Developmental Changes in the Interaction Between P2 and P1 Receptors Determines the Effects of ATP on the preBötzinger Complex Inspiratory Network
Authors: Reklow Robert J. , Funk Gregory D. 
Published: November 2023

Acute exposure to moderate hypoxia evokes a biphasic ventilatory response, comprising an initial increase in ventilation followed by a secondary depression. The initial increase is primarily attributed to activation of the peripheral chemoreceptors while the secondary depression is primarily central in origin. The hypoxic depression is much greater in premature infants compared to adults and is implicated in apnea of prematurity, cardiovascular disease accompanying obstructive sleep apnea and SUDEP (sudden unexplained death in epilepsy). Thus, there is significant interest in understanding the mechanisms that determine the time course and magnitude of the hypoxic respiratory depression. In rats, hypoxia evokes the release of ATP from astrocytes in the preBötzinger Complex (preBötC), which acts via P2Y1 receptors to attenuate the respiratory depression. However, ATP is rapidly broken down into adenosine (ADO), which, through its actions at the A1 subtype of ADO (P1) receptors, is hypothesized to underlie the respiratory depression. The objective of this study is to determine during postnatal development how the inhibitory actions of A1 receptors and the excitatory actions of P2Y1 receptors interact to shape the response of the preBötC to ATP. We prepared rhythmically‐active medullary slices from mice ranging in age from postnatal day 0–12 (P0–P12), and assessed developmental changes in the effects on inspiratory rhythm of locally microinjecting purinergic agonists and antagonists into the preBötC.ADO (500 μM, 30 s) evoked an approximate 30% decrease in inspiratory‐related frequency that was similar between P0 and P12. The P2Y1 receptor agonist MRS2365 (100 μM, 10 s) evoked an approximate 2.5‐fold increase in inspiratory‐related frequency that was also similar between P0‐12. We then assessed developmental changes in the interaction between P2Y1 and A1 receptor signaling by comparing the effects of locally microinjecting ATP (100 μM, 10 sec) alone and after application of the A1 receptor antagonist, DPCPX (2 μM, 90 s). ATP applied alone will activate P2 as well as P1 receptors due to its hydrolysis to ADO. Application of ATP after DPCPX reveals only the effects of P2Y1 receptor activation. ATP elicited a 50–90% increase in inspiratory‐related frequency that was constant between P0 and P12. However, when applied following DPCPX in P0–P3 mice, ATP caused a 2.5‐fold increase in inspiratory‐related frequency. When applied after DPCPX in P9–P11 mice, the effects of ATP were only marginally enhanced compared to ATP alone. These data indicate that in newborn mice the influence of A1 receptors on the ATP response is much greater than in juveniles. This observation, combined with the fact that the efficacy of P2Y1 and A1 receptors is similar over this time frame suggests either that the hydrolysis of ATP to ADO by ectonucleotidases is faster in newborns, or that the clearance of extracellular ADO by equilibrative nucleoside transporters (and ADO kinase) is much slower in newborns. Understanding the factors that determine the balance between P2Y1 and A1 receptor actions through development will provide key information for the development of purinergic strategies to counteract the hypoxic respiratory depression.Support or Funding InformationCIHR, NSERC, WCHRI, AIHS, CFI.