LIVER ENERGY-METABOLISM DURING HIBERNATION IN THE GOLDEN-MANTLED GROUND-SQUIRREL, SPERMOPHILUS-LATERALIS

Large changes in ATP production capacities and rates have been reporte d in mammalian hibernators throughout the different stages of the hibe rnation cycle. In this study we showed that total extractable liver [A TP], [ADP], and [ATP]/[ADP] do not differ among summer normothermic, h ibernating, and aroused golden-mantled ground squirrels, Spermophilus lateralis, indicating that metabolism remains well balanced throughout the hibernation cycle. This implies that rates of ATP consumption mus t be down-regulated during deep hibernation in order to maintain this balance. Despite this, basal oxygen-consumption rates (<V over dot o(2 )>) of hepatocytes isolated from hibernating, aroused, and summer cold -acclimated ground squirrels were 22.4-35.1% higher than those from gr ound squirrels in the summer normothermic condition when measured at 3 7 degrees C. The relatively high hepatocyte <V over dot o(2)> may help to minimize interbout arousal times, reducing energy demands during t he hibernation season. At 7 degrees C, hepatocyte <V over dot o(2)> va lues do not differ among the four groups; however, the Q(10) for hepat ocyte <V over dot o(2)> is significantly lower for the summer group, s uggesting lower temperature sensitivity. Despite the seasonal changes in thyroid hormone status known to occur in scuirid hibernators, the p roportion of hepatocyte <V over dot o(2)> attributed to Na+,K+-ATPase, estimated by inhibition with 1 mM ouabain, is only around 15% and doe s not differ among hibernation/seasonal conditions.