depletion-induced NaCl intake

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The role of purinergic signaling in the liver and in transplantation: effects of extracellular nucleotides on hepatic graft vascular injury, rejection and metabolism

Extracellular nucleotides (e.g. ATP, UTP, ADP) are released by activated endothelium, leukocytes and platelets within the injured vasculature and bind specific cell-surface type-2 purinergic (P2) receptors. This process drives vascular inflammation and thrombosis within grafted organs. Importantly, there are also vascular ectonucleotidases i.e. ectoenzymes that hydrolyze extracellular nucleotides in the blood to generate nucleosides (viz. adenosine). Endothelial cell NTPDase1/CD39 has been shown to critically modulate levels of circulating nucleotides. This process tends to limit the activation of platelet and leukocyte expressed P2 receptors and also generates adenosine to reverse inflammatory events. This vascular protective CD39 activity is rapidly inhibited by oxidative reactions, such as is observed with liver ischemia reperfusion injury. In this review, we chiefly address the impact of these signaling cascades following liver transplantation. Interestingly, the hepatic vasculature, hepatocytes and all non-parenchymal cell types express several components co-ordinating the purinergic signaling response. With hepatic and vascular dysfunction, we note heightened P2- expression and alterations in ectonucleotidase expression and function that may predispose to progression of disease. In addition to documented impacts upon the vasculature during engraftment, extracellular nucleotides also have direct influences upon liver function and bile flow (both under physiological and pathological states). We have recently shown that alterations in purinergic signaling mediated by altered CD39 expression have major impacts upon hepatic metabolism, repair mechanisms, regeneration and associated immune responses. Future clinical applications in transplantation might involve new therapeutic modalities using soluble recombinant forms of CD39, altering expression of this ectonucleotidase by drugs and/or using small molecules to inhibit deleterious P2-mediated signaling while augmenting beneficial adenosine-mediated effects within the transplanted liver.

Involvement of L-glutamate and ATP in the neurotransmission of the sympathoexcitatory component of the chemoreflex in the commissural nucleus tractus solitarii of awake rats and in the working heart-brainstem preparation

Peripheral chemoreflex activation with potassium cyanide (KCN) in awake rats or in the working heart-brainstem preparation (WHBP) produces: (a) a sympathoexcitatory/pressor response; (b) bradycardia; and (c) an increase in the frequency of breathing. Our main aim was to evaluate neurotransmitters involved in mediating the sympathoexcitatory component of the chemoreflex within the nucleus tractus solitarii (NTS). In previous studies in conscious rats, the reflex bradycardia, but not the pressor response, was reduced by antagonism of either ionotropic glutamate or purinergic P2 receptors within the NTS. In the present study we evaluated a possible dual role of both P2 and NMDA receptors in the NTS for processing the sympathoexcitatory component (pressor response) of the chemoreflex in awake rats as well as in the WHBP. Simultaneous blockade of ionotropic glutamate receptors and P2 receptors by sequential microinjections of kynurenic acid (KYN, 2 nmol (50 nl)(-1)) and pyridoxalphosphate-6-azophenyl-2',4'-disulphonate (PPADS, 0.25 nmol (50 nl)(-1)) into the commissural NTS in awake rats produced a significant reduction in both the pressor (+38 +/- 3 versus +8 +/- 3 mmHg) and bradycardic responses (-172 +/- 18 versus -16 +/- 13 beats min(-1); n = 13), but no significant changes in the tachypnoea measured using plethysmography (270 +/- 30 versus 240 +/- 21 cycles min(-1), n = 7) following chemoreflex activation in awake rats. Control microinjections of saline produced no significant changes in these reflex responses. In WHBP, microinjection of KYN (2 nmol (20 nl)(-1)) and PPADS (1.6 nmol (20 nl)(-1)) into the commissural NTS attenuated significantly both the increase in thoracic sympathetic activity (+52 +/- 2% versus +17 +/- 1%) and the bradycardic response (-151 +/- 17 versus -21 +/- 3 beats min(-1)) but produced no significant changes in the increase of the frequency of phrenic nerve discharge (+0.24 +/- 0.02+0.20 +/- 0.02 Hz). The data indicate that combined microinjections of PPADS and KYN into the commissural NTS in both awake rats and the WHBP are required to produce a significant reduction in the sympathoexcitatory response (pressor response) to peripheral chemoreflex activation. We conclude that glutamatergic and purinergic mechanisms are part of the complex neurotransmission system of the sympathoexcitatory component of the chemoreflex at the level of the commissural NTS.

Antidipsogenic effects of central adenosine-5'-triphosphate

Besides other physiological functions, adenosine-5'-triphosphate (ATP) is also a neurotransmitter that acts on purinergic receptors. In spite of the presence of purinergic receptors in forebrain areas involved with fluid-electrolyte balance, the effect of ATP on water intake has not been investigated. Therefore, we studied the effects of intracerebroventricular (icv) injections of ATP (100, 200 and 300 nmol/µL) alone or combined with DPCPX or PPADS (P1 and P2 purinergic antagonists, respectively, 25 nmol/µL) on water intake induced by water deprivation. In addition, the effect of icv ATP was also tested on water intake induced by intragastric load of 12% NaCl (2 mL/rat), acute treatment with the diuretic/natriuretic furosemide (20 mg/kg), icv angiotensin II (50 ng/µL) or icv carbachol (a cholinergic agonist, 4 nmol/µL), on sodium depletion-induced 1.8% NaCl intake, and on food intake induced by food deprivation. Male Holtzman rats (280-320 g, N = 7-11) had cannulas implanted into the lateral ventricle. Icv ATP (300 nmol/µL) reduced water intake induced by water deprivation (13.1 ± 1.9 vs saline: 19.0 ± 1.4 mL/2 h; P < 0.05), an effect blocked by pre-treatment with PPADS, but not DPCPX. Icv ATP also reduced water intake induced by NaCl intragastric load (5.6 ± 0.9 vs saline: 10.3 ± 1.4 mL/2 h; P < 0.05), acute furosemide treatment (0.5 ± 0.2 vs saline: 2.3 ± 0.6 mL/15 min; P < 0.05), and icv angiotensin II (2.2 ± 0.8 vs saline: 10.4 ± 2.0 mL/2 h; P < 0.05), without changing icv carbachol-induced water intake, sodium depletion-induced 1.8% NaCl intake and food deprivation-induced food intake. These data suggest that central ATP, acting on purinergic P2 receptors, reduces water intake induced by intracellular and extracellular dehydration.

Deletion of CD39 on natural killer cells attenuates hepatic ischemia/reperfusion injury in mice

Natural killer (NK) cells play crucial roles in innate immunity and express CD39 (Ecto-nucleoside triphosphate diphosphohydrolase 1 [E-NTPD1]), a rate-limiting ectonucleotidase in the phosphohydrolysis of extracellular nucleotides to adenosine. We have studied the effects of CD39 gene deletion on NK cells in dictating outcomes after partial hepatic ischemia/reperfusion injury (IRI). We show in mice that gene deletion of CD39 is associated with marked decreases in phosphohydrolysis of adenosine triphosphate (ATP) and adenosine diphosphate to adenosine monophosphate on NK cells, thereby modulating the type-2 purinergic (P2) receptors demonstrated on these cells. We note that CD39-null mice are protected from acute vascular injury after single-lobe warm IRI, and, relative to control wild-type mice, display significantly less elevation of aminotransferases with less pronounced histopathological changes associated with IRI. Selective adoptive transfers of immune cells into Rag2/common gamma null mice (deficient in T cells, B cells, and NK/NKT cells) suggest that it is CD39 deletion on NK cells that provides end-organ protection, which is comparable to that seen in the absence of interferon gamma. Indeed, NK effector mechanisms such as interferon gamma secretion are inhibited by P2 receptor activation in vitro. Specifically, ATPgammaS (a nonhydrolyzable ATP analog) inhibits secretion of interferon gamma by NK cells in response to interleukin-12 and interleukin-18, providing a mechanistic link between CD39 deletion and altered cytokine secretion. CONCLUSION: We propose that CD39 deficiency and changes in P2 receptor activation abrogate secretion of interferon gamma by NK cells in response to inflammatory mediators, thereby limiting tissue damage mediated by these innate immune cells during IRI.

Autocrine signaling through ATP release represents a novel mechanism for cell volume regulation.

Recovery of cell volume in response to osmotic stress is mediated in part by increases in the Cl- permeability of the plasma membrane. These studies evaluate the hypothesis that ATP release and autocrine stimulation of purinergic (P2) receptors couple increases in cell volume to opening of Cl- channels. In HTC rat hepatoma cells, swelling induced by hypotonic exposure increased membrane Cl- current density to 44.8 +/- 7.1 pA/pF at -80 mV. Both the rate of volume recovery and the increase in Cl- permeability were inhibited in the presence of the ATP hydrolase apyrase (3 units/ml) or by exposure to the P2 receptor blockers suramin and Reactive Blue 2 (10-100 microM). Cell swelling also stimulated release of ATP. Hypotonic exposure increased the concentration of ATP in the effluent of perfused cells by 170 +/- 36 nM in the presence of a nucleotidase inhibitor (P < 0.01). In whole-cell recordings with ATP as the charge carrier, cell swelling increased membrane current density approximately 30-fold to 16.5 +/- 10.4 pA/pF. These findings indicate that increases in cell volume lead to efflux of ATP through opening of a conductive pathway consistent with a channel, and that extracellular ATP is required for recovery from swelling. ATP may function as an autocrine factor that couples increases in cell volume to opening of Cl- channels through stimulation of P2 receptors.

O fator de crescimento do nervo inibe o edema citotóxico de células de Müller e células bipolares da retina de rato por meio da liberação de citocinas gliais: participação do sistema glutamatérgico e purinérgico

O fator de crescimento do nervo (NGF) pode retardar a degeneração celular na retina de ratos em diferentes injúrias retinianas. O acúmulo de água em células da retina contribui para o desenvolvimento de edema retiniano e degeneração neuronal. Em atribuição ao seu efeito protetor, este trabalho teve por objetivo avaliar se o NGF influencia o edema celular osmótico em células de Müller e células bipolares. Assim, montagens planas, fatias de retina e células isoladas da retina de ratos foram superfundidas com solução hipo-osmótica na presença de BaCl₂. Secções retinianas foram utilizadas para imunomarcações, e a liberação de adenosina foi medida por cromatografia líquida de alta eficácia, em montagens planas. A área de secção transversal celular foi medida antes e após a superfusão em meio hipo-osmótico, em fatias de retina e suspensões celulares. Tanto células de Müller quanto células bipolares foram imunopositivas para TrkA, mas somente células de Müller foram marcadas contra p75^NTR e NGF. A hipo-osmolaridade induziu um rápido e significativo aumento da liberação de adenosina endógena em retinas controle, mas não em retinas perfundidas com BaCl₂. O NGF inibiu o edema citotóxico em células de Müller e em células bipolares em fatias de retina controle e retinas pós-isquêmicas submetidas a condições hipo-osmóticas. Por outro lado, NGF impediu o edema citotóxico da célula de Müller isolada, mas não da célula bipolar isolada (em meio hipo-osmótico contendo íons Ba²⁺). Isto sugere que NGF induz a liberação de fatores por células de Müller, os quais inibem o edema citotóxico de células bipolares em fatias de retina. O efeito inibitório do NGF sobre o edema citotóxico de células de Müller foi mediado pela ativação do receptor TrkA, mas não de p75^NTR, e foi anulado por bloqueadores de receptores metabotrópicos de glutamato, receptores de adenosina A₁, e receptores do fator de crescimento de fibroblasto (FGF). O bFGF evitou o edema citotóxico de células de Müller isoladas, mas inibiu somente em parte o edema citotóxico de células bipolares isoladas. O bloqueio de FGFR impediu o efeito inibidor de edema celular da adenosina, sugerindo que a liberação de bFGF ocorre após à ativação autócrina/parácrina de receptores A_l. Além de bFGF, GDNF e TGF431 reduziram em parte o edema citotóxico da célula bipolar. Estes dados sugerem que o efeito neuroprotetor do NGF é em parte mediado pela prevenção de edema citotóxico de células gliais e bipolares da retina.

Role of adenosine signaling in penile erection and erectile disorders.

INTRODUCTION: Penile erection is a hemodynamic process, which results from increased flow and retention of blood in the penile organ due to the relaxation of smooth muscle cells. Adenosine, a physiological vasorelaxant, has been shown to be a modulator of penile erection. AIM: To summarize the research on the role of adenosine signaling in normal penile erection and erectile disorders. MAIN OUTCOME MEASURES: Evidence in the literature on the association between adenosine signaling and normal and abnormal penile erection, i.e., erectile dysfunction (ED) and priapism. METHODS: The article reviews the literature on the role of endogenous and exogenous adenosine in normal penile erection, as well as in erectile disorders namely, ED and priapism. RESULTS: Adenosine has been shown to relax corpus cavernosum from various species including human in both in vivo and in vitro studies. Neuromodulatory role of adenosine in corpus cavernosum has also been demonstrated. Impaired adenosine signaling through A(2B) receptor causes partial resistance of corpus cavernosum, from men with organic ED, to adenosine-mediated relaxation. Increased level of adenosine has been shown to be a causative factor for priapism. CONCLUSION: Overall, the research reviewed here suggests a general role of exogenous and endogenous adenosine signaling in normal penile erection. From this perspective, it is not surprising that impaired adenosine signaling is associated with ED, and excessive adenosine signaling is associated with priapism. Adenosine signaling represents a potentially important diagnostic and therapeutic target for the treatment of ED and priapism.

Adenosine signaling contributes to ethanol-induced fatty liver in mice.

Fatty liver is commonly associated with alcohol ingestion and abuse. While the molecular pathogenesis of these fatty changes is well understood, the biochemical and pharmacological mechanisms by which ethanol stimulates these molecular changes remain unknown. During ethanol metabolism, adenosine is generated by the enzyme ecto-5'-nucleotidase, and adenosine production and adenosine receptor activation are known to play critical roles in the development of hepatic fibrosis. We therefore investigated whether adenosine and its receptors play a role in the development of alcohol-induced fatty liver. WT mice fed ethanol on the Lieber-DeCarli diet developed hepatic steatosis, including increased hepatic triglyceride content, while mice lacking ecto-5'-nucleotidase or adenosine A1 or A2B receptors were protected from developing fatty liver. Similar protection was also seen in WT mice treated with either an adenosine A1 or A2B receptor antagonist. Steatotic livers demonstrated increased expression of genes involved in fatty acid synthesis, which was prevented by blockade of adenosine A1 receptors, and decreased expression of genes involved in fatty acid metabolism, which was prevented by blockade of adenosine A2B receptors. In vitro studies supported roles for adenosine A1 receptors in promoting fatty acid synthesis and for A2B receptors in decreasing fatty acid metabolism. These results indicate that adenosine generated by ethanol metabolism plays an important role in ethanol-induced hepatic steatosis via both A1 and A2B receptors and suggest that targeting adenosine receptors may be effective in the prevention of alcohol-induced fatty liver.

Phosphorylation of Tyrosine 992, 1068, and 1086 Is Required for Conformational Change of the Human Epidermal Growth Factor Receptor C-Terminal Tail

We reported previously that a conformation-specific antibody, Ab P2, to a 16-amino acid peptide (Glu-Gly-Tyr-Lys-Lys-Lys-Tyr-Gln-Gln-Val-Asp-Glu-Glu-Phe-Leu-Arg) of the cytoplasmic domain of the β-type platelet-derived growth factor receptor also recognizes the epidermal growth factor (EGF) receptor. Although the antibody is not directed to phosphotyrosine, it recognizes in immunoprecipitation the activated and hence phosphorylated form of both receptors. In P2 peptide, there are two tripeptide sequences, Asp-Glu-Glu and Tyr-Gln-Gln, that are also present in the EGF receptor. Our present studies using either EGF receptor C-terminal deletion mutants or point mutations (Tyr→Phe) and our previous studies on antibody inhibition by P2-derived peptides suggest that Gln-Gln in combination with Asp-Glu-Glu forms a high-affinity complex with Ab P2 and that such complex formation is dependent on tyrosine phosphorylation. Of the five phosphate acceptor sites in the EGF receptor, clustered in the extreme C-terminal tail, phosphorylation of three tyrosine residues (992, 1068, and 1086) located between Asp-Glu-Glu and Gln-Gln is necessary for Ab P2 binding. In contrast, the acceptor sites Tyr 1173 and 1148 play no role in the conformation change. Asp-Glu-Glu and Gln-Gln are located 169 amino acids apart, and it is highly likely that the interactions among three negatively charged phosphotyrosine residues in the receptor C terminus may result in the bending of the peptide chain in such a way that these two peptides come close to each other to form an antibody-binding site. Such a possibility is also supported by our finding that receptor dephosphorylation results in complete loss of Ab P2–binding activity. In conclusion, we have identified a domain within the cytoplasmic part of the EGF receptor whose conformation is altered by receptor phosphorylation; furthermore, we have identified the tyrosine residues that positively regulate this conformation.

Estudo da participação do receptor P2X7 no desempenho cognitivo de roedores: abordagens farmacológicas e genéticas

A memória é um fenômeno decorrente de um conjunto de processos fisiológicos denominado plasticidade. Várias formas de plasticidade são necessárias no processo de formação da memória e também são responsáveis pelo gerenciamento do comportamento. O fenômeno eletrofisiológico chamado potencialização de longa duração (PLD), cuja ocorrência no hipocampo merece destaque, foi proposto como sendo o mecanismo de plasticidade constitutivo das bases da consolidação da memória nesta região encefálica. A importância da plasticidade na região CA1 do hipocampo se manifesta em diversas formas de aprendizado, como espacial e condicionamento clássico. Os eventos bioquímicos que culminam na plasticidade e formação da memória sofrem influência de diversos sistemas de neurotransmissores e evidências indicam também a participação do sistema purinérgico, provavelmente através dos receptores ionotrópicos P2X. Receptores purinérgicos do subtipo P2X7 (P2X7R), largamente distribuídos no sistema nervoso central (SNC), além de possuírem várias características que os distinguem de outros subtipos de receptores P2X, estão envolvidos na regulação da liberação de neurotransmissores cruciais para a promoção da PLD na região hipocampal e formação da memória. Assim, este trabalho objetivou avaliar a participação dos P2X7R em camundongos geneticamente modificados (KO), que não expressam o receptor P2X7, e ratos através da exposição destes a diferentes tarefas comportamentais, bem como avaliar o efeito do enriquecimento ambiental sobre possíveis déficits mnemônicos resultantes da supressão gênica sobre o receptor P2X7. Os resultados sugerem que os P2X7R participam tanto da memória aversiva como da memória espacial: o bloqueio farmacológico com o antagonista específico de P2X7R A-740003 em diferentes janelas temporais causou prejuízos mnemônicos em ratos submetidos à tarefa do medo condicionado contextual (MCC), enquanto a deleção do P2X7R causou déficits mnemônicos a camundongos nas tarefas do labirinto aquático de Morris e no MCC, indicando prejuízos nas memórias espacial e aversiva, respectivamente. Experimentos com enriquecimento ambiental sugerem que esta forma de estimulação contribui na reversão dos déficits mnemônicos causado pela ausência do P2X7R. Por fim, nenhuma alteração na memória de habituação foi observada em animais com deleção gênica para o P2X7R.

P2 purinergic receptor mRNA in rat and human sinoatrial node and other heart regions.

It is known that adenosine 5'-triphosphate (ATP) is a cotransmitter in the heart. Additionally, ATP is released from ischemic and hypoxic myocytes. Therefore, cardiac-derived sources of ATP have the potential to modify cardiac function. ATP activates P2X(1-7) and P2Y(1-14) receptors; however, the presence of P2X and P2Y receptor subtypes in strategic cardiac locations such as the sinoatrial node has not been determined. An understanding of P2X and P2Y receptor localization would facilitate investigation of purine receptor function in the heart. Therefore, we used quantitative PCR and in situ hybridization to measure the expression of mRNA of all known purine receptors in rat left ventricle, right atrium and sinoatrial node (SAN), and human right atrium and SAN. Expression of mRNA for all the cloned P2 receptors was observed in the ventricles, atria, and SAN of the rat. However, their abundance varied in different regions of the heart. P2X(5) was the most abundant of the P2X receptors in all three regions of the rat heart. In rat left ventricle, P2Y(1), P2Y(2), and P2Y(14) mRNA levels were highest for P2Y receptors, while in right atrium and SAN, P2Y(2) and P2Y(14) levels were highest, respectively. We extended these studies to investigate P2X(4) receptor mRNA in heart from rats with coronary artery ligation-induced heart failure. P2X(4) receptor mRNA was upregulated by 93% in SAN (P < 0.05), while a trend towards an increase was also observed in the right atrium and left ventricle (not significant). Thus, P2X(4)-mediated effects might be modulated in heart failure. mRNA for P2X(4-7) and P2Y(1,2,4,6,12-14), but not P2X(2,3) and P2Y(11), was detected in human right atrium and SAN. In addition, mRNA for P2X(1) was detected in human SAN but not human right atrium. In human right atrium and SAN, P2X(4) and P2X(7) mRNA was the highest for P2X receptors. P2Y(1) and P2Y(2) mRNA were the most abundant for P2Y receptors in the right atrium, while P2Y(1), P2Y(2), and P2Y(14) were the most abundant P2Y receptor subtypes in human SAN. This study shows a widespread distribution of P2 receptor mRNA in rat heart tissues but a more restricted presence and distribution of P2 receptor mRNA in human atrium and SAN. This study provides further direction for the elucidation of P2 receptor modulation of heart rate and contractility.

Vasoactivity of Rucaparib, a PARP-1 Inhibitor, is a Complex Process that Involves Myosin Light Chain Kinase, P2 Receptors, and PARP Itself

Therapeutic inhibition of poly(ADP-ribose) polymerase (PARP), as monotherapy or to supplement the potencies of other agents, is a promising strategy in cancer treatment. We previously reported that the first PARP inhibitor to enter clinical trial, rucaparib (AG014699), induced vasodilation in vivo in xenografts, potentiating response to temozolomide. We now report that rucaparib inhibits the activity of the muscle contraction mediator myosin light chain kinase (MLCK) 10-fold more potently than its commercially available inhibitor ML-9. Moreover, rucaparib produces additive relaxation above the maximal degree achievable with ML-9, suggesting that MLCK inhibition is not solely responsible for dilation. Inhibition of nitric oxide synthesis using L-NMMA also failed to impact rucaparib's activity. Rucaparib contains the nicotinamide pharmacophore, suggesting it may inhibit other NAD+-dependent processes. NAD+ exerts P2 purinergic receptor-dependent inhibition of smooth muscle contraction. Indiscriminate blockade of the P2 purinergic receptors with suramin abrogated rucaparib-induced vasodilation in rat arterial tissue without affecting ML-9-evoked dilation, although the specific receptor subtypes responsible have not been unequivocally identified. Furthermore, dorsal window chamber and real time tumor vessel perfusion analyses in PARP-1-/- mice indicate a potential role for PARP in dilation of tumor-recruited vessels. Finally, rucaparib provoked relaxation in 70% of patient-derived tumor-associated vessels. These data provide tantalising evidence of the complexity of the mechanism underlying rucaparib-mediated vasodilation.

P2Y1 purinergic receptors in sensory neurons: contribution to touch-induced impulse generation.

Somatic sensation requires the conversion of physical stimuli into the depolarization of distal nerve endings. A single cRNA derived from sensory neurons renders Xenopus laevis oocytes mechanosensitive and is found to encode a P2Y1 purinergic receptor. P2Y1 mRNA is concentrated in large-fiber dorsal root ganglion neurons. In contrast, P2X3 mRNA is localized to small-fiber sensory neurons and produces less mechanosensitivity in oocytes. The frequency of touch-induced action potentials from frog sensory nerve fibers is increased by the presence of P2 receptor agonists at the peripheral nerve ending and is decreased by the presence of P2 antagonists. P2X-selective agents do not have these effects. The release of ATP into the extracellular space and the activation of peripheral P2Y1 receptors appear to participate in the generation of sensory action potentials by light touch.