Reinvestigation of the transepithelial P.D. in the proximal tubule of Necturus kidney.

Published values of transepithelial potential differences (VTE) in the proximal tubule of Necturus vary from approximately 0 to approximately -15 mV. In view of this disparity, we reinvestigated VTE. Our measured VTE was on the average -1.0 mV in early convolutions and +0.6 mV in terminal proximal segments. In the course of this study, we considered five distinct causes of artifacts. 1) Tip and pre-tip potentials: their occurrence was minimized by using Ringer's filled microelectrodes. 2) Interstitial tip localizations: the position of the tip was ascertained by the shift in potential, resulting in response to peritubular perfusion with gluconate solutions. 3) Leaky impalements: VTE responses to gluconate, input resistance determinations and the presence of positive VTE's rule out the leak hypothesis. 4) Zeroline shifts between pre- and postimpalement stages, and 5) Spontaneous VTE drifts in the positive direction, due to gradual passage of the tip from cell to lumen, or in the negative direction, resulting from tip contact with the lower cellular layer. All five causes of artifacts may be involved in the controversy regarding past VTE estimates.