Transporters are membrane proteins present in cells in many tissues of the body and play a pivotal role in the bioavailability, disposition and pharmacokinetics of xenobiotics (drugs) and endogenous chemicals (bile salts, cholesterol etc).
The location of different transporters is organ-specific, fulfilling different roles accordingly.
Orally exposed compounds that are substrates for efflux transporters in the intestine may have a lower systemic bioavailability than drugs that are not substrates and pass easily through the lipid membrane by diffusion.
In the liver, the polarised location of efflux transporters in hepatocytes results in the extrusion of the parent molecule or its metabolites into the sinusoidal blood for excretion via the kidneys or efflux of larger molecules into bile canaliculi and excretion in the faeces.
The kidney has a high level of organisation of transporters along the tubules that allow for the selective and efficient secretion and resorption of chemicals into the urine, thus determining their plasma concentrations.
Some of the processes of efflux and resorption in the kidneys can be modelled using renal cortical, distal and proximal cells cultured in conventional and trans-well monolayers.