Autocrine Role of Endothelin in Rat Inner Medullary Collecting Duct: Inhibition of AVP-Induced cAMP Accumulation

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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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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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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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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