THE EFFECT OF POTASSIUM ON INTRACELLULAR BICARBON- ATE IN SLICES OF KIDNEY CORTEX1 By HELEN M. ANDERSON AND GILBERT H. MUDGE 2 WITH THE TECHNICAL ASSISTANCE OF THEODORA J. LANNON (From the Department of Medicine, College of Physicians and Surgeons, Columbia University, and the Presbyterian Hospital, New York City, N. Y.) (Submitted for publication June 21, 1955; accepted July 20, 1955) An increase in serum bicarbonate concentration has been observed in association with potassium depletion in a variety of clinical and experimental conditions. Although the development of the al- kalosis may be extra-renal in origin, its perpetua- tion must depend upon an alteration in renal func- tion which can be characterized as either an in- crease in bicarbonate reabsorption or an increase in hydrogen ion excretion. Many instances of so- called "paradoxical" aciduria have been described (cf. 1, 2). Recent attempts to interpret this phenomenon have been predicated upon the concept that the extracellular alkalosis of potassium depletion is accompanied by an intracellular acidosis. Sup- porting evidence has been derived from a variety of experiments. In the muscle of potassium de- pleted rats Gardner, MacLachlan, and Berman (3) observed a decrease in the intracellular pH as calculated from whole tissue analyses corrected for extracellular space. Cooke and co-workers (4), on the basis of balance experiments and muscle analyses, concluded that the loss of intra- cellular potassium in rats was accompanied by an intracellular accumulation of both sodium and hy- drogen ions. In studying experimental potassium depletion in man, Black and Milne (5) interpreted their balance data as indicating a shift of hydrogen ions into cells. In an attempt to obtain direct evi- dence relating the electrolyte composition of the renal parenchyma to the excretion of acid urine, Darrow, Cooke, and Coville (6) analyzed the kid- neys of potassium depleted rats, but with inconclu- sive results. Since the intracellular sodium and potassium 1 This study was supported by a grant from the Rocke- feller Foundation to Dr. John V. Taggart. 2 Present Address: Department of Pharmacology and Experimental Therapeutics, The Johns Hopkins Uni- versity School of Medicine, Baltimore 5, Maryland. concentrations in the kidney cortex can be varied over a wide range by the use of in vitro techniques, studies of tissue slices were undertaken in order to define the relationships of intracellular potassium and bicarbonate. METHODS The preparation of tissues has been described previously in detail (7) and is summarized here. Fresh slices were made from the renal cortex of rabbits killed by carotid exsanguination and were depleted of potassium by leach- ing for one hour in 0.15 N NaCl at room temperature. Half the slices were then incubated in Warburg flasks in 3 ml. of a medium containing NaHCO, 18 mEq. per L., CaCl2 1.3 mEq. per L., sodium phosphate buffer (pH 7.4) 3.7 mM. per L. and sodium acetate 0.01 mM. per L.3 The remaining slices were incubated in a medium identi- cal in composition except for the addition of 10 mEq. per L. of KCl. Sufficient NaCl was added to both media to provide constant osmolar concentrations of 300 mOs. per L. The Warburg vessels were gassed with a mixture of 5 per cent CO2 and 95 per cent 02. The carbon dioxide- bicarbonate buffer system provided a pH of 7.4 in the external medium (8). Following incubation for 35 min- utes at 250 C. the slices were promptly removed, blotted, and then analyzed for water and electrolyte. This entire procedure will be referred to hereafter as the standard system; modification of individual variables will be de- scribed for each special circumstance. Tissue sodium and potassium were determined by flame photometry using lithium as an internal standard. In early experiments tissue chloride was determined by a modified Volhard titration. In later experiments, through the courtesy of Dr. Paul Marks, chlorides were meas- ured potentiometrically using a silver-silver chloride cell (9). "Acid-labile CO2" was determined by a modification of the technique devised by Conway and Fearon (10). Conway dishes (inner chamber 40 mm. diameter, 5 mm. high) were prepared with 1.3 ml. of 0.025 N Ba(OH), in the center well, covered with ground glass cover-slips and sealed with anhydrous lanolin. After incubation in the Warburg flasks, tissue slices (about 300 mg. per 3 Although these amounts of calcium and phosphate were routinely added, their omission did not influence the results. 1691
Transcript
THE EFFECT OF POTASSIUMON INTRACELLULARBICARBON-ATE IN SLICES OF KIDNEY CORTEX1
By HELENM. ANDERSONANDGILBERT H. MUDGE2 WITH THE TECHNICAL ASSISTANCEOF THEODORAJ. LANNON
(From the Department of Medicine, College of Physicians and Surgeons, Columbia University,and the Presbyterian Hospital, New York City, N. Y.)
(Submitted for publication June 21, 1955; accepted July 20, 1955)
An increase in serum bicarbonate concentrationhas been observed in association with potassiumdepletion in a variety of clinical and experimentalconditions. Although the development of the al-kalosis may be extra-renal in origin, its perpetua-tion must depend upon an alteration in renal func-tion which can be characterized as either an in-crease in bicarbonate reabsorption or an increasein hydrogen ion excretion. Many instances of so-called "paradoxical" aciduria have been described(cf. 1, 2).
Recent attempts to interpret this phenomenonhave been predicated upon the concept that theextracellular alkalosis of potassium depletion isaccompanied by an intracellular acidosis. Sup-porting evidence has been derived from a varietyof experiments. In the muscle of potassium de-pleted rats Gardner, MacLachlan, and Berman(3) observed a decrease in the intracellular pH ascalculated from whole tissue analyses correctedfor extracellular space. Cooke and co-workers(4), on the basis of balance experiments andmuscle analyses, concluded that the loss of intra-cellular potassium in rats was accompanied by anintracellular accumulation of both sodium and hy-drogen ions. In studying experimental potassiumdepletion in man, Black and Milne (5) interpretedtheir balance data as indicating a shift of hydrogenions into cells. In an attempt to obtain direct evi-dence relating the electrolyte composition of therenal parenchyma to the excretion of acid urine,Darrow, Cooke, and Coville (6) analyzed the kid-neys of potassium depleted rats, but with inconclu-sive results.
Since the intracellular sodium and potassium
1 This study was supported by a grant from the Rocke-feller Foundation to Dr. John V. Taggart.
2 Present Address: Department of Pharmacology andExperimental Therapeutics, The Johns Hopkins Uni-versity School of Medicine, Baltimore 5, Maryland.
concentrations in the kidney cortex can be variedover a wide range by the use of in vitro techniques,studies of tissue slices were undertaken in order todefine the relationships of intracellular potassiumand bicarbonate.
METHODS
The preparation of tissues has been described previouslyin detail (7) and is summarized here. Fresh slices weremade from the renal cortex of rabbits killed by carotidexsanguination and were depleted of potassium by leach-ing for one hour in 0.15 N NaCl at room temperature.Half the slices were then incubated in Warburg flasksin 3 ml. of a medium containing NaHCO, 18 mEq. perL., CaCl2 1.3 mEq. per L., sodium phosphate buffer (pH7.4) 3.7 mM. per L. and sodium acetate 0.01 mM. per L.3The remaining slices were incubated in a medium identi-cal in composition except for the addition of 10 mEq. perL. of KCl. Sufficient NaCl was added to both media toprovide constant osmolar concentrations of 300 mOs. perL. The Warburg vessels were gassed with a mixture of5 per cent CO2 and 95 per cent 02. The carbon dioxide-bicarbonate buffer system provided a pH of 7.4 in theexternal medium (8). Following incubation for 35 min-utes at 250 C. the slices were promptly removed, blotted,and then analyzed for water and electrolyte. This entireprocedure will be referred to hereafter as the standardsystem; modification of individual variables will be de-scribed for each special circumstance.
Tissue sodium and potassium were determined by flamephotometry using lithium as an internal standard. Inearly experiments tissue chloride was determined by amodified Volhard titration. In later experiments, throughthe courtesy of Dr. Paul Marks, chlorides were meas-ured potentiometrically using a silver-silver chloride cell(9).
"Acid-labile CO2" was determined by a modification ofthe technique devised by Conway and Fearon (10).Conway dishes (inner chamber 40 mm. diameter, 5 mm.high) were prepared with 1.3 ml. of 0.025 N Ba(OH),in the center well, covered with ground glass cover-slipsand sealed with anhydrous lanolin. After incubation inthe Warburg flasks, tissue slices (about 300 mg. per
3 Although these amounts of calcium and phosphatewere routinely added, their omission did not influencethe results.
1691
HELEN M. ANDERSONAND GILBERT H. MUDGE
TABLE I
Effect of potassium on tissue bicarbonate concentration
vessel) were quickly transferred to the outer well of a
prepared Conway dish. About 5 ml. of 2 N H2S04 was
then added to the outer well on the side opposite the tis-sues. At all times the cover glass was slipped open onlyfar enough to allow insertion of the sample or the pipettetip. The dish was promptly resealed and gently rotatedto provide complete penetration of acid into the slices.The Conway dishes so loaded with Ba(OH)2, tissue, andH2S04 were allowed to stand at room temperature for one
hour. A one ml. aliquot of fluid from the center wellwas then removed and its content of Ba(OH)2 deter-mined by titration with 0.005 N HCl, using thymol blueas indicator. Calculation by difference revealed thequantity of Ba(OH)2 converted to BaCO, and hence theamount of "acid-labile C02" present in the tissue. AConway dish without tissue was run with each experi-ment as a control. Standardization of this technique usingknown concentrations of NaHCO3 solution in the outerwell gave 95 to 105 per cent recoveries. Longer stand-ing, increased temperature, or gentle agitation of theConway dish did not significantly alter the recovery. Inone experiment, through the courtesy of Dr. DuncanHoladay, "acid-labile CO," of the slices was measured bythe gasometric method of Danielson and Hastings (11).4The results were the same as those obtained by the modi-fied Conway technique.
All expressions for the concentration of electrolyte intissues are given per kilogram wet weight. The q02 was
calculated as the cubic millimeters of 02 consumed perhour per mg. initial wet weight of tissue. Tissue bi-carbonate determinations were done in duplicate on tis-sue incubated in separate flasks and treated identically.Tissue Na, K, and Cl were determined in duplicate on
the specimen from a single flask.
4 "Acid-labile C02" is considered to include dissolvedC02, H2CO,, and HCO,7. For simplicity, except as indi-cated in Table VIII, the term bicarbonate is used as a
synonym for "acid-labile C02," since this is by far thelargest component of the C02-H2COs-HCO8- system. Itis recognized that Conway and Fearon (10) have pre-
sented evidence to suggest that compounds other thanC0-H2CO,-HC0O, are measured as "acid-labile C02."However, since the nature of these compounds is notclear and confirmation of this observation has not beenpresented, the conventions of Danielson and Hastings (11)have been adopted here.
RESULTS
A typical experiment employing the standardsystem is illustrated in Table I. Before incubation,the potassium concentration of the leached slicewas 35 mEq. per Kg. After incubation in a potas-sium-free medium there was no change in tissuepotassium, but incubation in the medium contain-ing 10 mEq. per L. of potassium resulted in an ac-
cumulation of potassium by the tissue to a finalconcentration of 77.2 mEq. per Kg. This valueis similar to that found in fresh tissue (7). Theuptake of potassium by the slices was associatedwith a loss of sodium, so that there was no signifi-cant change in the sum of sodium and potassium.5The bicarbonate concentration of the tissue incu-bated without potassium was 13.5 mEq. per Kg.;slices with added potassium had a significantlyhigher bicarbonate concentration (18.0 mEq. per
Kg.).TABLE 1I
Average values from 17 experiments employingthe Standard System *
* Eight analyses of fresh kidney cortex, removed asquickly as possible after killing the rabbit, yielded anaverage bicarbonate concentration of 14.4 mEq. per Kg.Fresh tissue values previously reported (7) are: K+, 69.3mEq. per Kg.; Na++K+, 138 mEq. per Kg.; H20, 77.1per cent wet weight.
A similar relationship was observed in a totalof 72 experiments. In Table II are summarizedthe results from 17 experiments in which tissuebicarbonate, sodium, potassium and water con-tent were measured. The average difference intissue bicarbonate between the slices with andwithout added potassium was 4.7 mEq. per Kg.;this was associated with an average change of39.6 mEq. per Kg. in the level of tissue potassium.
5 In this presentation the convention of correlating tis-sue bicarbonate to potassium will be employed. It isrecognized that because of the nature of the cationchanges, tissue sodium could be used as a referenceequally well.
1692
POTASSIUM AND TISSUE BICARBONATE
The sum of tissue sodium and potassium remainedconstant, although small changes may have es-caped detection because of difficulties inherent inthe measurement of tissue sodium. The accumula-tion of potassium was associated with a small, butstatistically significant, increase in tissue hydra-tion. As will be noted in subsequent tables, the ab-solute level of tissue bicarbonate varied somewhatfrom one experiment to another, but the differencebetween the slices with low and high tissue po-tassium remained constant. In every experiment,therefore, suitable internal controls were employed.
The dependence of tissue bicarbonate on the in-tracellular accumulation of potassium rather thanon the potassium concentration in the incubationmedium is illustrated by experiments in whichrespiration or aerobic phosphorylation was in-hibited. Previous studies (7) have shown thatthe uptake of potassium is related to aerobic meta-bolic activity. The effects of anaerobic incubation
* Before incubation the tissue contained 42.4 mEq. K+per Kg.
are illustrated in Table III. The experimentalconditions were the same as those of the standardsystem except that the gas mixture was 5 per centC02-95 per cent N2 instead of 5 per cent CO2-95 per cent 02. The anaerobic tissues showed anet loss of potassium and a tissue bicarbonate con-centration unchanged by the addition of potassiumto the external medium.
It has been shown that 2,4-dinitrophenol un-couples aerobic phosphorylation and prevents theuptake of potassium by kidney slices (12). Asshown in Table IV, this agent causes a failure ofbicarbonate accumulation and a parallel inhibitionof potassium uptake.
Previous observations have shown that thepresence of low concentrations of potassium in theexternal medium increases the rate of oxygen
* Before incubation the tissue contained 35.9 mEq. K+per Kg. The sum of Na+ plus K+ remained constant.
consumption (7). This suggested that the changein the tissue level of bicarbonate might be a directeffect of the respiratory stimulation produced bythe addition of potassium. The use of the indi-rect Warburg technique (8) permitted the deter-mination of the qO2 in the presence of CO2 inthe gas phase. Experiments were carried out with40 mEq. per L. of potassium in the incubationmedium, instead of 10 mEq. per L., since thishigher concentration is not generally accompaniedby respiratory stimulation. The results are shownin Table V, and clearly indicate that the changein bicarbonate in tissues incubated with added po-tassium is not dependent upon increased oxygenconsumption. In addition, in the earlier experi-ment with 2,4-dinitrophenol, despite marked re-spiratory stimulation there was a fall, ratherthan an increase, in the level of tissue bicarbonate.The substitution of succinate, citrate or a-keto-glutarate for acetate in the standard system did notchange the tissue level of either bicarbonate orpotassium. With succinate as substrate there wasapproximately a fifty per cent increase in oxygenconsumption. It is concluded, therefore, that theeffect of potassium on tissue bicarbonate is notthe direct result of respiratory stimulation.
The influence of different levels of tissue po-tassium on bicarbonate was examined over a widerange by varying the amount of potassium chlo-ride added to the medium. The osmolarity waskept constant by adjustments in sodium chloride.The results of four separate experiments are illus-trated in Figure 1. It is seen that tissue bicarbo-nate and potassium are linearly related except atthe very high tissue potassium levels, which wereachieved by raising the external concentration toas high as 120 mEq. per L. The results of highexternal concentrations are difficult to evaluate be-
1693
1694 HELEN M. ANDERSONAND GILBERT H. MUDGE
TABLE V
Relation of oxygen consumption to tissue bicarbonate *
Medium K+ qO2 Tissue HCOa-
mEq./L. mEq./Kg.0 .63 9.3
40 .54 15.7
*The qO2 was measured by the indirect method ofWarburg (8).
cause of marked respiratory depression and exces-sive tissue hydration.
The rise in tissue bicarbonate noted above couldresult from either an increase in the total numberof anions or a replacement of some anions by bi-carbonate. Evidence supporting the latter mecha-nism is afforded by two observations: 1) Thesum of tissue sodium and potassium remainedconstant (see Table II); and 2) the changes intissue chloride which were observed in a series ofexperiments (Table VI). The average changeupon the addition of potassium was + 4.0 mEq.per Kg. of bicarbonate and - 5.7 mEq. per Kg. ofchloride. Within the limits of the methods em-ployed, these changes are considered to be ap-proximately equivalent. The substitution of ni-trate for chloride in the external medium resultedin a fall in tissue chloride to about 6 mEq. per Kg.The tissue bicarbonates in the nitrate medium werethe same as in the chloride medium, and the usualchange in tissue bicarbonate was produced by theaddition of potassium. The results are inter-preted as evidence that the changes in tissue chlo-
20
o1 8
wE 16
0
I 14
R12 _ AK
1030 60 90 120
Tissue K+-mEq/Kg.
FIG. 1. RELATION OF TISSUE BICARBONATE TO TISSUEPOTASSIUM
Lines indicate four separate experiments. Tissue po-tassium was varied by changing external concentration.
ride (cf. Table VI) associated with the accumula-tion of potassium are secondary to changes intissue bicarbonate.
In a number of biological systems it has beenreported that rubidium and cesium behave in amanner similar to potassium. As shown in TableVII the addition of the chloride salts of these ele-ments to the incubation medium resulted inchanges in tissue bicarbonate resembling thoseproduced by potassium, whereas lithium was in-effective. It is of interest that hypokalemic alka-losis in the rat may be corrected by the adminis-tration of rubidium (13). However, the presentresults with lithium are not what might be antici-pated from previous studies in the dog in which
TABLE VI
Relation of tissue chloride and bicarbonate *
HCOa-, mEq./Kg. Cl-, mEq.lKg.
No K+ K+ NoK+ K+added added A dt S.D. added added zA i S.D.
15.2 19.2 +4.0i.41 64.9 59.2 -5.7-.52
* Values reported are averages from eight experimentsin which the standard system was employed. Chloride wasdetermined by a modified Volhard titration in four experi-ments, and by a potentiometric method (9) in the re-mainder. Similar results were obtained by both methods.The chloride concentration in the incubation medium was,initially, 118 mEq. per L.
it was shown that potassium excretion and urinepH were increased by the administration of thision (14, 15).
Studies of the effect of changes in the externalconcentration of bicarbonate were undertaken andthe results of a typical experiment are given inTable VIII. In this and five similar experiments,pCO2 was maintained constant so that the altera-tions in external bicarbonate were associated withparallel changes in the pH of the medium. Thephosphate buffer used in the standard incubationmedium was omitted. At low concentrations ofexternal bicarbonate the addition of potassiumhad a much greater effect on the level of tissuebicarbonate than in the standard system. Con-versely, at high external bicarbonate concentra-tions, the effect of potassium was negligible. ThepH of the external solution had no effect on thefinal tissue concentration of potassium or of po-tassium plus sodium, either with or without theaddition of potassium to the medium. Similarly,
POTASSIUM AND TISSUE BICARBONATE
respiration and tissue hydration were essentiallythe same at each pH.
Because of the changes in external bicarbonate,the data from these experiments can not be evalu-ated solely in terms of total tissue concentrations.Therefore, intracellular values were calculated onthe basis of the assumptions listed in Table VIII.Despite recognized limitations, these data prob-ably represent a reasonable approximation and af-ford a valid basis for comparison. As shown inFigure 2, in the potassium depleted slice the in-tracellular concentration of bicarbonate rises asthe external level is increased. In contrast, sliceswith normal tissue potassium maintain nearly con-
* Ten mEq. per L. of the chloride salt of the indicatedcations was added to the external medium. Total osmo-larity was kept constant by the addition of sodium chloridein a concentration of 105 mEq. per L., which, plus theother cup components, provided a total osmolar concen-tration of 300 mOs. per L. (See Methods.) The ionslisted above had no significant effect on the rate of oxygenconsumption.
stant intracellular bicarbonate despite a five-foldchange in external concentration.
DISCUSSION
These results directly demonstrate that the levelof tissue bicarbonate can be influenced by potas-sium. For reasons previously mentioned these ef-fects may be attributed to intracellular changes.If applied to certain physiological adjustmentswhich are observed in the intact animal, the find-ings could provide an explanation for the "para-doxical" aciduria of potassium depletion. Recentstudies indicate that the exchange of sodium fromthe tubular urine for hydrogen ion from the tubulecell is the mechanism by which bicarbonate is reab-sorbed and the urine acidified (16-18). Berliner,Kennedy, and Orloff (19) have postulated that thesodium-potassium exchange responsible for thetubular secretion of potassium may compete with
TABLE VIII
Effect of external bicarbonate on calculated intracellular pH *
* All cups were gassed with 5 per cent C02-95 per cent02. The pH of the medium was calculated from thenomogram of Umbreit, Burris, and Stauffer (8). Theintracellular values were calculated by the method ofWallace and Hastings (21), assuming: 1) tissue solids, 22per cent of total tissue; 2) extracellular space, 25 per centof total tissue; 3) pK' for carbonic acid, 6.1; 4) the samepCO2 in the intracellular water as in the external medium;5) solubility coefficient of CO2 in the water of the intra-cellular space, 0.592; 6) all acid-labile tissue CO2 to bebicarbonate ion.
sodium-hydrogen exchange. For example, theaciduria of potassium depletion might be at-tributed to a decrease in the rate of potassiumsecretion and an increase in sodium-hydrogen ex-change. The present results may define some ofthe regulatory factors more precisely, namely thatthe apparent competition between hydrogen andpotassium ions for an excretory mechanism maybe a reflection of their relative intracellular con-centrations. Thus, the internal environment ofthe tubule cell may directly modify the composition
30
J-j
wE
IF)I0U
With K+odded
20 _
10
No K+ added
10 20Incubation Medium HCO-mEq/L
30
FIG. 2. RELATION OF INTRACELLULAR BICARBONATE TO
EXTERNALBICARBONATECONCENTRATION
All tissues gassed with 5 per cent CO2-95 per cent 02.For initial pH values of media, see Table VIII.
1695
HELEN M. ANDERSONAND GILBERT H. MUDGE
of the urine, and extra-renal regulatory mecha-nisms need not be implicated.
In their studies on rat skeletal muscle, Cooke,Segar, Cheek, Coville, and Darrow (4) suggestedthat during the development and repair of hy-pokalemic alkalosis the quantitative relationshipsbetween intra- and extra-cellular univalent cationsmight be described by an ionic exchange in the ra-tio of three potassiums for two sodiums and onehydrogen. Because of the difficulties inherent inthe estimation of intracellular buffer capacity, thecalculation of this ratio is only an approximate de-scription. In the present experiments, at an ex-ternal pH of 7.4, an exchange of eight sodium foreight potassium ions is accompanied by a simul-taneous exchange of one chloride for one bicarbo-nate ion. Estimates of changes in intracellularhydrogen ion concentration in this system haveonly limited validity because of the following fac-tors: 1) The exact nature of intracellular "acid-labile" carbon dioxide has not been ascertained(10); and 2) calculations presented above for thekidney cortex have assumed a homogeneous cellpopulation. If the cells do not behave uniformly,the calculated changes would be smaller in somecells and greater in others.
Despite these limitations, the derived intracel-lular pH suggests that the level of potassiumwithin the cells is related to their buffer capacity.As shown in Table VIII and Figure 2, a normalpotassium concentration is associated with onlysmall changes in intracellular pH when the ex-ternal pH is varied. However, the results do notindicate an absolutely constant relationship be-tween intracellular potassium and hydrogen ionconcentrations. This is shown by the results ob-tained with the potassium depleted slice (Figure2). Although the level of intracellular potassiumremains constant, the pH of these slices is mark-edly influenced by the pH of the external en-vironment.
While some of the observations reported hereare qualitatively similar to those predicted by theBoyle-Conway (20) application of the Donnanequilibrium, the quantitative relationships betweenintra- and extra-cellular ions deviate so far fromthe predicted values that the hypothesis need notbe considered further. An interpretation of thepresent results on a physico-chemical basis is notNvarranted at this time.
SUMMARY
Studies on slices of rabbit kidney cortex havedirectly demonstrated that the intracellular con-centration of bicarbonate is related to that of po-tassium. These findings support the hypothesisthat the pH of the cells of the renal tubules may di-rectly influence renal excretion in the regulationof acid-base balance in conditions of potassium de-pletion or excess.
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3. Gardner, L. I., MacLachlan, E. A., and Berman, H.,Effect of potassium deficiency on carbon dioxide,cation, and phosphate content of muscle, with anote on the carbon dioxide content of humanmuscle. J. Gen. Physiol., 1952, 36, 153.
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5. Black, D. A. K., and Milne, M. D., Experimental po-tassium depletion in man. Clin. Sc., 1952, 11, 397.
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14. Foulks, J., Mudge, G. H., and Gilman, A., Renalexcretion of cation in the dog during infusion of
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POTASSIUM AND TISSUE BICARBONATE
isotonic solutions of lithium chloride. Am. J.Physiol., 1952, 168, 642.
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