ATP sensitivity of preBötzinger complex neurones in neonatal rat in vitro: mechanism underlying a P2 receptor‐mediated increase in inspiratory frequency

Abstract

P2 receptor (R) signalling plays an important role in the central ventilatory response to hypoxia. The frequency increase that results from activation of P2Y 1 Rs in the preBötzinger complex (preBötC; putative site of inspiratory rhythm generation) may contribute, but neither the cellular nor ionic mechanism(s) underlying these effects are known. We applied whole-cell recording to rhythmically-active medullary slices from neonatal rat to define, in preBötC neurones, the candidate cellular and ionic mechanisms through which ATP influences rhythm, and tested the hypothesis that putative rhythmogenic preBötC neurones are uniquely sensitive to ATP. ATP (1 mM) evoked inward currents in all non-respiratory neurones and the majority of respiratory neurons, which included inspiratory, expiratory and putative rhythmogenic inspiratory neurones identified by sensitivity to substance P (1 μM) and DAMGO (50 μM) or by voltage-dependent pacemaker-like activity. ATP current densities were similar in all classes of preBötC respiratory neurone. Reversal potentials and input resistance changes for ATP currents in respiratory neurones suggested they resulted from either inhibition of a K + channel or activation of a mixed cationic conductance. The P2YR agonist 2MeSADP (1 mM) evoked only the latter type of current in inspiratory and pacemaker-like neurones. In summary, putative rhythmogenic preBötC neurones were sensitive to ATP. However, this sensitivity was not unique; ATP evoked similar currents in all types of preBötC respiratory neurone. The P2Y 1 R-mediated frequency increase is therefore more likely to reflect activation of a mixed cationic conductance in multiple types of preBötC neurone than excitation of one, highly sensitive group.

Glia Contribute to the Purinergic Modulation of Inspiratory Rhythm-Generating Networks

“…The first, after 90 min incubation in MSO (0.1 mM) and restoration of rhythm with GLN (1.5 mM) and the second, after adding TTX (0.5 M), CNQX (10 M), and APV (100 M) to the bath to block synaptic transmission and glutamatergic receptors. We demonstrated, as expected based on data from Lorier et al (2008), that the neurons responded to ATP under both conditions, i.e., that neuronal ATP currents are not dependent on glutamate release from glia. As shown for a single inspiratory neuron (defined by the presence of synaptic currents in phase with rhythmic ͐XII activity) in Figure 4, D and E, ATP (1 mM, 10 s) evoked a current in MSO/GLN that was similar following bath application of TTX, CNQX, and APV.…”

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

“…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).…”

Mecanismos purinérgicos no bulbo ventrolateral rostral modulam respostas cardiovasculares e respiratórias promovidas pela ativação dos quimiorreceptores centrais e periféricos.

“…Of these, P2Y1 receptors have been shown to function as the primary substrate for ATP-mediated activation of inspiratory neurons in the preBötzinger complex (Lorier et al 2007(Lorier et al , 2008, a region critically involved in inspiratory rhythm generation (Smith et al 1991). Therefore, we considered the possibility that P2Y1 receptors also contribute to up-stream purinergic modulation of CO 2 /H + -sensitive RTN neurons.…”

“…Não podemos descartar a participação de outros receptores P2Y, pois resultados recentes mostraram que os receptores P2Y são os receptores purinérgicos mais abundantes na região do Complexo de Pré-Botzinger e medeiam as respostas respiratórias produzidas pelo ATP (FUNK, 2013;LORIER et al, 2007LORIER et al, , 2008.…”

“…n = 6 ratos. (GOURINE et al, 2005a; BAYLISS, 2015; MOREIRA et al, 2015;SOBRINHO et al, 2014; LOESCHCKE, 1979; LAZARENKO et al, 2011; TAKAKURA et al, 2008; (FUNK, 2013;LORIER et al, 2007LORIER et al, , 2008. …”