Thermoregulatory uncoupling of oxidative phosphorylation has been studied in heart and skeletal muscle mitochondria of ground squirrels. The respiratory rate ofmitochondria in the presence of oligornycin was found to be much higher in winter (in hibernating, arousing, or aroused animals) than in summer. This additional respiration is strongly (arousing animals) or completely (hibernating and aroused anhnals) inhibited by carboxyntractylate (CAtr) and bovine serum albumin (USA). The CAtr-and BSA-induced decreases in the rate of respiration arc accompanied by membrane potential increases, The rate of the CAtr-and BSA-sensitive respiration is proportional to the content of free fatty acids which, in the heart, dccrcascs in the order: arousing Z+ aroused = hibernating > summer animals. Maximal respiratory rates observed in the prcxncc of dinitrophenol (arousing > aroused > summer > hibernating animals) do not parallel the fatty acid Ievcl. It is assumed that some heat production in the winter animals is due to fatty acid-induced, ATP/ADP-antiportcr-mediated uncoupling in heart and skeletal muscle mitochondria. The peak of heat production during arousal after hibernation also includes some other stimulatory effect on mitochondrial respiration.
Energy coupling parameters were studied in liver mitochondria of ground squirrel during arousal from hibernation. It was found that such mitochondria become uncoupled during incubation with phosphate in a salt medium. The uncoupling was revealed by respiration rate increase and membrane potential decrease in the presence of oligomycin. Both effects were reversed by addition of cyclosporin A. Under the same in vitro conditions, mitochondria from aroused (active) animals showed no uncoupling but could be uncoupled by addition of palmitate in the cyclosporin A-sensitive fashion. It is proposed that formation ofeyclosporin A-sensitive pores can be involved in urgent heat production in arousing hibernators.
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