ISSN:
1432-1912
Keywords:
Ferret
;
Ventricular myocytes
;
Acetylcholine
;
Adenosine
;
Muscarinic K+
;
channel
;
G protein
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract The properties of the K+ channel activated by acetylcholine (ACh) and adenosine (Ado) were examined in single ferret ventricular myocytes using patch-clamp techniques. In the whole-cell configuration, ACh and Ado induced an inwardly rectifying K+ current and shortened the action potential duration. The effect of ACh was blocked by atropine, while the Ado effect was interrupted by 8-cyclopenty1,1,2-dipropyl xanthine, a specific Ado A1 receptor antagonist. In cell-attached recordings, ACh and Ado added to the pipette solution activated a single population of inwardly rectifying K+ channels, distinct from the i K1 channel. The channel had a slope conductance of ∼ 40 pS in symmetrical 150 mM K+ solutions and a mean open time of 0.8 ms. Excision of the patch into the inside-out patch configuration in guanosine triphosphate (GTP)-free solution abolished the channel activity. The channel was reversibly reactivated by adding GTP to the intracellular side of the patch. GTPγS activated the channel irreversibly. When the inside-out patch was treated with the A protomer of pertussis toxin (PTX), intracellular GTP no longer activated the K+ channel. The results show that ferret ventricular myocytes possess a K+ channel activated by both muscarinic and Ado A1 receptors. Its electrophysiological properties and the gating by a PTX-sensitive G protein in a membrane-delimited fashion are identical with those of the muscarinic K+ channels in nodal and atrial tissues of other species. In conclusion, the G protein-gated muscarinic K+ channel is expressed in ferret ventricular myocardium and may underlie the direct negative inotropism of ACh and Ado in this tissue.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00170160
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