I_KACh inhibitor 2-[(4-methylphenyl)sulfonylcarbamido]-1-(4-nitrobenzyl)pyridinium bromide (2-AP27) is a muscarinic M₂ receptor antagonist

Vytenis Arvydas Skeberdis, Vida Gendvilienė, Danguolė Zablockaitė, Irma Martišienė, Antanas Stankevičius

Institute of Cardiology, Kaunas University of Medicine, Lithuania

Key words: myocardial cells; carbachol; adenosine; sulfonylcarbamide derivative of 2-aminopyridine; 2-AP27; L-type Ca²⁺ current.

Summary. Aminopyridines are known to inhibit acetylcholine-activated K⁺ current (I_KACh) in cardiac myocytes. The aim of this study was to examine the effect of 2-aminopyridine sulfonylcarbamide derivative 2-AP27 on isoprenaline-stimulated L-type Ca²⁺ current (I_CaL) and to identify whether 2-AP27 acts via blocking of muscarinic M₂-receptors in frog cardiomyocytes.

The whole-cell configuration of the patch-clamp technique was used to record I_CaL in enzymatically isolated cardiac myocytes. Isoprenaline (0.1 µM), an agonist of β₁-β₂-adrenoreceptors, stimulated the I_CaL up to 475±61% (n=4) (P<0.05) vs. control. Then, in the first series of experiments, carbachol (0.01 µM), an agonist of M₂ muscarinic receptors, reduced the stimulatory effect of isoprenaline to 42±15% vs. isoprenaline alone. 2-AP27 (100 µM) alone completely abolished the inhibitory effect of carbachol on isoprenaline-stimulated I_CaL, which recovered to 95±5.8% of the effect of isoprenaline. In the second series of experiments, adenosine (1µM), an agonist of A₁-adenosine receptors, reduced the stimulatory effect of isoprenaline on I_CaL to 56±10% (n=3) (P<0.05). Then 2-AP27 (100 µM) applied in the presence of adenosine, had no effect on I_CaL, which remained at 51±7.9% (n=3) (P<0.05) of the effect of isoprenaline. These results suggest that 2-AP27, a new derivative of 2-AP, containing 4-toluolsulfonylcarbamide instead of amino group and quaternizated nitrogen by 4-nitrobenzylbromide in pyridine ring, is acting as an antagonist of muscarinic M₂ receptors in frog ventricular myocytes.

Correspondence to V. Gendvilienė, Institute of Cardiology, Kaunas University of Medicine, Sukilėlių 17, 50161 Kaunas. E-mail: membiof@kmu.lt

Received 1 July 2008, accepted 3 July 2009