P2 receptors modulate respiratory rhythm but do not contribute to central CO2 sensitivity in vitro

161

163

P2X 2 receptor subunits of the ATP-gated ion channels are expressed by physiologically identified respiratory neurons in the ventral respiratory column, implicating ATP in the control of respiratory activity. We now show that, during hypoxia, release of ATP in the ventrolateral medulla (VLM) plays an important role in the hypoxic ventilatory response in rats. By measuring ATP release in real time at the ventral surface of the medulla with novel amperometric biosensors, we found that hypoxia (10% O 2 ; 5 min) induced a marked increase in the concentration of ATP (ϳ3 M). This ATP release occurred after the initiation of enhanced respiratory activity but coincided with the later hypoxia-induced slowing of the respiratory rhythm. ATP was also released at the ventral surface of the medulla during hypoxia in peripherally chemodenervated animals (vagi, aortic, and carotid sinus nerve sectioned). By using horizontal slices of the rat medulla, we found that, during hypoxia, ATP is produced throughout the VLM in the locations corresponding to the ventral respiratory column. Blockade of ATP receptors in the VLM (microinjection of P2 receptor antagonist pyridoxal-5Ј-phosphate-6-azophenyl-2Ј,4Ј-disulphonic acid; 100 M) augmented the hypoxia-induced secondary slowing of the respiratory rhythm. Our findings suggest that ATP released within the ventral respiratory column is involved in maintenance of the respiratory activity in conditions when hypoxia-induced slowing of respiration occurs. These data illustrate a new functional role for ATP-mediated purinergic signaling in the medullary mechanisms controlling respiratory activity.

Section: Release Of Atp In the Ventral Medulla During Hypoxia In Ratsmentioning

confidence: 98%

Section: Release Of Atp In the Ventral Medulla During Hypoxia In Ratsmentioning

confidence: 99%

Release of ATP in the Ventral Medulla during Hypoxia in Rats: Role in Hypoxic Ventilatory Response

Gourine

Llaudet²,

Dale³

et al. 2005

161

163

“…Factors underlying these differences are not known. In vivo effects may represent depolarization block because 10 mM ATP also arrests rhythm in vitro (Lorier et al, 2004). However, it may also reflect development of purinergic signaling (Collo et al, 1996;Kanjhan et al, 1999;Brosenitsch et al, 2005) in neurons and glia that contribute to ATP responses (Fields and Burnstock, 2006) but are immature at birth (Liu et al, 2002).…”

Section: Activation Of P2rs In the Prebötc Increases Inspiratory Freqmentioning

confidence: 99%

“…In the adult rat in vivo, ATP increases the discharge of brainstem respiratory neurons but blocks phrenic nerve output causing apnea Gourine et al, 2005b). In the neonatal rat in vitro, ATP increases respiratory frequency (Lorier et al, 2002(Lorier et al, , 2004. However, comparison is difficult because the site(s) of drug action were poorly defined, and the experimental conditions and models (adults in vivo vs neonates in vitro) differed.…”

Section: Introductionmentioning

confidence: 99%

P2Y₁Receptor Modulation of the Pre-Bötzinger Complex Inspiratory Rhythm Generating NetworkIn Vitro

Lorier¹,

Huxtable²,

Robinson³

et al. 2007

154

ATP is released during hypoxia from the ventrolateral medulla (VLM) and activates purinergic P2 receptors (P2Rs) at unknown loci to offset the secondary hypoxic depression of breathing. In this study, we used rhythmically active medullary slices from neonatal rat to map, in relation to anatomical and molecular markers of the pre-Bötzinger complex (preBötC) (a proposed site of rhythm generation), the effects of ATP on respiratory rhythm and identify the P2R subtypes responsible for these actions. Unilateral microinjections of ATP in a three-dimensional grid within the VLM revealed a "hotspot" where ATP (

“…In the brainstem, recent data highlight the importance of P2R signaling for respiratory control. Neurons of brainstem respiratory nuclei, putative rhythmogenic neurons of the preBötzinger complex (preBötC) [proposed site of inspiratory rhythm generation (Smith et al, 1991)], and respiratory motoneurons express P2Rs and are sensitive to their activation (Funk et al, 1997;Yao et al, 2000;Miles et al, 2002;Lorier et al, 2004Lorier et al, , 2007Lorier et al, , 2008. ATP contributes to central respiratory responses to hypercapnia through P2Rs on the ventral medullary surface (Gourine et al, 2005b) and the biphasic hypoxic ventilatory response by partially offsetting the secondary respiratory depression (Gourine et al, 2005a).…”

Section: Introductionmentioning

confidence: 99%

Tripartite Purinergic Modulation of Central Respiratory Networks during Perinatal Development: The Influence of ATP, Ectonucleotidases, and ATP Metabolites

Huxtable¹,

Zwicker²,

Poon³

et al. 2009

ATP released during hypoxia from the ventrolateral medulla activates purinergic receptors (P2Rs) to attenuate the secondary hypoxic depression of breathing by a mechanism that likely involves a P2Y 1 R-mediated excitation of preBötzinger complex (preBötC) inspiratory rhythm-generating networks. In this study, we used rhythmically active in vitro preparations from embryonic and postnatal rats and ATP microinjection into the rostral ventral respiratory group (rVRG)/preBötC to reveal that these networks are sensitive to ATP when rhythm emerges at embryonic day 17 (E17). The peak frequency elicited by ATP at E19 and postnatally was the same (ϳ45 bursts/min), but relative sensitivity was threefold greater at E19, reflecting a lower baseline frequency (5.6 Ϯ 0.9 vs 19.0 Ϯ 1.3 bursts/min). Combining microinjection techniques with ATP biosensors revealed that ATP concentration in the rVRG/preBötC falls rapidly as a result of active processes and closely correlates with inspiratory frequency. A phosphate assay established that preBötC-containing tissue punches degrade ATP at rates that increase perinatally. Thus, the agonist profile [ATP/ADP/adenosine (ADO)] produced after ATP release in the rVRG/preBötC will change perinatally. Electrophysiology further established that the ATP metabolite ADP is excitatory and that, in fetal but not postnatal animals, ADO at A 1 receptors exerts a tonic depressive action on rhythm, whereas A 1 antagonists extend the excitatory action of ATP on inspiratory rhythm. These data demonstrate that ATP is a potent excitatory modulator of the rVRG/preBötC inspiratory network from the time it becomes active and that ATP actions are determined by a dynamic interaction between the actions of ATP at P2 receptors, ectonucleotidases that degrade ATP, and ATP metabolites on P2Y and P1 receptors.