Measurements of Electrical Potential Differences on Single Nephrons of the Perfused Necturus Kidney

Abstract

Stable electrical potential differences can be measured by means of conventional glass microelectrodes across the cell membrane of renal tubule cells and across the epithelial wall of single tubules in the doubly perfused kidney of Necturus. These measurements have been carried out with amphibian Ringer's solution, and with solutions of altered ionic composition. The proximal tubule cell has been found to be electrically asymmetrical inasmuch as a smaller potential difference is maintained across the luminal cell membrane than across the peritubular cell boundary. The tubule lumen is always electrically negative with respect to the peritubular exta'acellular medium. Observations on the effectiveness of potassium ions in depolarizing single tubule cells indicate that the transmembrane potential is essentially an inverse function of the logarithm of the external potassium concentration. The behavior of the peritubular transmembrane potential resembles more closely an ideal potassium electrode than that of the luminal transmembrane potential. From these results, and the effects of various ionic substitutions on the electrical profile of the renal tubular epithelium, a thesis concerning the origin of the observed potential differences is presented. A sodium extrusion mechanism is considered to be located at the peritubular cell boundary, and reasons are given for the hypothesis that the electrical asymmetry across the proximal renal tubule cell could arise as a consequence of differences in the relative sodium and potassium permeability at the luminal and peritubular cell boundaries. This paper describes the effects of changes in the ionic environment on electrical potential gradients maintained across proximal renal tubule cells of Necturus maculosus. Normally the cell interior is asymmetrically negative with respect to tubular and interstitial fluid. Since the tubular fluid itself is electronegative with respect to interstitial fluid, the potential difference across the luminal cell membrane is less than that across the peritubular membrane (1-4). The effects of various ion species on these electrical potential gradients can be studied in the doubly perfused kidney of Necturus. Such measurements,

Pressure Control of Sodium Reabsorption and Intercellular Backflux across Proximal Kidney Tubule

“…Morphological studies of each segment of the proximal tubule under controlled pressure conditions, controlled intratubular flow rate, and diameter, with adequate determination of its net transport rate, will be required to further elucidate the present discrepancy in transepithelial resistance. (16), might be due to some degree of cell damage provoked in the present series by the cell impalement with double-barreled microelectrodes. In all three experimental conditions, the transepithelial potential difference was found to be lumen negative.…”

Mechanism of glomerulotubular balance. II. Regulation of proximal tubular reabsorption by tubular volume, as studied by stopped-flow microperfusion.

“…The finding that tubular reabsorption varies proportionately with changes in tubular volume is difficult to explain in the framework of the current model of proximal tubular reabsorption of NaCl and water (10). According to this model, Na+ diffuses passively into the tubular cell and is actively transported out of the cell at the peritubular border.…”

The Mechanism of Potassium Reabsorption in the Proximal Tubule of the Rat*

“…In numerous previous studies, an average potential gradient of approximately 20 mV, with the lumen negative to extracellular fluid, has been found across proximal tubular epithelium in both Necturus (17)(18)(19)(20)(21) and the rat (11,12,15 (26), and 0.03 to 0.09 for Necturus tubular epithelium (27) (19) has offered evidence indicating that the peritubular membrane is permeable to sodium to a degree that significantly influences EP. Since the peritubular membrane is not a perfect potassium electrode (i.e., is permeable to cations other than potassium), the Goldman equation, which takes into account the influence of sodium as well as potassium, rather than the Nernst equation, is used.…”