Grant: Operating Grant

Blood pressure is controlled by regulating the amount of sodium and water in the blood space. This regulation occurs in the kidney where daily 180L of blood is filtered and then 178-179L is reabsorbed back into the blood via a process that generates urine. The bulk of renal (kidney) regulation occurs in the first part of the kidney's functional unit the nephron, called the proximal tubule. Inappropriate absorption of salt and water from the proximal tubule causes increased blood pressure/hypertension. It is known that sodium and water (re)absorption occurs in this segment through a complex series of events mediated by several different membrane proteins capable of coupling water, sodium and bicarbonate movement. In order to most efficiently mediate the flux of this prodigious quantity of salt and water we propose that a physical interaction exists between these proteins. Specifically, we propose that the physical attachment, or "stickiness", of one protein to another enables the product of one transport event to be readily available as the substrate for the next, thereby enhancing the ability for this large amount of sodium and water to be absorbed. To test our hypothesis we will perform two types of studies. The first will look at sodium and water transport across kidney cell membranes (in petri dishes). Experiments will be performed with individual proteins and then in the presence of the other proteins we predict will increase the transport process. This will show a functional interaction between the proteins we are studying. To demonstrate a physical interaction we will use classic biochemical approaches where purified proteins are employed to demonstrate that one sticks to the other. Ultimately we will show that such a physical and functional interaction occurs in the intact functioning kidney (through the use of genetically modified mice). Identifying these interactions are fundamental to understanding and developing treatments for increased blood pressure.