scholarly journals Structural aspects of the sarcoplasmic reticulum K+ channel revealed by gallamine block

1988 ◽  
Vol 54 (2) ◽  
pp. 233-239 ◽  
Author(s):  
M.A. Gray ◽  
B. Tomlins ◽  
R.A. Montgomery ◽  
A.J. Williams
Keyword(s):  
Sarcoplasmic Reticulum ◽  
K Channel ◽  
Structural Aspects

scholarly journals Modification of a voltage-gated K+ channel from sarcoplasmic reticulum by a pronase-derived specific endopeptidase.

1979 ◽  
Vol 74 (4) ◽  
pp. 457-478 ◽  
Author(s):  
C Miller ◽  
R L Rosenberg
Keyword(s):  
Free Energy ◽  
Sarcoplasmic Reticulum ◽  
Single Channel ◽  
Membrane Conductance ◽  
Phospholipid Bilayer ◽  
K Channel ◽  
Gating Charge ◽  
Voltage Dependent ◽  
Selective Membrane ◽  
Conformational Model

AK+ -selective membrane conductance channel from rabbit sarcoplasmic reticulum (SR) is studied in an artificial planar phospholipid bilayer. Membranes containing many such channels display voltage-dependent conductance, which is well described by a two-state conformational equilibrium with a free energy term linearly dependent on applied voltage. Pronase-derived alkaline proteinase b (APb), when added to the side of the membrane opposite to the SR vesicles (trans side), reduces the voltage dependence of the K+ conductance. Single-channel fluctuation experiments show that after APb treatment, the channel is still able to undergo transitions between its open and closed states, but that the probability of forming the open state is only slightly voltage-dependent. In terms of the conformational model, the enzyme's primary effect is to reduce the effective gating charge of the opening process by over 80%; a second effect of APb is to reduce the internal free energy of opening from +1.2 to +0.4 kcal/mol. The kinetics of APb action are strongly voltage-dependent, so as to indicate that the enzyme can react only with the channel's open state. The results imply that the channel contains a highly charged polypeptide region which moves in the direction perpendicular to the membrane plane when transitions between the open and closed states occur. A lysine or arginine residue in this region becomes exposed to the trans aqueous solution when the channel is in its open conformation.

Open-channel subconductance state of K+ channel from cardiac sarcoplasmic reticulum

1990 ◽  
Vol 258 (1) ◽  
pp. H159-H164 ◽  
Author(s):  
J. A. Hill ◽  
R. Coronado ◽  
H. C. Strauss
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Open Channel ◽  
State Transitions ◽  
K Channel ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Reaction Rate Constants ◽  
Binary Model ◽  
Voltage Dependent ◽  
Conductance States ◽  
Open States

We have characterized the K+ channel of canine cardiac sarcoplasmic reticulum in terms of its gating kinetics and conductance states. We demonstrate that the open channel dwells in two states, O1 and O2, where O1 is a true subconductance state of O2. The two open states are linked with a closed state by a cyclic gating scheme. Under certain circumstances, however, important information can be derived using a binary model. Each open state separately exhibited an ohmic current-voltage relation with unitary conductance values of 105 (O1) and 189 (O2) pS in 0.1 M K+. Gating between closed and open states was weakly voltage dependent, and we derive reaction rate constants for the state transitions. Finally, we postulate three models to explain the existence of a subconductance state (blockade, stenosis, flutter). We argue that a flutter model best accounts for our observations of O1.

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