IN-VIVO GLUCOSE-UPTAKE AND GLUCOSE-TRANSPORTER PROTEINS GLUT1 AND GLUT4 IN HEART AND VARIOUS TYPES OF SKELETAL-MUSCLE FROM STREPTOZOTOCIN-DIABETIC RATS

The in vivo glucose uptake and the levels of two glucose transporter p roteins (GLUT1 and GLUT4) were measured in heart and in various types of skeletal muscle from streptozotocin-diabetic rats. Diabetes (12-16 weeks) reduced the in vivo glucose uptake (glucose metabolic index, GM I), and the levels of GLUT1 and GLUT4 in heart by 75%, 60% and 70%, re spectively. In diaphragm consisting of approximately equal amounts of type I (slow-contracting oxidative), IIa (fast-contracting oxidative) and IIb (fast-contracting glycolytic) fibers, GMI and GLUT4 levels wer e reduced by 60% and 40%, respectively, with no change in GLUT1 levels . In muscle consisting mainly of type I fibers (e.g., m. soleus), GMI and GLUT4 levels were reduced by 60% and 30%, respectively, whereas GL UT1 levels were unaltered. In mixed-type muscle consisting of type IIa and IIb fibers (e.g., m. plantaris and red part of m. gastrocnemius), GMI and GLUT1 levels were unchanged, whereas GLUT4 levels were decrea sed by 45%. In contrast, GMI was increased by 100% in type IIb, fibers (e.g., the white part of m. gastrocnemius), probably reflecting the 4 -fold increase in blood glucose levels, whereas GLUT4 levels were lowe red by 55% with no change in GLUT1 levels. These data demonstrate a ma rked difference in the response of in vivo glucose uptake to long-term hypoinsulinemia between oxidative (type I) and glycolytic (type IIb) fibers. Furthermore, in contrast to the GLUT4, GLUT1 levels are regula ted differentially in heart and skeletal muscle in response to strepto zotocin-induced diabetes.