Background. Vasopressin is a peptide hormone that regulates water balance in the body by controlling the rate of urinary water excretion.  Several disorders of water balance ascribe to failures in this process.  It has long been recognized that vasopressin binds to receptors on the basolateral plasma membrane of collecting duct cells and increases the permeability of the cells to water, allowing water to be reabsorbed from the urine to blood. We are investigating the mechanisms of the water permeability increase on a cellular and molecular basis. Our experiments have demonstrated the presence of water-selective channels called “aquaporins” in collecting duct cells. One of these aquaporins (aquaporin-2) is regulated by vasopressin. We have demonstrated that aquaporin-2 water channels are present in intracellular vesicles that,  in response to a rise in intracellular cyclic AMP, fuse with the apical plasma membrane, increasing the water permeability of this membrane.   We have also shown that vasopressin positively regulates transcription of the aquaporin-2 gene.  

Current studies are utilizing a systems-level approach applied at the cellular level to discover 1) the signaling pathways triggered by vasopressin V2-receptor occupation in renal collecting duct cells;  2) the molecular apparatus responsible for trafficking water channel-laden vesicles; 3) the transcriptional network involved in aquaporin-2 gene transcription; and 4) effect of vasopressin on protein stability and translation throughout the collecting duct proteome. These studies utilize a wide variety of technical approaches including:  1) quantitative proteomics using protein mass spectrometry;  2)  oligonucleotide expression arrays (Affymetrix); 3) knockout mouse models; 4) in vitro perfusion of microdissected renal tubule segments from kidneys to measure water transport; 5) mutational and shRNA knockdown approaches in cultured collecting duct cells;  6) immunochemical approaches to assess the abundance, intracellular distribution, and post-translational modification of physiologically important transporters; 7) biochemical analysis of microdissected renal tubule segments; and 8) computational methods including differential-equation-based mathematical modeling.