Enzyme activities and morphology of Japanese brown frog (Rana japonica) mitochondria in the tibialis anterior muscle during hibernation and active life

Enzyme activities in the respiratory chain, as well as the structure and nu mbers of mitochondria of the tibialis anterior muscle, during hibernation w ere compared with those of normally active muscle in the Japanese brown fro g (Rana japonica). Morphological examination using an electron microscope s howed that during hibernation, mitochondria were larger and longer and had clearly distinguishable outer and inner membranes with developed cristae. A significantly greater number of glycogen granules was found in the tibiali s anterior muscle of hibernating frogs. The average cross-sectional area (C SA) of muscle fiber was much smaller in the samples from hibernating frogs than those from active frogs. The numbers of mitochondria per CSA were also much higher during hibernation than during active life. Measurements of th e enzyme activities of succinate dehydrogenase, NADH-ferricyanide reductase , and succinate-O-2 and NADH-O-2 oxidoreductases showed different profiles between hibernation and active life. That is, all four activities were sign ificantly higher during hibernation than during active life. Taken together , the results obtained suggest that the seasonal variations in the activiti es of respiratory-chain systems may be related to the seasonal morphologica l changes in muscle mitochondria in R. japonica.