[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(-6)M), an agonist of muscarinic acetylcholine receptor and activator of K(Ach) 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-AP22> or =2-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.

[Effects of ATP-regulated potassium channels modulators, N-(2-pyridyl)-N'-(4-toluol) sulfonylcarbamides, on electromechanical activity in guinea pig myocardium]

The aim of the study was to investigate the effects of 2-aminopyridine (2-AP) and its new sulfonylcarbamide derivatives AP21, AP22, AP26, and AP27 (10(-(5))-10(-(3)) M) on pinacidil (5x10(-(5)) M), an activator of K(ATP) channels, induced shortening of action potential duration and reduction of contraction force in guinea pig papillary muscles. Experiments were carried out using a standard method of myocardium electromechanical activity registration. Under control conditions (perfusion of papillary muscles with Tyrode solution), an average of action potential duration (APD), measured at 90% (APD(90)) and 50% (APD(50)) of repolarization, were 211.78+/-8.6 ms and 173.22+/-8.3 ms (n=18), respectively, and contraction force was 1.77+/-0.36 mN (n=18). Pinacidil markedly decreased APD(90) to 58.16+/-4.4%, APD(50) - to 52.51+/-4.85% (n=18), and contraction force - to 30.45+/-4.06% (n=18), (p<0.001) vs. control. 2-aminopyridine and its sulfonylcarbamide derivative AP22 (with 4-toluolsulfonylcarbamide fragment and methyl iodide-quaternized nitrogen of the pyridine ring) had no effect on the pinacidil-induced shortening of action potential and reduction of contraction force. 2-aminopyridine derivatives, AP21 (with 4-toluolsulfonylcarbamide fragment) and AP26 (with allyl bromide-quaternized nitrogen of the pyridine ring), showed a weak effect on pinacidil-induced shortening of action potential duration. The 2-aminopyridine derivative AP27 (with the 4-toluolsulfonylcarbamide fragment where nitrogen of the pyridine ring was quaternized by 4-nitrobenzyl bromide) had the most potent stimulatory effect on action potential duration and contraction force, which were reduced by pinacidil.

[Anticholinergic effect of procainamide and its sulfonylcarbamide derivatives on electromechanical activity in guinea pig atrium]

The aim of the study was to investigate the effect of class IA antiarrhythmic drug procainamide and its new derivatives PA20, PA23, PA28 and PA53 on carbachol-induced action potential duration and contraction force in guinea pig atrial muscles. Experiments were carried out using standard method of registration of myocardium electromechanical activity. Under control conditions (perfusion of atrial strips with Tyrode solution), mean action potential duration measured at 90% (AP90) and 50% (AP50) of repolarization were 92.5+/-4.5 ms and 44.4+/-2.9 ms (n=18), respectively, and contraction force was of 2.7+/-0.5 mN (n=12). Carbachol (10(-6) M), an agonist of muscarinic acetylcholine receptor and activator of K(Ach) channels, markedly decreased AP90 to 32.4+/-2.4%, AP50 - to 25.4+/-2.2% (n=18) (p<0.001) and contraction force - to 24.2+/-5.8% (n=16) (p<0.05), vs. control. Procainamide and its new sulfonylcarbamide derivatives PA20, PA23, PA28 (10(-5)-3x10(-3) M), and PA53 (10(-5)-10(-3) M) reversed the carbachol-induced action potential duration shortening at different extent: procainamide derivative PA20 (N-cyclohexylsulfonylcarbamide fragment is linked up to benzene ring) had the most potent anticholinergic effect on action potential duration and contraction force of guinea pig atrial muscles. N-ethylsulfonylcarbamide fragment in PA23 or permanent positive charge of aliphatic nitrogen in PA28 had a weaker anticholinergic effect (similar to procainamide action) on action potential duration and contraction force than PA20. The weakest anticholinergic effect was induced by procainamide derivative PA53 with isosteric form of sulfonylcarbamide.

Effect of hyperosmolarity on beta2-adrenergic stimulation in human atrium

The purpose of the present study was to determine whether extracellular osmotic pressure modulates beta2-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 beta2-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)x10(-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)x10(-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(-6) M) increased ICaL with an EC50 value of (2.9+/-0.9)x10(-9) M and Emax 182.3+/-19.8% (n=4). In hyperosmotic solutions the EC50 and Emax for ICaL were (1.2+/-0.5)x10(-8) M and 217.2+/-70.5%, respectively (n=5). These results indicated that hyperosmolarity reduced the effect of beta2-adrenergic stimulation on human atrial cells.

The force-frequency relationship in human heart failure: effect of pyruvate and isoproterenol

PURPOSE

The purpose of present study was to investigate the effect of metabolic substrate pyruvate and beta-adrenergic agonist isoproterenol and combination of these agents on the force- and relaxation-frequency relationship in human heart failure.

MATERIAL AND METHODS

The experiments were performed on isolated human ventricle strips from patients undergoing cardiac corrective open heart surgery, using conventional method of registration of electromechanical activity. The stimulation frequency of myocardial strips was 0.2, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 Hz.

RESULTS

In control, i.e. at perfusion of myocardial strips by Tyrode solution and stimulation frequency 1 Hz, the contraction force (F) was 0.94 +/- 0.18 mN, half time of relaxation (tr)--178.8 +/- 9.3 ms (n= 12). Pyruvate (10 mmol/L) increased F to 176.0 +/- 13.4%, tr--104.6 +/- 3.1% (n=8, p<0.05) vs control. By the action of isoproterenol (10(-5) mol/L) F increased to 122.1 +/- 10.2%, tr decreased to 58.9 +/- 3.1% (n=4, p<0.05) vs control. The relationship of F and tr from stimulation frequency in the absence of pyruvate and isoproterenol was negative. Pyruvate and isoproterenol didn't alter the shape of force-frequency relationships but F was augmented at all stimulation frequencies. The positive inotropic effect of isoproterenol was potentiated by pyruvate.

CONCLUSIONS

Pyruvate and isoproterenol alone can improve cardiac contractility in wide-range of stimulation frequency. The combination of these inotropic agents results in even more effective increase of contractile performance and therefore may be of therapeutic value in heart failure.