HEART MITOCHONDRIAL PROPERTIES AND AEROBIC CAPACITY ARE SIMILARLY RELATED IN A MAMMAL AND A REPTILE

The heart mitochondrial properties and the aerobic capacity (VO2max) o f the rat (Sprague-Dawley breed) and the Cuban iguana (Cyclura nubila) were used to evaluate the relationship between the oxidative capacity of the heart and the maximum oxygen delivery rate, Both species are a ctive at body temperatures of 37-39 degrees C, have similar heart mito chondrial volumes [V-mt; 0.43+/-0.02 ml (S.E.M.) in the rat and 0.48+/ -0.02 ml in the iguana] and differ less than twofold in V-O2max (29.2/-1.6 and 16.9+/-0.6 ml min(-1), respectively), We found that V-mt was closely correlated with VO2max in the rat (r(2)=0.77, P<0.005) and th e iguana (r(2)=0.82; P<0.001). Furthermore, the inner mitochondrial me mbrane (cristae) area (S-im) per unit VO2max did not differ between th e rat and the iguana (0.60+/-0.02 and 0.71+/-0.02 m(2) min ml(-1) O-2, respectively), This correspondence of S-im/VO2max indicates that the rat and the iguana have the same cardiac oxidative capacity at the max imum oxygen delivery rate, These results suggest that, despite the dif ferences between the cardiovascular systems of these species, the card iac cost of delivering oxygen at the aerobic capacity is similar in th is mammal and this reptile.