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The Journal of Membrane Biology

, Volume 61, Issue 1, pp 31–38 | Cite as

A K+-selective, three-state channel from fragmented sarcoplasmic reticulum of frog leg muscle

  • Pedro P. Labarca
  • Christopher Miller
  • Pedro P. Labarca
    • 1
  • Christopher Miller
    • 1
  1. 1.Graduate Program in Biophysics and Graduate Department of BiochemistryBrandeis UniversityWaltham
Articles

Summary

Sarcoplasmic reticulum (SR) vesicles from frog leg muscle were fused with a planar phospholipid bilayer by a method described previously for rabbit SR. As a result of the fusion, K+-selective conduction channels are inserted into the bilayer. Unlike the two-state rabbit channel, the frog channel displays three states: a nonconducting (“closed”) state and two conducting states “α” and “β”. In 0.1m K+ the single-channel conductances are 50 and 150 pS for α and β, respectively. The probabilities of appearearance of the three states are voltage-dependent, and transitions between the closed and β states proceed through the α state. Both open states follow a quantitatively identical selectivity sequence in channel conductance: K+>NH 4 + >Rb+>Na+>Li+>Cs+. Both open states are blocked by Cs+ asymmetrically in a voltage-dependent manner. The zero-voltage dissociation constant for blocking is the same for both open states, but the voltage-dependences of the Cs+ block for the two states differ in a way suggesting that the Cs+ blocking site is located more deeply inside the membrane in the β than in the α state.

Key words

Sarcoplasmic reticulum K-channel, planar bilayer ion selectivity Cs-block excitation-contraction coupling 

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© Springer-Verlag New York Inc. 1981

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A K+-selective, three-state channel from fragmented sarcoplasmic reticulum of frog leg muscle