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The Journal of Membrane Biology

, Volume 74, Issue 2, pp 165–173 | Cite as

Voltage-dependent interaction of Barium and Cesium with the Potassium Conductance of the Cortical Collecting Duct Apical cell membrane

  • Roger G. O'Neil
Articles

Summary

The influence of Ba++ and Cs+ on the K+ conductive properties of the rabbit isolated perfused cortical collecting tubule were assessed using electrophysiological methods. As before, elevation of K+ from 5 to 25 or 50mm (choline+ for K+ substitution) in the luminal perfusate, caused a marked hyperpolarization (lumen negative) of the transepithelial voltage,Vte, and increase in the transepithelial conductance,Gte-indicative of a high luminal (apical) K+ conductance-where-as a similar elevation of K+ in the bath caused only minor changes inVte andGte. In the presence of 5mm K+ in perfusate and bath, addition of 5mm Ba++ to the perfusate causedGte to decrease from 16.1 to 7.4 mScm−2 (10mm Cs+ had qualitatively similar effects) and greatly diminished the response ofVte andGte to K+ elevation in the lumen, reflecting a decrease in the apical membrane K+ conducatance. In contrast, a similar addition of 5mm Ba++ to the bath caused only a modest reduction inGte of 0.4 mScm−2, consistent with a relatively low K+ conductance of the basolateral membrane and tight junction. In other studies the effects of luminal addition of Ba++ and amiloride were found to be relatively independent, with the magnitude of the Ba++-sensitiveGte (8.7 mScm−2) being several-fold greater than the amiloride-sensitiveGte (1.4 mScm−1), indicative of a dominat K+ conductance at that border which is spatially distinct from the Na+ conductance. Furthermore, from the input current-voltage relation of the tubule, the effects of Ba++ (0.1–5mm) and Cs+ (10mm) at the luminal border on tissue conductance were found to be highly voltage-dependent — the effects on conductance being diminished with lumennegative voltages and more pronounced, approaching a maximum, with lumen-positive voltages. It is concluded that the apical (luminal) cell membrane contains a dominant K+ conductive pathway that is blocked by luminal addition of Ba++ and Cs+. The voltage-dependent nature of the block is consistent with a K+ conductive pathway which has a binding site for Ba++ and Cs+, and presumably K+, located deep within the channel.

Key Words

renal epithelium cortical collecting duct barium cesium potassium transport potassium channel potassium conductance 

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Copyright information

© Springer-Verlag New York Inc. 1983

Authors and Affiliations

  • Roger G. O'Neil
    • 1
  1. 1.Department of Physiology and Cell BiologyUniversity of Texas Medical SchoolHouston

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