Role of adenosine A _2A receptors in the respiratory adjustments in response to 2 hours of sustained hypoxia in mice

The initial period of hypoxic challenges is critical for adjustments in the respiratory neural network in order to keep the partial pressure of oxygen in the arterial blood within the physiological range. In this context, A 2A receptors are important players in mediating adenosine actions during hypoxia due to their expression in neurons involved in generation and modulation of respiratory function. In previous studies performed in awake condition, we verified that adenosine A 2A receptors knockout (A 2A KO) mice presented a baseline respiratory frequency significantly higher than Balb/c wild type (WT). In response to 24 hours of sustained hypoxia (SH) the baseline respiratory frequency increased in WT but not in A 2A KO mice, indicating the involvement of these receptors in the modulation of the baseline respiratory frequency. In the present study we evaluated the impact of 2 hours of SH (2h-SH) on the frequency of phrenic nerve discharge (PND) and on the incidence of active expiration (Late-E) in WT and A 2A KO mice in response to hypercapnic challenge (10% CO 2 ). To reach this goal, the frequency of PND and the incidence of Late-E in the abdominal nerve (AbN) were recorded during baseline condition and in response to activation of CO 2 /H + sensors by hypercapnic challenge in mice previously exposed to 2h-SH (FiO 2 : 0.10). The PND and AbN activities of WT and A 2A KO mice (6-8 weeks old) were assessed using the in situ working heart-brainstem preparation. Data are expressed as mean and standard deviation (mean ± SD) and were analyzed by two-way ANOVA followed by Bonferroni's post-test. The institutional ethical committee approved the experimental protocols (CEUA #070/2021). The baseline PND of A 2A KO mice was significantly higher than WT in both normoxia (WT: 0.26 ± 0.09 Hz, n = 8; A 2A KO: 1.57 ± 0.73 Hz, n = 9, p<0.0001) and 2h-SH condition (WT: 0.32 ± 0.20 Hz, n = 7; A 2A KO: 1.59 ± 0.46, n = 8, p<0.0001), indicating that the baseline PND in WT is modulated by A 2A receptors. Hypercapnia produced no significant change in PND in WT in both normoxia (PND in 10% CO 2 = 0.33 ± 0.12 Hz, n = 9; PND in 5% CO 2 = 0.26 ± 0.09 Hz, n = 8) and 2h-SH (PND in 10% CO 2 = 0.22 ± 0.14 Hz, n = 7; PND in 5% CO 2 = 0.32 ± 0.20 Hz, n = 7). The incidence of Late-E events of AbN in response to hypercapnia was observed only in normoxia WT, indicating that the incidence of Late-E was reduced in response to 2h-SH in both WT and A 2A KO mice. In summary, our data demonstrate that A 2A receptors modulate the baseline respiratory frequency and that the incidence of active expiration (Late-E) was reduced 2h-SH. We conclude that adenosine A 2A receptors plays a critical role in modulating the baseline respiratory frequency and apparently are not involved in the reduction in the incidence of active expiration in response to hypercapnia in mice previously exposed to 2h-SH. FAPESP (2018/15957-2, 2024/06385-6) and CNPQ (309338/2020-4). This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.