Ionic Permeability and Electrical Potential Differences in Necturus Kidney Cells

Abstract

The cellular concentrations of Na, K, and C1 have been measured in kidney slices of the amphibian, Necturus maculosus. Permeability coefficients have been determined for Na, K, C1, Rb, Cs, and choline, from studies both of the uptake of radioactive isotopes and the rate of cell swelling in anisotonic solutions. The results of both methods were found to agree well. Measurements were also made of electrical potential differences across the peritubular face of the kidney cells using bathing solutions in which the electrolyte composition and concentrations could be varied. The data obtained are consistent with a model cell in which the potential difference arises as a result of differences in Na permeability relative to K on the two faces of the cell. The intracellular Na concentration is considered to be regulated by a Na-K coupled pump located at the peritubular face of the cell.Electrical potential gradients have been demonstrated between the interstitial fluid and the lumen of the proximal tubule of the kidney of the amphibian, Necturus rnaculosus, by Giebisch (1, 2), Whittembury (3), and Whittembury and Windhager (4). These authors have also shown that the electrical potential difference across the peritubular face of the cell is larger than that across the luminal face. The relationship between electrical potential differences and ionic permeabilities has been studied in nerve by Hodgkin and Katz (5). The present studies are concerned with similar relationships in Necturus proximal tubule cells.For this purpose we have used kidney slices. The permeability of kidney slices to a variety of small ions and molecules has been studied using a combination of radioactive techniques and studies of cell swelling. It is possible to make chemical analyses of the slices before and after exposure to permeant molecules and to measure potential differences in the slices under the same conditions. The combination of the present results with those obtained in situ has enabled us to put forward a hypothetical model kidney cell which 689

Intracellular potassium in cells of the distal tubule

“…In contrast, the amplhibian kidney may be sliced to yield segments that are composecl predominantly of distal tubules. Analyzing kidney slices chemically, Sullivan(4) found a K+ concentration in dlistal cells of Amphi7nma of 97.5 ± 3.6 mM while Whlittembury et al (5) foundl a K+ concentration of 108 mM in distal cells of the Nectuirnis kidney. Our electrometric finding of a low effective [K+] may be consistent with the recent radiokinetic observation of Wiederlholt et al (6) that only a small fraction of total cell K+ of Amphiuima kidney is involved in the overall transport process.…”

The distribution of sodium-potassium-activated adenosine triphosphatase in medulla and cortex of the kidney

“…It seems likely, however, that the difference in sodium concentration between distal and proximal tubules is related to a difference in permeability to water and sodium rather than to the mechanism of active transport. Sodium is presumably pumped from the interior of the cell across the periluminal border (29), and the concentration of sodium within distal tubular cells is probably close to that in proximal tubular cells (30,31). The concentration gradient against which sodium must be transported is therefore similar in cells of the proximal and distal cortical convolutions, though external sodium tends to be higher in the medulla of the kidney than in the cortex, at least during hydropenia (32).…”

Sodium Extrusion and Potassium Uptake in Guinea Pig Kidney Cortex Slices

“…It would also explain why the membrane potential was more negative in sucrose than in choline (29). The entry of choline (52,11) would make the membrane potential less negative and, secondarily, would lower the cell K concentration. However, this type of pump could not explain the findings of Whittam and Willis (38), where it was noticed that K influx stops in Na-depleted cells.…”

“…Na and K concentrations were determined by flame photometry (11) in aliquots of the extraction fluid.…”