Vesicular transport as a new paradigm in short-term regulation of transepithelial transport.

The vectorial transepithelial transport of water and electrolytes in the renal epithelium is achieved by the polarized distribution of various transport proteins in the apical and basolateral membrane. The short-term regulation of transepithelial transport has been traditionally thought to be mediated by kinetic alterations of transporter without changing the number of transporters. However, a growing body of recent evidence supports the possibility that the stimulus-dependent recycling of transporter-carrying vesicles can alter the abundance of transporters in the plasma membrane in parallel changes in transepithelial transport functions. The abundance of transporters in the plasma membrane is determined by net balance between stimulus-dependent exocytic insertion of transporters into and endocytic retrieval of them from the plasma membrane. The vesicular recycling occurs along the tracts of the actin microfilaments and microtubules with associated motors. This review is to highlight the importance of vesicular transport in the short-term regulatory process of transepithelial transport in the renal epithelium. In the short-term regulation of many other renal transporters, vesicular transport is likely to be also involved. Thus, vesicular transport is now emerged as a wide-spread general regulatory mechanism involved in short-term regulation of renal functions.