The cardiac acetylcholine-activated, inwardly rectifying K+-channel subunit GIRK1 gives rise to an inward current induced by free oxygen radicals.
Reactive oxygen species (ROS) play a crucial role in pathophysiology of the cardiovascular system. The present study was designed to analyze the redox sensitivity of G-protein-activated inward rectifier K+ (GIRK) channels, which control cardiac contractility and excitability. GIRK1 subunits were heterologously expressed in Xenopus laevis oocytes and the resulting K+ currents were measured with the two-electrode voltage clamp technique. Oxygen free radicals generated by the hypoxanthine/xanthine oxidase system led to a marked increase in the current through GIRK channels, termed superoxide-induced current (I(SO)). Furthermore, I(SO) did not depend on G-protein-dependent activation of GIRK currents by coexpressed muscarinic m2-receptors, but could also be observed when no agonist was present in the bathing solution. Niflumic acid at a concentration of 0.5 mmol/l did not abolish I(SO), whereas 100 micromol/l Ba2+ attenuated I(SO) completely. Catalase (10(6) i.u./l) failed to suppress I(SO), whereas H2O2 concentration was kept close to zero, as measured by chemiluminescence. Hence, we conclude that O2*- or a closely related species is responsible for I(SO) induction. Our results demonstrate a significant redox sensitivity of GIRK1 channels and suggest redox-activation of G-protein-activated inward rectifier K+ channels as a key mechanism in oxidative stress-associated cardiac dysfunction.
Jeglitsch
G
G
Institute for Medical Physics and Biophysics, University of Graz, Austria.
Ramos
P
P
Encabo
A
A
Tritthart
H A
HA
Esterbauer
H
H
Groschner
K
K
Schreibmayer
W
W
D000109:Acetylcholine / Q000502:physiology*; D000818:Animals; D005260:Female; D005609:Free Radicals; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D008564:Membrane Potentials / Q000502:physiology; D009200:Myocardial Contraction / Q000502:physiology*; D009865:Oocytes / Q000378:metabolism; D018384:Oxidative Stress / Q000502:physiology; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying; D017382:Reactive Oxygen Species / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000502:physiology*; D014982:Xenopus laevis
D005609:Free Radicals; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D017382:Reactive Oxygen Species; D011976:Receptors, Muscarinic; D000109:Acetylcholine