Downregulation and upregulation

As downregulation ( English: down-regulation ) is called induced by a sustained high ligand concentration decrease in the number of receptors on a cell, including the degradation of the receptors. In receptors deficiency of the ligand is no longer able to exert its effect in the target organ, regardless of its concentration in the blood. This temporal limitation of Ligandwirkung serves to protect the cell or organism.

Mechanism for peptide hormones

When peptide hormones are bound for a long period to the hormone receptor of the target cell, there is a lateral displacement of the hormone -receptor complexes on the cell membrane. For long-lasting excess of hormone to form clusters (cluster ) of these hormone -receptor complexes in specific areas (so-called " coated pits ") of the cell membrane. These are picked up by endocytosis into the cell interior ( internalized ). Prolonged hormone excess thus reducing the number of receptors on the surface of target cells, which are insensitive for the hormone. Most peptide hormones are therefore released in batches ( pulsatile ), whereby the down-regulation is physiologically prevented.

Another important mechanism in the regulation of receptor density represent Phosphorylierungseffekte, which lead to the internalisation of the receptors and loss of effect by binding to arrestins or conformational change.

Example

• Downregulation of G- protein -coupled receptors