Cytological Mechanism Of Compretin Disodium Phosphate-induced QT Interval Prolongation

Part I Inhibition of action potential duration by combretastatin A4 phosphateObjectiveTo evaluate the effects of combretastatin A4 phosphate(CA4P)on action potential duration(APD)of guinea pig ventricular myocytes.MethodsThe whole cell patch clamp technique method was used to observe the impact of 10? mol·L-1 and 100? mol·L-1 CA4P on the action potential duration of guinea pig ventricular myocytes(APD),resting membrane potential(RMP),action potential amplitude(APA),and maxium rate of depolarization in phase 0(Vmax),APD at 50%of repolarization(APD50)and APD at 90%of repolarization(APD90).ResultsCA4P(10,100?mol·L-1)significantly prolonged APD50and APD90,the extension rates of APD50 was 15.7%and 42.01%,the extension rates of APD90 was 10.15%and 31.36%(P<0.05);There was no effect on the resting membrane potential,action potential amplitude and maximal depolarization rate in phase 0.ConclusionsCA4P can prolong APD of ventricular myocytes.Part II Inhibition of hERG channel by combretastatin A4 phosphateObjectiveTo study the effects of combretastatin A4 phosphate(CA4P)on K+channel encoded by human ether-a-go-go-related gene(hERG)and to explore the cytological mechanism in vitro of cardiotoxicity.MethodsThe whole cell patch clamp technique method was established and using the hERG current that were stably transfected and expressed hERG channel in HEK293 cells.The terfenadine was used as positive control,different concentrations of CA4P(3,10,30,100,300 1 mol·L-1)were given to observe the inhibitory effect of drugs on the tail current of hERG channel;At 30? mol·L-1,the inhibitory effect of the drug on the tail current of hERG channel was observed under different voltage stimulation(10mV,20mV,30mV,40mv and 50mV).When the concentration of CA4P was 300? mol·L-1 to recorded the time dependence of hERG current;The half-maximal inhibitory concentration(IC50)and safety margin were calculated to assess the risk of torsade de pointe(Tdp).According to hERG safety margin calculation formula=IC50/Cmax,the result less than 30 times is positiveResultsCA4P induced a concentration dependent inhibition of the current amplitude in the hERG tail current.After CA4P(3,10,30,100,300?mol·L-1)was given,the inhibition rates of the tail currents of hERG channel were(9.8±4.8)%,(19.2±5.0)%,(44.3±2.5)%,(77.2±2.9)%and 100%,n=5-8,respectively;CA4P induced a voltage dependent inhibition of the current amplitude in the hERG tail current.The inhibition rates of CA4P(30?mol·L-1)on hERG tail current at 10mV,20mV,30mV,40mV and 50mV were(9.9±8.5)%,(23.7±9.1)%,(27.3±7.5)%,(32.3±9.4)%and(31.8±10.5)%,n=5-8,respectively;The time dependence of CA4P(300?mol·L-1)on blocking hERG current show a decrease gradually trend.After 8min,the tail current of hERG channel could be inhibited completely and recovered after elution;The IC50 was 54.9 ?mol·L-1.The safety margin ratio was 30.5 and 2.8(<30 fold).ConclusionsCA4P can inhibit hERG channel current.According to the safe margin it has a high risk of leading to Tdp,which indicates that in patients receiving CA4P overdose or co-treatment with other QT interval prolonging drugs should be greater concern.