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J Exp Biol. 2014 May 15;217(Pt 10):1745-51. doi: 10.1242/jeb.098509. Epub 2014 Feb 13.

A new potassium ion current induced by stimulation of M2 cholinoreceptors in fish atrial myocytes.

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Department of Human and Animal Physiology, Moscow State University, Leninskiye Gory, 1, 12, Moscow 119991, Russia Department of Fundamental and Applied Physiology, Russian National Research Medical University, Moscow 117997, Russia
Department of Human and Animal Physiology, Moscow State University, Leninskiye Gory, 1, 12, Moscow 119991, Russia.
Department of Biology, University of Eastern Finland, FI-80101 Joensuu, Finland.


A novel potassium ion current induced by muscarinic stimulation (IKACh2) is characterized in atrial cardiomyocytes of teleost fishes (crucian carp, Carassius carassius; rainbow trout, Oncorhynchus mykiss) by means of the whole-cell patch-clamp technique. The current is elicited in atrial, but not ventricular, cells by application of carbamylcholine (CCh) in moderate to high concentrations (10(-7)-10(-4) mol l(-1)). It can be distinguished from the classic IKACh, activated by the βγ-subunit of the Gi-protein, because of its low sensitivity to Ba(2+) ions and distinct current-voltage relationship with a very small inward current component. Ni(2+) ions (5 mmol l(-1)) and KB-R7943 (10(-5) mol l(-1)), non-selective blockers of the sodium-calcium exchange current (INCX), strongly reduced and completely abolished, respectively, the IKACh2. Therefore, IKACh2 was initially regarded as a CCh-induced outward component of the INCX. However, the current is not affected by either exclusion of intracellular Na(+) or extracellular Ca(2+), but is completely abolished by intracellular perfusion with K(+)-free solution. Atropine (10(-6) mol l(-1)), a non-selective muscarinic blocker, completely eliminated the IKACh2. A selective antagonist of M2 cholinoreceptors, AF-DX 116 (2×10(-7) mol l(-1)) and an M3 antagonist, 4-DAMP (10(-9) mol l(-1)), decreased IKACh2 by 84.4% and 16.6%, respectively. Pertussis toxin, which irreversibly inhibits Gi-protein coupled to M2 receptors, reduced the current by 95%, when applied into the pipette solution. It is concluded that IKACh2, induced by stimulation of M2 cholinoceptors and subsequent Gi-protein activation, represents a new molecular target for the cardiac parasympathetic innervation.


Acetylcholine; Atrial myocytes; Fish heart; IKACh; Ionic currents; Muscarinic receptors

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