Internalization (pharmacology)
In pharmacology, internalization refers to the withdrawal (translocation) of receptors (e.g. G-protein-coupled receptors ) and similar structures ( transporters , channels ) from the cell surface into the interior of the cell.
Internalization is triggered by persistently high concentrations of stimulating receptor ligands ( agonists ) and leads to the receptor density on the cell membrane being reduced and the withdrawn receptors no longer available for signal transmission ; Above-average strong / long neural stimuli are throttled in this way. Internalization is therefore one of the compensatory adaptation mechanisms ; these underlie the phenomenon of tolerance .
Internalization can be followed by the storage (sequestration) of these intact receptor structures - a step that is reversible and corresponds to a “stand-by” function. Internalization can also be followed by the breakdown ( degradation ) of the receptors. The reduction in the sensitivity of the cell to ligands brought about by (compensatory) degradation is called down-regulation .