Submitted on December 7, 2005
Accepted on August 27, 2006
Role of internalisation of M2 muscarinic receptor via clathrin-coated vesicles in desensitization of the muscarinic K+ current in heart
TOMOKO T YAMANUSHI1, Zhigang Shui2, Robert N. Leach3, Halina Dobrzynski2, Thomas W Claydon4, and Mark Richard Boyett2*
1 Kagawa Prefectural College of Health Sciences, Kagawa, Japan
2 Division of Cardiovascular and Endocrine Sciences, University of Manchester, Manchester, United Kingdom
3 Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
4 Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, Canada
* To whom correspondence should be addressed. E-mail: mark.boyett{at}manchester.ac.uk.
In the heart, ACh activates the ACh-activated K+ current (iK,ACh) via the M2 muscarinic receptor. The relationship between desensitization of iK,ACh and internalisation of the M2 receptor has been studied in rat atrial cells. On application of the stable muscarinic agonist, carbachol, for 2 h, iK,ACh declined by ~62 % with time constants of 1.5 and 26.9 min, whereas ~83 % of the M2 receptor was internalised from the cell membrane with time constants of 2.9 and 51.6 min. Transfection of the cells with 
-adrenergic receptor kinase 1 (GRK2) and -arrestin 2 significantly increased iK,ACh desensitization and M2 receptor internalisation during a 3 min application of agonist. Internalised M2 receptor in cells exposed to carbachol for 2 h was co-localized with clathrin and not caveolin. It is concluded that a GRK2- and -arrestin 2 dependent internalisation of the M2 receptor into clathrin coated vesicles could play a major role in iK,ACh desensitization.
