作者：DING Zhongren ZHANG Yan ZHANG Guiqing KE Jun HU Xiangjie
单位：DING Zhongren(Department of Hematology,Peking Union Medical Hospital,Chinese Academy of Medical Sciences,Beijing 100730)；ZHANG Yan,ZHANG Guiqing,KE Jun,HU Xiangjie(Department of Pharmacology,Henan Medical University,Zhengzhou 450052)
关键词：benactyzine；papillary；muscle；action；potential；myocardial；contraction；tetrodotoxin▲
河南医科大学学报000212Abstract：Aim:To explore the effects of benactyzine (BEN) on the action potential and contractile force in guinea pig papillary muscles.Methods:Conventional microelectrode technique was used to record the fast action potentials (FAP) and slow action potentials (SAP) of guinea pig papillary muscles.Results:Benactyzine 5,10,50 μmol.L-1 suppressed the maximal upstroke velocity (vmax) of FAP and contractile force (Fc) concentration-dependently while prolonged the action potential duration at 50%,90% repolarization (APD50,APD90) and effective refractory period (ERP) of FAP.The suppression on the vmax was frequency-dependent.Benactyzine 5,10,50μmol.L-1 lengthened the APD50,APD90 of SAP induced by isoprenaline or histamine when perfused with KCl 22 mmol.L-1 Tyrode's solution.The vmax of the SAP was not decreased by benactyzine 5,10 μmol.L-1 but by 50 μmol.L-1.The effects on the SAP were antagonized by elevation of the extracellular calcium from 2.0 to 5.6 mmol.L-1.The effects of benactyzine on SAP elicited by tetrodotoxin resembled that by isoprenaline or histamine except the more pronounced suppression on vmax and action potential amplitude (APA).The persistent rapid spontaneous activity and triggered tachyarrhythmia induced by ouabain were also abolished immediately by benactyzine 5 μmol.L-1.Conclusion:Benactyzine can inhibit Na+,K+,Ca2+ transmembrane movement and intracellular Ca2+ mobilization in the myocardium,and this may be the electrophysiological basis of its effects against experimental arrhythmias.
INTRODUCTION
Benactyzine is a synthetic blocker of M-receptor possessing smooth muscle relaxant properties and quinidine-like action on heart[1].Benactyzine is effective in restoring circulatory function disturbed by organophosphate poisoning[2,3].Previous studies suggested that benactyzine had antiarrhythmic effects in animals[4～6] and calcium antagonistic action on smooth muscle[7,8].The electrophysiological effects of benactyzine on myocardium have not been examined.The purpose of this study is to explore its electrophysiological effects and calcium antagonistic action on myocardium.
MATERIALS AND METHODS
Drugs and chemicals
benactyzine (Sigma);tetrodotoxin (Dalian Institute of Marine Materia Medica,Liaoning Province,China);ouabain (Merck);isoprenaline (Shanghai Tianfeng Pharmaceutical Factory);histamine (Shanghai Institute of Biochemistry,Shanghai,China).
Animals
Fifty-six guinea pigs of either sex,weighting 250～350 g were supplied by Experimental Animal Center of Henan Medical University (Certificate No 981002).
Guinea pigs were stunned and papillary muscles were taken from the right ventricle and pinned in a 1.5 ml chamber.The preparations of papillary muscle were perfused with Tyrode's solution (8 ml/min) aerated with 95% O2 + 5% CO2 at (32±0.5)℃ and pH 7.2 ～7.4 and electrically driven with pulses of 1 ms duration and 1.5 times threshold voltage at 1Hz frequency from a stimulator.For fast action potential (FAP),the Tyrode solution contained(mmol.L-1):NaCl 134,KCl 4.0,MgCl2 0.5,CaCl2 2.0,NaHCO3 12,NaH2PO4 0.42,Glucose 5.5.
Induction of fast action potential and contraction
Contractile force (Fc) of papillary muscle was measured with an isometric force transducer connected to the tendinous end of the muscle.Initial length was adjusted to yield maximal contraction amplitude upon stimulation.Transmembrane action potentials were recorded with a conventional glass microelectrode filled with KCl 3.0 mol.L-1 having a resistance of 15 ～ 30 MΩ.The maximal upstroke velocity (vmax) was obtained by an electronic differentiator.The electronic and mechanical signals were displayed on the screen of oscilloscope and photographed with camera.
Induction of slow action potential
After the impalement of the microelectrode was stabilized for 30 min,the preparations were changed to be driven with pulses of 3 ms and 0.5 Hz and fast Na+ channels were inactivated to induce slow action potential (SAP) either by perfusing preparations with high K+ (22 mmol.L-1) Tyrode solution or by tetrodotoxin 20 μmol.L-1.When perfused with high K+ Tyrode solution,isoprenaline 1 μmol.L-1 or histamine 10 μmol.L-1 was added to induce SAP.
Induction of triggered tachyarrhythmia
Oubaine 1.5 μmol.L-1 was added to Tyrode solution to induce oscillatory potential or triggered activity.When tachyarrhythmia was induced and persisted for 10 min,benactyzine was given to observe its effect.After induced action potentials were stabilized for 40 min,benactyzine 5,10,50 μmol.L-1 was administered in accumulative manner to observe its effects on FAP,Fc and SAP,only the results obtained from a single cell throughout the whole experimental period were subjected to statistical analysis.
RESULTS
The effects of benactyzine on FAP and Fc of guinea pig papillary muscles
Benactyzine 5,10,50 μmol.L-1 obviously suppressed vmax and Fc concentration-dependently while prolonged APD50,APD90 and effective refractory period (ERP) without affecting resting potential (RP),action potential amplitude (APA) and action potential duration at 20% (APD20) (Tab 1).
Tab 1 Effects of benactyzine on FAP and Fc of guinea pig papillary muscles ( n= 7 ......
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