Skeletal muscle mitochondria as a source of non-shivering thermogenesis in the marsupial Anthechinus flavipes

Abstract

The source of non-shivering thermogenesis (NST) in non-placental mammals is not known as they apparently lack brown adipose tissue (BAT) and uncoupling protein 1 (UCP1). In placental mammals, UCP1 mediates uncoupled respiration in BAT to generate heat. A thermogenic role of UCP3 and the adenine nucleotide transporter (ANT) has been debated for bird skeletal muscle. It has been established that 4-hydroxy-2-trans-nonenal (HNE) induces uncoupling activity by UCPs and/or ANT. Whether UCP or ANT is activated can be distinguished by GDPinhibition of UCPs or carboxyatractyloside (CAT)-inhibition of the ANT. Here, we investigate the role of proton conductance, UCP3 and ANT in skeletal muscle mitochondria during cold exposure of marsupials. We acclimated the yellow-footed Antechinus (A. flavipes) to either 10° C or 24°C for 3-4 weeks and measured proton leakage in isolated skeletal muscle mitochondria. Whereas basal proton conductance was unchanged between different acclimation temperatures, a higher inducible proton conductance by HNE was observed in the cold acclimated group. Inhibition by CAT indicated uncoupling activity by the ANT. Pertaining to UCP3, GDP-inhibition could not be observed and might have been missed by applying assay conditions routinely used for rodents. Regarding the dominant contribution of skeletal muscle to body mass, we demonstrate a potential role of their mitochondria in adaptive thermogenesis. The capacity of proton leakage is increased in the cold and can be regulated by an ANTdependent mechanism. The present study provides no evidence for the involvement of UCP3 in adaptive thermogenesis of marsupials.