LIMITED CAPACITY FOR GLYCONEOGENESIS FROM ALANINE BY DIAPHRAGM MUSCLE

The mammalian diaphragm (Dial is a unique skeletal muscle because of i ts chronic contractile activity. Chronically active muscles have highe r capacities for glycogen synthesis from lactate and glucose. In this study, the contribution of alanine to glycogen synthesis in the predom inantly fast-twitch mouse Dia was determined. Chronically active fast- and slow-twitch muscles From dy(2J)/dy(2J) pseudomyotonic mice were a lso analyzed. Alanine aminotransferase (AlaAT) activity was significan tly (P < 0.05) greater in Dia and chronically active gastrocnemius mus cle (Gast) than control Gast. C-14-label incorporation into glycogen f ollowing in vivo injection of C-14-alanine, was significantly higher i n Dia and chronically active Gast than control Gast. A direct incorpor ation of C-14 from C-14-alanine into glycogen is also observed in vitr o. The incorporation rate shows a linear concentration dependent relat ionship and a pH optimum of 6.3. Insulin had no effect on glycogen syn thesis from alanine by Dia in vitro. The extensor digitorum longus mus cle (EDL) and chronically active EDL and soleus muscle (Sol) had highe r rates of glycogen synthesis from alanine than control Sol and Dia. T he oxidation of alanine to CO2 was the primary route for alanine metab olism by the Dia. These results demonstrate that the Dia can synthesiz e glycogen from alanine, but only at low rates.