Pancreatic beta cell line MIN6 exhibits characteristics of glucose metabolism and glucose-stimulated insulin secretion similar to those of normal islets

Abstract

Glucose-stimulated insulin secretion, glucose transport, glucose phosphorylation and glucose utilization have been characterized in the insulinoma cell line MIN6, which is derived from a transgenic mouse expressing the large T-antigen of SV40 in pancreatic beta cells. Glucose-stimulated insulin secretion occurred progressively from 5 mmol/l glucose, reached the maximal level approximately seven-fold above the basal level at 25 mmol/l, and remained at this level up to 50 mmol/l. Glucose transport was very rapid with the half-maximal uptake of 3-O-methyl-d-glucose being reached within 15 s at 22 °C. Glucose phosphorylating activity in the cell homogenate was due mainly to glucokinase; the V_max value of glucokinase activity was estimated to be 255±37 nmol·h⁻¹·mg protein⁻¹, constituting approximately 80% of total phosphorylating activity, whereas hexokinase activity constituted less than 20%. MIN6 cells exhibited mainly the high K_m component of glucose utilization with a V_max of 289±18 nmol·h⁻¹·mg protein⁻¹. Thus, glucose utilization quantitatively and qualitatively reflected glucose phosphorylation in MIN6 cells. In contrast, MIN7 cells, which exhibited only a small increase in insulin secretion in response to glucose, had 4.7-fold greater hexokinase activity than MIN6 cells with a comparable activity of glucokinase. These characteristics in MIN6 cells are very similar to those of isolated islets, indicating that this cell line is an appropriate model for studying the mechanism of glucose-stimulated insulin secretion in pancreatic beta cells.