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

Aminopyridines are known to inhibit acetylcholine-activated K+ current (IKACh) 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 (ICaL) 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 ICaL in enzymatically isolated cardiac myocytes. Isoprenaline (0.1 μM), an agonist of β1-β2-adrenoreceptors, stimulated the ICaL 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 ICaL, which recovered to 95±5.8% of the effect of isoprenaline. In the second series of experiments, adenosine (1 μM), an agonist of A1-adenosine receptors, reduced the stimulatory effect of isoprenaline on ICaL to 56±10% (n=3) (P<0.05). Then 2-AP27 (100 μM) applied in the presence of adenosine, had no effect on ICaL, 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