Department of Physiology and Biophysics, Weill Medical College of Cornell University, New York, New York 10021
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The ROMK family of proteins has biophysical properties and distribution within the kidney similar to those of secretory potassium channels of the distal nephron. To study the regulation of ROMK during variations in dietary potassium, we measured the abundance of ROMK protein in rat kidney by immunoblotting. Neither 2 nor 5 days of a high-potassium diet had an effect on protein abundance in the cortex or medulla. Potassium deprivation (2 or 5 days) decreased ROMK protein content in both cortical and medullary fractions, to 51 and 40% of controls, respectively. To see whether the Na-K-2Cl cotransporter is similarly affected by potassium restriction, we analyzed immunoblots by using an antibody for the rat type 1 bumetanide-sensitive cotransporter (BSC-1). Like ROMK, BSC-1 protein content was found to decrease significantly in the renal medulla of potassium-deprived rats. In the thick ascending limb of Henle's loop, a decrease in ROMK and BSC-1 could result in decreased reabsorption of NaCl, a finding associated with hypokalemia.
ascending limb of henle's loop; cortical collecting tubule; secretory potassium channel; potassium excretion; sodium-potassium-chlorine cotransporter; type 1 bumetanide-sensitive cotransporter
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
REGULATION OF SERUM POTASSIUM levels takes place in the kidney in part through an inwardly rectifying potassium channel. This channel, termed SK for secretory potassium channel, has been well characterized by using the patch-clamp technique in the cortical collecting tubule (CCT) and in the thick ascending limbs of Henle's loop (TALH) (7, 31). In the CCT the SK channel is upregulated to increase potassium secretion in response to increased potassium intake (22, 24, 30). The SK channel in the TALH is believed to primarily act to recycle potassium, which is essential for the reabsorption of NaCl through the apical Na-K-2Cl cotransporter (9). The TALH may also play a role in potassium adaptation as part of the pathway of potassium recycling (14) from the medullary collecting duct (MCD), into the medullary interstitium, and then into the loop of Henle. Altered dietary potassium intake could therefore affect SK channel activity in both the CCT and the TALH.
The cloning of the ROMK family of potassium channels (3, 12, 34) has enabled further study of potassium channel regulation at the molecular level. These channels are believed to correspond to SK, because they have similar biophysical properties (23) and distribution (3, 15, 20, 33) within the kidney. So far, four rat ROMK isoforms have been cloned, ROMK1-3 (3, 12, 34) and ROMK6 (16). These isoforms are derived from different splicing of the ROMK gene, generating proteins that differ in the amino acid sequence and length of their NH2 termini but are identical to one another in the rest of the peptides. Previous patch-clamp studies have shown a three- to fourfold increase in SK channel density from CCT of animals fed a high-potassium diet (22, 24, 30). Wald et al. (27) studied the effects of changes in potassium intake and adrenalectomy on the abundance of ROMK mRNA in rat kidney. Increased intake did not alter the cortical mRNA level, and it augmented only slightly the medullary abundance of message. Low potassium intake markedly reduced cortical and medullary ROMK mRNA levels both in intact and adrenalectomized animals. ROMK mRNA levels in isolated rat CCTs were not altered by feeding the animals a high potassium diet (8). No information is available yet on the regulation of ROMK protein expression under these conditions.
The purpose of the present study was to examine the effects of potassium intake on the regulation of ROMK protein in the renal cortex and medulla. We found ROMK protein levels do not change with increased dietary potassium, but there was a marked decrease with potassium depletion. This decrease in ROMK protein with potassium depletion was paralleled by a decrease in the apical membrane Na-K-2Cl cotransporter protein.
![]() |
METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Antibodies. Two affinity-purified rabbit polyclonal antibodies to the COOH-terminal of the rat ROMK1 channel were used in this study. The APC-001 (Alomone Laboratories, Jerusalem, Israel) antibody is directed against amino acids 342-391, and LL309 anti-ROMK is directed against amino acids 369-391. Both of these peptides are identical in all four ROMK isoforms. The LL309 antibody has been previously characterized in our laboratory (20). In addition, an affinity-purified rabbit polyclonal antibody to the Na-K-2Cl cotransporter BSC-1, which is specific to the cortical and medullary TALH in rat (5) was provided by Dr. Mark Knepper (National Institutes of Health, Bethesda, Md.). A mouse monoclonal anti-actin antibody (AC-40) was obtained from Sigma Chemical (St. Louis, MO).
Preparation of membrane fractions. Adult Sprague-Dawley rats (100-140 gm) were fed matched diets containing either high K (HK, 10% KCl), low K (LK, no KCl added), or control K (CK, 1.2% KCl) for 2 or 5 days. All diets were obtained from Harlan-Teklad (Madison, WI). Rats were killed by cervical dislocation, and both kidneys were removed and placed in chilled PBS. The kidneys were dissected to obtain cortical, outer medullary and inner medullary sections. These samples were homogenized with a polytron in ice-cold lysis buffer (250 mM sucrose, 1 mM ethylenediaminetetraacetic acid and 10 mM triethanolamine, pH 7.5 with HCl) containing 0.1 mg/ml phenylmethylsulfonylfluoride and 1 µg/ml leupeptin. The homogenized tissue was centrifuged at 1,000 g for 20 min at 4°C, and the supernatant was removed and saved. The pellet was rehomogenized and centrifuged again at 1,000 g for 20 min. The supernatant was pooled with the previous supernatant and centrifuged at 200,000 g for 1 h at 4°C. This high-speed supernatant is cytosol enriched. The pellet was briefly sonicated to resuspend it in lysis buffer and then centrifuged at 1,000 g for 10 min at 4°C. This final supernatant resulting from the high-speed pellet is membrane enriched. The 1,000 g spins were accomplished by using a refrigerated Eppendorf microcentrifuge. The 200,000 g spin was carried out with a Beckman Tl-100 Ultracentrifuge fitted with a TLA100.2, S.N.1033 rotor. The high-speed supernatant and pellet fractions were analyzed for protein concentration (Micro BCA Protein Assay Reagent Kit, Pierce, Rockford, IL). The membrane fractions were solubilized at 60°C for 15 min in Laemlli sample buffer containing 30 mg/ml of dithiothreitol (DTT).
Oocytes were prepared and injected as previously described (34). After incubation for 3 days in Barth's solution at 19°C, seven control oocytes and seven ROMK2 cRNA-injected oocytes were incubated in 2 ml of PBS with 5 mM EGTA for 10 min at 4°C. The oocytes were broken by trituration with a Pasteur pipette and homogenized by using a 2-ml Dounce homogenizer with a Teflon pestle, in ice-cold lysis buffer as above. Homogenates were spun in an Eppendorf microcentrifuge at 2,500 rpm for 5 min at 4°C to remove nuclei and incompletely homogenized cells. Then the supernatant was respun in an Eppendorf microcentrifuge at 14,000 rpm for 2 h at 4°C. The membrane fractions were solubilized at 60 °C for 15 min in Laemlli sample buffer containing 30 mg/ml of DTT.Electrophoresis and immunoblotting of membranes. Samples of 4-25 µg of total protein were separated by SDS-PAGE on minigels of 8% polyacrylamide for assessment of ROMK and actin expression and on minigels of 6% polyacrylamide for BSC-1 protein expression. The gels were then electrophoretically transferred to polyvinylidene difluoride (PVDF) membranes (Immobilon-P; Millipore, Bedford, MA). The membranes were blocked with 5% milk blocker (150 mM NaCl, 50 mM sodium phosphate, 50 µl/100 ml Tween-20, and 5% nonfat dry milk) for 30 min, and then probed with one of the antibodies (LL309, APC-001, or BSC-1 at 1:2000 dilution or anti-actin at 1:500 dilution) overnight. The antibodies were prepared in an antibody diluent containing 150 mM NaCl, 50 mM sodium phosphate, 1.5 mM sodium azide, 50 µl/100ml Tween-20, and 0.1% bovine serum albumin (BSA). Membranes were then washed six times with the antibody dilution buffer (without BSA or sodium azide) before incubation with horseradish peroxidase-conjugated donkey anti-rabbit IgG (1:30,000) or anti-mouse IgG (1:8,000) (Pierce). After washing, sites of antibody-antigen reaction were visualized by using luminol-based enhanced chemiluminescence (SuperSignal Substrate; Pierce) and exposure to X-ray film (Biomax MR; Eastman Kodak, Rochester, NY) for 5-30 min. The control for the APC-001 antibody consisted of APC-001 serum preadsorbed with a fourfold excess of APC-001 fusion protein. Specificity of ROMK LL309 and BSC-1 antibodies was previously demonstrated (5, 20).
Densitometric analysis of immunoblots. The bands in the films were scanned using an AGFA ARCUS II scanner. Relative quantitation of the immunoblot band densities was then carried out using National Institutes of Health Image 1.60. For each film the densitometry values were averaged for samples from rats on a CK diet and on either a HK or LK diet. One LK/CK or HK/CK ratio was then computed for each blot. Ratios from different blots were averaged and data are presented as mean ± SE, where the number of observations corresponds to the number of different blots. Both the number of animals used and the number of blots analyzed are given in the text. Comparisons were always made between signals from equal amounts of total protein on the same film. To verify equality of loading, a few representative gels were not transferred to membranes but instead stained with Brilliant Blue G-Colloidal (Sigma). The gels were then scanned and regions spanning a similar size range in each lane were analyzed by densitometry. With the cell membrane fractions no difference was found between the density of the bands in lanes containing LK and CK (LK/CK ratio, cortex = 1.05, outer medulla = 1.03, 6 rats, 2 measurements/rat, n = 2 gels) or HK and CK (HK/CK ratio for rats on diet for 2 days, cortex = 1.04, medulla = 1.22, 6 rats, 2 measurements/rat, n = 2 gels; and for rats on diet for 5 days, cortex = 0.94, medulla = 1.01, 2 measurements/rat, n = 2 gels).
Tissue preparation for immunocytochemistry. Adult Sprague-Dawley rats were fed either a HK or a CK diet for 7-14 days. Rats were anesthetized with methoxyflurane (Mallinckrodt Veterinary, Mundelein, IL), and their kidneys were perfused via the aorta, first with heparinized PBS for 1-2 min, then with 2% paraformaldehyde in PBS for 3-5 min at a pressure of ~100 mmHg. Once fixed, kidneys were sliced (~3 mm thickness), immersed in PBS containing 30% sucrose at 4°C for 4 h, and immersed for an additional 30 min in Tissue-Tek OCT (Sakura Finetech USA, Torrance, CA). Subsequently the kidney tissue was frozen over dry ice in Tissue-Tek OCT, cut into 5- to 8-µm thick sections with a cryostat, and sections were picked up on Superfrost Plus microslides (VWR, West Chester, PA).
Immunocytochemistry. Sections were incubated with fetal calf serum for 30 min at 37°C to block nonspecific antibody binding and then permeabilized with 0.2% Triton X-100 in PBS for an additional 30 min at 37°C. Sections were incubated overnight at 4°C with either anti-ROMK LL309 (1:100 dilution) or APC-001 (1:25 dilution). After five washes in PBS the sections were incubated for 30 min at 37°C with FITC-conjugated donkey (1:160) anti-rabbit IgG (Jackson ImmunoResearch Laboratories, West Grove, PA). After washing in PBS five times, the sections were mounted with vectashield (Vector Labs, Burlingame, Ca). Controls for the APC-001 anti-ROMK consisted of either omitting the primary or the secondary antibodies or staining with APC-001 antibody preincubated with a fourfold excess of APC-001 fusion protein. Controls for LL309 anti-ROMK were previously demonstrated (20).
Stained sections were viewed and photographed on Kodak film by using a Zeiss Axioskop fluorescence microscope equipped with a fluorescein filter, differential interference contrast (DIC) optics, and an automatic camera. ![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
ROMK immunocytochemistry. We performed indirect immunofluorescence labeling of cryosections of paraformaldehyde-fixed rat kidneys with LL309 and APC-001 anti-ROMK sera to compare the localization of ROMK by the two antibodies. The LL309 anti-ROMK was previously characterized in our laboratory (20).
The antibodies labeled similar tubules of both the cortical and outer medullary sections of the kidney. Figure 1A shows the distribution of immunoreactivity of the APC-001 anti-ROMK in a cortical section. No specific staining was observed in glomeruli or proximal tubules, although the proximal tubules show punctate yellow autofluorescence. The two CCTs (marked by C) show that some of the cells are apically stained. This is consistent with our previous study (20), using the LL309 antiROMK, which demonstrated CCT cells that were positive for LL309 did not stain with the H-ATPase antibody (an intercalated cell marker), suggesting that they were principal cells. Connecting tubules also express the APC-001 anti-ROMK on their apical membrane (not shown).
|
Immunoblot analysis.
Figure 2 compares the selectivity of the
APC-001 and LL309 ROMK antibodies as evaluated by immunoblot of rat
kidney membrane preparations. Twenty-five micrograms of protein of
either high-speed supernatant (s) or pellet (p) from medullary
preparations were loaded per lane. Similar to what we have shown (20),
the LL309 anti-ROMK recognizes a predominant band at ~60 kDa and a
fainter band at ~45 kDa. Surprisingly, both of these bands are
primarily in the high-speed supernatant, with a faint upper band seen
in the pellet. The APC-001 anti-ROMK recognizes one band at ~45 kDa, which is predominantly in the high-speed pellet. One faint upper band
at ~100 kDa is seen in the high-speed pellet lane.
|
|
|
|
Regulation of ROMK by potassium intake.
We used immunoblots of the APC-001 antibody to compare the effects of
changes in potassium intake on ROMK protein expression. First, a
calibration curve was made to ensure the method could detect
differences in protein concentration per lane. Increasing concentrations (from 4 to 32 µg of protein) of a high-speed pellet preparation were used. Figure 6 shows the
measured 45-kDa band densities plotted against the protein
concentration. Within this range the signal is a monotonic function of
protein concentration. We therefore used 10 µg of protein per lane
for all of the comparisons between membranes prepared from animals with
various potassium intakes.
|
|
|
|
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Our studies characterize the APC-001 anti-ROMK serum and compare it with the previously characterized LL309 anti-ROMK. We found that the antibody recognizes epitopes at the apical surface of both medullary and cortical TALH, connecting tubules, CCT, and outer MCD. This distribution of ROMK is similar to that seen previously by us (20) and others (15, 33), all using anti-ROMK COOH-terminal antibodies. The peptides used to make these antibodies are common to all four ROMK isoforms found in the kidney.
Results of immunoblot studies from these laboratories, using the same antibodies as for the localization studies, were somewhat more variable. Xu et al. (33) found a ~45-kDa band, as well as several species between 85 and 90 kDa, in blots of renal cortex and outer medulla. Faint bands at ~45 and 85 kDa were also detected in the inner medulla. They found similar labeling with an antibody to an NH2-terminal peptide common to all four ROMK isoforms. They suggested the 85- to 90-kDa proteins could represent homodimeric and/or heterodimeric complexes formed by ROMK isoforms. The antibody in the study by Kohda et al. (15) recognized ~42-, 44-, and 77-kDa bands in whole kidney homogenate. They also made an antibody to the NH2-terminal of ROMK, which was not useful for immunoblot analysis but showed a pattern of labeling by immunocytochemistry similar to that of their COOH-terminal antibody (15). This antibody is specific to a 28-amino acid sequence of ROMK1, which overlaps with 18 amino acids of ROMK2 and ROMK6 and 26 amino acids of ROMK3. We previously identified species at ~42 and 75 kDa with the LL309 anti-ROMK serum and argued that the larger one could be a dimer of ROMK, a tightly bound complex with another protein, or an unrelated protein sharing a similar epitope with ROMK (20).
In this study, we find the LL309 antibody recognizes proteins at ~45 and 60 kDa. These presumably correspond to the 42- and 75-kDa species we identified previously (20). A few adjustments to our immunoblot technique were made in this study which may be responsible for the differences. In particular, we have utilized a differential centrifugation technique to separate cytosolic from membrane fractions and switched to transferring our gels to a PVDF membrane instead of nitrocellulose and hence switched our solutions accordingly. The APC-001 antibody recognizes one band at ~45 kDa, close to the predicted molecular size of ROMK (39-43 kDa without glycosylation) and consistent with the band seen in ROMK2 cRNA-injected oocytes (Fig. 2).
Our further characterization of the APC-001 antibody supports the idea that it specifically recognizes ROMK in immunoblots. The 45-kDa species is found predominately in the high-speed pellet fraction, which is membrane enriched, consistent with the immunocytochemical localization of ROMK to the apical surface. The appearance of the band, albeit at lower intensity, in the high-speed supernatant is unexpected. Although no cytoplasmic staining of ROMK was found by immunocytochemistry, it is possible ROMK exists in a subapical area that is visibly indiscernible from the membrane or in a form or amount undetectable to immunocytochemistry. The band is more dominant in the outer medulla than the cortex, as predicted by the abundance of ROMK in the TALH. The faint species in the inner medulla was not expected given the lack of staining of sections of this part of the kidney, although Xu et al. (33) also found ROMK bands in the inner medulla, and Lee and Hebert (18) reported a low abundance of ROMK. The ubiquitous distribution of ROMK6 mRNA in various rat tissues (16) makes this isoform a possible candidate for immunoblot detection in the inner medulla. No labeling was seen when the APC-001 antibody was preadsorbed with the APC-001 fusion protein.
All of these studies (15, 20, 33) have in common their recognition of a protein at ~42-45 kDa, which is most likely ROMK. We therefore believe this lower-molecular-weight species can be used to study regulation of ROMK protein in the kidney. In particular, APC-001 anti-ROMKs predominant detection of the lower band make it a good choice for further studies.
The identities of the higher molecular weight proteins and what, if any, relationship they have to ROMK remains to be understood. In the case of the predominant 60-kDa band recognized by the LL309 antiserum, the facts that most of the protein was found in the cytosolic fraction and that it was not recognized by APC-001 suggest that it may be a nonmembrane protein unrelated to ROMK. However, we cannot rule out the possibility that it represents a potassium channel protein within a very light vesicular compartment.
Patch-clamp studies previously identified a three- to fourfold increase in active potassium channel density from the CCT of rats fed a HK diet (22, 24, 30). Yet we identified no increase in the expression of ROMK protein in the cortex or medulla of rats fed a HK diet. Our results, consistent with studies finding a potassium-enriched diet, did not change ROMK mRNA abundance in the rat CCT (8) or in total rat cortex (27). In the medulla, Wald et al. (27) saw a slight increase in ROMK mRNA (122% of control). The CCT and MCD are minor fractions of the ROMK-expressing tubules in the whole cortex and whole medulla, thus this method may not be sensitive enough to identify changes in ROMK expression specific to those segments. Our results imply there is no effect of a potassium-enriched diet on expression of ROMK protein, at least in the TALH. Electrophysiological measurements indicated that the density of conducting, ROMK-like channels in the TAL was not changed under these conditions (29).
In rats fed a LK diet for 5 days we found a large decrease in ROMK protein content in both whole cortex and medulla. The results of our studies on potassium deprivation correlate well with the mRNA expression studies of Wald et al. (27). They found a potassium-deficient diet downregulated ROMK mRNA expression in both the cortex (47% of control) and the medulla (56% of control). The cortex of adrenalectomized rats also showed a decrease in ROMK mRNA expression which could be further reduced by a LK diet, suggesting separate aldosterone-dependent and aldosterone-independent regulatory processes (27). In the medulla, they found ROMK mRNA depended on serum potassium levels irrespective of aldosterone. The preponderance of ROMK in the TALH suggests that one effect of potassium deprivation is a decrease in ROMK mRNA and protein in TALH. Single-tubule studies will be required to determine whether expression in the CCT is similarly affected.
Impaired NaCl reabsorption in the TALH has been shown to occur in
potassium depletion (10, 19) although the mechanisms by which this
occurs are controversial. Potassium-depleted rats have a reduction in
luminal potassium concentration (10, 28), but it is minimal and
therefore potassium may not be rate-limiting for NaCl transport.
Potassium deprivation was found to decrease expression of mRNA coding
for - and
-subunits of Na-K-ATPase (27) and the apical Na-K-2Cl
cotransporter (1). These studies support our finding that BSC-1 protein
expression is downregulated in the outer medulla of potassium depleted
rats. A decrease in SK and Na-K-2Cl cotransporter function in the TALH
would result in decreased absorption of NaCl and may explain the
reduced concentrating ability found with chronic hypokalemia (21).
Is decreased ROMK expression in potassium depletion an adaptive response? If the primary purpose for ROMK expression in CCT is to secrete potassium, then downregulation of ROMK in the CCT might be adaptive by suppressing secretion and promoting potassium retention. In addition, functional studies (17, 32) suggest one of the primary effects of an LK diet on CCT and MCD is enhancement of H-K-ATPase activity for absorption of potassium. A consequence of upregulating H-K-ATPase and downregulating ROMK, should be a decreased urine potassium. However, we cannot conclude from our data that the CCT expresses less ROMK protein. In fact, patch-clamp studies showed no detectable change in the density of conducting channels in the CCT (24).
In the TALH, it is believed that the primary role of SK is to recycle potassium across the apical membrane, to support the function of the Na-K-2Cl cotransporter (9). According to the mouse mTALH model of Hebert and Andreoli (11) there is also a net secretion of potassium into the lumen through SK. Thus a reduction in ROMK with potassium deprivation could reduce secretion in this segment and potentially give rise to an increase in the amount of potassium reabsorbed through a transcellular pathway. However, the amount of Na-K-2Cl cotransporter was similarly reduced, arguing against a role for these effects in conserving potassium. The interpretation is further complicated by the finding that mutations in ROMK, as well as Na-K-2Cl, can cause Bartter's syndrome, a disease associated with sodium and potassium wasting, hypokalemic acidosis, and major defects in urinary concentrating and diluting capacity (25, 26). It seems unlikely that downregulation of ROMK and BSC-1 proteins is an adaptive response to low potassium intake, because the malfunctioning of either protein causes a disease characterized by hypokalemia.
The combined decrease of ROMK, BSC-1, and Na-K-ATPase, may implicate an overall suppression of transporters in the TALH during potassium depletion. In addition, Imbert-Teboul et al. (13) found a reduced adenylate cyclase response to arginine vasopressin and glucagon in mTAL of potassium-depleted rats. Arginine vasopressin and glucagon have been shown to stimulate reabsorption of electrolytes in the TALH (2, 4). Morphologically, Elger et al. (6) showed that although overall hypertrophy of the kidney occurs with potassium depletion, there is decreased growth of all segments of both short and long loops of Henle except that corresponding to the outer stripe of the medulla.
In summary we studied the regulation of ROMK expression at the protein level by immunoblotting. Our findings show ROMK expression is downregulated by potassium depletion in both the cortex and the medulla. Under the same conditions, in the medulla, we find a decrease in BSC-1 protein expression. No effect was identified in rats fed a HK diet. Further work is required to identify the mechanisms responsible for the modulation of ROMK and BSC-1 expression by potassium depletion.
![]() |
ACKNOWLEDGEMENTS |
---|
We thank Dr. Doris Herzlinger for the use of her fluorescence microscope. We are grateful to Dr. Mark Knepper for providing us with the BSC-1 antibody.
![]() |
FOOTNOTES |
---|
This work was supported by National Institute of Diabetes and Digestive and Kidney Diseases Grants DK-27847, DK-45828, and DK-11489.
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Address for reprint requests and other correspondence: L. G. Palmer, Dept. of Physiology and Biophysics, Weill Medical College of Cornell Univ., 1300 York Ave., New York, NY 10021 (E-mail: lgpalm{at}med.cornell.edu).
Received 24 March 1999; accepted in final form 10 January 2000.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Amlal, H,
Wang Z,
and
Soleimani M.
Potassium depletion downregulates chloride-absorbing transporters in rat kidney.
J Clin Invest
101:
1045-1054,
1998
2.
Bailly, C,
Roinel N,
and
Amiel C.
PTH-like glucagon stimulation of Ca and Mg reabsorption in Henle's loop of the rat.
Am J Physiol Renal Fluid Electrolyte Physiol
246:
F205-F212,
1984[ISI][Medline].
3.
Boim, MA,
Ho K,
Shuck ME,
Bienkowski MJ,
Block JH,
Slightom JL,
Yang Y,
Brenner BM,
and
Hebert SC.
ROM inwardly rectifying ATP-sensitive K+ channel II. Cloning and distribution of alternative forms.
Am J Physiol Renal Fluid Electrolyte Physiol
268:
F1132-F1140,
1995
4.
DeRouffignac, C,
Corman B,
and
Roinel N.
Stimulation by antidiuretic hormone of electrolyte tubular reabsorption in rat kidney.
Am J Physiol Renal Fluid Electrolyte Physiol
244:
F156-F164,
1983[ISI][Medline].
5.
Ecelbarger, CA,
Terris J,
Hoyer JR,
Nielsen S,
Wade JB,
and
Knepper MA.
Localization and regulation of the rat renal Na+-K+-2Cl cotransporter, BSC-1.
Am J Physiol Renal Fluid Electrolyte Physiol
271:
F619-F628,
1996
6.
Elger, M,
Bankir L,
and
Kriz W.
Morphometric analysis of kidney hypertrophy in rats after chronic potassium depletion.
Am J Physiol Renal Fluid Electrolyte Physiol
262:
F656-F667,
1992
7.
Frindt, G,
and
Palmer LG.
Low-conductance K channels in apical membrane of rat cortical collecting tubule.
Am J Physiol Renal Fluid Electrolyte Physiol
256:
F143-F151,
1989
8.
Frindt, G,
Zhou H,
Sackin H,
and
Palmer LG.
Dissociation of K channel density and ROMK mRNA in rat cortical collecting tubule during K adaptation.
Am J Physiol Renal Physiol
274:
F525-F531,
1998
9.
Giebisch, G.
Renal potassium transport: mechanisms and regulation.
Am J Physiol Renal Physiol
274:
F817-F833,
1998
10.
Gutsche, HU,
Peterson LN,
and
Levine DZ.
In vivo evidence of impaired solute transport by the thick ascending limb in potassium-depleted rats.
J Clin Invest
73:
908-916,
1984[ISI][Medline].
11.
Hebert, SC,
and
Andreoli TE.
Control of NaCl transport in the thick ascending limb.
Am J Physiol Renal Fluid Electrolyte Physiol
246:
F745-F756,
1984
12.
Ho, KH,
Nichols CG,
Lederer WJ,
Lytton J,
Vassilev PM,
Kanazirska MV,
and
Hebert SC.
Cloning and expression of an inwardly rectifying ATP-regulated potassium channel.
Nature
362:
31-37,
1993[ISI][Medline].
13.
Imbert-Teboul, M,
Doucet A,
Marsy S,
and
Siaume-Perez S.
Alterations of enzymatic activities along rat collecting tubule in potassium depletion.
Am J Physiol Renal Fluid Electrolyte Physiol
253:
F408-F417,
1987
14.
Jamison, RL.
Potassium recycling.
Kidney Int
31:
695-703,
1987[ISI][Medline].
15.
Kohda, Y,
Ding W,
Phan E,
Housini I,
Wang J,
Star RA,
and
Huang C-L.
Localization of the ROMK potassium channel to the apical membrane of distal nephron in rat kidney.
Kidney Int
54:
1214-1223,
1998[ISI][Medline].
16.
Kondo, C,
Isomoto S,
Matsumoto S,
Yamada M,
Horio Y,
Yamashita S,
Takemura-Kameda K,
Matsuzawa Y,
and
Kurachi Y.
Cloning and functional expression of a novel isomorm of ROMK inwardly rectifying ATP-dependent K channel, ROMK6 (Kir1.1f).
FEBS Lett
399:
122-126,
1996[ISI][Medline].
17.
Kone, BC.
Renal H,K-ATPase: structure, function and regulation.
Miner Electolyte Metab
22:
349-365,
1996[ISI][Medline].
18.
Lee, W-S,
and
Hebert SC.
The ROMK inwardly rectifying ATP-sensitive K+ channel. I: expression in rat distal nephron segments.
Am J Physiol Renal Fluid Electrolyte Physiol
268:
F1124-F1131,
1995
19.
Luke, RG,
Wright FS,
Fowler N,
Kashgarian M,
and
Giebisch G.
Effects of potassium depletion on renal tubular chloride transport in the rat.
Kidney Int
14:
414-427,
1978[ISI][Medline].
20.
Mennitt, PA,
Wade JB,
Ecelbarger CA,
Palmer LG,
and
Frindt G.
Localization of ROMK channels in the rat kidney.
J Am Soc Nephrol
8:
1823-1830,
1997[Abstract].
21.
Mujais, SK,
and
Katz AI.
Potassium Deficiency.
In: The Kidney: Physiology and Pathophysiology (Second ed.), edited by Seldin D.W.,
and Giebisch G.. New York: Raven, 1992, p. 2249-2278.
22.
Palmer, LG,
Antonian L,
and
Frindt G.
Regulation of apical K and Na channels and Na/K pumps in rat cortical collecting tubule by dietary K.
J Gen Physiol
104:
693-710,
1994[Abstract].
23.
Palmer, LG,
Choe H,
and
Frindt G.
Is the secretory K channel in the rat CCT ROMK?
Am J Physiol Renal Physiol
273:
F404-F410,
1997
24.
Palmer, LG,
and
Frindt G.
Regulation of apical K channels in rat cortical collecting tubule during changes in dietary K intake.
Am J Physiol Renal Physiol
277:
F805-F812,
1999
25.
Simon, DB,
Karet FE,
Hamdan JM,
DiPietro A,
Sanjad SA,
and
Lifton RP.
Bartter's Syndrome, hypokalaemic alkalosis with hypercalciuria, is caused by mutations in the Na-K-2Cl cotransporter NKCC2.
Nat Genet
13:
183-188,
1996[ISI][Medline].
26.
Simon, DB,
Karet FE,
Rodriguez-Soriano J,
Hamdan JH,
DiPietro A,
Trachtman H,
Sanjad SA,
and
Lifton RP.
Genetic heterogeneity of Bartter's syndrome revealed by mutations in the K+ channel, ROMK.
Nat Genet
14:
152-156,
1996[ISI][Medline].
27.
Wald, H,
Garty H,
Palmer LG,
and
Popovtzer MM.
Differential regulation of ROMK expression in kidney cortes and medulla by aldosterone and potassium.
Am J Physiol Renal Physiol
275:
F239-F245,
1998
28.
Walter, SJ,
Shore AC,
and
Shirley DG.
Effect of potassium depletion on renal tubular function in the rat.
Clin Sci (Colch)
75:
621-628,
1988[ISI][Medline].
29.
Wang, W.
Two types of K+ channel in thick ascending limb of rat kidney.
Am J Physiol Renal Fluid Electrolyte Physiol
267:
F599-F605,
1994
30.
Wang, W,
Schwab A,
and
Giebisch G.
Regulation of small conductance K channel in apical membrane of rat cortical collecting tubule.
Am J Physiol Renal Fluid Electrolyte Physiol
259:
F494-F502,
1990
31.
Wang, W,
White S,
Geibel J,
and
Giebisch G.
A potassium channel in the apical membrane of rabbit thick ascending limb of Henle's loop.
Am J Physiol Renal Fluid Electrolyte Physiol
258:
F244-F253,
1990
32.
Wingo, CS,
and
Cain BD.
The renal H-K-ATPase: physiological significance and role in potassium homeostasis.
Annu Rev Physiol
55:
323-347,
1993[ISI][Medline].
33.
Xu, JZ,
Hall AE,
Peterson LN,
Bienkowski MJ,
Eesalu TB,
and
Hebert SC.
Localization of the ROMK protein on apical membranes of rat kidney nephron segments.
Am J Physiol Renal Physiol
273:
F739-F748,
1997[ISI][Medline].
34.
Zhou, H,
Tate SS,
and
Palmer LG.
Primary structure and functional properties of an epithelial K channel.
Am J Physiol Cell Physiol
266:
C809-C824,
1994