Biomedical subjects

Geoffrey Burnstock

Publications and source records attributed to Geoffrey Burnstock.

At least 73 records · Page 4Linked to original sources

PubMed2004

Purinoceptor expression in regenerating skeletal muscle in the mdx mouse model of muscular dystrophy and in satellite cell cultures.

ATP is an important extracellular signaling molecule mediating its effects by activation of P2X and P2Y receptors. P2 receptors are expressed during muscle development, and recent findings demonstrate that ATP can regulate myoblast proliferation and differentiation in vitro. However, the role of purinergic signaling during regeneration of injured skeletal muscle has not been investigated. To examine this process in a clinically relevant system, we used the mouse model of muscular dystrophy (mdx), in which muscle degeneration is rapidly followed by regeneration. The latter process, in vivo muscle regeneration, was the focus of this study, and to study the cellular mechanisms involved in it, a parallel study on normal rat skeletal myoblast cultures was conducted. Using immunohistochemistry, RT-PCR, and electrophysiology, we investigated the expression of the P2X1-7 receptor subtypes and the P2Y1,2,4,6 receptors. Experiments in vitro and in vivo demonstrated the sequential expression of the P2X5, P2Y1, and P2X2 receptors during the process of muscle regeneration. The P2X5 and P2Y1 receptors were expressed first on activated satellite cells, and the P2Y1 receptor was also expressed on infiltrating immune cells. Subsequent P2X2 receptor expression on newly formed myotubes showed significant colocalization with AChRs, suggesting a role in regulation of muscle innervation. Thus, this study provides the first evidence for a role for purinergic signaling in muscle regeneration and raises the possibility of new therapeutic strategies in the treatment of muscle disease.

Adenosine Triphosphate↗

PubMed2004

Investigation of the effects of P2 purinoceptor ligands on the micturition reflex in female urethane-anaesthetized rats.

1 The effects of purinoceptor ligands for P2X1 and/or P2X3 receptors (alpha,beta-meATP, IP(5)I, TNP-ATP, MRS 2179, PPADS, Phenol red and RO116-6446/008; i.v., n=4-5) and for P2Y1 receptors (PPADS, MRS 2179 and MRS 2269; i.v., n=3-5) were investigated on the distension-evoked 'micturition reflex' in the urethane-anaesthetized female rat. 2 Alpha,beta-meATP (180 nmol kg(-1) min(-1)), IP5I (10, 30 and 100 nmol kg(-1)), TNP-ATP (1 micromol kg(-1)), MRS 2179 (1 micromol kg(-1)) and PPADS (17 micromol kg(-1)) each caused maintained bladder contractions to occur during the infusion of saline into the bladder. PPADS (17 micromol kg(-1) min(-1)) had a similar effect when infused intravesicularly. Regular bladder contractions were not observed until the infusion of saline was halted. For IP5I, TNP-ATP, MRS 2179 and PPADS, the magnitude of postinfusion isovolumetric contractions was significantly reduced and, for IP5I, this action was also associated with a significant reduction in urethral relaxation. Additionally, TNP-ATP caused a significant increase in the pressure and volume thresholds required to initiate a reflex. 3 Phenol red (a P2X1/P2X3 antagonist; 0.1 and 1 micromol kg(-1)) caused a significant increase in the pressure and volume thresholds required to initiate a reflex and, at the higher dose, also caused a reduction in postinfusion isovolumetric contractions. 4 RO116-6446/008 (a P2X1-selective antagonist; 1 and 10 micromol kg(-1)) only caused a reduction in postinfusion isovolumetric contractions. 5 It is concluded that P2X1 and P2X3 receptors play a fundamental role in the micturition reflex in urethane-anesthetized female rats. P2X3 receptor blockade raised the pressure and volume thresholds for the reflex, whereas P2X1 receptor blockade diminished motor activity associated with voiding. P2Y1 receptors may be involved in inhibition of rat detrusor tone.

Anesthesia↗

PubMed2004

P2X2 and P2X3 receptor expression in the gallbladder of the guinea pig.

We investigated for the first time, the distribution pattern of P2X2 and P2X3 receptors in the gallbladder of the guinea pig using immunohistochemistry. P2X2 and P2X3 receptor-immunoreactive nerve fibers were observed within the ganglia, in the interganglionic connectives, in the muscularis and in the paravascular plexus. Immunoreactivity for P2X2 and P2X3 was also observed in most neurons in the ganglionated plexus. Double-labeling studies revealed that 58.1% of all P2X2-positive neurons and 54.3% of all P2X3-positive neurons were found to display nitric oxide synthase. Over 90% of the neurons that were immunoreactive for P2X2 and P2X3 receptor were also immunoreactive for calretinin. We also found that 30.5% of P2X2- and 32.6% of P2X3-immunoreactive neurons were also immunoreactive for vasoactive intestinal peptide. No P2X2- or P2X3- immunoreactive neurons stained for calcitonin gene-related peptide; a few calcitonin gene-related peptide-immunoreactive nerve fibers also showed immunoreactivity to P2X2 or P2X3 receptors. These results further demonstrate the neurotransmitter diversity of the nerves of the gallbladder and provide an incentive for studies of the actions of these compounds in the gallbladder wall.

Animals↗

PubMed2004

Treatment with arimoclomol, a coinducer of heat shock proteins, delays disease progression in ALS mice.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative condition in which motoneurons of the spinal cord and motor cortex die, resulting in progressive paralysis. This condition has no cure and results in eventual death, usually within 1-5 years of diagnosis. Although the specific etiology of ALS is unknown, 20% of familial cases of the disease carry mutations in the gene encoding Cu/Zn superoxide dismutase-1 (SOD1). Transgenic mice overexpressing human mutant SOD1 have a phenotype and pathology that are very similar to that seen in human ALS patients. Here we show that treatment with arimoclomol, a coinducer of heat shock proteins (HSPs), significantly delays disease progression in mice expressing a SOD1 mutant in which glycine is substituted with alanine at position 93 (SOD1(G93A)). Arimoclomol-treated SOD1(G93A) mice show marked improvement in hind limb muscle function and motoneuron survival in the later stages of the disease, resulting in a 22% increase in lifespan. Pharmacological activation of the heat shock response may therefore be a successful therapeutic approach to treating ALS, and possibly other neurodegenerative diseases.

Amyotrophic Lateral Sclerosis↗

PubMed2004

P2X2 and P2X3 purinoceptors in the rat enteric nervous system.

Adenosine 5'-triphosphate receptors are known to be involved in fast excitatory postsynaptic currents in myenteric neurons of the digestive tract. In the present study, the distribution of P2X2 and P2X3 receptor mRNA was examined by in situ hybridisation while P2X2 and P2X3 receptor protein was localised by immunohistochemical methods. In addition, P2X2 and P2X3 receptors were colocalised with calbindin and calretinin in the myenteric and submucosal plexus. P2X2- and P2X3- immunoreactive neurons were found in the myenteric and submucosal plexuses throughout the entire length of the rat digestive tract from the stomach to the colon. Approximately 60%, 70% and 50% of the ganglion cells in the myenteric plexus of the gastric corpus, ileum and distal colon, and 56% and 45% in the submucosal plexus of the ileum and distal colon, respectively, showed positive immunoreactivity to the P2X2 receptor. Approximately 10%, 2% and 15% of the ganglion cells in the myenteric plexus of the gastric corpus, ileum and distal colon, and 62% and 40% in the submucosal plexus of the ileum and distal colon, respectively, showed positive immunoreactivity to the P2X3 receptor. Double-labelling studies showed that about 10-25% of the neurons with P2X2 immunoreactivity in myenteric plexus and 30-50% in the submucosal plexus were found to express calbindin or calretinin. About 80% of the neurons with P2X3 receptor immunoreactivity in the myenteric plexus and about 40% in the submucosal plexus expressed calretinin. Approximately 30-75% of the neurons with P2X3 receptor immunoreactivity in the submucosal plexus expressed calbindin, while none of them were found to express calbindin in the myenteric plexus.

Animals↗

PubMed2004

Cotransmission.

After some early hints, cotransmission was proposed in 1976 and the 'chemical coding' gradually established for sympathetic, parasympathetic, sensory-motor, enteric and some invertebrate nerves. More recently, cotransmission has been recognised in the central nervous system. ATP appears to be a primitive signalling molecule that has been retained as a cotransmitter in every nerve type in both peripheral and central nervous systems, although the relative role of ATP varies considerably in different species and pathological conditions. In the past two years, interest has focused on the mechanisms underlying cotransmission, plasticity and differential control of cotransmitter expression.

Adenosine Triphosphate↗

PubMed2004

Identification of P2X receptors in cultured mouse and rat parasympathetic otic ganglion neurones including P2X knockout studies.

We have used patch-clamp recording from cultured neurones, immunohistochemistry and gene deletion techniques to characterize the P2X receptors present in mouse otic ganglion neurones, and demonstrated the presence of similar receptors in rat neurones. All neurones from wild-type (WT) mice responded to ATP (EC(50) 109 microM), but only 38% also responded to alpha beta-meATP (EC(50) 39 microM). The response to alpha beta-meATP was blocked by TNP-ATP with an IC(50) of 38.6 nM. Lowering extracellular pH and co-application of Zn(2+) potentiated responses to ATP and alpha beta-meATP. In P2X(3)(-/-) mouse otic ganglion, all neurones tested responded to 100 microM ATP with a sustained current, but none responded to alpha beta-meATP. In P2X(2)(-/-) mice, no sustained currents were observed, but 36% of neurones responded to both ATP and alpha beta-meATP with transient currents. In P2X(2)/P2X(3)(Dbl-/-) mice, no responses to ATP or alpha beta-meATP were detected, suggesting that other P2X subunits were not involved. In rat otic ganglia, 96% of neurones responded to both ATP and alpha beta-meATP with sustained currents, suggesting a greater proportion of neurones expressing P2X(2/3) receptors. The maximum response to alpha beta-meATP was 40-60% of that evoked by ATP in the same cell. Immunohistochemistry revealed staining for P2X(2) and P2X(3) subunits in WT mouse otic ganglion neurones, which was absent in knockout animals. In conclusion, we have shown for the first time that at least two distinct P2X receptors are present in mouse and rat otic neurones, probably homomeric P2X(2) and heteromeric P2X(2/3) receptors.

Adenosine Triphosphate↗

PubMed2004

The effect of pregnancy and the oestrus cycle on purinergic and cholinergic responses of the rat urinary bladder.

The urinary bladder undergoes plastic changes during physiological alterations such as pregnancy. This study has shown that bladders from pregnant rats weighed three times more than bladders from virgin rats. Each milligram of detrusor muscle from pregnant rats contracted more strongly to nerve stimulation (150% greater) and agonists (50% greater or more) compared to detrusor from virgin rats at any stage during the oestrus cycle. The purinergic component of nerve-mediated responses altered during the oestrus cycle, being greatest during oestrus (oestrogen and progesterone fall rapidly) and dioestrus (low oestrogen and progesterone), smaller during pregnancy and even smaller during pro-oestrus (high oestrogen and progesterone); in contrast the cholinergic component remained relatively unchanged. In conclusion, during pregnancy the detrusor muscle generates larger contractions compared to virgin detrusor muscle, probably due to hormonal influences on smooth muscle contraction mechanisms. As agonist responses were unchanged during the oestrus cycle, changes in the purinergic component of nerve stimulation was not due to altered P2 receptor expression but possibly to an increase in ATP release or a reduction in breakdown. The hormonal effect may have implications for the treatment of bladder disorders due to alterations in hormones, such as stress incontinence in post-menopausal women.

Animals↗

PubMed2004

Activation of ureter nociceptors by exogenous and endogenous ATP in guinea pig.

This study was conducted to determine whether adenosine 5'-triphosphate (ATP) contributes to nociceptor activity induced by ureter distension. Multifibre recordings of ureter afferents were made using the guinea pig ureter preparation perfused in vitro. Distension of the ureter resulted in an initial rapid and later maintained increase in afferent nerve discharge. Intraluminal application of ATP (10-1000 microM, 0.1 ml/min for 3 min) or alpha,beta-meATP (10-1000 microM) mimicked these increases in afferent activity. The afferent responses consisted of fast and slow components. Both agonists caused a sensitisation of the afferents to ureter distensions. TNP-ATP (30 microm), a P2X3 receptor antagonist, and the non-specific P2 antagonist, PPADS (100 microm), blocked the rapid and reduced the slower response to ATP. The remaining responses were blocked by the selective A1 receptor antagonist, DPCPX. TNP-ATP and PPADS reduced distension-induced afferent activity. The selective ecto-ATPase inhibitor, ARL-67156 (100, 200 microM) and suramin (100, 200 microM), an ecto-nucleotidase inhibitor as well as a P2 receptor antagonist, produced an increase in baseline and distension-induced discharge. These results indicate that the ureter epithelium may tonically (at rest) as well as phasically (on distension) release ATP, which stimulates afferent terminals by interacting with multiple P2 and P1 receptors.

Adenosine Triphosphatases↗

PubMed2004

Varicose disease affects the P2 receptor-mediated responses of human greater saphenous vein.

The aim of the present study was to investigate in vitro the differences in P2 receptor mediated responses of human greater saphenous vein (GSV) taken from patients with varicose disease and obliterating atherosclerosis. Samples of the inguinal part of the GSV were taken from the patients who underwent phlebectomia operation due to varicose disease (n=9, VD group) or femoropoplitea bypass operation using auto-vein due to obliterating atherosclerosis of lower extremities (n=11, OA group). The mechanical responses of the isolated segments of GSV to P2 receptor agonists were tested using standard organ-bath technique. ATP (10(-6)-10(-4) M), ADP (10(-6)-10(-4) M) and alpha,betamethyleneATP (10(-8)-10(-5) M) caused concentration-dependent contractions of the veins of both groups, the latter agonist being approximately tenfold more active than first two. ATP at all concentrations tested, alpha,betamethyleneATP at concentrations of 10(-6) and 10(-5) M and ADP at a concentration of 10(-6) M produced significantly higher contractions of the GSV taken from OA group than from VD group. UTP (10(-6)-10(-4) M) caused concentration-dependent contractions of the veins taken from OA group, while in VD group this agonist was virtually without effect. Adenosine (10(-6)-10(-4) M) and 2-methylthio-ATP (10(-7)-10(-5) M) had no significant contractile activity in this tissue in both groups. It is concluded from this study that there are P2 receptor and adrenoceptor mediated contractions in human greater saphenous veins, which are impaired by varicose disease, in contrast to contractions produced by histamine and carbachol which are, if anything, enhanced.

Adenosine Diphosphate↗

PubMed2004

Cellular distribution and functions of P2 receptor subtypes in different systems.

This review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ?cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.

Animals↗

PubMed2004

Glomerular expression of the ATP-sensitive P2X receptor in diabetic and hypertensive rat models.

BACKGROUND: The molecular identification and characterization of the adenosine triphosphate (ATP)-sensitive family of P2 receptors is comparatively new. There are two main subgroups, each with several subtypes and widespread tissue distribution, including the kidney. A unique member of the P2X subgroup of P2 receptors is the ATP-gated ion channel P2X(7), which on activation can cause cell blebbing, cytokine release, and cell death by necrosis or apoptosis. We report expression of this receptor in normal rat kidney and in two chronic models of glomerular injury: streptozotocin-induced (STZ) diabetes and ren-2 transgenic (TGR) hypertension. METHODS: At different time points in these models, we used a polyclonal antibody to the P2X(7) receptor and immunohistochemistry to determine its expression and distribution. We also used Western blotting and real-time polymerase chain reaction (PCR) to detect changes in P2X(7) receptor protein and mRNA expression, respectively. RESULTS: We found only low-level glomerular immuno-staining for the P2X(7) receptor in normal rat kidney, but intense P2X(7) receptor immunostaining of glomeruli in kidneys from diabetic animals at 6 and 9 weeks, and in hypertensive animals at 12 weeks. In diabetic animals, real-time PCR demonstrated a approximately tenfold increase in glomerular P2X(7) receptor mRNA relative to control, and Western blotting confirmed an increase in protein. Immunohistochemistry and immunoelectron microscopy showed staining of glomerular podocytes, which was both intracellular and at the plasma membrane. CONCLUSION: We conclude that the P2X(7) receptor is not expressed appreciably under normal conditions, but that following glomerular injury it is significantly up-regulated, mainly in podocytes, though also in endothelial and mesangial cells, of animals with STZ-induced diabetes mellitus or TGR hypertension. Although the exact function and regulation of this receptor remain unclear, its association with inflammatory cytokine release and cell death suggests that increased expression might be involved in the pathogenesis of glomerular cell injury or repair.

Adenosine Triphosphate↗

PubMed2004

Geoffrey Burnstock: most highly cited scientist.

If you haven't taken the time to read up on purinergic signaling, consider this: of the ten most cited scientists in pharmacology for the past decade, no less than four work on biological responses to purines and related molecules(1). If you're surprised by this statistic, you're in good company: until a few weeks ago, the fact was also unknown to Geoffrey Burnstock, the single-most cited researcher on the list and the scientist who coined the term "purinergic nerves" in the early 70s. (He is also about to launch a new journal devoted to the discipline, Purinergic Signalling, as Editor-in-Chief ). At that time, Burnstock's depiction of ATP as an important neurotransmitter was met with considerable skepticism, even among those who otherwise accepted and studied the intracellular actions of purines. This year in June, Burnstock appeared at the Purines 2004 Meeting, appropriately enough, to deliver the "First Burnstock Lecture." Many of the symposia presenters openly acknowledged Burnstock's work in driving the purinergic field to its present state of fruition; this acknowledgment, along with the genuine affection that typically accompanies it, seems to surprise as much as it delights Burnstock, who remembers very well the many meetings where his results went hotly challenged. The following interview took place at Purines 2004 in Chapel Hill.

Adenosine Triphosphate↗

PubMed2004

Purinergic component of mechanosensory transduction is increased in a rat model of colitis.

ATP contributes to mechanosensory transduction in the rat colorectum. P2X3 receptors are present on dorsal root ganglia (DRG) neurons that supply this area of the gut. Previous studies have shown an increased role for ATP in inflamed tissues. We aimed to investigate whether an increased purinergic component exists during mechanosensory transduction in a rat model of colitis. An in vitro rat colorectal preparation was used to investigate whether distension increased ATP release and to evaluate the role of purinergic antagonists in distension-evoked sensory discharges in the pelvic nerve in normal and colitis preparations. DRG neuron purinoceptors were also studied. Distension-evoked responses in the colitis model were attenuated to a significantly greater extent by 2',3'-O-trinitrophenyl-ATP and pyridoxyl 5-phosphate 6-azophenyl-2',4'-disulfonic acid. Inflammation caused augmented distension-evoked sensory nerve excitation after application of ATP and alpha,beta-methylene ATP. Single-fiber analysis confirmed that mean firing per unit was increased. Distension-evoked increases in ATP release from epithelial cells were substantially higher. The number of DRG neurons responding to ATP and the number of those staining for the P2X3 receptor, particularly those containing calcitonin gene-related peptide, were increased. Adenosine, after ectoenzymatic breakdown of ATP, is involved to a lesser degree in the longer-lasting distension-evoked sensory discharge, suggesting reduced ATPase activity. It was therefore concluded that ATP has an enhanced role in mechanosensory transduction in the inflamed rat colorectum. The underlying mechanisms appear to involve increased distension-evoked release of ATP as well as an increase in the number of DRG neurons supplying the colorectum expressing P2X3 receptors, especially those containing calcitonin gene-related peptide.

Adenosine Triphosphate↗

PubMed2004

Purinergic signalling to rat ovarian smooth muscle: changes in P2X receptor expression during pregnancy.

The expression of P2X and P2Y receptor subtypes in the smooth muscle of the rat ovary during the oestrus cycle and pregnancy was examined using immunohistochemistry. RT-PCR studies of P2X receptor mRNA were also carried out. In the non-pregnant rats, P2X2 receptor protein was dominant in the smooth muscle of perifollicular rings and blood vessels. P2X1 protein expression was seen on vascular smooth muscle too, but little, if any, was present on perifollicular smooth muscle. No changes in P2X1 or P2X2 receptor expression were seen during the oestrous cycle. During early and mid-late pregnancy, there was a switch from P2X2 to P2X1 receptor protein expression in the smooth muscle of the perifollicular ring; P2X1 receptors were also more prominently expressed than P2X2 receptors on ovarian vascular smooth muscle in non-pregnant animals, but during late pregnancy the expression of P2X2 receptors was found to equal that of the P2X1 receptors. There was a return to non-pregnant P2 receptor subtype distribution 2 days after birth. Ovarian vascular and perifollicular smooth muscle showed immunoreactivity for P2Y1, but not for P2X3-7, P2Y2 or P2Y4 receptors. P2Y1 receptor expression in ovarian smooth muscle of both blood vessels and follicular rings did not show significant changes during the oestrus cycle or pregnancy. RT-PCR studies indicated that P2X1 and P2X2 receptor mRNA was present in the ovary during pregnant and non-pregnant conditions. P2X4-6 receptor mRNA was also present in all stages studied, however no immunostaining showing receptor protein for these subtypes was seen on the ovarian sections examined. In summary, purinergic signalling to ovarian perifollicular smooth muscle changed from P2X2 to P2X1 receptors during pregnancy, while there was an increase in P2X2 receptor expression on vascular smooth muscle.

Amino Acid Sequence↗

PubMed2004

Levels of gap junction proteins in coronary arterioles and aorta of hamsters exposed to the cold and during hibernation and arousal.

There are marked changes in vascular dynamics during prolonged periods in the cold, entrance into hibernation, and arousal to euthermy. Cell-to-cell communication through gap junction channels plays a pivotal role in the control of vasomotor function. Multiple gap junction proteins are expressed in blood vessels, including connexins 37 (Cx37), 40 (Cx40), 43 (Cx43), and 45 (Cx45). Using immunolabeling techniques combined with confocal microscopy, we quantitated the levels of these connexins in coronary arterioles and the thoracic aorta of the golden hamster in four physiological conditions: normal control animals at euthermy; cold-exposed animals (before entrance into hibernation); during hibernation; and after 2-hr arousal from hibernation. In all groups, Cx37 was localized between endothelial cells of the aorta and Cx40 was observed between endothelial cells of coronary arterioles and the aorta. Cx43 was confined to smooth muscle cells of the aorta. Labeling for Cx45 was detected in the endothelium of the ascending aorta. The expression of Cx37 was significantly reduced in cold-exposed, hibernating, and aroused animals. Immunolabeling for Cx40 was increased in the coronary arteriolar endothelium of the cold-exposed group compared with normal controls, hibernating, and aroused animals, perhaps to facilitate intercellular communication during the prolonged circulatory changes to vascular dynamics required to maintain core temperature during cold adaptation. Cx40 expression was unchanged in the aorta. Cx43 immunoexpression in the aorta remained constant under all conditions examined. These changes in connexin expression did not occur during the rapid circulatory changes associated with arousal from hibernation.

Animals↗

PubMed2004

Introduction: P2 receptors.

The current status of ligand gated ion channel P2X and G protein-coupled P2Y receptor subtypes is described. This is followed by a summary of what is known of the distribution and roles of these receptor subtypes. Potential therapeutic targets of purinoceptors are considered, including those involved in cardiovascular, nervous, respiratory, urinogenital, gastrointestinal, musculo-skeletal and special sensory diseases, as well as inflammation, cancer and diabetes. Lastly, there are some speculations about future developments in the purinergic signalling field.

Animals↗

PubMed2003

Pivotal role of nucleotide P2X2 receptor subunit of the ATP-gated ion channel mediating ventilatory responses to hypoxia.

In mammals, the ventilatory response to decreased oxygen tension in the arterial blood is initiated by excitation of specialized O2-sensitive chemoreceptor cells in the carotid body that release neurotransmitters to activate endings of the sinus nerve afferent fibers. We investigated the role of ATP acting via ionotropic P2X receptors in the carotid body function and ventilatory response to hypoxia in mice. Mice deficient in P2X2 receptor subunit showed a markedly attenuated ventilatory response to hypoxia, whereas the response to hypoxia in P2X3-deficient mice was comparable with that seen in wild-type controls. P2X2 and P2X3 receptor subunit deficiency did not affect the ventilatory responses to hypercapnia. P2X2 subunit deficiency resulted in a dramatic reduction in the responses of the carotid sinus nerve to hypoxia in the in vitro carotid body-sinus nerve preparation. ATP and its stable analog alpha,beta-methyleneATP both evoked rapid excitation of sinus nerve afferents, and the P2 receptor antagonist PPADS (pyridoxal-5'-phosphate-6-azophenyl-2',4'-disulphonic acid) (100 microm) blocked hypoxia-induced increase in sinus nerve discharge. Immunoreactivities for P2X2 and P2X3 subunits were both detected on afferent terminals surrounding clusters of glomus cells in the wild-type animals but were absent in mice deficient in P2X2 and P2X3 receptor subunits. These observations provide the first definitive evidence that, in the carotid body, ATP is a key transmitter released by chemoreceptor cells to activate endings of the sinus nerve afferent fibers. We conclude that P2X receptors containing the P2X2 subunit play a pivotal role in carotid body function and in mediating ventilatory responses to hypoxia.

Action Potentials↗