Canine-specific adaptation of energy metabolism of latissimus dorsi muscle in response to chronic electrical stimulation.

Continuous electrical stimulation ot canine latissimus dorsi (LD) muscle in situ during 24 weeks induced an increase of immunohistochemically assayed type I fibers from about 30 to 80%. Concomitantly, the activity of fructose-6-phosphate kinase, a key enzyme of the glycolytic pathway, declined markedly, but the capacity for fatty acid oxidation remained unaltered. With respect to myofibrillar and metabolic properties the dog LD muscle initially resembled soleus muscle, and after 24 weeks of stimulation had acquired the properties of gastrocnemius muscle. It is concluded that in the dog, unlike the rat, the LD muscle has an inherently fixed capacity for oxidative energy production. Further expansion of its resistance to fatigue, as induced by chronic stimulation, most likely results mainly from a more efficient coupling between tension development and energy production.