Fig. 1

Self-referencing ion-selective electrode method. The electrode (probe) tip oscillates a distance of about 30 μm (double-headed arrow). The mean position is first set remote from the source (about 500 μm away; not shown) and the difference signal from the oscillation is taken as zero. The oscillating probe is then set within several μm of the a artificial source or b epithelium, and the difference signal in the concentration gradient is taken as a relative measure of the ion flux. Changes in ion flux are monitored during bath perfusion of control and experimental solutions. (Top panels) diagram; (Bottom panels) photomicrographs of artificial and epithelial sources and adjacent probe. Liquid ion exchanger (selective for K⁺ or H⁺) is visible in the tip of the electrode