Measurement of intracellular pH with microelectrodes in rat kidney in vivo.

The construction of two types of double-barreled microelectrodes of sufficiently small tip size to record cytosolic pH (pHc) in renal tubular epithelial cells is described. Mean pHc in control anesthetized rats was 7.10 and mean basolateral membrane potential (Em) was -51.8 mV. These results suggest that hydrogen ions are actively extruded from either or both poles of the proximal tubular cell but that bicarbonate exit across the basolateral membrane is passive. In animals treated with acetazolamide, pHc was significantly elevated (mean 7.35) but Em was unchanged, suggesting that proton extrusion continues but that the rate of reaction of OH- with CO2 is diminished due to carbonic anhydrase inhibition. A pH higher than that of arterial blood was obtained from sites presumed to be in the interstitium. The evidence for the various assignments of microelectrode tip position is discussed.