Acetylcholine activation of single muscarinic K+ channels in isolated pacemaker cells of the mammalian heart

• Published in: Nature (London) Vol. 303; no. 5914; p. 250
• Main Authors: Sakmann, B, Noma, A, Trautwein, W
• Format: Journal Article
• Language: English
• Published: England 01.05.1983
• Subjects: Acetylcholine - physiology; Animals; Atrioventricular Node - physiology; Electric Conductivity; Heart Conduction System - physiology; Ion Channels - physiology; Potassium - physiology; Rabbits; Receptors, Cholinergic - physiology; Receptors, Muscarinic - physiology; Sinoatrial Node - physiology
• ISSN: 0028-0836
• DOI: 10.1038/303250a0

Acetylcholine (ACh) released on vagal stimulation reduces the heart rate by increasing K+ conductance of pacemaker cells in the sinoatrial (S-A) node. Fluctuation analysis of ACh-activated currents in pacemaker tissue showed this to be due to opening of a separate class of K+ channels gated by muscarinic ACh receptors (m-AChRs). On the other hand, it has been suggested that m-AChRs may simply regulate the current flow through inward rectifying resting K+ channels (gk1). We report here the measurement of ACh-activated single channel K+ currents and of resting K+ channel currents in isolated cells of the atrioventricular (A-V) and S-A node of rabbit heart. The results show that the ACh-dependent K+ conductance increase in nodal cells is mediated by K+ channels which are different in their gating and conductance properties from the inward rectifying resting K+ channels in atrial and ventricular cells. The resting K+ channels in nodal cells are, however, similar to those activated by ACh.