Role of the medullary collecting duct in potassium excretion in potassium-adapted animals

Osmotic reabsorption of water through aquaporin-2 (AQP2) in the inner medulla is largely dependent on the urea concentration gradients generated by urea transporter (UT) isoforms. Vasopressin (AVP) increases expression of both AQP2 and UT-A isoforms. Activation of the P2Y2 receptor (P2Y2-R) in the medullary collecting duct inhibits AVP-induced water flow. To gain further insights into the overarching effect of purinergic signaling on urinary concentration, we compared the protein abundances of AQP2 and UT-A isoforms between P2Y2-R knockout (KO) and wild-type (WT) mice under basal conditions and following AVP administration. Under basal conditions (a gel diet for 10 days), KO mice concentrated urine to a significantly higher degree, with 1.8-, 1.66-, and 1.29-fold higher protein abundances of AQP2, UT-A1, and UT-A2, respectively, compared with WT, despite comparable circulating AVP levels in both groups. Infusion of 1-desamino-8-d-arginine vasopressin (dDAVP; desmopressin; 1 ng/h sc) for 5 days resulted in 2.14-, 2.6-, and 2.22-fold higher protein abundances of AQP2, AQP3, and UT-A1, respectively, in the inner medullas of KO mice compared with WT mice. In response to acute (45 min) stimulation by AVP (0.2 unit/mouse sc), UT-A1 protein increased by 1.39- and 1.54-fold in WT and KO mice, respectively. These data suggest that genetic deletion of P2Y2-R results in increased abundances of key proteins involved in urinary concentration in the inner medulla, both under basal conditions and following AVP administration. Thus purinergic regulation may play a potential overarching role in balancing the effect of AVP on the urinary concentration mechanism.

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Role of SNAP-23 in trafficking of H+-ATPase in cultured inner medullary collecting duct cells

AJP Cell Physiology ◽

10.1152/ajpcell.2001.280.4.c775 ◽

2001 ◽

Vol 280 (4) ◽

pp. C775-C781 ◽

Cited By ~ 36

Author(s):

Abhijit Banerjee ◽

Guangmu Li ◽

Edward A. Alexander ◽

John H. Schwartz

Keyword(s):

Botulinum Toxin ◽

Apical Membrane ◽

Collecting Duct ◽

Snare Complex ◽

Attachment Protein ◽

Regulated Exocytosis ◽

Inner Medullary Collecting Duct ◽

Sensitive Factor ◽

Medullary Collecting Duct

The trafficking of H+-ATPase vesicles to the apical membrane of inner medullary collecting duct (IMCD) cells utilizes a mechanism similar to that described in neurosecretory cells involving soluble N-ethylmaleimide-sensitive factor attachment protein target receptor (SNARE) proteins. Regulated exocytosis of these vesicles is associated with the formation of SNARE complexes. Clostridial neurotoxins that specifically cleave the target (t-) SNARE, syntaxin-1, or the vesicle SNARE, vesicle-associated membrane protein-2, reduce SNARE complex formation, H+-ATPase translocation to the apical membrane, and inhibit H+ secretion. The purpose of these experiments was to characterize the physiological role of a second t-SNARE, soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP)-23, a homologue of the neuronal SNAP-25, in regulated exocytosis of H+-ATPase vesicles. Our experiments document that 25–50 nM botulinum toxin (Bot) A or E cleaves rat SNAP-23 and thereby reduces immunodetectable and35S-labeled SNAP-23 by >60% within 60 min. Addition of 25 nM BotE to IMCD homogenates reduces the amount of the 20 S-like SNARE complex that can be immunoprecipitated from the homogenate. Treatment of intact IMCD monolayers with BotE reduces the amount of H+-ATPase translocated to the apical membrane by 52 ± 2% of control and reduces the rate of H+ secretion by 77 ± 3% after acute cell acidification. We conclude that SNAP-23 is a substrate for botulinum toxin proteolysis and has a critical role in the regulation of H+-ATPase exocytosis and H+ secretion in these renal epithelial cells.

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Response of rat inner medullary collecting duct to epidermal growth factor

AJP Renal Physiology ◽

10.1152/ajprenal.1989.256.6.f1117 ◽

1989 ◽

Vol 256 (6) ◽

pp. F1117-F1124 ◽

Cited By ~ 2

Author(s):

R. C. Harris

Keyword(s):

Growth Factor ◽

Binding Sites ◽

Collecting Duct ◽

Affinity Binding ◽

Inner Medullary Collecting Duct ◽

Duct Cells ◽

Epidermal Growth ◽

Collecting Duct Cells ◽

Medullary Collecting Duct

Urine is an abundant source of epidermal growth factor (EGF) and prepro-EGF has been localized to the thick ascending limb and distal convoluted tubule of the kidney. However, the functional role of EGF in the kidney is poorly understood. Determination of EGF receptors and functional responses to EGF in intrarenal structures distal to the site of renal EGF production may prove critical to our understanding of the role of this peptide. These studies were designed to investigate the response to EGF of rat inner medullary collecting duct cells in culture and in freshly isolated suspensions. Primary cultures of inner medullary collecting duct cells demonstrated equilibrium binding of 125I-labeled EGF at 4 and 23 degrees C. At 23 degrees C, there was 89 +/- 1% specific binding (n = 30). Scatchard analysis of 125I-EGF binding suggested the presence of both high-affinity binding with a dissociation constant (Kd) of 5 X 10(-10) M and maximal binding sites (Ro) of 2.7 X 10(3) binding sites/cell and low-affinity binding, with Kd of 8.3 X 10(-9) M and Ro of 1.8 X 10(4) binding sites/cell. Bound EGF, 68 +/- 3%, was internalized by 45 min. EGF binding was not inhibited by antidiuretic hormone, atrial natriuretic peptide or bradykinin at 23 degrees C, but there was concentration-dependent inhibition of binding by transforming growth factor-alpha. Incubation with phorbol myristate acetate decreased 125I-EGF binding in a concentration-dependent manner. 125I-EGF binding was also demonstrated in freshly isolated suspensions of rat inner medullary collecting duct cells.(ABSTRACT TRUNCATED AT 250 WORDS)

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Role of PKC and AMPK in hypertonicity-stimulated water reabsorption in rat inner medullary collecting ducts

AJP Renal Physiology ◽

10.1152/ajprenal.00491.2017 ◽

2019 ◽

Vol 316 (2) ◽

pp. F253-F262 ◽

Cited By ~ 4

Author(s):

Josephine K. Liwang ◽

Joseph A. Ruiz ◽

Lauren M. LaRocque ◽

Fitra Rianto ◽

Fuying Ma ◽

...

Keyword(s):

Water Permeability ◽

Collecting Duct ◽

Adenosine Monophosphate ◽

Osmotic Water Permeability ◽

Water Reabsorption ◽

Compound C ◽

Ampk Phosphorylation ◽

Osmotic Water ◽

Medullary Collecting Duct

Hypertonicity increases water permeability, independently of vasopressin, in the inner medullary collecting duct (IMCD) by increasing aquaporin-2 (AQP2) membrane accumulation. We investigated whether protein kinase C (PKC) and adenosine monophosphate kinase (AMPK) are involved in hypertonicity-regulated water permeability. Increasing perfusate osmolality from 150 to 290 mosmol/kgH2O and bath osmolality from 290 to 430 mosmol/kgH2O significantly stimulated osmotic water permeability. The PKC inhibitors chelerythrine (10 µM) and rottlerin (50 µM) significantly reversed the increase in osmotic water permeability stimulated by hypertonicity in perfused rat terminal IMCDs. Chelerythrine significantly increased phosphorylation of AQP2 at S261 but not at S256. Previous studies show that AMPK is stimulated by osmotic stress. We tested AMPK phosphorylation under hypertonic conditions. Hypertonicity significantly increased AMPK phosphorylation in inner medullary tissues. Blockade of AMPK with Compound C decreased hypertonicity-stimulated water permeability but did not alter phosphorylation of AQP2 at S256 and S261. AICAR, an AMPK stimulator, caused a transient increase in osmotic water permeability and increased phosphorylation of AQP2 at S256. When inner medullary tissue was treated with the PKC activator phorbol dibutyrate (PDBu), the AMPK activator metformin, or both, AQP2 phosphorylation at S261 was decreased with PDBu or metformin alone, but there was no additive effect on phosphorylation with PDBu and metformin together. In conclusion, hypertonicity regulates water reabsorption by activating PKC. Hypertonicity-stimulated water reabsorption by PKC may be related to the decrease in endocytosis of AQP2. AMPK activation promotes water reabsorption, but the mechanism remains to be determined. PKC and AMPK do not appear to act synergistically to regulate water reabsorption.

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Lipopolysaccharide directly inhibits bicarbonate absorption by the renal outer medullary collecting duct

Scientific Reports ◽

10.1038/s41598-020-77363-w ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Shuichi Tsuruoka ◽

Jeffrey M. Purkerson ◽

George J. Schwartz

Keyword(s):

Lipid A ◽

Kinase Inhibitor ◽

Collecting Duct ◽

Therapeutic Interventions ◽

E Coli ◽

Monophosphoryl Lipid A ◽

Tlr4 Agonist ◽

Medullary Collecting Duct ◽

Phosphoinositide 3 Kinase

AbstractAcidosis is associated with E. coli induced pyelonephritis but whether bacterial cell wall constituents inhibit HCO3 transport in the outer medullary collecting duct from the inner stripe (OMCDi) is not known. We examined the effect of lipopolysaccharide (LPS), on HCO3 absorption in isolated perfused rabbit OMCDi. LPS caused a ~ 40% decrease in HCO3 absorption, providing a mechanism for E. coli pyelonephritis-induced acidosis. Monophosphoryl lipid A (MPLA), a detoxified TLR4 agonist, and Wortmannin, a phosphoinositide 3-kinase inhibitor, prevented the LPS-mediated decrease, demonstrating the role of TLR4-PI3-kinase signaling and providing proof-of-concept for therapeutic interventions aimed at ameliorating OMCDi dysfunction and pyelonephritis-induced acidosis.

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Autocrine role of endothelin in rat IMCD: inhibition of AVP-induced cAMP accumulation

AJP Renal Physiology ◽

10.1152/ajprenal.1993.265.1.f126 ◽

1993 ◽

Vol 265 (1) ◽

pp. F126-F129 ◽

Cited By ~ 6

Author(s):

D. E. Kohan ◽

A. K. Hughes

Keyword(s):

Arginine Vasopressin ◽

Collecting Duct ◽

Camp Accumulation ◽

Semipermeable Membranes ◽

Endothelin 1 ◽

Cyclic Monophosphate ◽

Nephron Segment ◽

Specific Receptors ◽

Medullary Collecting Duct

Exogenous endothelin-1 (ET-1) inhibits arginine vasopressin (AVP)-induced adenosine 3',5'-cyclic monophosphate (cAMP) accumulation in the inner medullary collecting duct (IMCD). Since ET-1 is produced by, and binds to specific receptors on, the IMCD, the possibility exists that ET-1 is an autocrine regulator of AVP action in this nephron segment. To test this hypothesis, rat IMCD cells grown on semipermeable membranes were exposed to rabbit anti-ET antisera or nonimmune rabbit sera (NRS). AVP (10(-9)M) caused a significantly greater accumulation of cAMP in confluent IMCD monolayers preincubated in ET-1 antisera compared with NRS. ET-1 (10(-8) M) inhibited the AVP-induced rise in cAMP by 65% in cells preincubated in ET-1 antisera, but had no effect in NRS-treated cells. Finally, 125I-ET-1 (30 pM) binding was increased sixfold in IMCD preincubated in anti-ET-1 antisera. These data indicate that ET causes tonic autocrine inhibition of AVP responsiveness in the IMCD.

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Effects of endothelin on rat renal proximal tubule Na(+)-Pi cotransport and Na+/H+ exchange

AJP Renal Physiology ◽

10.1152/ajprenal.1994.266.4.f658 ◽

1994 ◽

Vol 266 (4) ◽

pp. F658-F666 ◽

Cited By ~ 7

Author(s):

J. Guntupalli ◽

T. D. DuBose

Keyword(s):

Protein Kinase ◽

Proximal Tubule ◽

Collecting Duct ◽

Second Messengers ◽

Indirect Evidence ◽

Low Concentrations ◽

Proximal Tubular ◽

Dependent Protein ◽

Medullary Collecting Duct

Endothelin (ET), a powerful vasoconstrictive peptide, is distributed ubiquitously in various organs, including the vascular endothelium and tubules of the kidney. Although localized more abundantly to the glomerulus and inner medullary collecting duct, ET receptors have been identified in the proximal tubule. The possible effects of ET on proximal tubule transport and the potential role of second messengers in this process have not been described fully. To define the role of ET in proximal tubule transport, renal cortical slices were incubated for 3 min in the presence of various concentrations of ET. Incubation with low concentrations of ET-1 (1 x 10(-9) to 1 x 10(-11) M) within the physiological range stimulated both Na(+)-Pi cotransport and Na+/H+ exchange. Pretreatment with staurosporine (0.6 microM) for 25 min abolished completely the ET-induced effects on Na(+)-Pi cotransport and Na+/H+ exchange. Similarly, preincubation with phorbol ester 12-O-tetradecanoylphorbol-13-acetate (200 nM) also abolished the effects of ET on these transporters. Incubation with ET decreased significantly intracellular adenosine 3',5'-cyclic monophosphate (cAMP). Intravenous administration of pertussis toxin for 2 days prevented the ET-induced decrease in cAMP and abolished the stimulatory effects of ET on Na(+)-Pi cotransport and Na+/H+ exchange. These findings provide indirect evidence that ET participates in the regulation of proximal tubular Pi and bicarbonate homeostasis. These effects of ET are mediated by activation of protein kinase C and cAMP-dependent protein kinase A.

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Role of cGMP in Atrial Natriuretic Peptide (ANP) Inhibition of Na* Transport by Rabbit Inner Medullary Collecting Duct (IMCD) Cells

Journal of Cardiovascular Pharmacology ◽

10.1097/00005344-198611000-00174 ◽

1986 ◽

Vol 8 (6) ◽

pp. 1321

Author(s):

M. L. Zeidel ◽

P. Silva ◽

B. M. Brenner ◽

J. L. Seifter

Keyword(s):

Atrial Natriuretic Peptide ◽

Natriuretic Peptide ◽

Collecting Duct ◽

Na Transport ◽

Inner Medullary Collecting Duct ◽

Medullary Collecting Duct ◽

Atrial Natriuretic

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Effect of adrenal enucleation on inner medullary collecting duct function in the rat

AJP Renal Physiology ◽

10.1152/ajprenal.1982.242.5.f453 ◽

1982 ◽

Vol 242 (5) ◽

pp. F453-F456

Author(s):

H. H. Bengele ◽

E. A. Alexander

Keyword(s):

Sodium Chloride ◽

Collecting Duct ◽

Potassium Excretion ◽

Collection Site ◽

Salt Load ◽

Inner Medullary Collecting Duct ◽

Impaired Ability ◽

Potassium Secretion ◽

Medullary Collecting Duct ◽

And Control

After adrenal enucleation rats have an impaired ability to excrete a salt load. From micropuncture studies comparing data obtained from the late distal collection site and the urine, it has been suggested that this antinatriuretic effect occurs along the collecting duct. These studies are indirect, however, and cannot evaluate the contribution of deep nephrons. We have performed studies directly measuring inner medullary collecting duct (IMCD) function in saline-loaded rats 6 days after adrenal enucleation (AE). The fraction of filtered fluid, sodium, chloride, and potassium was analyzed as a function of IMCD length. In six AE rats 35% of the fluid, 35% of the sodium, and 31% of the chloride delivered to the IMCD was reabsorbed. In six saline-loaded control rats, however, no statistically significant net reabsorption of fluid sodium, or chloride was detected. Net potassium secretion along the IMCD was found in both AE and control rats. No difference between groups was noted, and net addition accounted for 17% of the potassium excreted. We conclude that after AE, the excretion of fluid, sodium, and chloride is impaired during saline expansion because of enhanced reabsorption along the IMCD. AE does not affect potassium handling along the IMCD or potassium excretion.

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Epac-mediated Ca2+ mobilization and exocytosis in inner medullary collecting duct

AJP Renal Physiology ◽

10.1152/ajprenal.00411.2005 ◽

2006 ◽

Vol 291 (4) ◽

pp. F882-F890 ◽

Cited By ~ 66

Author(s):

Kay-Pong Yip

Keyword(s):

Collecting Duct ◽

Basolateral Membrane ◽

Competitive Antagonist ◽

Inner Medullary Collecting Duct ◽

Camp Analog ◽

Osmotic Water ◽

Confocal Fluorescence ◽

Intracellular Ca ◽

Medullary Collecting Duct

PKA has traditionally been thought as the binding protein of cAMP for mediating arginine vasopressin (AVP)-regulated osmotic water permeability in kidney collecting duct. It is now known that cAMP also exerts its effects via Epac (exchange protein directly activated by cAMP) and that intracellular Ca2+ mobilization is necessary for AVP-induced apical exocytosis in inner medullary collecting duct (IMCD). The role of Epac as an effector of cAMP action in addition to PKA was investigated using confocal fluorescence microscopy in perfused IMCD. PKA inhibitors (1 μM H-89 or 10 μM KT-5720) at concentrations known to inhibit aquaporin-2 (AQP2) phosphorylation did not prevent AVP-induced Ca2+ mobilization and oscillations. Epac-selective cAMP agonist (8-pCPT-2′- O-Me-cAMP) mimicked AVP in triggering Ca2+ mobilization and oscillations, which was blocked by ryanodine but not by Rp-cAMP (a competitive antagonist of cAMP binding to PKA). 8-pCPT-2′- O-Me-cAMP also triggered apical exocytosis in the presence of a PKA inhibitor. Immunolocalization of AQP2 in perfused IMCD demonstrated that 8-pCPT-2′- O-Me-cAMP induces apical targeting of AQP2 and that AQP2 is abundant in junctional regions of basolateral membrane. Immunofluorescence study also confirmed the presence of Epac (isoform I) in IMCD. These results indicate that activation of Epac by an exogenous cAMP analog triggers intracellular Ca2+ mobilization and apical exocytotic insertion of AQP2 in IMCD.

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