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作者：Dongun Kim, Jeff M. Sands,, and Janet D. Klein作者单位：1 Renal Division, Department of Medicine, and 2 Department of Physiology, Emory University School ofMedicine, Atlanta, Georgia 30322
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【摘要】
# I$ Q* @8 b3 `0 w1 |, a We tested whether the abundance of transport proteins involved in theurinary concentrating mechanism was altered in rats with uncontrolled diabetesmellitus (DM). Rats were injected with streptozotocin and killed 5, 10, 14, or20 days later. Blood glucose in DM rats was 300-450 mg/dl (control: 70-130 mg/dl). Urine volume increased in DM rats from 41 ± 7ml/100 g body wt (BW) at 5 days to 69 ± 3 ml/100 g BW at 20 days(control: 9 ± 1). Urine osmolality of DM rats decreased at 5 days DMand remained low at 20 days. UT-A1 urea transporter protein in the innermedullary (IM) tip was 55% of control in 5-day DM rats but increased to 170, 220, and 280% at 10, 14, and 20 days DM, respectively, due to an increase inthe 117-kDa glycoprotein form. UT-A1 in the IM base was increased to 325% ofcontrol at 5 days DM with no further increase at 20 days. Aquaporin-2 (AQP2)increased to 290% in the IM base at 5 days DM and 150% in the IM tip at 10days; both showed no further increase at 20 days. NKCC2/BSC1 increased to 240%in outer medulla at 20 days DM, but not at 5 or 10 days. UT-B and ROMK wereunchanged at any time point. The increases in UT-A1, AQP2, and NKCC2/BSC1proteins during uncontrolled DM would tend to limit the loss of fluid andsolute during uncontrolled diabetes.
H% t" \6 j$ J 【关键词】 urea water urea transporter aquaporin sodium2 T, @% E) w4 W$ c, a% a
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v9 ^. V( _( ?8 C( i2 H( [PATIENTS WITH UNCONTROLLED type I diabetes mellitus (DM) are polyuric due to the osmotic diuresis caused by glucosuria. The persistentosmotic diuresis frequently results in a serious degree of volume depletion,but these patients rarely present for medical attention with shock andcardiovascular collapse. Instead, they generally present with severehyperglycemia and diabetic ketoacidosis. This clinical presentation suggests the hypothesis that compensatory changes occur within the kidney that permitsufficient solute and water reabsorption, despite the ongoing osmoticdiuresis, to prevent hypovolemic shock.& ]+ q- l% P" D5 [
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The goal of this study was to test this hypothesis using rats made diabeticby streptozotocin (STZ) injection. The STZ-treated rat is a commonly usedanimal model of type I diabetes. These rats rapidly develop hyperglycemia andpolyuria, although they do not develop ketoacidosis. Because the renal medullais responsible for the production of concentrated or dilute urine, wehypothesized that any compensatory mechanism to conserve water and solute mayinvolve changes in the abundance of the medullary transport proteins involvedin the urinary concentrating mechanism. Therefore, we measured the abundanceof the UT-A1 and UT-B urea transporters, the aquaporin-2 (AQP2) water channel,the NKCC2/BSC1 Na -K -2Cl - cotransporter, and the ROMK K channel from rats made diabetic for5, 10, 14, or 20 days.8 c9 \2 m/ H# n7 H) i2 j
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METHODS
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W9 y' e; r6 x8 j$ }; J% Z! r! tAnimal preparation. Male Sprague-Dawley rats (Charles River Laboratories, Wilmington, MA) weighing 125-200 g received free access to23% protein rat chow and water for at least 3 days after delivery. Rats wereinjected with STZ (Sigma, St. Louis, MO; 62.5 mg/kg body wt prepared fresh in0.1 M citrate buffer, pH 4.0) or vehicle into a tail vein at 7 AM( 9 ). Subsequently, theSTZ-injected diabetic rats or vehicle-injected control rats were fed 23%protein chow and water ad libitum until they were killed at 5, 10, 14, or 20days after injection (6 control and 6 diabetic rats were used at each timepoint). At 24 h after STZ injection, diabetes was confirmed by measuring the urine glucose (Ames-Multistix SG, Miles, Elkhart, IN). One day before death, a24-h urine collection was obtained to measure urinary volume, osmolality, ureaconcentration, and creatinine concentration( 10 ). Rats were killed bydecapitation, and blood was collected and assayed for glucose (One TouchProfile Diabetes Tracking Kit, Life-scan, Milpitas, CA), blood urea nitrogen(Infinity BUN reagent, Sigma), osmolality (model 5500 vapor pressureosmometer, Wescor, Logan, UT), and creatinine concentration (CreatinineAnalyzer 2, Beckman Instruments, Fullerton, CA). Vasopressin levels weredetermined using the Arg8-vasopressin correlate-EIA kit (Assay Designs, AnnArbor, MI) according to the manufacturer's instructions. Kidneys and liverwere removed for tissue protein analysis( 18 ).4 R& w1 r8 K. o/ ~* _$ q5 x3 M3 R# `. u
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Western blot analysis. The kidney medulla was dissected into threeregions: outer medulla, base of the inner medulla, and tip of the innermedulla, as previously described( 9, 13, 20 ). Tissue from liver or thepooled tissue from both kidneys of a single rat was placed into an ice-coldisolation buffer (10 mM triethanolamine, 250 mM sucrose, pH 7.6, 1 µg/ml leupeptin, and 0.1 mg/ml PMSF), homogenized, and diluted 1:1 with 1% SDS forWestern blot analysis of total cell lysate ( 9, 13, 20 ). Total protein in eachsample was measured by the Bradford method (Bio-Rad, Richmond, CA). Proteins(10 µg/lane) were size separated by SDS-PAGE using 7.5, 10, or 15%polyacrylamide gels. Proteins were blotted to polyvinylidene difluoridemembranes (Gelman Scientific, Ann Arbor, MI), and Western blot analysis wasperformed as described previously( 9 ). Blots were quantified using an Imaging Densitometer GS670 and Molecular Analyst software (Bio-RadLaboratories, Hercules, CA). Where multiple bands were observed resulting frommultiple glycosylated forms of a single protein (UT-A1: 110-120 kDa;UT-B: 41-54 kDa; AQP2: 35-50 kDa), all bands in the group weremeasured together and designated the molecular mass of the major form. In allcases, parallel gels were stained with Coomassie blue to confirm uniformity ofloading (data not shown). Results are expressed as arbitrary units permicrogram of protein.
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& T4 d- E' y! Z' K1 }4 Q+ I- pDeglycosylation of UT-A1 protein in inner medullary homogenates. Asample of inner medullary (IM) homogenate (45µg) containing 0.5% SDS and 1% -mercaptoethanol was denatured by heating to 100°C for 10 min. Afteraddition of NP-40 detergent to 1% and addition of 2,500 U of peptide N -glycosidase F (PNGase F; catalog no. 704S, New England Biolabs,Beverly, MA), the mixture was incubated at 37°C for 60 min. The reaction was quenched by the addition of an equal volume of 2 x Laemmli samplebuffer. These samples were heated again to 60°C for 15 min before SDS-PAGEand immunoblotting.- j. Y( L2 L) @" A# }) m
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Antibodies. Western blot analyses were probed with antibodies (diluted in TBS/Tween) to the following proteins: 1 ) UT-A1 and UT-A2( 13 ); 2 ) AQP2( 8, 15 ); 3 ) UT-B( 22 ); 4 ) NKCC2/BSC1 ( 6, 7 ); and 5 ) ROMK(generous gift from Dr. M. A. Knepper, National Institutes of Health)( 4 ).0 z6 E0 Y. b8 X( x. w$ C
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Statistics. Data are presented as means ± SE ( n ),where n indicates the number of rats studied. To test forstatistically significant differences between two groups, a paired Student's t -test was used. To test for statistically significant differences among three groups, an ANOVA was used followed by a multiple comparison,protected t -test( 21 )., h) r' c( w+ Q2 K
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Animal parameters. The weight gain of control rats at both 5 and20 days was significantly greater than the weight gain of the diabetic rats(5-day control: 39 ± 1 vs. diabetic: 19 ± 3 g; 20-day control:170 ± 5 vs. diabetic: 109 ± 7 g). Food intake was assessedduring the final 2 days of 5- and 20-day STZ treatments. At 5 days DM, thefood intake of control rats was 14.6 ± 0.4 g, whereas the DM ratsconsumed 19.5 ± 4.5 g/100 g body wt. The food intake of the more maturecontrol animals of the 20-day group was 10.9 ± 0.4 g compared with 20.3± 1.0 g/100 g body wt for the 20-day DM rats. At both time points, the DM rats ate significantly more than control rats ( P
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0 @9 m; D5 Z0 B0 TTable 1. In vivo blood and urinary parameters
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' `+ o L6 T: p3 P. w# ~UT-A1. The abundance of UT-A1 protein in IM tip of control and diabetic rats is shown in Fig.1. UT-A1 exists as two distinct glycoproteins with molecularmasses of 117 and 97 kDa ( 3 ). To determine whether the 117- and 97-kDa proteins that increase in thediabetic rats are the same glycoproteins as in control rats and representglycosylated forms of the same base UT-A1 protein, kidney lysates from bothcontrol and 20-day diabetic rats were treated with PNGase F. Deglycosylationof UT-A1 protein from diabetic and control rats revealed the identical 88-kDa nonglycosylated base protein ( Fig.2 ). When reporting on the total UT-A1 protein abundancedifferences, we make the assumption that the antibody recognizes bothglycoproteins equally. However, we are also providing information about shiftsin the relative abundances of each of the two forms to better characterize the changes in UT-A1 that occur in the diabetic animal (reviewed in Ref. 19 ). The functional differencebetween these two glycoproteins, if any, is not known.& x6 F: \1 O; b' C0 x
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Fig. 1. UT-A1 protein in inner medullary (IM) tip of control (CTR) vs. diabetic(DM) rats. The time after streptozotocin treatment is indicated as days on the left of the blots and below the bars. A : Western blotanalyses of representative samples of IM tip lysates probed with anti-UT-Aantibody. Samples from 3 different CTR rats ( left ) and 3 different DMrats ( right ) are shown. Arrows indicate the glycosylated bands at 117and 97 kDa. B : bar graphs showing the summary densitometry (totalUT-A1 protein of CTR rats is 100%) from all rats. Bars = means, * P 8 t5 W3 z5 ~( B: @' d
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Fig. 2. Deglycosylation of UT-A1 protein in CTR vs. DM rats. IM tip lysates fromCTR and 20-day DM rats were treated with PNGase F ( ) or vehicle (-).Western blot analysis of these samples is shown. Left : arrowsindicate the glycosylated bands at 117 and 97 kDa in the untreated lysates andthe deglycosylated band at 88 kDa that is common to both CTR and DM rats.4 b$ a6 }% Y1 l# g- w: m& P" Q
7 f& v( X/ K" |/ ]9 `Compared with control rats, the abundance of UT-A1 in 5-day diabetic ratswas significantly decreased to 55% of control rats in the IM tip. The decreaseof UT-A1 in the IM tip was mainly due to a decrease in the abundance of the97-kDa UT-A1 protein (to 26% of control) rather than a change in the abundance of the 117-kDa UT-A1 protein (87% of control). In contrast, the abundance ofUT-A1 was significantly increased in the IM tip of rats made diabetic for 10,14, or 20 days: UT-A1 increased to 170% of control at 10 days; 220% of controlat 14 days; and 280% of control at 20 days. The amount of the 117-kDa UT-A1 protein relative to total UT-A1 protein in diabetic rats also increased withtime to 56, 66, and 70% at 10, 14, and 20 days, respectively. At each timepoint, six control and six diabetic rats were used and the results arerepresentative of four experiments.$ G0 N- O; V& f( e2 J5 t& f
9 D$ d5 N& N6 ZThe abundance of UT-A1 protein in the IM base of control and diabetic ratsis shown in Fig. 3. In contrastto the IM tip, the abundance of UT-A1 in the IM base was significantlyincreased to 325% of control levels by 5 days of diabetes and did not increasefurther at 10, 14, or 20 days (300, 390, and 340% of control, respectively).The increase in UT-A1 protein abundance in the IM base of diabetic rats wasmainly due to an increase in the 117-kDa UT-A1 protein (to 2,000% of control)rather than an increase in the 97-kDa UT-A1 protein (135-190% ofcontrol). The percentage of 117-kDa UT-A1 protein to total UT-A1 protein (62,55, 56, and 55% at 5, 10, 14, and 20 days, respectively) did not vary with theduration of diabetes in the IM base.
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5 n! x/ O" _5 r$ J% M- D2 l# KFig. 3. UT-A1 protein in IM base of CTR vs. DM rats. The time after streptozotocintreatment is indicated as days on the left of the blots and below thebars. A : Western blot analyses of representative samples of IM baselysates probed with anti-UT-A antibody. Samples from 3 different CTR rats( left ) and 3 different DM rats ( right ). Arrows indicate theglycosylated bands at 117 and 97 kDa. B : bar graphs showing thesummary densitometry (total UT-A1 protein of CTR rats is 100%) from all rats.Bars = means, * P 5 j! n, _: G* G; {; ~. @# ]. m
* C9 d6 W2 V, V: jUT-B. UT-B is normally expressed in the IM tip, base, and outer medulla ( 22 ). It is foundexclusively in red blood cells and descending vasa recta but not in tubules(reviewed in Ref. 19 ). Therewas no significant difference in UT-B protein abundance in any of these kidneyregions at 20 days of diabetes compared with control rats( Fig. 4 ) nor at 5 or 10 days ofdiabetes (data not shown).( K3 o" T c0 T- |- j/ H- ?
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Fig. 4. UT-B in IM tip, base, and outer medulla (OM) of CTR vs. 20-day DM rats.Western blot analyses of representative samples of lysates from these 3regions probed with anti-UT-B antibody are shown. Each blot shows samples from3 different CTR rats ( left ) and 3 different DM rats ( right ). Right : 41- to 54-kDa UT-B bands and the 98-kDa high-molecular-massUT-B band are indicated by arrows. There was no change in the abundance ofUT-B in any region ( n = 6 rats/group). V1 d- _( L+ ]; l
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AQP2 in the IM tip and base. AQP2 protein abundance in the IM tip( Fig. 5 A ) wasunchanged at 5 days, but significantly increased to 150% of control at 10 daysof diabetes and remained elevated at 20 days. In the IM base( Fig. 5 B ), AQP2protein abundance was significantly increased to 290% of control at 5 days of diabetes and remained elevated at 10 and 20 days. At each time point, sixcontrol and six diabetic rats were used and the results are representative offour experiments.
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Fig. 5. Aquaporin-2 (AQP2) protein in IM tip ( A ) and base ( B ) ofCTR vs. DM rats. Left : time after streptozotocin treatment isindicated as days. Western blot analyses of representative samples of IM tipand base lysates probed with anti-AQP2 antibody are shown. A and B : samples from 3 different CTR rats ( left ) and 3 differentDM rats ( right ). Right : 35- to 50-kDa glycosylated and the28-kDa unglycosylated AQP2 bands are indicated by arrows.# D- B7 I/ d4 Q! X" Q5 a
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NKCC2/BSC1 and ROMK abundance in the outer medulla. At 5 or 10days of diabetes, there was no significant difference in the abundance ofeither NKCC2/BSC1 or ROMK protein between control and diabetic rats (data notshown). At 20 days of diabetes, NKCC2/BSC1 was significantly increased to 245%of control levels ( Fig. 6 ). Incontrast, ROMK was not significantly increased at 20 days of diabetes( Fig. 7 )./ a( W( l9 x1 [ O) G7 o" c
. v1 C# s- g! m4 T, l* LFig. 6. NKCC2/BSC1 protein in OM of CTR vs. 20-day DM rats. Samples from 6different CTR rats and 6 different DM rats probed with an antibody toNKCC2/BSC1 are shown. There was a significant 244% increase in NKCC2/BSC1abundance in DM rats.4 \% A: o7 n" z1 K3 H
( @' ]$ L% l" ?$ z2 v9 v6 P4 ]Fig. 7. ROMK protein in OM of CTR vs. 20-day DM rats. Samples from 6 different CTRrats and 6 different DM rats probed with an antibody to ROMK are shown. Therewas no change in the abundance of ROMK in the DM rat.9 ]0 X& }7 t( T0 E% P7 A. A( g
6 c# J: B- S6 [. F) a1 ZUT-A in liver. UT-A is found in several extrarenal tissues including the liver ( 11 ), thesite of ureagenesis. We previously reported that the liver form of UT-A isregulated by uremia and acidosis( 10, 11 ). The 49-kDa UT-A proteinwas significantly increased to 400% of control in liver from 20-day diabetic rats but not in liver from rats with diabetes for 5 or 10 days ( Fig. 8 ). The abundance of the36-kDa protein was not significantly different at any time point. Theabundance of the 36-kDa protein was also unchanged in the liver from uremicrats ( 11 ).
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% G; u! S g3 ?Fig. 8. UT-A protein in liver of CTR vs. DM rats. Left : time afterstreptozotocin treatment is indicated as days. Western blot analyses ofrepresentative samples of liver lysates probed with anti-UT-A antibody areshown. Four samples from different CTR rats are shown on the left and4 samples from different DM rats are shown on the right. Right : 49- and 36-kDa UT-A liver protein bands are indicated byarrows. The 49-kDa UT-A band was significantly increased to 403% of CTR in the20-day DM rats. There was no change in the 49-kDa band at 5 or 10 days ofdiabetes and no change in the 36-kDa band at any time point ( n = 6rats).1 I; g: ^7 H: B- G. V& ~
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The major finding in the present study is that the abundance of the majormedullary transport proteins involved in the urinary concentrating mechanismincreases from 5 to 20 days after rats are made diabetic by STZ. At 5 days,UT-A1 and AQP2 proteins are upregulated in the IM base, which would tend toincrease urea and water reabsorption from the initial IM collecting duct (IMCD). At 10 days, UT-A1 and AQP2 proteins are also upregulated in the IMtip, which would tend to increase urea reabsorption into the deep innermedulla, where it is needed for maximal urinary concentrating ability, andwater reabsorption from the terminal IMCD. At 20 days, NKCC2/BSC1 protein isupregulated in the outer medulla, which would tend to increase sodiumreabsorption, and through counter-current multiplication, increase urinary concentrating ability. These findings tend to support the hypothesis that theincreases in UT-A1, AQP2, and NKCC2/BSC1 proteins during uncontrolled diabetesare compensatory changes that prevent a progressive decline in urinaryconcentrating ability despite the continuing osmotic diuresis.# a4 h) ^" X* i4 A& [
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The diabetic rats have reduced urinary osmolality, but urinary osmolalitydoes not vary between 5 and 20 days, even though urinary volume progressivelyincreases ( Table 1 ). Thepolyuria of diabetes results from nonreabsorbable glucose in the tubule lumen.Theoretically, 300 mosmol of nonreabsorbable solute will retain about 1 literof water in the tubular lumen and reduce urinary osmolality to 300mosmol/kgH 2 O. However, the diabetic rats were able to maintaintheir urinary osmolality at 850-950 mosmol/kgH 2 O. The presentfindings suggest that the increases in UT-A1, AQP2, and NKCC2/BSC1 proteins play a role in maintaining urinary osmolality above isotonicity. If urinaryosmolality had continued to decrease as urinary volume increased with thelonger duration of diabetes, it is likely that the rats would have lost morewater and solute.
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UT-A1. The findings in the present study appear to resolve some discrepancies between previous studies of the effect of diabetes on UT-A1abundance. We previously showed that at 3 days of diabetes, UT-A1 proteinabundance is downregulated in the IM tip, compared with control rats( 9 ), and the present study shows that UT-A1 protein is downregulated in the IM tip at 5 days. Incontrast, Bardoux and colleagues( 1 ) showed that at 21 dayspost-STZ treatment, diabetic rats show an increase in UT-A1 mRNA and proteinin the IM base. In particular, they showed that the 117-kDa band was increasedwithout a change in the 97-kDa band( 1 ). Consistent with Bardouxand colleagues ( 1 ), the presentstudy shows that the 117-kDa form of UT-A1 is consistently upregulated in theIM base from 5 to 20 days of diabetes and also shows that it is increased inthe IM tip from 10 to 20 days. Thus both previous studies( 1, 9 ) were correct, but neitherrecognized that there are temporal and IM regional changes in UT-A1 proteinduring the first 3 wk after STZ.- A4 e3 f; d( _4 O/ n
+ J2 b, Y, s* w x1 ]( AAQP2. The findings in the present study also appear to resolve some discrepancies between previous studies on the effect of diabetes on AQP2abundance. We previously showed that at 3 days of diabetes, AQP2 proteinabundance is unchanged in the IM tip, compared with control rats( 9 ), and the present study shows that AQP2 protein is unchanged in the IM tip at 5 days. In contrast,Nielsen and colleagues ( 14 )showed that AQP2 and phospho-AQP2 protein abundances increase in the whole IM (base tip) of diabetic rats at 15 days post-STZ. Bardoux and colleagues( 1 ) also show that AQP2 proteinis increased in the IM at 21 days post-STZ. Consistent with these latterstudies ( 1, 14 ), the present study showsthat AQP2 is consistently upregulated in the IM base from 5 to 20 days ofdiabetes and also shows that it is increased in the IM tip from 10 to 20 days.Thus all previous studies ( 1, 9, 14 ) were correct, but againthey did not recognize that there are temporal and IM regional changes in AQP2protein during the first 3 wk after STZ. The present study does not addresswhether diabetic rats have an abnormality in the regulated trafficking of AQP2nor whether there is a change in the abundance of AQP3 or AQP4 (located in thebasolateral membrane of the collecting duct), and future studies will beneeded to test these possibilities. `3 q/ c3 M1 R0 G7 W
8 z, Q1 t4 U+ R0 sNKCC2/BSC1. Nielsen and colleagues( 14 ) found no significant change in NKCC2/BSC1 protein at 15 days post-STZ. The present study shows thatNKCC2/BSC1 is unchanged at 10 days but increases at 20 days. However, ROMKprotein was unchanged at all time points.
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Interestingly, UT-A1, AQP2, and NKCC2/BSC1 protein abundances are decreasedin 6-mo-old, obese Zucker rats, a model of type II diabetes( 2 ). Thus more prolongedperiods of diabetes or type II (vs. type I) diabetes may have differenteffects on these transporters. Regardless, the present and previous( 1, 9, 14 ) findings suggest a complexcompensatory response in which UT-A1, AQP2, and NKCC2/BSC1 are upregulated atdifferent times after STZ injection in different medullary regions, but all ofthese changes will tend to limit the loss of water and solute duringuncontrolled diabetes. b( s, \& ~& |# ]. J; d
" f7 f, G& |9 S5 X* UPossible mechanisms. Several metabolic and hormonal abnormalities present in diabetes could contribute to the changes in medullary transportprotein abundances. In normal rats, we showed that glucocorticoidsdownregulate UT-A1 protein abundance in the IM tip and lower basal andvasopressin-stimulated facilitated urea permeability in rat terminal IMCDs( 13 ) by decreasing thetranscription of UT-A promoter I( 17 ). Rats with uncontrolled DM induced by STZ have increased corticosterone production and urea excretionat 3-6 days ( 12 ). Wepreviously showed that glucocorticoids mediate the downregulation of UT-A1protein abundance in rats with uncontrolled diabetes at 3 days( 9 ). Thus the decrease in UT-A1at 3-5 days after STZ treatment is likely to be mediated by repressiveeffect of glucocorticoids on UT-A1 transcription." {' A8 X: w; B
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What about the upregulation of UT-A1, AQP2, and NKCC2/BSC1 at the latertime points? Vasopressin upregulates AQP2 protein long term by atranscriptional mechanism (reviewed in Ref. 16 ). Vasopressin alsoupregulates NKCC2/BSC1 and ROMK proteins ( 4, 5, 7 ). A previous study showedthat diabetic rats have polyuria despite elevated plasma vasopressin levels( 23 ). However, we did not finda significant change in vasopressin levels in the present study. In addition,the difference in time course for AQP2 between IM base and tip, and the lackof change in ROMK, suggests that factors other than vasopressin may play arole.
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" _4 t1 H% n3 r) nRegardless of the mechanism, the increase in UT-A1 protein is likely topromote the production of a more concentrated urine. Given the sustainedincrease in urinary volume, and presumably urinary flow rates, the increase inUT-A1 protein may be an important compensatory mechanism to maintain ureadelivery to the IM interstitium. Vasopressin does mediate the rapid increase in urea reabsorption by phosphorylating UT-A1( 24 ). Because vasopressinlevels are not suppressed in diabetic rats, vasopressin is likely to result inUT-A1 phosphorylation and an increase in urea transport per UT-A1 molecule,potentially compensating for the reduced time for urea transport due to theincrease in urinary flow rate. Consistent with this hypothesis, the percentage of urea in total urinary solute excretion remained constant from 5 to 20 daysof diabetes ( Table 1 ).# ^3 h4 @. S, o. H
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Summary. The abundance of the major medullary transport proteins involved in the urinary concentrating mechanism varies with time and kidneyregion after rats are made diabetic by STZ. These findings tend to support thehypothesis that increases in UT-A1, AQP2, and NKCC2/BSC1 proteins duringuncontrolled diabetes are compensatory changes that prevent a progressive decline in urinary concentrating ability despite the continuing osmoticdiuresis. Future studies in which knockout mice lacking one or more of thesetransport proteins are made diabetic may be very useful in defining theimportance of each transporter to the compensatory response. However, ifsimilar changes in these medullary transport proteins occur in patients withuncontrolled type I diabetes, they would tend to lessen the degree of volume depletion that occurs in these patients." a5 v. q! M/ i0 m
( ]7 h: W: G, gDISCLOSURES
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Portions of this work have been published in abstract form ( J Am SocNephrol 13: 67A, 2002). This work was supported by National Institutes ofHealth Grants R01-DK41707 and R01-DK63657.
: ~* k8 q- _* v0 ~0 N* M6 v 【参考文献】* M3 I9 L5 N( E5 V
Bardoux P,Ahloulay M, Le Maout S, Bankir L, and Trinh-Trang-Tan MM. Aquaporin-2 andurea transporter-A1 are upregulated in rats with type I diabetes mellitus. Diabetologia 44:637-645, 2001.
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Bickel CA,Knepper MA, Verbalis JG, and Ecelbarger CA. Dysregulation of renal saltand water transport proteins in diabetic Zucker rats. KidneyInt 61:2099-2110, 2002.# `, t# F2 d: F
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5 P6 _6 j7 k' S7 sBradford AD,Terris J, Ecelbarger CA, Klein JD, Sands JM, Chou CL, and Knepper MA. 97-And 117-kDa forms of the collecting duct urea transporter UT-A1 are due todifferent states of glycosylation. Am J Physiol RenalPhysiol 281:F133-F143, 2001.
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$ \ D; ?# Q+ IEcelbarger CA,Kim GH, Knepper MA, Liu J, Tate M, Welling PA, and Wade JB. Regulation ofpotassium channel Kir 1.1 (ROMK) abundance in the thick ascending limb ofHenle's loop. J Am Soc Nephrol 12: 10-18,2001.
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& w$ Z7 e' ^: f9 Q/ {* VEcelbarger CA,Knepper MA, and Verbalis JG. Increased abundance of distal sodiumtransporters in rat kidney during vasopressin escape. J Am SocNephrol 12:207-217, 2001.
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发表于 2009-4-21 13:41
