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The Journal of Membrane Biology

, Volume 66, Issue 1, pp 41–54 | Cite as

The electrophysiology of rabbit descending colon

I. Instantaneous transepithelial current-voltage relations and the current-voltage relations of the Na-entry mechanism
  • Stephen M. Thompson
  • Yuichi Suzuki
  • Stanley G. Schultz
Article

Summary

A method is described for determining the “instantaneous” transepithelial current-voltage (I-V) relations across rabbit descending colon and deriving theI-V relations of the amiloride-sensitive Na-entry step across the apical membrane. The latter conforms closely to the predictions of the Goldman-Hodgkin-Katz “constant-field” flux equation over a wide range of values of the transapical electrical potential difference (−120 to +50 mV), suggesting that Na entry is the result of simple electrodiffusion through homogeneous pores or channels. The permeability of the apical membrane to Na averaged 0.012 cm/hr, and the intracellular Na activity averaged 10mm. In the studies, the rate of Na entry across the apical membrane varied, spontaneously, over a fourfold range; this variation is entirely attributable to parallel variations in the partial conductance of the apical membrane to Na with no change in the driving force for this movement.

Bathing the serosal surface of the tissue with a high-K solution abolishes the electrical potential difference across the basolateral membrane and markedly reduces the resistance of that barrier. Under these conditions, theI-V relations of the amiloride-sensitive Na-entry step across the apical membrane also conform closely to the predictions of the “constant-field” flux equation.

Finally, the significance of the point at which the transepithelialI-V relations in the absence and presence of amiloride intersect (“ENa”) and the origin of the “bends” in theseI-V relations at or around this point are discussed. We demonstrate that the point of intersection is simply that value of the transepithelial electrical potential difference at which Na entry is abolished and has no direct bearing on the energetics of the basolateral pump. The “bend” in theI-V relations appears to be due to an increase in the conductance of a pathway in the apical membrane that parallels the Na-entry pathway in the apical membrane that parallels the Na-entry pathway as well as an increase in the conductance of the paracellular pathway; thus, this “bend” does not appear to be directly related to changes in the “active Na transport pathway”.

Key words

colon Na entry electrophysiology current-voltage relations apical membrane amiloride 

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Copyright information

© Springer-Verlag New York Inc. 1982

Authors and Affiliations

  • Stephen M. Thompson
    • 1
  • Yuichi Suzuki
    • 1
  • Stanley G. Schultz
    • 1
  1. 1.Department of Physiology and Cell BiologyUniversity of Texas Medical SchoolHouston

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