Detection of NHE1-induced proton fluxes by oscillating an extracellular pH microelectrode. (A) The cell is held in whole cell configuration with its edge 5 μm from the tip of a pH microelectrode, and it is manually oscillated laterally by 50 μm to detect pH gradients. Both bath and pipette solution can be changed rapidly, the latter by the intra-pipette perfusion technique (see Materials and methods). (B) Example of a recording set for NHE1 transport activity in a single CHO cell using different bath sodium concentrations at fixed extracellular (8.2) and intracellular pH (6.0). Black bars mark time points when the cell was moved away from the pH microelectrode.