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.

Duke Scholars

Author Robert J. Lefkowitz Medicine, Cardiology

Author Walter J. Koch Surgery, Cardiovascular and Thoracic Surgery

Author Madan Mohan Kwatra Anesthesiology

Author Augustus Oliver Grant Medicine, Cardiology