The primary function of pancreatic ß cells is to store and release Insulin. Insulin is a hormone regulating blood glucose concentration. ß cells respond quickly to spikes in blood glucose concentrations by secreting stored Insulin whilst simultaneously producing more.
When the glucose concentration outside the cell is high, glucose move into the cell, down its concentration gradient, through the GLUT2 transporter. ß cells use Glucokinase to catalyze the first step of glycolysis. Metabolism of this first step of glycolysis occurs only at physiological blood glucose levels and above. Metabolism of the glucose produces ATP and increases the ATP to ADP ratio.
ATP-sensitive potassium ion channels close when this ratio rises. This means that potassium ions can no longer diffuse out of the cell. As a result, the potential difference across the membrane becomes more positive (as potassium ions accumulate inside the cell). This change in potential difference opens voltage-gated calcium channels, which allows calcium ions from outside the cell to diffuse in down their concentration gradient. When calcium ions enter the cell, they cause release of Insulin via exocytosis.
Pancreatic ß cells also produce and secrete other hormones. C-peptide, secreted into the bloodstream in equimolar quantities to insulin and plays a role in the prevention of neuropathy and other vascular deterioration related symptoms of Diabetes mellitus. C-peptide concentrations are measured to obtain an estimate of the viable ß cells mass. Amylin lowers the rate of glucose entering into the bloodstream. Amylin is a synergistic partner to Insulin: where Insulin regulates long term food intake and Amylin regulates short term food intake.
Diabetes mellitus Type I is known as Insulin-dependent Diabetes. It is caused by an autoimmune response where the body's own immune system attacks and destroys ß cells. This means the body can no longer produce and secrete Insulin into the blood and regulate the blood glucose concentration. Diabetes mellitus Type I can be experimentally induced for research purposes by Streptozotocin or Alloxan which are both toxic to ß cells.
Diabetes mellitus Type II is known as non-Insulin-dependent Diabetes and is caused by many factors including Age, Obesity, Consuming Western high glucose, high fat diets, to name but a few. ß cells still secrete Insulin but the body has developed an Insulin-resistance significantly declining its response to Insulin. The increasing Insulin-resistance typical for Diabetes mellitus Type II is thought to be due decreased expression of specific receptors on the surface of the liver and muscle cells which lose their ability to respond to insulin that circulates in the blood.