Exogenous compounds, transport

The vesicular transporters are capable of concentrating neurotransmitters from 10-to 100,000-fold, with important implications for Ca2+-dependent quantal release. These transporters also protect neurons from the toxicity of exogenous compounds... 

The transport of exogenous compounds has been investigated recently by determining the amount of modified intraluminal proteins upon addition of nonphysiologic biotin-derivatives capable of chemical protein modification (7). The ER membrane has been shown to be permeable to three different biotin-derivatives, and it has been concluded that it does not form a barrier to small molecules that is, either the lipid bilayer or the integral membrane proteins allow their diffusion unspeciticaUy. 

Morris ME, Lee HJ, Predko LM. Gender differences in the membrane transport of endogenous and exogenous compounds. Pharmacol Rev 2003 55 229—40. 

Besides MRP2, the other important canalicular transporter in terms of biliary drug excretion is MDRl (Pgp). This widely studied transporter plays a major role in the excretion of numerous endogenous and exogenous compounds by the liver. Drug substrates for Pgp include anticancer agents, antivirals. 

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