ABSTRACT
AIM: To study the electrophysiological effects of nitric oxide (NO) on the pacemaker cells in guinea-pig left ventricular outflow tract under the condition of ischemia/reperfusion ( I/R) .METHODS:The spontaneous slow action potentials of guinea-pig left ventricular outflow tract were recorded by conventional intracellular microelectrode technique.The effects of NO donor sodium nitroprusside ( SNP) on the spontaneous slow action potentials under normal or I/R condition were investigated.RESULTS:SNP at concentrations of 1, 10 and 100μmol/L but not 1000μmol/L signif-icantly increased velocity of diastolic depolarization ( VDD) and rate of pacemaker firing ( RPF) , SNP at concentrations of 1, 10, 100 and 1 000μmol/L notably increased maximal diastolic potential (MDP), amplitude of action potential (APA) and maximal rate of depolarization ( Vmax ) , shortened 50%and 90%of the duration ( APD50 and APD90 ) .In ischemia 10 min group, VDD and RPF were significantly decreased, APA and Vmax were notably increased, and APD50 and APD90 were markedly lengthened compared with control group.In reperfusion 10 min group, VDD and RPF were significantly in-creased, MDP and APA were notably decreased, and APD50 and APD90 were markedly shortened compared with I 10 min group.In reperfusin 10 min group, the pacemaker activity was always irregular.In reperfusion 10 min group, the parame-ters of spontaneous slow action potentials restored to the levels of control group except for VDD and Vmax .In 1, 10 and 100 μmol/L SNP+R groups, VDD and RPF were significantly increased than in ischemia 10 min group .In 1, 10, 100 and 1 000 μmol/L SNP+R groups, APA, APD50 and APD90 were restored to the levels of control group.CONCLUSION:SNP significantly increases the spontaneous activity of left ventricular outflow tract, and relieves the effects of I/R on the sponta-neous slow action potential markedly.
ABSTRACT
AIM:To study the electrophysiological effects of amiodarone on the pacemaker cells in guinea-pig left ventricular outflow tract under the conditions of hypoxia,acidosis and treatment with epinephrine.METHODS:The action potentials of the pacemaker cells in guinea-pig left ventricular outflow tract were recorded by conventional intracellular microelectrode technique.The effects of amiodarone on the spontaneous slow response potentials were investigated under the conditions of hypoxia,acidosis and treatment with epinephrine.RESULTS:(1) Amiodarone at concentration of 0.1 ?mol/L markedly decreased the rate of pacemaker firing (RPF) and maximal diastolic potential (MDP),lengthened 80% of the duration of action potential (APD80).Amiodarone at concentration of 1 ?mol/L significantly decreased the velocity of diastolic depolarization (VDD) and RPF,the maximal rate of depolarization (Vmax),MDP and amplitude of action potential (APA),lengthened 50% of the duration of action potential (APD50) and APD80.Amiodarone at concentration of 10 ?mol/L led to a significant decrease in VDD and RPF,Vmax,MDP and APA,a notable lengthening in APD50 and APD80 was also observed.(2) Under the condition of hypoxia and perfusion with deprived glucose content for 15 min,VDD,RPF,MDP,Vmax and APA decreased significantly,APD50 was shortened notably.Under the condition of hypoxia,amiodarone at concentration of 1 ?mol/L significantly decreased VDD,RPF and Vmax,increased MDP,lengthened APD50 and APD80 as compared to the cells treated with hypoxia only.(3) Perfusion with pH 6.8 solution for 10 min,VDD and RPF significantly decreased,Vmax and APA notably reduced,APD80 was markedly shortened.Under the condition of acidosis for 10 min,amiodarone significantly decreased VDD,RPF,MDP and APA,lengthened APD50 and APD80 as compared to the cells under the condition of acidosis only.(4) Perfusion of epinephrine at concentration of 10 ?mol/L for 10 min resulted in a significant increase in VDD,RPF,Vmax,MDP and APA,a notable shorting in APD50 and APD80 was also observed.Compared to 10 ?mol/L epinephrine group,1 ?mol/L amiodarone+ 10 ?mol/L epinephrine significantly reduced VDD,RPF,Vmax,MDP and APA,lengthened APD50 and APD80.CONCLUSION:Amiodarone markedly decreases the autorhythmicity of the pacemaker cells in guinea-pig left ventricular outflow tract.This electrophysiological effects were significantly influenced by hypoxia,acidosis and epinephrine.