Effect of inhibitors of mitochondrial respiratory chain complexes on the electromechanical activity in human myocardium

The aim of the study was to investigate the effect of inhibitors of mitochondrial respiratory chain complexes I, III, and IV on the electromechanical activity in human myocardium. Material and methods. The experiments were performed on the human myocardial strips obtained from patients with heart failure (NYHA class III or IV) using a conventional method of registration of myocardial electromechanical activity. Under the perfusion with physiological Tyrode solution (control), contraction force (P) was 0.94±0.12 mN (n=16), relaxation time (t50) was 173.38±5.03 ms (n=15), action potential durations measured at 50% (AP50) and 90% (AP90) repolarization were 248.96±13.38 ms and 398.59±17.93 ms, respectively (n=13). Results. The inhibition of respiratory chain complex I by rotenone (3×10–5 M, the highest concentration applied) decreased contraction force of human myocardium to 48.99%±14.74% (n=3) (P<0.05); AP50, to 81.34%±15.81%; and AP90, to 87.28%±7.25% (n=3) (P>0.05) of control level, while relaxation time and resting tension remained almost unchanged. Antimycin A, an inhibitor of complex III, applied at the highest concentration (3×10–4 M) reduced P to 41.66%±8.8% (n=5) (P<0.001) and marginally increased t50 and decreased the durations of AP. Anoxia (3 mM Na2S2O4) that inhibits the activity of complex IV reduced the contraction force to 9.23%±3.56% (n=6) (P<0.001), AP50 and AP90 to 65.46%±9.95% and 71.07%±8.39% (n=5) (P<0.05) of control level, respectively; furthermore, the resting tension augmented (contracture developed). Conclusions. Our results show that the inhibition of respiratory chain complex IV had the strongest inhibitory effect on the electromechanical activity of failing human myocardium

Anticholinergic effect of 2-aminopyridine and its sulfonylcarbamide derivatives on electromechanical activity in guinea pig atrium

The aim of the study was to investigate an action of 2-aminopyridine and its new sulfonylcarbamide derivatives 2-AP21, 2-AP22, 2-AP26, and 2-AP27 (10–5–10–3 M) on carbachol-induced shortening of action potential duration and reduction of contraction force in guinea pig atrial muscles. Experiments were carried out using a standard method of myocardium electromechanical activity registration. Under control conditions (perfusion of atrial strips with Tyrode solution), an average of action potential duration, measured at 90% (AP90) and 50% (AP50) of repolarization, were 112.32±6.07 ms and 50.21±3.25 ms, (n=19), respectively, and contraction force was of 1.42±0.28 mN (n=20). Carbachol (10–6M), an agonist of muscarinic acetylcholine receptor and activator of KAch channels, markedly decreased AP90 to 35.31±4.21%, AP50 – to 26.42±2.66% (n=19) (P<0.001), and contraction force – to 24.23±2.0% (n=20) (P<0.001) vs. control. Modification of 2-aminopyridine structure by replacing 2-amino group by 4-toluolsulfonylcarbamide fragment and quaternization of nitrogen in pyridine ring increased anticholinergic effect on action potential duration and contraction force. According to their maximal prolongation of AP at 90% of repolarization, all new drugs ranked as follows: 2-AP27>>2-AP26>2-AP22³2-AP>2-AP21. 2-aminopyridine derivative 2-AP27, containing 4-toluolsulfonylcarbamide fragment and 4-nitrobenzyl radical at quaternized nitrogen of the pyridine, had the most potent anticholinergic effect on AP90 (936.60±178.23%). 2-AP22 and 2-AP26 (containing methyl or allyl radicals at quaternized nitrogen of the pyridine, respectively) showed a much weaker anticholinergic effect (231.39±28.48% and 318.25±63.81%, respectively). The weakest anticholinergic effect (63.59±34.38%) was induced by 2-aminopyridine derivative 2-AP21, which had non-quaternized nitrogen of the pyridine

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

Hipertoniškumo įtaka žmogaus prieširdžio β²-adrenerginei stimuliacijai

Summary. The purpose of the present study was to determine whether extracellular osmotic pressure modulates b2-adrenergic stimulation of the contraction force and L-type Ca2+ current in human atrial myocytes. Experiments were performed on human atrial trabeculae and myocytes isolated from the right atrium. We have studied the effect of salbutamol (SAL), a β²-adrenoceptor agonist, on peak tension (P), time to half peak tension (tc), time to half relaxation (tr), resting tension (contracture) (C) and L-type calcium current (ICaL) under isosmotic (345 mOsm) and hyperosmotic (525 mOsm in experiments for P, and 405 mOsm for ICaL) conditions. Salbutamol (10–8÷10–5 M) added to the control solution increased P, with a half-stimulation constant EC50=(2.7±0.6)×10-8 M (p<0.05) and the maximal stimulation of contraction force Pmax=180.6±45.8% (n=10). The time to half peak and time to half relaxation were reduced by salbutamol to 89.1±2.7% and 78.8±4.1% (n=8), respectively. Mannitol (180 mM) added to the Tyrode solution decreased Pmax to 34±5.5%; tc, tr and C were increased to 126.3±7.2%, 158.3±22.6% (n=4) and 0.54±0.22 (n=5) of the control level, respectively. Under these hyperosmotic conditions the same concentrations of SAL increased P with a half-stimulation constant EC50=(6.4±2.6)×10–7 M and Pmax=57.2±12.6% (n=4). The tc and tr were reduced by 23.2±5.9% and 53.1±19.4% (n=4), respectively (as compared to mannitol). There was no significant effect of salbutamol on the resting tension induced by mannitol. Under isosmotic conditions salbutamol (10–9÷10–6M) increased ICaL with an EC50 value of (2.9±0.9)×10–9 M and Emax 182.3±19.8% (n=4). In hyperosmotic solutions the EC50 and Emax for ICaL were (1.2±0.5)×10–8 M and 217.2±70.5%, respectively (n=5). These results indicated that hyperosmolarity reduced the effect of β2-adrenergic stimulation on human atrial cells