Modulation of vasopressin-elicited water transport by trafficking of aquaporin2-containing vesicles

Vasopressin or AVP regulates water reabsorption by the kidney inner medulla ry collecting duct (IMCD) through the insertion and removal of aquaporin (A QP) 2 water channels into the IMCD apical membrane. AVP-elicited traffickin g of AQP2 with the apical membrane occurs via a specialized population of v esicles that resemble synaptic vesicles in neurons. AQP2 vesicles and the I MCD apical membrane contain homologs of vesicle-targeting and signal transd uction proteins found in neurons. Expression studies of AQP2, including hum an AQP2 mutants, suggest that the carboxyl-terminal domain of AQP2 is impor tant in AQP2 trafficking, particularly as a site for cAMP-dependent protein kinase phosphorylation. These present data reveal that IMCD cells possess a complex integrated-signaling and vesicle-trafficking machinery that provi des integration of AVP-elicited water transport with many other parameters within the IMCD cell as well as kidney.