AJP - Heart and Circulatory Physiology, Vol 258, Issue 1 159-H164, Copyright © 1990 by American Physiological Society
Open-channel subconductance state of K+ channel from cardiac sarcoplasmic reticulum
J. A. Hill Jr, R. Coronado and H. C. Strauss
Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710.
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.
