21.1 Wednesday, Jan. 4 Burrowing rodents are not necessarily tolerant of hypercapnia BRICKNER-BRAUN, I*; PINSHOW, B; Ben-Gurion University of the Negev, Jacob Blaustein Institutes for Desert Research; Ben-Gurion University of the Negev, Jacob Blaustein Institutes for Desert Research email@example.com
Burrow geometry, coupled with low permeability of soils to gases, and the respiration of its tenant(s), are assumed to generate fractional concentrations of CO2 (FCO2) and O2 (FO2), respectively above and below those in the free atmosphere. In mammals, breathing air containing high FCO2 is likely to cause respiratory acidosis. Thus, burrow-dwelling rodents are generally presumed to be adapted to hypercapnic and/or hypoxic conditions. Assuming that burrowing rodents are in fact hypercapnia-tolerant, we examined the physiological responses of a semi-fossorial rodent, Meriones crassus to changes in inspired FCO2. First, we measured O2 uptake (VO2) of 6 female M. crassus that were exposed to gradually changing FCO2, from 0.04% CO2 (atmospheric) to 1, 2, 4 and 7%, and again to 0.04%. Then, VO2 was measured while M. crassus were exposed to a step change, from 0.04% CO2 to 7%, and back to 0.04%. Second, blood samples of 13 M. crassus were equilibrated in a tonometer to each of 4 humidified gas mixtures, simulating arterial and venous blood in animals breathing fresh or high FCO2 air, and blood [H+] was determined. We found that M. crassus pay a significant energetic price if FCO2 rises above that of atmospheric air; VO2 of M. crassus breathing 7% CO2 averaged 23% higher than when breathing fresh air. The [H+] of mixed venous and arterial blood equilibrated to high FCO2 were respectively 26.73 ± 4.95 and 27.27 ± 7.04 nmol/l higher than the [H+] of mixed venous and arterial blood equilibrated to “normal” (5%) PCO2 (p < 0.01). Since M. crassus are apparently not especially adapted to breathing air with high FCO2, we question the assumption that burrowing rodents are generally hypercapnia-tolerant.