Transfection of AtT-20_ins cells with GLUT-2 but not GLUT-1 confers glucose-stimulated insulin secretion: Relationship to glucose metabolism

Glucose is thought to stimulate insulin release from islet β-cells through generation of metabolic signals. In the current study we have introduced the genes encoding the facilitated glucose transporters known as GLUT-1 and GLUT-2 into AtT-20_ins cells to assess their impact on glucose-stimulated insulin release and glucose metabolism. We find that transfection of AtT-20_ins cells with GLUT-2, but not GLUT-1, confers glucose-stimulated insulin release in both static incubation and perifusion studies. Cells transfected with GLUT-1 have a K_m for 3-O-methyl glucose uptake of 4 mM and a V_max of 5-6 mmol/min/liter cell space. These values are increased compared to untransfected AtT-20_ins cells (K_m = 2 mM; V_max = 0.5 mol/min/liter cell space), but are less than observed in GLUT-2-transfected lines (K_m = 16-17 mM; V_max = 17-25 mmol/ min/liter cell space). Despite these dramatic differences in glucose transport affinity and capacity, the rates of [5-³H]glucose usage are not different in the control and transfected lines over a range of glucose concentrations from 10 μM to 20 mM. We conclude that the specific effect of GLUT-2 on glucose-stimulated insulin release in AtT-20_ins cells is not related to changes in the overall rate of glucose metabolism and may instead involve physical coupling of GLUT-2 with cellular proteins and/or structures involved in glucose signaling.