Advertisement

The Journal of Membrane Biology

, Volume 165, Issue 1, pp 45–52 | Cite as

Characterization of the Driving Force as a Modulator of Gating in Cardiac ATP-sensitive K+ Channels — Evidence for Specific Elementary Properties

  • I.  Benz
  • K.  Haverkampf
  • M.  Kohlhardt

Abstract.

Single cardiac ATP-sensitive K+ channels and, comparatively, two other members of the inwardly rectifying K+ channel family, cardiac K+ (ir) and K+ (ACh) channels, were studied in the inside-out recording mode in order to analyze influence and significance of the electrochemical K+ gradient for open-state kinetics of these K+ channels.

The conductive state of K+ (ATP) channels was defined as a function of the electrochemical K+ gradient in that increased driving force correlates with shortened open-channel lifetime. Flux coupling of gating can be largely excluded as the underlying mechanism for two reasons: (i) τopen proved identical in 23 pS, 56 pS and 80 pS channels; (ii) K+ (ATP) channel protonation by an external pH shift from 9.5 to 5.5 reduced conductance without a concomitant detectable change of τopen. Since gating continued to operate at E K , i.e., in the absence of K+ permeation through the pore, K+ driving force cannot be causally involved in gating. Rather the driving force acts to modulate the gating process similar to Rb+ whose interference with an externally located binding site stabilizes the open state. In K+ (ir) and K+ (ACh) channels, the open state is essentially independent on driving force meaning that their gating apparatus does not sense the electrochemical K+ gradient. Thus, K+ (ATP) channels differ in an important functional aspect which may be tentatively explained by a structural peculiarity of their gating apparatus.

Key words: Cardiac inward rectifier K+ channels — Kinetics — Permeation — Electrochemical K+ gradient — pH — Rubidium 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

Copyright information

© Springer-Verlag New York Inc. 1998

Authors and Affiliations

  • I.  Benz
    • 1
  • K.  Haverkampf
    • 1
  • M.  Kohlhardt
    • 1
  1. 1.Physiological Institute of the University, Hermann-Herder-Str. 7, D-79104 Freiburg/Br., GermanyDE

Personalised recommendations