A source of nonshivering thermogenesis in fur seal skeletal muscle.

The mitochondria from the subscapular muscle of naturally cold-stressed 10- to 15-year-old northern fur seals (Callorhinus ursinus) were loosely coupled upon isolation, whereas the mitochondria from the same muscle of warm-acclimated pups of the same age were tightly coupled. Thus, loose-coupled muscle mitochondria might provide an important vehicle for nonshivering thermogenesis in this species.