Membrane transporters in PET imaging

Cellular membranes form a barrier to most of organic and inorganic solutes. Specific transporter proteins enable strictly regulated transport of solutes across the membranes, down or against their concentration gradient. Transport against the concentration gradient ("active" transport) requires energy, which is obtained by exploiting ion gradients or from subsequent ATP turnover. For reviews on transporters, see the references. In the absence of transporter, membrane permeability is correlated with the solutes oil/water partition coefficient. Lipid bilayer membranes are heterogeneous, with higher lipophilicity in the centre of the bilayer, which is taken into account in inhomogeneous solubility-diffusion model.

PET radiopharmaceuticals are being used and actively developed for studying the function and localization of transporters. Transporters are not only important as targets of functional PET imaging, but transporters indirectly affect the usability of PET radiopharmaceuticals for studying other functions, since transporters are needed for the radiopharmaceuticals to reach their targets across epithelial barriers (such as endothelial barriers, especially BBB) and in intracellular organelles. Transporters are also involved in the excretion of PET radiopharmaceuticals from the body, and the distribution of their radioactive metabolites. Labelled drug molecules can be used to study the effect of transporter systems on drug biodistribution and transporter-mediated drug-drug interaction.

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Updated at: 2021-02-22
Created at: 2015-08-17
Written by: Vesa Oikonen