application) The renal collecting duct plays an active role in acid-base, electrolyte and H2O homeostasis. Although cells in the cortical and medullary collecting duct have distinct functions, they also share similarities in their repertoire of hormone receptors, and in the signal transduction pathways linking those receptors to various effectors and transport processes. For example, arginine vasopressin (AVP, antidiuretic hormone) V2 receptors are expressed on the basolateral face of cells ranging from the cortical collecting duct to the terminal segment of inner medullary collecting duct. These receptors can regulate transcellular resistance, ion fluxes and water transport. These processes can be initiated by the release of AVP from the pituitary. Circulating AVP binds to vasopressin V2 receptors on the basolateral surface of cells in the collecting duct, resulting in activation of the stimulatory G protein, Gs, and increased conversion of ATP to cAMP. Elevated cAMP results in activation of protein kinase A (PKA). The activation of PKA can ultimately result in alterations of transcellular transport. The best example of this phenomenon is the stimulation by circulating AVP/V2 receptor/cAMP/PKA of insertion of specialized H2O channels (aquaporin-2, AQP-2) into apical membranes of collecting duct cells. This results in movement of H2O from the urine space into the cytosol of IMCD cells. Basolateral aquaporin (AQP3 & AQP4) H20 channels then convey this water into the renal interstitium. One of my mentors, David Ploth, recently established the putative presence of functional luminal bradykinin receptors in the collecting ducts of rats. Since submission of the last application, we have obtained data that suggest that bradykinin B2 receptors represent another conserved hormonal regulatory system in two types of model cells derived from the collecting duct. We have detected functional bradykinin receptors in the M-1 cell line (derived from the cortical collecting duct of SV40 transgenic mice) and in the IMCD-3 cell line (derived from the terminal portion of the medullary collecting duct of SV40 transgenic mice). In both cases, the receptors are pharmacologically of the B2, type, couple to elevations of intracellular calcium and to proton efflux pathways from the respective cell lines. The hypothesis of my proposal is that bradykinin receptors in these cells, probably on their apical surfaces, play a role in regulating cellular pH. I would like to understand the regulatory mechanism linking the B2 receptors in these two cell lines. My goal in performing these studies will be to obtain training in signal transduction methods so that I can eventually integrate my background in physics into the study of renal problems.
