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

Bloomer, H. Allan; Rector, Floyd C.; Seldin, Donald W.

doi:10.1172/jci104714

Cited by 46 publications

(20 citation statements)

References 22 publications

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“…Nevertheless, the data are consistent with a potassium pump located on the luminal surface of the tubule cell, which transports potassium out of the tubule lumen against its electrochemical gradient, as previously proposed by a number of investigators (21,4,8).…”

Section: Proximal Transtubular Potential Differences (Et)supporting

confidence: 90%

“…Figure 7 illustrates the TF/P K ratios obtained from three rats undergoing mannitol diuresis. Although the majority of ratios was not less than 1.0, as was the case in dogs during mannitol infusion, the mean TF/P K ratio of 1.09 (SD + 0.15) was sig- (12) and rat (4,(16)(17)(18)(19). All of the studies demonstrate a scatter of potentials ranging from 5 to 50 mv, lumen negative to extracellular fluid, with an average potential approximating 20 mv in the normal animal.…”

Section: Proximal Transtubular Potential Differences (Et)mentioning

confidence: 71%

“…A number of investigators (1)(2)(3)(4)(5)(6)(7)(8)(9) have recently studied the potassium concentration in the proximal tubule of rat and Necturus. Unfortunately, there are significant differences in the results obtained by different observers.…”

mentioning

confidence: 99%

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Micropuncture Study of Potassium Concentration in Proximal Tubule of Dog, Rat, and Necturus*

Watson¹,

Clapp²,

Berliner³

1964

J. Clin. Invest.

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A number of investigators (1-9) have recently studied the potassium concentration in the proximal tubule of rat and Necturus. Unfortunately, there are significant differences in the results obtained by different observers. The general conclusion, however, that potassium is reabsorbed against an electrochemical gradient in the proximal tubule of the rat seems justified. Furthermore, if one compares the ratio of the concentration of potassium in tubule fluid to that in plasma (TF/P K) to the corresponding ratio for inulin, potassium appears to be extensively reabsorbed from the proximal tubule.The study reported in this paper was undertaken in an attempt to define the mechanism by which potassium is handled in the proximal tubule of the dog nephron. It was made possible by the development of a sensitive ultramicromethod for the determination of potassium in biological fluids and the adaptation of micropuncture techniques to the study of renal function in dog (10). The concentrations of inulin and potassium were determined in the same samples of proximal tubule fluid. In separate sets of experiments, proximal transtubular potential differences were also determined. The concentrations of inulin and potassium in tubule fluid were compared with the respective concentrations in plasma in order to evaluate net potassium reabsorption, and the TF/P K ratio was compared with equilibrium ratios calculated from the transtubular potential by the Nernst equation.The results of this study differ quantitatively, although not qualitatively, from those reported by others using rat and Necturus as experimental * Submitted for publication July 12, 1963; accepted November 26, 1963. Presented in part at the 55th Annual Meeting of the American Society for Clinical Investigation, April 28, 1963. t Special Public Health Fellow. animals. To determine whether this difference was related to species differences or to methodology, a limited number of proximal TF/P K ratios were also determined in rats and Necturus. MethodsStudies were performed on male and female mongrel dogs weighing from 9 to 15 kg. The dogs were anesthetized by rapid injection of 200 mg of sodium pentothal administered intravenously as a 2.5% solution in distilled water; small additional doses were administered from time to time to maintain the desired level of anesthesia. The left kidney was exposed through a flank incision, and indwelling catheters were inserted into the ureter of the experimental kidney, the foreleg vein, and the femoral vein. Methods of exposing and supporting the kidney for micropuncture as well as the techniques of tubule fluid collection and identification have previously been reported (10). The samples of tubule fluid were generally 0.03 to 0.05 IAI in volume and were collected in 5 minutes or less.In all dog experiments, 15-minute urine collection periods for the determination of inulin and potassium clearances were obtained while tubule fluid samples were being collected. After appropriate priming and sustaining infusions of inulin ha...

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Section: Proximal Transtubular Potential Differences (Et)supporting

confidence: 90%

Section: Proximal Transtubular Potential Differences (Et)mentioning

confidence: 71%

See 1 more Smart Citation

Micropuncture Study of Potassium Concentration in Proximal Tubule of Dog, Rat, and Necturus*

Watson¹,

Clapp²,

Berliner³

1964

J. Clin. Invest.

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“…The relatively small intraluminal/peritubular phosphate concentration ratio (0.73) is similar in magnitude to the corresponding ratios for sodium during mannitol infusions, and for potassium and calcium (35)(36)(37). A comparison of inulin with phosphate TF/P ratios between the end of the proximal convolution and the final urine suggests that, in general, little additional reabsorption of this ion takes place either in the distal tubule or in the collecting duct.…”

Section: Methodssupporting

confidence: 53%

Micropuncture Study of Inorganic Phosphate Excretion in the Rat *

Strickler¹,

Thompson²,

Klose³

et al. 1964

J. Clin. Invest.

152

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“…The tubular puncture site was localized by injecting the tubule with latex as previously described (13).…”

Section: Methodsmentioning

confidence: 99%

The Mechanism of Bicarbonate Reabsorption in the Proximal and Distal Tubules of the Kidney*

Rector¹,

Carter²,

Seldin³

1965

J. Clin. Invest.

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277

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Considerable evidence (1-6) has been adduced to support the hypothesis that the reabsorption of filtered HCO3-by the kidney is mediated by a single mechanism, operative in both the proximal and distal portions of the nephron, which involves the secretion of cellular He in exchange for luminal Na+. The secreted Ho reacts with filtered HC03-to form H2CO3, which then decomposes to C02 and H20.Difficulties arise, however, when the details of the process are examined. In the steady state, the rate at which the H2CO3 is removed from the luminal fluid must equal the rate at which H+ is secreted. Walser and Mudge (7) have estimated that for the uncatalyzed dehydration of H2C03 to account for the observed rates of HC03-reabsorption, the steady-state concentration of H2C03 in luminal fluid must be at least tenfold greater than the concentration that would exist were H2C03 in equilibrium with the C02 tension of luminal fluid and plasma. As a result of the excess H2C03, the steady-state pH would be approximately 1 pH U lower than would be predicted from the luminal concentration of HC03-and the C02 tension of plasma, assuming complete equilibration of luminal H2C03 with plasma C02. A marked disequilibrium pH ' would exist.Two lines of evidence have been advanced to support the presence of a disequilibrium pH in the proximal tubule. Rector and Carter (8) perfused single proximal tubules with NaHCO3 * Submitted for publication July 27, 1964; accepted October 29, 1964. Supported in part by a grant from the American Heart Association and in part by grants 5 TI AM-5028 and 5 TI HE-5469 from the National Institutes of Health.'The difference between the actual pH, under conditions where C02 and H2CO0 are not in equilibrium, and the calculated equilibrium pH will be termed "disequilibrium" pH. and estimated the steady-state intraluminal pH from the change in color of various acid-base indicators. The pH was found to be about 1.5 U lower than the predicted equilibrium pH. However, since the color change could result from loss of dyes by either reabsorption or binding to cell proteins, the validity of these results may be questioned. Bank and Aynedjian (9) measured intratubular pH by aspirating tubular fluid into quinhydrone microelectrodes and comparing the readings while the electrode was still in the tubular lumen with the values obtained when the fluid was removed from the tubule and permitted to reach equilibrium. With this technique, they found the intratubular pH to be 2.0 to 2.5 pH U below the equilibrium pH. These results, however, are open to the serious objection that a disequilibrium pH of this magnitude would require the generation of H2CO3 at a rate 10 to 50 times greater than is theoretically possible, as judged from the rate of HC03-reabsorption.The presence of a disequilibrium pH, however, is not a necessary consequence of the hypothesis that H+ secretion mediates HC03-reabsorption. An equilibrium pH could obtain if H2CO3 were rapidly removed from the tubular urine by either of two mechanisms: 1) nonionic diffusion...

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

Cited by 46 publications

References 22 publications

Micropuncture Study of Potassium Concentration in Proximal Tubule of Dog, Rat, and Necturus*

Micropuncture Study of Potassium Concentration in Proximal Tubule of Dog, Rat, and Necturus*

Micropuncture Study of Inorganic Phosphate Excretion in the Rat *

The Mechanism of Bicarbonate Reabsorption in the Proximal and Distal Tubules of the Kidney*

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