A glucagon receptor is a G protein-coupled receptor found mainly in the liver. These receptors bind to the hormone glucagon made by the pancreas, and they cause the break down of glycogen, a storage form of sugar. Together, the hormones glucagon and insulin control blood glucose levels. When blood glucose dips, glucagon is released and attaches to a glucagon receptor to increase glucose levels. Glucagon receptors have been found to be important for the health of liver cells, called hepatocytes.
The pancreas makes two hormones, insulin and glucagon. After a meal, when blood glucose levels are too high, beta cells in the pancreatic islets release insulin, which allows cells throughout the body to take up glucose for use in energy production. This then lowers blood glucose levels. Some of that glucose is taken into liver cells where it is converted to glycogen, a polysaccharide that stores glucose.
When blood glucose levels lower between meals, the alpha cells in the pancreatic islets release the hormone glucagon. Most of the glucagon receptors are located in the liver, so when they attach to glucagon, the glycogen that has been stored in the liver cells is broken down into glucose and released into the blood. Blood sugar levels then increase back to normal.
A glucagon receptor is in the G protein-coupled receptor family. The GCGR gene has been found to code for the glucagon receptor protein, and using this gene for research has aided in studying it. When glucagon attaches to the glucagon receptor, it triggers the coupling of G proteins and begins a cascade effect, producing cyclic adenine monophosphate (cAMP), and it causes a release of calcium in the cell. Besides the liver, glucagon receptors have been found in the kidneys, small intestines, brain, fat tissue and beta pancreatic cells. In beta cells, glucagon receptors likely cause the inhibition of insulin production by these cells.
Glucagon mainly affects glucose levels in the body, but it might also be involved in fasting metabolism, during which the body runs low on glucose and mainly uses fats for energy production. The presence of glucagon receptors in hepatocytes is involved in the proper metabolism of these cells. This would explain why properly working glucagon receptors might be important for hepatocyte and liver health. Mutations in the glucagon receptor might be linked to type II diabetes. This receptor is likely to be studied further because it does do more in the body than simply increase blood glucose levels.