THE PANCREATIC BETA-CELL GLUCOSE SENSOR

Pancreatic beta cells secrete insulin in response to an increase in th e level of blood glucose above 5 mM, which is characteristic of the fa sting state. Glucose metabolism is essential for glucose sensing, and both the high-K-m the high-K-m glucose phosphorylating enzyme glucokin ase have been implicated in coupling insulin secretion to extracellula r glucose levels. Experiments in isolated islets, immortalized beta-ce ll lines and transgenic animals, together with findings in humans with maturity-onset diabetes of the young, indicate that the primary beta- cell glucose sensor is glucokinase. Although the level of GLUT2 is fre quently reduced in animal models of type II diabetes, GLUT2 does not l imit glucose metabolism in beta cells and does not appear to regulate glucose induction of insulin secretion.