Advances in renal (patho)physiology using multiphoton microscopy

Multiphoton excitation fluorescence microscopy is a state-of-the-art confocal imaging technique ideal for deep optical sectioning of living tissues. It is capable of performing ultrasensitive, quantitative imaging of organ functions in health and disease with high spatial and temporal resolution which other imaging modalities cannot achieve. For more than a decade, multiphoton microscopy has been successfully used with various in vitro and in vivo experimental approaches to study many functions of different organs, including the kidney. This study focuses on recent advances in our knowledge of renal (patho)physiological processes made possible by the use of this imaging technology. Visualization of cellular variables like cytosolic calcium, pH, cell-to-cell communication and signal propagation, interstitial fluid flow in the juxtaglomerular apparatus (JGA), real-time imaging of tubuloglomerular feedback (TGF), and renin release mechanisms are reviewed. A brief summary is provided of kidney functions that can be measured by in vivo quantitative multiphoton imaging including glomerular filtration and permeability, concentration, dilution, and activity of the intrarenal renin-angiotensin system using this minimally invasive approach. New visual data challenge a number of existing paradigms in renal (patho)physiology. Also, quantitative imaging of kidney function with multiphoton microscopy has tremendous potential to eventually provide novel non-invasive diagnostic and therapeutic tools for future applications in clinical nephrology.