Fossorial giant Zambian mole-rats have blunted ventilatory responses to environmental hypoxia and hypercapnia.

Fossorial giant Zambian mole-rats are believed to live in a hypoxic and hypercapnic subterranean environment but their physiological responses to these challenges are entirely unknown. To investigate this, we exposed awake and freely-behaving animals to i) 6 h of normoxia, ii) acute graded normocapnic hypoxia (21, 18, 15, 12, 8, and 5% O, 0% CO, balance N; 1 h each), or iii) acute graded normoxic hypercapnia (0, 2, 5, 7, 9, and 10% CO, 21% O, balance N; 1 h each), followed by a 1 h normoxic normocapnic recovery period, while non-invasively measuring ventilation, metabolic rate, and body temperature (T). We found that these mole-rats had a blunted hypoxic ventilatory response that manifested at 12% inhaled O, a robust hypoxic metabolic response (up to a 68% decrease, starting at 15% O), and decreased T (at or below 8% O). Upon reoxygenation, metabolic rate increased 52% above normoxic levels, suggesting the paying off of an O debt. Ventilation was less sensitive to environmental hypercapnia than to environmental hypoxia and animals also exhibited a blunted hypercapnic ventilatory response that did not manifest below 9% inhaled CO. Conversely, metabolism and T were not affected by hypercapnia. Taken together, these results indicate that, like most other fossorial rodents, giant Zambian mole-rats have blunted hypoxic and hypercapnic ventilatory responses and employ metabolic suppression to tolerate acute hypoxia. Blunted physiological responses to hypoxia and hypercapnia likely reflect the subterranean lifestyle of this mammal, wherein intermittent but severe hypoxia and/or hypercapnia may be common challenges.