Cardiac muscarinic potassium channel activity is attenuated by inhibitors of G beta gamma.
The cardiac muscarinic potassium channel (IK.ACh) is activated by a G protein upon receptor stimulation with acetylcholine. The G protein subunit responsible for activation (G alpha versus G beta gamma) has been disputed. We used G beta gamma inhibitors derived from the beta-adrenergic kinase 1 (beta ARK1) to assess the relative importance of G beta gamma in IK.ACh activation. In rabbit atrial myocytes, IK.ACh had a conductance of 49 +/- 6.2 pS. In inside-out patches, the mean open time was 1.60 +/- 0.57 ms, mean time constant (tau o) was 1.59 +/- 0.53 ms, and mean closed time was 3.02 +/- 1.35 ms (n = 38). beta ARK1 is a G beta gamma-sensitive enzyme that interacts with G beta gamma through a defined sequence near its carboxyl terminus. A 28-amino-acid peptide derived from the carboxyl terminus of beta ARK1 (peptide G) increased the closed time to 10.04 ms (P < .001) and decreased opening probability (NPo) by 71% (P < .001). Fusion proteins containing the entire carboxyl terminus of beta ARK1, glutathione S-transferase beta ARK1ct and hexahistidine beta ARK1ct, decreased NPo by 67% (P = .03) and 48% (P = .009), respectively. They also both significantly increased the closed time. None of the inhibitors affected mean open time or channel amplitude. A control peptide derived from a neighboring region of beta ARK1 had no significant effect on IK.ACh activity. These results provide further evidence for the role of G beta gamma in the activation of IK.ACh.
Nair
L A
LA
Department of Medicine, Duke University Medical Center, Durham, NC 27710, USA.
Inglese
J
J
Stoffel
R
R
Koch
W J
WJ
Lefkowitz
R J
RJ
Kwatra
M M
MM
Grant
A O
AO
D000818:Animals; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors*; D006325:Heart Atria / Q000378:metabolism*; D008297:Male; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D011817:Rabbits; D051552:beta-Adrenergic Receptor Kinases
D015221:Potassium Channels; D017868:Cyclic AMP-Dependent Protein Kinases; D051552:beta-Adrenergic Receptor Kinases; D019204:GTP-Binding Proteins