Figure 1. Respiratory responses to hypercapnia and hypoxia in mice with selective deletion of genes encoding P2X₂ and P2X₃ receptor subunits.

A, changes in ventilation during hypercapnia (3 and 6% CO₂ in the inspired air) in conscious P2X₂ and P2X₃ receptor double knockout (P2X_2/3^Dbl−/−) and wildtype (P2X_2/3^Dbl+/+) mice. B, changes in ventilation during hypoxia (15, 10 and 7.5% O₂ in the inspired air) in conscious P2X_2/3^Dbl−/− and P2X_2/3^Dbl+/+ mice. The resting ventilation during normocapnia/normoxia was identical in the wildtype and knockout animals. The ventilatory response to hypoxia in the P2X₃^−/− mice was not significantly different from that in P2X₃^+/+ mice, while in the P2X₂^−/− mice it was markedly reduced and was similar to that in the P2X_2/3^Dbl−/−. V_E, minute ventilation (respiratory rate × tidal volume). Data are presented as means ± s.e.m. Numbers in parentheses indicate sample sizes. *Significant difference, P < 0.05. Data redrawn with permission from Rong et al. (2003). Copyright 2003 by the Society for Neuroscience.