RENAL TUBULAR SECRETION OF ORGANIC-ANIONS

A general secretory transport system for organic anions, located in th e renal tubules, plays a major role in regulating the concentrations i n the body of various endogenous and exogenous compounds, including ma ny pharmacologically active substances. Net transepithelial transport involves entry into the tubule cells against an electrochemical gradie nt at the basolateral membrane via a tertiary active process followed by movement through the cytoplasm and exit from the cells into the lum en down an electrochemical gradient. The final step in the tertiary ac tive process at the basolateral membrane involves countertransport of the organic anion against its electrochemical gradient for a-ketogluta rate moving down its electrochemical gradient. Movement from the cells into the lumen down an electrochemical gradient may involve carrier-m ediated 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 anion s from the basolateral membrane to the luminal membrane through the cy toplasm may involve diffusion or movement within some form of compartm ent (possibly in vesicles) or a combination of these.