Imaging renin content and release in the living kidney

Renin release is the first, and at least initially, the rate-limiting step in the activation of the renin-angiotensin system, which helps to maintain body salt and water balance. Recent advances in our understanding of pathophysiology have generated a renewed interest in the multiple roles of renin and prorenin as a hormone, enzyme, and signaling molecule. The assays available to measure renin content, release and tissue activity are complex, indirect and work with significant internal errors. We developed an imaging approach to directly visualize renin content and study the dynamics of both the release and tissue activity of renin. Our experimental model uses multiphoton fluorescence microscopy, which is ideal for deep optical sectioning of the living renal tissue. Here we review the application of this renin imaging approach to the dissected, in vitro microperfused glomerulus as well as in the intact kidney in vivo.