PLASTICITY OF THE PROPERTIES OF MITOCHONDRIA FROM RAINBOW-TROUT RED MUSCLE WITH SEASONAL ACCLIMATIZATION

Cold-acclimation of rainbow trout brings only limited changes in muscl e metabolic capacities, but marked modifications in membrane compositi on. Thus, we examined whether the functional properties of mitochondri a from trout red muscle were modified by seasonal temperature acclimat ization. Mitochondria from fall-acclimatized trout had higher maximal capacities (state 3 rates) for the oxidation of pyruvate and acyl carn itines at 12 and 20 degrees C than mitochondria isolated from summer-a cclimatized trout. For these substrates, the increased oxidative capac ity completely compensated for the seasonal drop in temperature. Pyruv ate and palmitoyl carnitine were consistently the preferred substrates , while decanoyl and octanoyl carnitine were oxidized at higher rates than glutamine, particularly in fall trout. State 4 rates of oxygen up take (obtained when all ADP has been converted to ATP) differed less a mong substrates, but varied seasonally. State 4 rates at 12 and 20 deg rees C were higher in mitochondria isolated from fall than summer trou t. At low temperatures, the Q(10) of both maximal and state 4 rates of substrate oxidation tended to be higher for mitochondria from fall tr out. The apparent Arrhenius activation energy (E-a) for mitochondrial pyruvate oxidation was higher in fall than summer trout whereas the E- a's for palmitoyl carnitine and decanoyl carnitine oxidation did not c hange. The fatty acids of mitochondrial phospholipids from fall trout were more polyunsaturated than those from summer trout, with 12% more double bonds occurring than in summer trout, suggesting that membrane restructuring may be involved in the observed compensatory responses.