The Anion-Exchanger AE1 is a Diffusion Pathway for Taurine Transport in Rat Erythrocytes
A putative osmolyte is required to meet two main criteria: to be highly concentrated inside the cell, and to possess a specific pathway across the plasma membrane allowing for its osmotic efflux12. In the case of taurine, an admitted osmolyte in several animal species, high intracellular levels are maintained in most mammalian tissues by the action of well characterized sodium/chloride-dependent carriers14,20,24,25. The nature of the taurine efflux carrier, however, remains to be assessed, although it has been demonstrated in several cell types11,17,22 that it consists of a diffusion pathway with pharmacological properties similar to a chloride channel. An alternative pathway for taurine exit has been proposed based on extensive studies with red blood cells (RBCs). This release occurs through a transport system that is sensitive to compounds that are well-known inhibitors of the RBC’s anion-exchanger (AE1)8. It has been claimed, therefore, that taurine uses this diffusion transport system to exit the erythrocyte9 (but see16). This assumption is supported by the fact that some N-derivative analogs of taurine such as, NBD-taurine, Cl-taurine, NAP-taurine or NIP-taurine, are either substrates and/or competitive inhibitors of this anion-exchanger1. In addition, AE1 transports many different organic compounds, including some amino acids such as glycine15.
KeywordsChloride Channel Regulatory Volume Decrease Diffusion Pathway Taurine Transport Taurine Uptake
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