Effect of peritubular hypertonicity on water and urea transport of inner medullary collecting duct

1992 ◽  
Vol 262 (3) ◽  
pp. F338-F347 ◽  
Author(s):  
L. H. Kudo ◽  
K. R. Cesar ◽  
W. C. Ping ◽  
A. S. Rocha
Keyword(s):  
Hydraulic Conductivity ◽  
Collecting Duct ◽  
Osmotic Gradient ◽  
Urea Transport ◽  
Perfusion Fluid ◽  
Cyclic Monophosphate ◽  
Inner Medullary Collecting Duct ◽  
Medullary Collecting Duct ◽  
Series Of Experiments

The effect of bath fluid hypertonicity on hydraulic conductivity (Lp) and [14C]urea permeability (Pu) of the distal inner medullary collecting duct (IMCD) was studied in the absence and in the presence of vasopressin (VP) using the in vitro microperfusion technique of rat IMCD. In the first three groups of IMCD, we observed that in the absence of VP the Lp was not different from zero when the osmotic gradient was created by hypotonic perfusate and isotonic bath fluid, but it was significantly greater than 1.0 x 10(-6) cm.atm-1.s-1 when the osmotic gradient was created by hypertonic bath and isotonic perfusion fluid. The increase in Lp was observed when the hypertonicity of the bath fluid was produced by the addition of NaCl or raffinose, but no such effect was observed with urea. The stimulated effect of bath fluid hypertonicity on Lp was also observed in the IMCD obtained from Brattleboro homozygous rats in which VP is absent. The NaCl hypertonic bath increased the Pu in the absence of VP. In another series of experiments with VP (10(-10) M) we observed that the hypertonic bath fluid increased in a reversible manner the VP-stimulated Lp of distal IMCD. However, the NaCl hypertonicity of the bath fluid was not able to increase dibutyryladenosine 3',5'-cyclic monophosphate-stimulated Lp. The Pu stimulated by VP (10(-10) M) increased twofold when the bath fluid was hypertonic. Therefore hypertonicity of the peritubular fluid produced by the addition of NaCl or raffinose increases the Lp and Pu in the absence and in the presence of VP. No such effect was noted with the addition of urea.

scholarly journals Effect of amphotericin B on water and urea transport in the inner medullary collecting duct.

1994 ◽  
Vol 5 (1) ◽  
pp. 68-74 ◽  
Author(s):  
Y Yano ◽  
J L Monteiro ◽  
A C Seguro
Keyword(s):  
Hydraulic Conductivity ◽  
Amphotericin B ◽  
Arginine Vasopressin ◽  
Initial Conditions ◽  
Collecting Duct ◽  
Potassium Excretion ◽  
Urea Transport ◽  
Inner Medullary Collecting Duct ◽  
Medullary Collecting Duct

The clinical usefulness of amphotericin B (AMP-B) is limited by its nephrotoxicity, as characterized by decreased RPF, decreased GFR, impaired urinary acidification, and potassium excretion defects. Defects of renal concentrating ability have been noted, but the mechanisms responsible for them have not been investigated. The chief objective of this research was to analyze directly the effect of AMP-B on arginine-vasopressin (AVP)- or dibutyrl cAMP (DcAMP)-stimulated water and urea transport of the inner medullary collecting duct (IMCD) obtained from rats by the in vitro microperfusion technique. AMP-B (10(-5) M) added to the bath fluid in the absence of AVP did not impair the hydraulic conductivity (Lp) and the urea permeability (Pu) of rat IMCD. AMP-B (10(-5) M) added to the bath fluid decreased the AVP-stimulated Lp (x 10(-6) cm/s.atm) of rat IMCD from 19.41 +/- 2.19 to 10.00 +/- 1.39 (P < 0.001), and the reversibility of its action was observed during a third period when Lp increased to 19.80 +/- 2.19 (P < 0.001) after the initial conditions were restored. In addition, AMP-B reduced DcAMP-stimulated Lp from 20.95 +/- 1.75 to 10.52 +/- 0.71 (P < 0.01) in a reversible manner when the drug was withdrawn from the bath. AMP-B also decreased AVP-stimulated Pu (x 10(-5) cm/s) when added to the bath fluid from 36.60 +/- 2.05 to 29.88 +/- 1.36 (P < 0.001), and this effect was reversible after AMP-B was withdrawn from the bath (37.40 +/- 1.36; P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of ANF on cGMP synthesis in inner medullary collecting duct subsegments of rats

1990 ◽  
Vol 259 (3) ◽  
pp. F535-F538
Author(s):  
K. Ujiie ◽  
H. Nonoguchi ◽  
K. Tomita ◽  
F. Marumo
Keyword(s):  
Atrial Natriuretic Factor ◽  
Collecting Duct ◽  
Target Site ◽  
Cyclic Monophosphate ◽  
Inner Medullary Collecting Duct ◽  
Camp Synthesis ◽  
Target Sites ◽  
Medullary Collecting Duct ◽  
Cgmp Synthesis ◽  
Major Target

The inner medullary collecting duct (IMCD) is thought to be a major target site for atrial natriuretic factor (ANF) action. The IMCD is divided into two subsegments (IMCD1, outer third; and IMCD2,3, inner two-thirds) based on differences in urea and water permeability. IMCD1 has similar characteristics to the outer medullary collecting duct (OMCD). To elucidate whether there are any differences among these segments in ANF actions, we investigated the effects of ANF on guanosine 3',5'-cyclic monophosphate (cGMP) synthesis in IMCD subsegments and the OMCD. We also examined the effects of arginine vasopressin (AVP) on adenosine 3',5'-cyclic monophosphate (cAMP) synthesis. IMCD subsegments (IMCD1,2,3) and OMCD were microdissected; and ANF-stimulated cGMP synthesis and AVP-stimulated cAMP synthesis were measured. cGMP synthesis stimulated by 10(-6) M ANF in IMCD1,2,3 (0.78 +/- 0.15, 0.81 +/- 0.19, 0.62 +/- 0.10 fmol.mm-1 x 3 min-1, mean +/- SE respectively, n = 10-11) was significantly (greater than 20-fold) higher than that in OMCD (0.03 +/- 0.02 fmol.mm-1 x 3 min-1, n = 7), and there was no difference among IMCD subsegments. On the other hand, cAMP synthesis stimulated by 10(-7) M AVP in IMCD subsegments was similar to that in OMCD. We conclude that IMCD is homogenous as a target site of ANF and is clearly distinguished from OMCD. In addition, more than half of ANF-stimulated cGMP synthesis in IMCD are considered to occur in IMCD1, simply because IMCD1 is dominant in population among IMCD subsegments. As target sites of AVP, IMCD subsegments are similar to OMCD.

NF-κB inhibits transcription of the H+-K+-ATPase α2-subunit gene: role of histone deacetylases

2002 ◽  
Vol 283 (5) ◽  
pp. F904-F911 ◽  
Author(s):  
Wenzheng Zhang ◽  
Bruce C. Kone
Keyword(s):  
Histone Deacetylases ◽  
Transcriptional Control ◽  
Protein Complexes ◽  
Trichostatin A ◽  
Collecting Duct ◽  
Proximal Promoter ◽  
Inner Medullary Collecting Duct ◽  
Nuclear Extracts ◽  
Medullary Collecting Duct

The H+-K+-ATPase α2 (HKα2) gene plays a central role in potassium homeostasis, yet little is known about its transcriptional control. We recently demonstrated that the proximal promoter confers basal transcriptional activity in mouse inner medullary collecting duct 3 cells. We sought to determine whether the κB DNA binding element at −104 to −94 influences basal HKα2 gene transcription in these cells. Recombinant NF-κB p50 footprinted the region −116/−94 in vitro. Gel shift and supershift analysis revealed NF-κB p50- and p65-containing DNA-protein complexes in nuclear extracts of mouse inner medullary collecting duct 3 cells. A promoter-luciferase construct with a mutated −104/−94 NF-κB element exhibited higher activity than the wild-type promoter in transfection assays. Overexpression of NF-κB p50, p65, or their combination trans-repressed the HKα2 promoter. The histone deacetylase (HDAC) inhibitor trichostatin A partially reversed NF-κB-mediated trans-repression of the HKα2 promoter. HDAC6 overexpression inhibited HKα2 promoter activity, and HDAC6 coimmunoprecipitated with NF-κB p50 and p65. These results suggest that HDAC6, recruited to the DNA protein complex, acts with NF-κB to suppress HKα2 transcription and identify NF-κB p50 and p65 as novel binding partners for HDAC6.

The vasopressin-regulated urea transporter in renal inner medullary collecting duct

1990 ◽  
Vol 259 (3) ◽  
pp. F393-F401 ◽  
Author(s):  
M. A. Knepper ◽  
R. A. Star
Keyword(s):  
Apical Membrane ◽  
Collecting Duct ◽  
Water Channel ◽  
Toad Urinary Bladder ◽  
Urea Transport ◽  
Urea Transporter ◽  
Transport Pathway ◽  
Inner Medullary Collecting Duct ◽  
Urea Permeability ◽  
Medullary Collecting Duct

The terminal part of the inner medullary collecting duct (terminal IMCD) is unique among collecting duct segments in part because its permeability to urea is regulated by vasopressin. The urea permeability can rise to extremely high levels (greater than 100 x 10(-5) cm/s) in response to vasopressin. Recent studies in isolated perfused IMCD segments have established that the rapid movement of urea across the tubule epithelium occurs via a specialized urea transporter, presumably an intrinsic membrane protein, present in both the apical and basolateral membranes. This urea transporter has properties similar to those of the urea transporters in mammalian erythrocytes and in toad urinary bladder, namely, inhibition by phloretin, inhibition by urea analogues, saturation kinetics in equilibrium-exchange experiments, and regulation by vasopressin. The urea transport pathway is distinct from and independent of the vasopressin-regulated water channel. The increase in transepithelial urea transport in response to vasopressin is mediated by adenosine 3',5'-cyclic monophosphate and is associated with an increase in the urea permeability of the apical membrane. However, little is known about the physical events associated with the activation or insertion of urea transporters in the apical membrane. Because of the importance of this transporter to the urinary concentrating mechanism, efforts toward understanding its molecular structure and the molecular basis of its regulation appear to be justified.

scholarly journals Vasopressin regulation of multisite phosphorylation of UT-A1 in the inner medullary collecting duct

2015 ◽  
Vol 308 (1) ◽  
pp. F49-F55 ◽  
Author(s):  
Carol A. Hoban ◽  
Lauren N. Black ◽  
Ronald J. Ordas ◽  
Diane L. Gumina ◽  
Fadi E. Pulous ◽  
...  
Keyword(s):  
Apical Membrane ◽  
Collecting Duct ◽  
Phosphorylation Site ◽  
Urea Transport ◽  
Urea Transporter ◽  
Inner Medullary Collecting Duct ◽  
Camp Pathway ◽  
Multisite Phosphorylation ◽  
Medullary Collecting Duct ◽  
Stimulation Of

Vasopressin signaling is critical for the regulation of urea transport in the inner medullary collecting duct (IMCD). Increased urea permeability is driven by a vasopressin-mediated elevation of cAMP that results in the direct phosphorylation of urea transporter (UT)-A1. The identification of cAMP-sensitive phosphorylation sites, Ser486 and Ser499, in the rat UT-A1 sequence was the first step in understanding the mechanism of vasopressin action on the phosphorylation-dependent modulation of urea transport. To investigate the significance of multisite phosphorylation of UT-A1 in response to elevated cAMP, we used highly specific and sensitive phosphosite antibodies to Ser486 and Ser499 to determine cAMP action at each phosphorylation site. We found that phosphorylation at both sites was rapid and sustained. Furthermore, the rate of phosphorylation of the two sites was similar in both mIMCD3 cells and rat inner medullary tissue. UT-A1 localized to the apical membrane in response to vasopressin was phosphorylated at Ser486 and Ser499. We confirmed that elevated cAMP resulted in increased phosphorylation of both sites by PKA but not through the vasopressin-sensitive exchange protein activated by cAMP pathway. These results elucidate the multisite phosphorylation of UT-A1 in response to cAMP, thus providing the beginning of understanding the intracellular factors underlying vasopressin stimulation of urea transport in the IMCD.

H(+)-K(+)-ATPase mediates net acid secretion in rat terminal inner medullary collecting duct

1996 ◽  
Vol 271 (5) ◽  
pp. F1037-F1044 ◽  
Author(s):  
S. M. Wall ◽  
A. V. Truong ◽  
T. D. DuBose
Keyword(s):  
Acid Secretion ◽  
Collecting Duct ◽  
Specific Inhibitor ◽  
Co2 Absorption ◽  
Atpase Inhibitor ◽  
Inner Medullary Collecting Duct ◽  
Total Ammonia ◽  
Medullary Collecting Duct ◽  
Atpase Inhibition

Studies in our laboratory have demonstrated total CO2 absorption (JtCO2) and total ammonia secretion in the terminal inner medullary collecting duct (tIMCD) perfused in vitro. The purpose of the present study was to determine whether the H(+)-K(+)-adenosinetriphosphatase (H(+)-K(+)-ATPase) participates in proton secretion or JtCO2 in this segment. Tubules from the middle third of the tIMCD were dissected from rats with chronic metabolic acidosis (300 mM NH4Cl, 3-4 days in drinking water) and perfused in vitro. Perfusate and bath were symmetrical solutions containing 5 mM KCl, 6 mM NH4Cl, and 25 mM NaHCO3. Bafilomycin A1 (5 nM), a specific inhibitor of the H(+)-ATPase, did not affect JtCO2 compared with baseline (JtCO2, 3.0 +/- 1.0 and 3.0 +/- 0.8; n = 6, P = not significant) or with time controls (n = 4). With removal of luminal K+, JtCO2 fell from 2.8 +/- 0.6 to 1.6 +/- 0.4 pmol.mm-1.min-1 (n = 5, P < 0.05). To further evaluate K(+)-sensitive JtCO2, the effect of H(+)-K(+)-ATPase inhibition on JtCO2 was explored using the specific H(+)-K(+)-ATPase inhibitor, Sch-28080. Addition of 10 microM Sch-28080 to the luminal perfusate decreased JtCO2 (2.7 +/- 0.4 to 1.4 +/- 0.5 pmol.mm-1. min-1; n = 5, P < 0.05) but did not alter transepithelial membrane potential. Thus luminal Sch-28080 addition, as well as luminal K+ removal, limits apical H+ exit or OH-/HCO3- entry. These results demonstrate that net acid secretion is mediated by the H(+)-K(+)-ATPase in the tIMCD.

Effect of insulin on water and urea transport in the inner medullary collecting duct

1994 ◽  
Vol 266 (3) ◽  
pp. F394-F399 ◽  
Author(s):  
A. J. Magaldi ◽  
K. R. Cesar ◽  
Y. Yano
Keyword(s):  
Water Transport ◽  
Collecting Duct ◽  
Water Channel ◽  
Polymyxin B ◽  
Dependent Manner ◽  
Urea Transport ◽  
Inner Medullary Collecting Duct ◽  
Medullary Collecting Duct ◽  
Dose Dependent ◽  
Rule Out

The effect of insulin on water and urea transport was examined in normal isolated rat inner medullary collecting duct (IMCD). Hydraulic conductivity (Lp, x 10(-6) cm.atm-1.s-1), diffusional water permeability (Pdw, x 10(-5) cm/s) and [14C]urea permeability (x 10(-5) cm/s) were studied at 37 degrees C and pH 7.4. Insulin (6 x 10(-8) M; 200 microU/ml) added to the bath fluid enhanced Lp from 0.40 +/- 0.10 to 1.21 +/- 1.40 (P < 0.01) and Pdw from 42.40 +/- 3.40 to 58.50 +/- 5.00 (P < 0.02) and also stimulated Lp in a dose-dependent manner. In the presence of antidiuretic hormone (ADH)-stimulated Pdw (10 microU/ml), insulin increased Pdw even more. Prostaglandin E2 (10(-5) M) added to the bath reversibly increased insulin-induced Lp. Forskolin (10(-4) M) blocked the action of insulin. Colchicine (10(-4) M) and V1-receptor antagonist (10(-4) M) inhibited the development but not the maintenance of insulin-stimulated Pdw. Vanadate (2.5 x 10(-6) M) enhanced Pdw. Polymyxin B (10(-5) M) inhibited the insulin-stimulated Pdw, whereas in a glucose-free medium insulin did not enhance Pdw. Urea transport was not affected by insulin. These data suggest that insulin may enhance water transport, probably by stimulating glucose transporters, which would serve as a water channel. We cannot rule out the possibility that insulin may be eliciting existing ADH-like mechanisms of water transport, beyond the microtubule step, to establish water transport.

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