Abstract | AIMS: Although atrial tachycardia (AT) remodelling promotes agonist-independent, constitutively active, acetylcholine-regulated K+-current (I K,ACh) that increases susceptibility to atrial fibrillation (AF), the underlying changes in I K,Ach channel function are unknown. This study aimed to establish how AT remodelling affects I K,ACh single-channel function. METHODS AND RESULTS: I K,ACh single-channel activity was studied via cell-attached patch-clamp in isolated left atrial cardiomyocytes of control and AT (7 days, 400 min(-1)) dogs. Atrial tachycardia prolonged the mean duration of induced AF from 44 +/- 22 to 413 +/- 167 s, and reduced atrial effective refractory period at a 360 ms cycle length from 126 +/- 3 to 74 +/- 5 ms (n = 9/group, P < 0.001). In the absence of cholinergic stimulation, single-channel openings with typical I K,ACh conductance and rectification properties were sparse under control conditions. Atrial tachycardia induced prominent agonist-independent I K,ACh activity because of increased opening frequency (fo) and open probability (Po: approximately seven- and 10-fold, respectively, vs. control), but did not alter open time-constant, single-channel conductance, and membrane density. With maximum I K,ACh activation (10 micromol/L carbachol), channel Po was enhanced much more in control cells ( approximately 42-fold) than in AT-remodelled myocytes (approximately five-fold). The selective Kir3 current blocker tertiapin-Q (100 nmol/L) reduced fo and Po at -100 mV by 48 and 51%, respectively (P < 0.05 for each), without altering other channel properties, confirming the identity of I K,ACh. Atrial tachycardia had no significant effect on mRNA or protein expression of either of the subunits (Kir3.1, Kir3.4) underlying I K,ACh. CONCLUSION: Atrial tachycardia increases agonist-independent constitutive I K,ACh single-channel activity by enhancing spontaneous channel opening, providing a molecular basis for AT effects on macroscopic I K,ACh observed in previous studies, as well as associated refractoriness abbreviation and tertiapin-suppressible AF promotion. These results suggest an important role for constitutive I K,Ach channel opening in AT remodelling and support its interest as a potential target for AF therapy.
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Authors | Niels Voigt, Ange Maguy, Yung-Hsin Yeh, Xiaoyan Qi, Ursula Ravens, Dobromir Dobrev, Stanley Nattel |
Journal | Cardiovascular research
(Cardiovasc Res)
Vol. 77
Issue 1
Pg. 35-43
(Jan 2008)
ISSN: 0008-6363 [Print] England |
PMID | 18006448
(Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
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Chemical References |
- Bee Venoms
- G Protein-Coupled Inwardly-Rectifying Potassium Channels
- Potassium Channels, Inwardly Rectifying
- tertiapin
- Carbachol
- Acetylcholine
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Topics |
- Acetylcholine
(pharmacology)
- Animals
- Atrial Fibrillation
(etiology)
- Bee Venoms
(pharmacology)
- Carbachol
(pharmacology)
- Dogs
- Female
- G Protein-Coupled Inwardly-Rectifying Potassium Channels
(analysis, physiology)
- Heart Atria
- Male
- Myocytes, Cardiac
(metabolism)
- Potassium Channels, Inwardly Rectifying
(drug effects, physiology)
- Tachycardia
(complications, metabolism)
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