Amide transport channels across toad urinary bladder
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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.
KeywordsAmide Water Flow Acetamide Water Permeability Mobile Carrier
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- 2.Bentley, P.J. 1958. The effects of neurohypophyseal extracts on water transfer across the wall of the isolated urinary bladder of the toadBufo marinus.J. Endorcrinol. 17:201Google Scholar
- 4.DiBona, D.R. 1972. Passive intercellular pathways in amphibian epithelia.Nature, New Biol. 238:179Google Scholar
- 9.Heckman, K. 1972. Single file difusion.In: Pasive Permeability of Cell Membranes. F. Kreuzer and J.F.G. Slegers, editors. p. 127, Plenum Press, New YorkGoogle Scholar
- 10.Hodgkin, A.L., Keynes, R.D. 1955. The potassium permeability of a giant nerve fiber.J. Physiol. 128:61Google Scholar
- 15.Levine, S.D., Levine, R.D., Worthington, R.E., Hays, R.M. 1975. Selective inhibition of osmotic water flow by methoxyflurane and halothane.Clin. Res. 23:432AGoogle Scholar
- 16.Levine, S.D., Levine, R.D., Worthington, R.E., Hays, R.M. 1975. Selective inhibition of osmotic water flow in toad urinary bladder by general anesthetics.Proc V. Int. Biophys. Cong. p. 68Google Scholar
- 22.Patlak, C.S. 1957. Contributions to the theory of active transport.Bull. Math. Biophys. 19:209Google Scholar
- 23.Rubin, M.S. 1975. Chemical modification of vasopressin (ADH)-induced urea transport across toad bladder.Fed. Proc. 34:327Google Scholar
- 24.Schmidt-Nielsen, B. 1970. Urea analogues and tubular transport competition.In: Urea and the Kidney. B. Schmidt-Nielsen, editor. p. 252. Excerpta Medica Foundation, AmsterdamGoogle Scholar
- 26.Snedecor, G.W., Cochran, W.G. 1967. Statistical Methods (6th ed). p. 91. Iowa State University Press, Ames, IowaGoogle Scholar
- 32.Vidaver, G.A. 1966. Inhibition of parallel flux and augmentation of counter flux shown by transport models not involving a mobile carrier.J. Theoret. Biol. 10:301Google Scholar