Impact of K+ homeostasis on net acid secretion in rat terminal inner medullary collecting duct: Role of the Na+,K-ATPase

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.

Download Full-text

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)

Download Full-text

Suppression of acidification along inner medullary collecting duct

AJP Renal Physiology ◽

10.1152/ajprenal.1988.255.2.f307 ◽

1988 ◽

Vol 255 (2) ◽

pp. F307-F312 ◽

Cited By ~ 2

Author(s):

H. H. Bengele ◽

E. R. McNamara ◽

J. H. Schwartz ◽

E. A. Alexander

Keyword(s):

Acid Secretion ◽

Collecting Duct ◽

Respiratory Alkalosis ◽

Inner Medullary Collecting Duct ◽

Titratable Acid ◽

Arterial Ph ◽

Medullary Collecting Duct ◽

Collection Sites

The purpose of these experiments was to evaluate the effect of acute respiratory alkalosis (ARA) and chronic bicarbonate drinking (CBD) on inner medullary collecting duct (IMCD) acidification. Microcatheterization was used to measure pH and PCO2, and samples were simultaneously obtained for measurement of bicarbonate, titratable acid (TA), and ammonium. In ten ARA rats (arterial pH was 7.54 +/- 0.02; PCO2 was 20 +/- 1 mmHg), IMCD equilibrium pH was not different (deep pH was 5.65 +/- 0.06 and PCO2 was 20 +/- 1 mmHg; tip pH was 5.54 +/- 0.07 and PCO2 was 22 +/- 1 mmHg). Delivery of bicarbonate, TA, and ammonium also did not differ between collection sites. Thus net acidification along the IMCD was negligible. Nine rats drank NaHCO3 for 5-8 days (pH = 7.48 +/- 0.02) but did not receive NaHCO3 during the experiment so that arterial pH fell to 7.40 +/- 0.01. IMCD equilibrium pH was different at deep (pH was 5.68 +/- 0.06; PCO2 was 32 +/- 1 mmHg) and tip (pH was 5.57 +/- 0.04; PCO2 was 27 +/- 1 mmHg; P less than or equal to 0.05) collection sites. However, only minimal changes in the delivery of bicarbonate, TA, and ammonium were noted, and net acidification along the IMCD was negligible. In ten control rats, net acidification was 219 nmol/min between collection sites (P less than 0.001). We conclude that ARA and CBD abolish acidification along the IMCD. In addition, CBD produces an intrinsic modification along the IMCD, which suppresses acid secretion and persists after acute recovery from alkalemia.

Download Full-text

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

Download Full-text

A mathematical model of the inner medullary collecting duct of the rat: acid/base transport

AJP Renal Physiology ◽

10.1152/ajprenal.1998.274.5.f856 ◽

1998 ◽

Vol 274 (5) ◽

pp. F856-F867 ◽

Cited By ~ 11

Author(s):

Alan M. Weinstein

Keyword(s):

Mathematical Model ◽

Acid Secretion ◽

Collecting Duct ◽

Model Calculations ◽

Principal Mode ◽

Inner Medullary Collecting Duct ◽

Tubule Lumen ◽

Nephron Segment ◽

The Face ◽

Medullary Collecting Duct

A mathematical model of the inner medullary collecting duct (IMCD) of the rat has been developed that is suitable for simulating luminal buffer titration and ammonia secretion by this nephron segment. Luminal proton secretion has been assigned to an H-K-ATPase, which has been represented by adapting the kinetic model of the gastric enzyme by Brzezinski et al. (P. Brzezinski, B. G. Malmstrom, P. Lorentzon, and B. Wallmark. Biochim. Biophys. Acta 942: 215–219, 1988). In shifting to a 2 H+:1 ATP stoichiometry, the model enzyme can acidify the tubule lumen ∼3 pH units below that of the cytosol, when luminal K+ is in abundance. Peritubular base exit is a combination of ammonia recycling and[Formula: see text] flux (either via[Formula: see text] exchange or via a Cl− channel). Ammonia recycling involves[Formula: see text] uptake on the Na-K-ATPase followed by diffusive NH3 exit [S. M. Wall. Am. J. Physiol. 270 ( Renal Physiol. 39): F432–F439, 1996]; model calculations suggest that this is the principal mode of base exit. By virtue of this mechanism, the model also suggests that realistic elevations in peritubular K+ concentration will compromise IMCD acid secretion. Although ammonia recycling is insensitive to carbonic anhydrase (CA) inhibition, the base exit linked to [Formula: see text] flux provides a CA-sensitive component to acid secretion. In model simulations, it is observed that increased luminal NaCl entry increases ammonia cycling but decreases peritubular [Formula: see text]exchange (due to increased cell Cl−). This parallel system of peritubular base exit stabilizes acid secretion in the face of variable Na+ reabsorption.

Download Full-text

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

AJP Renal Physiology ◽

10.1152/ajprenal.1996.271.5.f1037 ◽

1996 ◽

Vol 271 (5) ◽

pp. F1037-F1044 ◽

Cited By ~ 15

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.

Download Full-text

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.

Download Full-text