Limited capacity for glyconeogenesis from alanine by diaphragm muscle

The mammalian diaphragm (Dia) is a unique skeletal muscle because of its chronic contractile activity. Chronically active muscles have higher capacities for glycogen synthesis from lactate and glucose. In this study, the contribution of alanine to glycogen synthesis in the predominantly fast-twitch mouse Dia was determined. Chronically active fast- and slow-twitch muscles from dy2J/dy2J pseudomyotonic mice were also analyzed. Alanine aminotransferase (AlaAT) activity was significantly (P < 0.05) greater in Dia and chronically active gastrocnemius muscle (Gast) than control Gast. 14C-label incorporation into glycogen following in vivo injection of 14C-alanine, was significantly higher in Dia and chronically active Gast than control Gast. A direct incorporation of 14C from 14C-alanine into glycogen is also observed in vitro. The incorporation rate shows a linear concentration dependent relationship and a pH optimum of 6.3. Insulin had no effect on glycogen synthesis from alanine by Dia in vitro. The extensor digitorum longus muscle (EDL) and chronically active EDL and soleus muscle (Sol) had higher rates of glycogen synthesis from alanine than control Sol and Dia. The oxidation of alanine to CO2 was the primary route for alanine metabolism by the Dia. These results demonstrate that the Dia can synthesize glycogen from alanine, but only at low rates.