Micropuncture analysis of tubuloglomerular feedback regulation in transgenic mice

Micropuncture methods have been used widely as a means to define the function of single tubules and study the functional connection between tubules and afferent arterioles (so-called tubuloglomerular feedback [TGF]). Transgenic mouse strains have become a new research tool with the potential of shedding new light on the role of specific gene products in renal tubular and vascular function. The micropuncture approach has therefore been adapted to studies in the mouse kidney. Although the data presented here support the feasibility of using this technique in the mouse, technical improvements are desirable in the areas of anesthesia, ureteral urine collections, blood collections, volume replacement, and functional stability for extended time periods. During ketamine/inactin anesthesia, TGF responses could regularly be elicited in wild-type mice. In contrast, changes in loop flow did not alter stop-flow pressure in angiotensin II type 1A receptor and angiotensin-converting enzyme knockout mice. Infusion of angiotensin II in subpressor doses partially restored TGF responsiveness in angiotensin-converting enzyme knockout animals. Normal TGF responses compared to wild type were found in nitric oxide synthase I and thromboxane receptor knockout mice. Using free-flow micropuncture techniques, the proximal-distal single-nephron GFR difference was found to be augmented in aquaporin-1 and Na/H exchanger-3 knockout mice, suggesting TGF activation in these strains of mice. These results support an essential role of angiotensin II in TGF regulation mediated through the angiotensin II type 1A receptor. Chronic nitric oxide synthase I and thromboxane receptor deficiency did not change TGF responsiveness. Aquaporin-1 and Na/H exchanger-3 deficiency enhances TGF suppression of TGF probably by volume depletion-mediated TGF sensitization. The use of micropuncture methodology in transgenic mice combines old and new research tools in a way that promises to yield important new insights into single-nephron function in physiologic and pathophysiologic conditions.