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

Abstract

Glucose is thought to stimulate insulin release from islet beta-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-20ins cells to assess their impact on glucose-stimulated insulin release and glucose metabolism. We find that transfection of AtT-20ins 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 Km for 3-O-methyl glucose uptake of 4 mM and a Vmax of 5-6 mmol/min/liter cell space. These values are increased compared to untransfected AtT-20ins cells (Km = 2 mM; Vmax = 0.5 mmol/min/liter cell space), but are less than observed in GLUT-2-transfected lines (Km = 16-17 mM; Vmax = 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 microM to 20 mM. We conclude that the specific effect of GLUT-2 on glucose-stimulated insulin release in AtT-20ins 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.