A receptor can move from the cell surface to an internal compartment while the total number of receptors remains stable. In cell experiments with the human serotonin 5-HT7 receptor, researchers measured both that movement and changes in receptor density.

Which compounds changed both measurements?

In engineered HEK293 cells, serotonin and several inverse agonists increased receptor internalization. Among the compounds that increased internalization, clozapine and olanzapine also promoted lysosomal sorting and reduced receptor density by about 60% within 24 hours. Inhibiting lysosomal degradation with chloroquine blocked the reduction in receptor density induced by those two drugs.

What the experiment can support

Internalization describes a change in location. Reduced receptor density and the inhibitor experiment provide additional evidence about what happened to receptors afterward. In forensic interpretation, keep this evidence at the level of receptor handling in the engineered cells. It cannot establish an individual’s exposure, symptoms, or behavior from a reported drug concentration.

Source

Andressen and colleagues, British Journal of Pharmacology (2015). Journal article · Full text.