Transepithelial potential difference in the proximal tubule of Necturus kidney

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Abstract
Summary Transepithelial potential difference (p.d.) was measured in the proximal tubule of Necturus kidney in vivo, by means of microelectrodes filled either with a 3M KCl solution or with a Ringer's solution for amphibians. The average transepithelial p.d., measured with KCl-tips, was: −1.4±2.4 mV (early convolutions), −0.1±2.0 mV (middle convolutions) and +0.1±2.4 mV (straight segment). The corresponding values obtained with Ringer's-filled microelectrodes were −2.3±1.8 mV, −1.3±1.1 mV and +0.1±1.2 mV, respectively. Tip localization into the lumen was ascertained by luminal injection of either oil (KCl electrode measurements) or artificial solutions which produced a measurable shift of transepithelial p.d. (determinations obtained with Ringer's-tips). Transepithelial p.d. in split-drops (mean reabsorptive half time 27.1±2.5 min) was −1.8±1.1 mV. The magnitude of transepithelial p.d. is discussed with respect to an equivalent electrical circuit; it is shown that high transepithelial p.d.'s are inconsistent with the known values of relative conductances of cell membranes in series and shunt pathway, respectively.