Meeting Abstract

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 inbalbr@bgu.ac.il

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.