doi: 10.1161/CIRCRESAHA.108.183384
© 2008 American Heart Association, Inc.
Editorials |
And the Winner Is ... RGS4!
From the Departments of Pharmacology and Internal Medicine, University of Michigan Medical School, Ann Arbor.
Correspondence to Richard R. Neubig, MD, PhD, Department of Pharmacology, University of Michigan Medical School, 1150 W Medical Center Dr, 1303 MSRB III, Ann Arbor, MI 48109. E-mail RNeubig@umich.edu
See related article, pages 527–535
Key Words: arrhythmia • automaticity • mouse mutants • potassium channels • G proteins
An extract of the first 250 words of the full text is provided, because this article has no abstract. |
RGS proteins play a major role in controlling G protein signaling. Cifelli et al1 show very high expression of RGS4 in sinoatrial (SA) node in the mouse. Of the 10 RGS proteins expressed supraventricularly, genetic disruption of RGS4 alone produces a profound slowing of IK,Ach turnoff kinetics in SA node and enhanced carbachol-induced bradycardia in vivo. This is accompanied by a loss of rapid desensitization of the IK,Ach current, suggesting a selective action of RGS4 in controlling prolonged vagal responses. This has implications for clinical conditions dependent on cholinergic signals such as atrial fibrillation (AF), vasovagal syncope, and possibly torsades de point. These results make RGS4 an intriguing candidate gene in certain arrhythmias.
Approximately 12 years ago, the G protein and G protein–coupled receptor fields were rocked by the discovery of the RGS (regulators of G protein signaling) proteins.2,3 Here was a key regulatory protein family that inhibited G protein signaling but was virtually unknown a year earlier. Very rapidly, the core molecular function of RGS proteins was defined as GTPase accelerator protein activity, which sped the deactivating GTP hydrolysis step,4 which, for G proteins, was notoriously slow. The crystal structure of a complex of G
i1 and RGS4 "caught in the act" of GTP hydrolysis5 followed shortly thereafter.
Cardiac atrial function figured prominently in early studies of RGS proteins. The negative chronotropic actions of acetylcholine via the M2 muscarinic receptor involved activation of the IK,Ach current, which is carried by the G protein–coupled inwardly rectifying K+ (GIRK) channel, composed of
Related Article:
Circ. Res. 2008 103: 527-535.