DIFFERENTIAL REGULATION OF GLUT1 AND GLUT4 GLUCOSE TRANSPORTERS IN SKELETAL-MUSCLE OF A NEW MODEL OF TYPE-II DIABETES - THE OBESE SHR N-CP RAT/

The obese diabetic SHR/N-cp rat is a newly developed strain that inher its obesity as an autosomal recessive trait. These rats display early- onset hyperinsulinemia and hyperglycemia, which are hallmarks of type II diabetes. This study was undertaken to determine the expression and the subcellular distribution of the GLUT1 and GLUT4 glucose transport ers in skeletal muscle of obese diabetic SHR rats. D-glucose-protectab le cytochalasin-B binding to subcellular membrane fractions of hindlim b muscles was used to determine glucose transporter number. GLUT1 and GLUT4 glucose transporter isotypes were detected using antibodies to t he COOH-terminal region of the GLUT1 and GLUT4 proteins. Glucose trans porter number was significantly lower (-40%) in crude unfractionated m embranes of obese diabetic SHR than of lean SHR muscles. When crude me mbranes were fractionated to separate plasma membranes and the intrace llular membranes containing glucose transporters, the number of cytoch alasin-B binding sites was found to be markedly lower (-50%) in intrac ellular membranes and slightly but not significantly reduced (-20%) in plasma membranes of muscle from obese diabetic SHR compared with lean SHR rats. Western blot analysis revealed that a lower GLUT4 protein a bundance (-40%) accounts for the reduced glucose transporter number in intracellular membranes of obese diabetic SHR compared with lean SHR muscles. GLUT4 protein content was also reduced by 50% in plasma membr anes from obese SHR muscles relative to lean rat muscles. In contrast, GLUT1 glucose transporters were more abundant (40%) in plasma membran es of obese diabetic SHR rats compared with their lean counterparts. T he latter finding may explain the lack of phenotypic difference in pla sma membrane total glucose transporter number as measured by cytochala sin-B binding. GLUT4 and GLUT1 mRNA levels were both found to be signi ficantly decreased in obese SHR rats compared with their lean litterma tes. These results demonstrate that 1) GLUT4 transporter expression is reduced in skeletal muscle of obese diabetic SHR rats, a model of typ e II diabetes; 2) the decreased GLUT4 abundance was localized to both the sarcolemmal and intracellular membrane fractions; 3) in contrast t o the GLUT4 glucose transporter, GLUT1 protein content was greater in plasma membranes of skeletal muscle from obese diabetic SHR rats, sugg esting that these transporter isoforms are inversely regulated in musc le of these diabetic animals; and 4) posttranscriptional mechanisms ap pear to be responsible for the differential expression of GLUT1 and GL UT4 proteins in muscle of obese diabetic SHR rats. Diabetes