Real Time Microelectrode Measurement of Nitric Oxide in Kidney Tubular Fluid in vivo

Abstract: In this review we summarize our experience using a microelectrode to measure nitric oxide concentrations [NO] in living rat kidney tubules. In the anaesthetized living rat, the abdomen can be opened, and the kidney can be placed in a cup such that one can puncture a surface single tubular segment, 1-2 mm long, connected to one of 30,000 filtering glomeruli. The tubular segment can be viewed with a stereo microscope and punctured using sophisticated micromanipulators. The segment, ranging in diameter from about 15- 35 um contains freely flowing RBC-free fluid, electrolytes, O2, pCO2 and NO gas concentrations, and a host of other known and unknown substances. After a “pre ” puncture with a 7-10 um beveled glass pipette, intratubular [NO] can be directly determined by inserting, into the tubular lumen, the tip of a specially modified amperometric integrated electrode (WPI P/N ISO-NOP007). We review our in vivo experience with this electrode, emphasizing optimal practice to ensure appropriate calibration, stability, and selectivity for in vivo use. The electrode is highly selective for NO, and, despite fragility, with appropriate precautions, it can provide reproducible and highly sensitive NO measurements in the 40-1000 nM range. Key words: Nitric oxide, kidney tubules, in vivo NO measurement