The abnormality of glucose transporter in the erythrocyte membrane of Chinese type 2 diabetic patients

Type 2 diabetes mellitus is characterized by impaired glucose uptake. With a photometric method of recording the erythrocyte suspension absorption dur ing the course of glucose transport across the membranes, we observed that the initial rate of glucose zero-trans entry was decreased significantly in 30 Chinese type 2 diabetic patients as compared to 25 healthy controls. Th e rate of glucose infinite-cis efflux exhibited no difference between the p atients and controls. The measurement of temperature dependence of glucose transport showed that the activation energy for glucose entry was increased in diabetic patients. The inhibitory constant of glucose entry by cytochal asin B (CB) in patients was similar to that of the controls, However, we fo und that the inhibitory constant was increased significantly in the patient erythrocytes after phloretin treatment, After the erythrocytes were made i nto stripped white ghosts, the fluorescence quenching experiment was perfor med. Glucose, CB and phloretin can quench the fluorescence of tryptophan re sidues in the glucose transporter 1, GLUT1. The abnormality of fluorescence quenching in the erythrocyte membranes of patients was observed. The trans fer tendency of tryptophan residues from the hydrophilic environment to the hydrophobic environment was decreased in patient ghosts as binding with gl ucose, and the opposite tendency appeared as CB and phloretin instead of gl ucose, We conclude that the decreased in glucose entry in the erythrocyte m embranes of diabetic patients was due to the GLUT1 change in structure most ly the outer domain of the glucose transporter. (C) 2000 Elsevier Science B .V. All rights reserved.