ISSN:
1432-1424
Keywords:
Sarcoplasmic reticulum
;
K-channel, planar bilayer
;
ion selectivity
;
Cs-block
;
excitation-contraction coupling
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01870750
Permalink
