WORKING UNDERGROUND - RESPIRATORY ADAPTATIONS IN THE BLIND MOLE-RAT

Mole rats (Spalax ehrenbergi superspecies) perform the heavy work of d igging their subterranean burrows in Israel under highly hypoxic/hyper capnic conditions, Unlike most other mammals, they can achieve high le vels of metabolic rate under these conditions, while their metabolic r ate at low work rates is depressed, We explored, by comparing mole rat s with white rats,whether and holy this is related to adaptations in t he design of the respiratory system, which determines the transfer of O-2 from the lung to muscle mitochondria, At the same body mass, mole rats were found to have a significantly smaller total skeletal muscle mass than ordinary white rats (-22%), In contrast, the fractional volu me of muscle mitochondria was larger by 46%, As a consequence, both sp ecies had the same total amount of mitochondria and achieved, under no rmoxia, the same V-O2max. Whereas the O-2 transport capacity of the bl ood was not different, we found a larger capillary density (+31%) in t he mole rat muscle, resulting in a reduced diffusion distance to mitoc hondria, The structural pulmonary diffusing capacity for Oz was greate r in the mole rat (+44%), thus facilitating Oz uptake in hypoxia. We c onclude that structural adaptations in lung and muscle tissue improve O-2 diffusion conditions and serve to maintain high metabolic rates in hypoxia but have no consequences for achieving V-O2max under normoxic conditions.