Renal tubular secretion of organic anions

A general secretory transport system for organic anions, located in the renal tubules, plays a major role in regulating the concentrations in the body of various endogenous and exogenous compounds, including many pharmacologically active substances. Net transepithelial transport involves entry into the tubule cells against an electrochemical gradient at the basolateral membrane via a tertiary active process followed by movement through the cytoplasm and exit from the cells into the lumen down an electrochemical gradient. The final step in the tertiary active process at the basolateral membrane involves countertransport of the organic anion against its electrochemical gradient for α-ketoglutarate moving down its electrochemical gradient. Movement from the cells into the lumen down an electrochemical gradient may involve carrier-mediated diffusion driven by the potential gradient, some form of anion-exchange (whether neutral or potential-driven), or movement through a channel driven by the potential. Translocation of these organic anions from the basolateral membrane to the luminal membrane through the cytoplasm may involve diffusion or movement within some form of compartment (possibly in vesicles) or a combination of these.