Inverse Relationship of Skeletal Muscle Glycogen from Wild-Type and Genetically Modified Mice to Their Phosphorylase a Activity

Leg muscle was biopsied and frozen for storage at −70°C. from 5 wild-type mice, two knocked out acid α-glucosidase (GAA) gene mice, and seven glycogen synthase plus glucose muscle transporter transgenic mice. All of the wild-type mice had very little muscle glycogen (3.58 ± 1.67 μmols glucosyl subunits per g muscle), and 52% or more of its glycogen phosphorylase activity without AMP (69% ± 17% glycogen phosphorylase a). In contrast the GAA knockout and transgenic mice had glycogen ranging from 63 to 297 μmols glucosyl subunits per g muscle, and very little or no glycogen phosphorylase activity without 1.00 mM AMP (4.8% and less glycogen phosphorylase a). This suggests that there is an inverse relationship between mouse muscle phosphorylase a and the muscle's glycogen content.