Mercury 502

Here is some more background on the Pancreatic Beta cell.

The resting potential of the cell is between negative 60-70 mV. This occurs when glucose levels are low and the K-ATP channels are working. Each beta cell has thousands of these channels. When glucose enters the cell from the bloodstream after a meal, ATP and ADP is made which cause the K-ATP channels to close quickly. More than 90% of the K-ATP channels become closed. The K-ATP channels that are still open cannot balance the depolarizing influences that are entering the cell. When glucose levels reach about 20mM the cell potential has changed to about negative 10 to 20 mV. When the cell potential becomes this low, it reaches threshold and a graded potential is generated. This causes a chain reaction of Voltage gated Ca +2 channels to activate. The opening of these Ca+2 channels causes Ca+2 to flood the cell opening even more of these channels. This initiates exocytosis of insulin into the bloodstream. The insulin causes glucose levels to go back down and thus the K-ATP channels reopen and get the membrane potential back to -70mV.

The life span of a pancreatic beta cell in a mouse is more than 3 months. We haven't found what it is in humans.