Physiological role of skeletal muscle glycogen in starved mice

Abstract

To study the physiological role of skeletal muscle glycogen in starved animals, effects of starvation on glycogen and glycogen phosphorylase (EC 2.4.1.1.) activity were studied in muscle fibers (morphologic study) and in whole muscles (biochemical study) of the rectus femoris muscle of mouse. Glycogen content in the liver of the starved animals was also measured. PAS reaction, strong in muscle fibers of fed animals, became weak predominantly in type IIB fibers after 2 days and almost disappeared after 4 days of starvation. Glycogen particles, numerous in the sarcoplasm between myofibrils of muscle fibers, decreased markedly predominantly in type IIB fibers after 2 days and almost disappeared after 4 days. Phosphorylase a activity, undetected in fibers of fed mice, appeared weak in type IIB fibers and very weak in type IIA fibers after 2 days and became moderate in type IIB fibers and weak in type IIA fibers after 4 days. Muscle glycogen content did not differ by 16 hours from the values of corresponding fed animals. However, liver glycogen content had already decreased after 8 hours and markedly so after 12 hours. The results support our hypothesis-"skeletal muscle glycogen is used for maintaining the blood glucose level in starved mice" (Hirose et al.: Anat. Rec., 216:133-138, 1986)-and show that type IIB fibers play a main role in maintaining the glucose level and that muscle glycogen is utilized after depletion of liver glycogen.

The structure of cardiac glycogen in healthy mice

“…2. Mouse skeletal muscle glycogen, like the corresponding polymer in humans, has previously been shown to consist only of ␤ particles [39]. We assume after Takeuchi et al [40] that the maximum diameter of the cardiac ␤-particles is 50 nm.…”

Reduced metabolic capacity in fast and slow skeletal muscle via oxidative stress and the energy‐sensing of AMPK/SIRT1 in malnutrition

“…Several previous studies reported that excessive dietary restriction or ingestion of a low‐protein diet results in loss of muscle mass in fast muscles (Kim, 2013; Pereyra‐Venegas et al, 2015; Ruiz‐Rosado et al, 2013; Toyoshima et al, 2014) and no atrophy was induced in slow muscles (Alaverdashvili et al, 2015; Salles et al, 2014; Walrand et al, 2000). In addition, Sakaida et al, (1987) reported that glycogen content in muscle fibers decreased predominantly in type IIB fibers after 2 days of starvation and almost disappeared after 4 days. Thus, malnutrition results in a major impact on fast muscles.…”

High glucose‐6‐phosphatase activity in osteoblasts in the metaphysis of femur of growing rats

“…The role of the enzyme in the liver and kidney is to release glucose into blood by hydrolyzing G6P produced via gluconeogenesis and glycogeno-lysis (Krebs, 1963;Nordlie, 1972). We postulated that the role of relatively high activity in epididymal principal cells or in the seminal epithelium is to supply glucose into the epididymal fluid or fructose into the seminal fluid (Kanai et al, 1981 and that the role of the increased activity in skeletal muscle cells of starved mice is to release glucose into the blood (Hirose et al, 1986;Sakaida et al, 1987). However, the role of this enzyme in other various cell types containing low or moderate activities is unknown, although we supposed a role of regulation of G6P concentration in the cells, hydrolyzing if there is any excess (Kanamura, 1975a;Watanabe et al, 1983Watanabe et al, , 1986.…”