Document Detail

Regulation of acidification in the rat inner medullary collecting duct.
MedLine Citation:
PMID:  1659187     Owner:  NLM     Status:  MEDLINE    
The inner medullary collecting duct (IMCD) is the most distal portion of the nephron and plays an important role in urinary net acid excretion. The terminal or distal two thirds of the IMCD is lined by a single cell type, now termed the IMCD cell, which not only secretes protons, but transports sodium and potassium and responds to many hormones. The IMCD may account for greater than 50% of the excreted acid under control conditions and, during acidosis, absolute acid secretion may increase fivefold. Conversely, during alkalemia, acid secretion by this segment is abolished. Thus, the IMCD responds appropriately to perturbations in systemic acid-base balance. Furthermore, models of renal tubular acidosis have been demonstrated along this nephron segment. Three transporters that are important in acid-base control, the Na+/H+ and the Cl-/HCO3- exchanger and an active proton pump, presumably an H(+)-adenosine phosphatase (ATPase), have been demonstrated in IMCD cells. The former two are situated in the basolateral membrane, while the latter is situated in the apical membrane. Only the proton pump is responsible for actual acid addition to the urine. The intracellular mechanisms that modulate the proton pump are just beginning to be defined. It is likely that acid secretory activity involves exocytic insertion of additional pumps, and is dependent on cell pH changes, which are the primary signal, and on changes in intracellular calcium concentration and calmodulin activity, which are the second messengers.
E A Alexander; J H Schwartz
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.; Review    
Journal Detail:
Title:  American journal of kidney diseases : the official journal of the National Kidney Foundation     Volume:  18     ISSN:  0272-6386     ISO Abbreviation:  Am. J. Kidney Dis.     Publication Date:  1991 Nov 
Date Detail:
Created Date:  1991-11-27     Completed Date:  1991-11-27     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  8110075     Medline TA:  Am J Kidney Dis     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  612-8     Citation Subset:  IM    
Thorndike Memorial Laboratory, Boston City Hospital, MA.
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MeSH Terms
Acid-Base Equilibrium / physiology*
Acidosis, Renal Tubular / metabolism
Biological Transport, Active
Carbonic Anhydrases / metabolism
Carrier Proteins / metabolism
Chloride-Bicarbonate Antiporters
Hydrogen-Ion Concentration
Kidney Concentrating Ability
Kidney Tubules, Collecting / physiology*
Membrane Proteins / metabolism
Proton-Translocating ATPases / metabolism
Second Messenger Systems / physiology
Sodium-Hydrogen Antiporter
Grant Support
Reg. No./Substance:
0/Carrier Proteins; 0/Chloride-Bicarbonate Antiporters; 0/Membrane Proteins; 0/Sodium-Hydrogen Antiporter; EC ATPases; EC Anhydrases

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