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The Journal of Membrane Biology

, Volume 26, Issue 1, pp 91–107 | Cite as

Amide transport channels across toad urinary bladder

  • Sherman D. Levine
  • Ronald E. Worthington
Article

Summary

Urea and other small amides cross the toad urinary bladder by a vasopressinsensitive pathway which is independent of somotic water flow. Amide transport has characteristics of facilitated transport: saturation, mutual inhibition between amides, and selective depression by agents such as phloretin. The present studies were designed to distinguish among several types of transport including (1) movement thought a fixed selective membrane channel and (2) movement via a mobile carrier. The former wold be characterized by co-transport (acceleration of labele amide flow in the direction of net flow in the opposite direction). Mucosal to serosal (M→S) and serosal to mucosal (S→M) permeabilities of labeled amides were determined in paired bladers. Unlabeled methylurea, a particularly potent inhibitor of amide movement, was added to either the M or S bath, while osmotic water flow was eliminated by addition of ethylene glycol to the opposite bat. Co-transport of labeled methylurea and, to a lesser degree, acetamide and urea with unlabeled methylurea was observed. Co-transport of the nonamides ethylene glycol and ethanol could not be demonstrated. Methylurea did not alter water permeability or transmembrane electrical resistance. The demonstration of co-transport is consistent with the presence of ADH-sensitive amide-selective channcels rather than a mobile carrier.

Keywords

Amide Water Flow Acetamide Water Permeability Mobile Carrier 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag New York Inc. 1976

Authors and Affiliations

  • Sherman D. Levine
    • 1
  • Ronald E. Worthington
    • 1
  1. 1.Department of Medicine, Division of NephrologyAlbert Einstein College of MedicineBronx

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