PLASTICITY OF FISH MUSCLE MITOCHONDRIA WITH THERMAL-ACCLIMATION

Short-horned sculpin Myoxocephalus scorpius were acclimated to 5 and 1 5 degrees C to evaluate the impact of thermal acclimation upon maximal rates of substrate oxidation by mitochondria and upon the thermal sen sitivity of their ADP affinity, Cold acclimation virtually doubled max imal rates of pyruvate oxidation at all experimental temperatures (2.5 , 7.5, 12.5 and 20 degrees C). Rates of palmitoyl carnitine oxidation were also enhanced by cold acclimation, but to a lesser degree. At the ir respective acclimation temperatures, the mitochondria attained simi lar rates of pyruvate oxidation. For warm-acclimated sculpin, the Q(10 ) values for mitochondrial pyruvate and palmitoyl carnitine oxidation were higher between 2.5 and 7.5 degrees C than between 7.5 and 12.5 de grees C or between 12.5 and 20 degrees C. In contrast, for cold-acclim ated fish, the Q(10) values did not differ over these thermal ranges. The Arrhenius activation energy for pyruvate oxidation was reduced by cold acclimation (from 70 to 55 kJ mol(-1)), whereas that for palmitoy l carnitine oxidation was unchanged (approximately 75 kJ mol(-1)). Col d acclimation did not alter the ADP affinity of mitochondria at low te mperatures but markedly increased the apparent K-m for ADP (K-m,K-app) at 12.5 and 20 degrees C. At the acclimation temperatures, mitochondr ial ADP K-m,K-app values did not differ. The loss of ADP affinity at h igher temperatures may represent a cost of the enhanced maximal oxidat ive capacity achieved during cold acclimation.