AMERICAN
Vol.
JOURNAL
OF PHYSIOLOGY
229, No. 5, November
1975.
Printed
in U.S.A.
Potassium
transport
collecting
duct of the rat
H. JOHN Department
REINECK,
H.
JOHN,
JAY H. STEIN. duct of the rat. Am. AND
REINECK, of Medicine,
W.
RICHARD
Potassium
transport
in the distal
RICHARD W. OSGOOD, THOMAS Ohio State University College of Medicine,
OSGOOD,
‘I‘IHOMAS
in the distal
tubule
F.
FERRIS,
and collecting
J. Physiol. 229(5) : 1403-1409. 1975.-Because of recent conflicting results, micropuncture studies were performed to clarify the respective role of the distal convoluted tubule and collecting duct in the regulation of urinary potassium excretion. Five groups of Sprague-Dawley rats were studied: group I, hydropenia (n = 10); group II, Ringer loading (n = 7) ; group III, acute KC1 loading (n = 6); group IV, mannitol diuresis (n = 6); group V, KC1 infusion during mannitol diuresis (n = 7). Early and late distal tubules were identified with intravenous injections of lissamine green. In each animal net secretion of potassium occurred along the distal convoluted tubule, and a direct relationship between distal tubular flow rate and potassium secretion was observed. The magnitude of potassium secretion at high distal tubular flow rates was dependent on the inodel studied. Potassium transport beyond the distal tubule was evaluated by comparing end distal potassium delivery and fractional potassium excretion. At low urinary flow rates net reabsorption was observed, whereas at higher flow rates no net transport occurred. Thus, flow rate along the collecting duct may be a major determinant of urinary potassium excretion. potassium secretory mechanism; ture
potassium
excretion;
micropunc-
1937, MCCANCE AND WIDDOWSON (14) first demonstrated that urinary potassium excretion could exceed the filtered load, indicating the existence of a potassium secretory mechanism. Clearance studies by Berliner and Kennedy (2) and stop-flow studies by Vander (21) suggested that the bulk of excreted potassium was primarily derived from a distal secretory process. Subsequently, Malnic and co-workers (9, 12), utilizing micropuncture techniques in albino rats, located the secretory site in the distal convoluted tubule. Recently, however, Bank and Aynedjian (1) described net potassium reabsorption along the distal convoluted tubule of Sprague-Dawley rats under a variety of conditions including hydropenia, a reduction in renal mass, and acute KC1 loading. Further, these authors described net secretion of potassium along the collecting duct in the latter two groups. Thus, it is not clear whether the regulation of urinary potassium excretion occurs primarily in the distal tubule or collecting duct system. The present study was undertaken to clarify this issue and to further investigate the role of the collecting duct in the regulation of urinary potassium excretion. The results indiIN
tubule
and
F. FERRIS, AND JAY Columbus, Ohio 43210
H. STEIN
cate that net potassium secretion does occur along the distal convoluted tubule of the Sprague-Dawley rats utilized in this study but that transport beyond this segment may modify urinary potassium excretion. METHODS
Adult male Sprague-Dawley rats obtained from the Schmidt, Co. (Madison, Wis.) weighing 250-350 g were anesthetized with Inactin 100 mg/kg (Promonta, Hamburg, West Germany). A tracheostomy was performed, and polyethylene catheters were placed in each jugular vein for infusions and in the femoral artery for blood pressure monitoring and withdrawal of blood samples. The left kidney was exposed through a left subcostal incision and gently dissected from the surrounding perirenal fat. The rats were prepared for micropuncture as previously described (19, 20) . The aniinals were initially given 0.5 ml of a 10 % inulin solution dissolved in Ringer and then a maintenance infusion at a rate of .02 ml/min. While the inulin was equilibrating, early and late distal tubular segments were localized with two to three intravenous injections of lissamine green (0.05 ml of a 10 % solution). The validity of this method of localization has been previously demonstrated (19). Further confirmation of this technique was also obtained in the present study (vida infra). No puncture was obtained until at least 5, min after the last lissamine green injection and 1 h after the inulin infusion had been started. The tubules were punctured with sharpened pipettes with tip diameters varying from 6 to 8 pm diam. Only distal tubular samples were obtained in these studies. With the pipette tip positioned within the tubular lumen, a large column of mineral oil stained with Sudan black was injected into the tubule. After initial gentle aspiration to begin the collection, most of the samples were collected either spontaneously or with only occasional aspiration to maintain the oil column in a constant position. All tubular fluid collections were timed. The following experimental groups were studied : Group I. Ten hydropenic rats received Ringer solution at an infusion rate of 0.02 ml/min throughout the study. Group II. Seven animals were volume expanded with 10 % body wt Ringer solution over 50-60 min. The infusion rate was then reduced to that of urinary flow, and distal collections and clearances were obtained. In four of these studies, d-aldosterone, 20 pg/kg was given subcutaneously 2-3 h 1403
Downloaded from www.physiology.org/journal/ajplegacy by ${individualUser.givenNames} ${individualUser.surname} (132.174.254.157) on January 12, 2019.
1404
REINECK,
before the study followed by an intravenous infusion of 20 pg/kg per h throughout the rernainder of the experiment. Group ZZZ. Six hydropenic rats were infused with 0.15 M KC1 at a rate of .05 ml/min. Thirty rninutes after the infusion had begun, tubular fluid and urine collections were obtained. During the collections, the KC1 infusion was continued. Group IV. Six animals were given 10 % rnannitol at an infusion rate varying from 0.1 to 0.2 ml/min. Twenty to thirty minutes after the infusion had begun, collections were obtained. Group V. In seven anirnals, hypertonic mannitol was given at a rate of .I-.3 ml/min, concomitant with an infusion of 0.15 M KC1 at a rate of .05-.07 ml/min. Thirty rninutes after the infusion was initiated, distal tubular and urine collections were begun. The infusions were continued throughout the collections. In two further studies performed during acute KC1 loading (group ZZZ), early and late distal samples were collected in the usual rnanner. The respective tubules were then injected with latex and microdissected with the technique described by Cortell (3). Two clearance periods were obtained in each study. Plasma and urine inulin concentrations were measured by the anthrone rnethod (5), while tubular fluid inulin was determined by the method of Vurek and Pegram (22). Tubular fluid sodium and potassium concentrations were measured with an Aminco helium-glow flame photometer (American Instrument Co., Inc., Silver Spring, Md.), and urine and plasma concentrations were measured with an Instrumentation Laboratory flame photometer (Instrurnentation Laboratory, Inc. 9 Watertown, Mass.). The data were analyzed by standard statistica l methods as the rneans * standard and all are presented error. Calculations I) Fractional delivery of potassium to early or late distal tubule the tubular fluid-to-plasma potas= m/p)K/In, sium-to-inulin ratio in either the early distal tubule (ED) or late distal tubule (LD). 1. Summary of clearance
TABLE
GFR,
ml/min ~.
OSGOOD,
FERRIS,
AND
STEIN
2) Absolute delivery of potassium = VF X TFK, where V, is the tubular flow rate in nanoliters per minute and TFK is the tubular fluid potassiurn concentration. 3) Absolute distal tubular potassiurn secretion = (v, x TFK)LD - 0% x TF,).D 4) Fractional reabsorption of potassium along the collecting duct was estimated by the following formula : 1
- L-FEK/(TF/P)o,,,,, ml x 100
RESULTS
Group Z (hydropenia). The clearance and rnicropuncture results of all studies are summarized in Tables 1 and 2 and in Fig. 1. Each point reprethe group Z data are summarized sents the mean value of all punctures obtained in either the early or late distal tubule in the respective experiment. The mean total GFR was 1.10 ml/min, serum K concentration was 4.2 rneq/liter, and fractional K excretion was 11.6 %. In each experirnent, the TF/Pr, and TF/PK were less in the early than in the late distal tubule. The TF/Pr, increased from 4.97 to 13.3 (P < .OOl), and the TF/PK rose frorn .42 in the early distal tubule to 2.78 in the late segrnent (P < .OOl). Th e mean (TF/P)K/rn in the early distal tubule was 8.30 % of the filtered load and 21 .O % in the late distal tubule (P < .OOl). In neither this or any subsequent group was there overlap in this parameter between an early and late collection in a given experiment. There was a rnean absolute K secretion rate of 27 peq/min along the distal tubule (Table 2). In each of these 10 studies, fractional delivery of potassium to the late distal puncture site exceeded the fractional excretion of potassium, the mean values being 21 .O and 11.6 % of the filtered load of potassium, respectively, (P < .OOl). Using this comparison as an index of potassium transport beyond the distal tubule, 42.6 % of the potassium delivered to the late distal puncture site was reabsorbed along the collecting duct. Group ZZ (Ringer loading). The clearance results are summarized in Table 1. LMean fractional sodium excretion was 4.96 %, a value significantly higher than in all other groups (P < .OOl for all values). As is demonstrated in Fig. 2 and
reSdtS
PN%, meq/liter -_--
PK, meq/liter
V, pl/min
UK\‘,
Lceq/min
=K,
o/o
--
UN~V,
peq/min
% ____
FEN,,
Group I n = 10
1.10 h.04
143 *l
4.2 k.1
3.3 zk.2
.54 zk.03
11.6 AZ.7
Group II n = 7
1.53 AZ.05
144 *l
4.4 *.2
175.7 ztl7.7
2.50 zk.22
37.2 h3.5
10.8 Al.1
4.96 h.50
Group III n = 6
1.07 LO8
144 =tl
6.9 A.3
5.0 A.6
1.04 zk.19
13.8 zt2.4
.30 AZ.03
.20 h.03
Group n=6
IV
1.06 A.08
137 *l
4.4 zt.1
61.6 zk8.3
1.67 A.21
37.3 zt4.6
.66 k.22
.47 zt.18
Group
V 7
1.07 *.07
133 Al
6.1
AZ.2
120.0 zk15.7
3.59 h.43
54.3 h5.7
26 1t.24
.75 h.22
n =
Values are means & SE. GFR, glomerular filtration FEK, urine volume; UKV, urinary potassium excretion; sodium excretion. Group I, hydropenia; group II, Ringer KC1 loading and mannitol diuresis.
concentration; rate; PN~, plasma sodium UN*V, fractional potassium excretion; loading; group III, acute KC1 infusion;
.13 A.02
PK, plasma potassium urinary sodium excretion group
ZV, mannitol
diuresis;
.08 zt.02
concentration; v, ; FEN,, fractional group
V, acute
Downloaded from www.physiology.org/journal/ajplegacy by ${individualUser.givenNames} ${individualUser.surname} (132.174.254.157) on January 12, 2019.
POTASSIUM
TABLE
1405
TRANSPORT
2. Summary of micropuncture TW’r
results --
n
E
‘WPK
L
Distal
(TF/P)K/I~
E
E
L
L
Tubular Rate
E
nl/min
o/o
Flow
Absolute
K+ Delivery
E
L
peq/min
('WP)N~/I~
L
E
L %I
Group I n = 10
4.97 zt.24 (1%
13.30 zt.89 (24)
.42 AZ.07
2.78 zt.19
8.3 ztl.3
21 .o *1.4
8.1 A.4
3.1 zt.2
16.5 zt2.5
43.7 h2.2
6.6 A.5
1.7 zk.2
Group III n = 7
2.85 A.23 (1%
3.60 zk.30 (18)
.42 zt.04
1.31 LO8
15.1 *I .4
37.8 zt3.4
20.6 Al.5
16.5 *I .3
37.5 zk3.1
93.1 zt6.2
14.6 zt1.0
6.8 zt.6
Group III n = 6
3.56 A.75 (11)
6.78 zk.75 (16)
.54 h.08
2.30 zk.18
13.8 zk2.1
36.2 Are.4
10.3 zkl.6
6.6 k.6
38.3 zk5.9
103.7 zt9.3
12.2 h.7
4.8 zt.8
Group n=6
IV
3.78 zt.54 (12)
7.20 AZ.97 (15)
.59 zk.09
2.94 AZ.34
17.6 zt3.6
43.1 zk5.0
11.5 zkl.2
6.6 zkl.2
30.2 zt3.3
78.9 HO.4
9.1 Ad.4
2.8 rt.5
Group V n = 7
2.67 zt.24 (11)
4.04 A.43 (14)
.39 zt.04
2.12 A.26
16.1 zk2.9
54.4 zk5.0
14.3 Al.5
10.5 Al.1
33.9 zt6.7
127.5 zt9.5
10.8 k2.0
2.8 zt.8
______~ Values are means tubular fluid-to-plasma inulin ratio.
=t SE. Numbers inulin ratio;
____-- -----_l_________-~-_in parentheses are numbers of observations. E, early distal tubule; I,, late distal tubule; (TF/P) K, tubular fluid-to-plasma potassium ratio; (TF/P) Na/In, tubular fluid-to-plasma
N=IO
(TF/P)1,, sodium-to-
N=7
30
60
25
50
o\” 20
40
Iqjq
p
Vol.
JOURNAL
OF PHYSIOLOGY
229, No. 5, November
1975.
Printed
in U.S.A.
Potassium
transport
collecting
duct of the rat
H. JOHN Department
REINECK,
H.
JOHN,
JAY H. STEIN. duct of the rat. Am. AND
REINECK, of Medicine,
W.
RICHARD
Potassium
transport
in the distal
RICHARD W. OSGOOD, THOMAS Ohio State University College of Medicine,
OSGOOD,
‘I‘IHOMAS
in the distal
tubule
F.
FERRIS,
and collecting
J. Physiol. 229(5) : 1403-1409. 1975.-Because of recent conflicting results, micropuncture studies were performed to clarify the respective role of the distal convoluted tubule and collecting duct in the regulation of urinary potassium excretion. Five groups of Sprague-Dawley rats were studied: group I, hydropenia (n = 10); group II, Ringer loading (n = 7) ; group III, acute KC1 loading (n = 6); group IV, mannitol diuresis (n = 6); group V, KC1 infusion during mannitol diuresis (n = 7). Early and late distal tubules were identified with intravenous injections of lissamine green. In each animal net secretion of potassium occurred along the distal convoluted tubule, and a direct relationship between distal tubular flow rate and potassium secretion was observed. The magnitude of potassium secretion at high distal tubular flow rates was dependent on the inodel studied. Potassium transport beyond the distal tubule was evaluated by comparing end distal potassium delivery and fractional potassium excretion. At low urinary flow rates net reabsorption was observed, whereas at higher flow rates no net transport occurred. Thus, flow rate along the collecting duct may be a major determinant of urinary potassium excretion. potassium secretory mechanism; ture
potassium
excretion;
micropunc-
1937, MCCANCE AND WIDDOWSON (14) first demonstrated that urinary potassium excretion could exceed the filtered load, indicating the existence of a potassium secretory mechanism. Clearance studies by Berliner and Kennedy (2) and stop-flow studies by Vander (21) suggested that the bulk of excreted potassium was primarily derived from a distal secretory process. Subsequently, Malnic and co-workers (9, 12), utilizing micropuncture techniques in albino rats, located the secretory site in the distal convoluted tubule. Recently, however, Bank and Aynedjian (1) described net potassium reabsorption along the distal convoluted tubule of Sprague-Dawley rats under a variety of conditions including hydropenia, a reduction in renal mass, and acute KC1 loading. Further, these authors described net secretion of potassium along the collecting duct in the latter two groups. Thus, it is not clear whether the regulation of urinary potassium excretion occurs primarily in the distal tubule or collecting duct system. The present study was undertaken to clarify this issue and to further investigate the role of the collecting duct in the regulation of urinary potassium excretion. The results indiIN
tubule
and
F. FERRIS, AND JAY Columbus, Ohio 43210
H. STEIN
cate that net potassium secretion does occur along the distal convoluted tubule of the Sprague-Dawley rats utilized in this study but that transport beyond this segment may modify urinary potassium excretion. METHODS
Adult male Sprague-Dawley rats obtained from the Schmidt, Co. (Madison, Wis.) weighing 250-350 g were anesthetized with Inactin 100 mg/kg (Promonta, Hamburg, West Germany). A tracheostomy was performed, and polyethylene catheters were placed in each jugular vein for infusions and in the femoral artery for blood pressure monitoring and withdrawal of blood samples. The left kidney was exposed through a left subcostal incision and gently dissected from the surrounding perirenal fat. The rats were prepared for micropuncture as previously described (19, 20) . The aniinals were initially given 0.5 ml of a 10 % inulin solution dissolved in Ringer and then a maintenance infusion at a rate of .02 ml/min. While the inulin was equilibrating, early and late distal tubular segments were localized with two to three intravenous injections of lissamine green (0.05 ml of a 10 % solution). The validity of this method of localization has been previously demonstrated (19). Further confirmation of this technique was also obtained in the present study (vida infra). No puncture was obtained until at least 5, min after the last lissamine green injection and 1 h after the inulin infusion had been started. The tubules were punctured with sharpened pipettes with tip diameters varying from 6 to 8 pm diam. Only distal tubular samples were obtained in these studies. With the pipette tip positioned within the tubular lumen, a large column of mineral oil stained with Sudan black was injected into the tubule. After initial gentle aspiration to begin the collection, most of the samples were collected either spontaneously or with only occasional aspiration to maintain the oil column in a constant position. All tubular fluid collections were timed. The following experimental groups were studied : Group I. Ten hydropenic rats received Ringer solution at an infusion rate of 0.02 ml/min throughout the study. Group II. Seven animals were volume expanded with 10 % body wt Ringer solution over 50-60 min. The infusion rate was then reduced to that of urinary flow, and distal collections and clearances were obtained. In four of these studies, d-aldosterone, 20 pg/kg was given subcutaneously 2-3 h 1403
Downloaded from www.physiology.org/journal/ajplegacy by ${individualUser.givenNames} ${individualUser.surname} (132.174.254.157) on January 12, 2019.
1404
REINECK,
before the study followed by an intravenous infusion of 20 pg/kg per h throughout the rernainder of the experiment. Group ZZZ. Six hydropenic rats were infused with 0.15 M KC1 at a rate of .05 ml/min. Thirty rninutes after the infusion had begun, tubular fluid and urine collections were obtained. During the collections, the KC1 infusion was continued. Group IV. Six animals were given 10 % rnannitol at an infusion rate varying from 0.1 to 0.2 ml/min. Twenty to thirty minutes after the infusion had begun, collections were obtained. Group V. In seven anirnals, hypertonic mannitol was given at a rate of .I-.3 ml/min, concomitant with an infusion of 0.15 M KC1 at a rate of .05-.07 ml/min. Thirty rninutes after the infusion was initiated, distal tubular and urine collections were begun. The infusions were continued throughout the collections. In two further studies performed during acute KC1 loading (group ZZZ), early and late distal samples were collected in the usual rnanner. The respective tubules were then injected with latex and microdissected with the technique described by Cortell (3). Two clearance periods were obtained in each study. Plasma and urine inulin concentrations were measured by the anthrone rnethod (5), while tubular fluid inulin was determined by the method of Vurek and Pegram (22). Tubular fluid sodium and potassium concentrations were measured with an Aminco helium-glow flame photometer (American Instrument Co., Inc., Silver Spring, Md.), and urine and plasma concentrations were measured with an Instrumentation Laboratory flame photometer (Instrurnentation Laboratory, Inc. 9 Watertown, Mass.). The data were analyzed by standard statistica l methods as the rneans * standard and all are presented error. Calculations I) Fractional delivery of potassium to early or late distal tubule the tubular fluid-to-plasma potas= m/p)K/In, sium-to-inulin ratio in either the early distal tubule (ED) or late distal tubule (LD). 1. Summary of clearance
TABLE
GFR,
ml/min ~.
OSGOOD,
FERRIS,
AND
STEIN
2) Absolute delivery of potassium = VF X TFK, where V, is the tubular flow rate in nanoliters per minute and TFK is the tubular fluid potassiurn concentration. 3) Absolute distal tubular potassiurn secretion = (v, x TFK)LD - 0% x TF,).D 4) Fractional reabsorption of potassium along the collecting duct was estimated by the following formula : 1
- L-FEK/(TF/P)o,,,,, ml x 100
RESULTS
Group Z (hydropenia). The clearance and rnicropuncture results of all studies are summarized in Tables 1 and 2 and in Fig. 1. Each point reprethe group Z data are summarized sents the mean value of all punctures obtained in either the early or late distal tubule in the respective experiment. The mean total GFR was 1.10 ml/min, serum K concentration was 4.2 rneq/liter, and fractional K excretion was 11.6 %. In each experirnent, the TF/Pr, and TF/PK were less in the early than in the late distal tubule. The TF/Pr, increased from 4.97 to 13.3 (P < .OOl), and the TF/PK rose frorn .42 in the early distal tubule to 2.78 in the late segrnent (P < .OOl). Th e mean (TF/P)K/rn in the early distal tubule was 8.30 % of the filtered load and 21 .O % in the late distal tubule (P < .OOl). In neither this or any subsequent group was there overlap in this parameter between an early and late collection in a given experiment. There was a rnean absolute K secretion rate of 27 peq/min along the distal tubule (Table 2). In each of these 10 studies, fractional delivery of potassium to the late distal puncture site exceeded the fractional excretion of potassium, the mean values being 21 .O and 11.6 % of the filtered load of potassium, respectively, (P < .OOl). Using this comparison as an index of potassium transport beyond the distal tubule, 42.6 % of the potassium delivered to the late distal puncture site was reabsorbed along the collecting duct. Group ZZ (Ringer loading). The clearance results are summarized in Table 1. LMean fractional sodium excretion was 4.96 %, a value significantly higher than in all other groups (P < .OOl for all values). As is demonstrated in Fig. 2 and
reSdtS
PN%, meq/liter -_--
PK, meq/liter
V, pl/min
UK\‘,
Lceq/min
=K,
o/o
--
UN~V,
peq/min
% ____
FEN,,
Group I n = 10
1.10 h.04
143 *l
4.2 k.1
3.3 zk.2
.54 zk.03
11.6 AZ.7
Group II n = 7
1.53 AZ.05
144 *l
4.4 *.2
175.7 ztl7.7
2.50 zk.22
37.2 h3.5
10.8 Al.1
4.96 h.50
Group III n = 6
1.07 LO8
144 =tl
6.9 A.3
5.0 A.6
1.04 zk.19
13.8 zt2.4
.30 AZ.03
.20 h.03
Group n=6
IV
1.06 A.08
137 *l
4.4 zt.1
61.6 zk8.3
1.67 A.21
37.3 zt4.6
.66 k.22
.47 zt.18
Group
V 7
1.07 *.07
133 Al
6.1
AZ.2
120.0 zk15.7
3.59 h.43
54.3 h5.7
26 1t.24
.75 h.22
n =
Values are means & SE. GFR, glomerular filtration FEK, urine volume; UKV, urinary potassium excretion; sodium excretion. Group I, hydropenia; group II, Ringer KC1 loading and mannitol diuresis.
concentration; rate; PN~, plasma sodium UN*V, fractional potassium excretion; loading; group III, acute KC1 infusion;
.13 A.02
PK, plasma potassium urinary sodium excretion group
ZV, mannitol
diuresis;
.08 zt.02
concentration; v, ; FEN,, fractional group
V, acute
Downloaded from www.physiology.org/journal/ajplegacy by ${individualUser.givenNames} ${individualUser.surname} (132.174.254.157) on January 12, 2019.
POTASSIUM
TABLE
1405
TRANSPORT
2. Summary of micropuncture TW’r
results --
n
E
‘WPK
L
Distal
(TF/P)K/I~
E
E
L
L
Tubular Rate
E
nl/min
o/o
Flow
Absolute
K+ Delivery
E
L
peq/min
('WP)N~/I~
L
E
L %I
Group I n = 10
4.97 zt.24 (1%
13.30 zt.89 (24)
.42 AZ.07
2.78 zt.19
8.3 ztl.3
21 .o *1.4
8.1 A.4
3.1 zt.2
16.5 zt2.5
43.7 h2.2
6.6 A.5
1.7 zk.2
Group III n = 7
2.85 A.23 (1%
3.60 zk.30 (18)
.42 zt.04
1.31 LO8
15.1 *I .4
37.8 zt3.4
20.6 Al.5
16.5 *I .3
37.5 zk3.1
93.1 zt6.2
14.6 zt1.0
6.8 zt.6
Group III n = 6
3.56 A.75 (11)
6.78 zk.75 (16)
.54 h.08
2.30 zk.18
13.8 zk2.1
36.2 Are.4
10.3 zkl.6
6.6 k.6
38.3 zk5.9
103.7 zt9.3
12.2 h.7
4.8 zt.8
Group n=6
IV
3.78 zt.54 (12)
7.20 AZ.97 (15)
.59 zk.09
2.94 AZ.34
17.6 zt3.6
43.1 zk5.0
11.5 zkl.2
6.6 zkl.2
30.2 zt3.3
78.9 HO.4
9.1 Ad.4
2.8 rt.5
Group V n = 7
2.67 zt.24 (11)
4.04 A.43 (14)
.39 zt.04
2.12 A.26
16.1 zk2.9
54.4 zk5.0
14.3 Al.5
10.5 Al.1
33.9 zt6.7
127.5 zt9.5
10.8 k2.0
2.8 zt.8
______~ Values are means tubular fluid-to-plasma inulin ratio.
=t SE. Numbers inulin ratio;
____-- -----_l_________-~-_in parentheses are numbers of observations. E, early distal tubule; I,, late distal tubule; (TF/P) K, tubular fluid-to-plasma potassium ratio; (TF/P) Na/In, tubular fluid-to-plasma
N=IO
(TF/P)1,, sodium-to-
N=7
30
60
25
50
o\” 20
40
Iqjq
p
