Effect On Electrophysiology Of Fosinopril Late Preconditioning In Ventricular Myocytes During Ischemic/reperfusion Period

Effect on electrophysiology of fosinopril late preconditioning in ventricular myocytes during ischemic/reperfusion period Myocardial ischemic/reperfusin can lead to membrane current abnormal,then make the disorder of electrophysioloy,at last bring about arrhythemic. L-type calcium current and sodium calcium exchange current have been described predominantly in this pathophysiology. Being a protect medium,ischemic preconditioning can relieve myocardial ischemic/reperfusion injury , reduce the morbidity of arrhythemic. Previous research have been showed that angiotensin converting enzyme inhibitor-fosinopril can mimic ischemic preconditioning to produce cardioprotective effect.This research using whole-patch clamp method to study the changes of guinea pig ventricular myocytes L-type calcium current and sodium calcium exchange current during ischemia/ reperfusion period,in order to discuss the electrophysiologic mechanism of fosinopril late preconditioning cardioprotective effect.Adult female guinea pig were randomly assigned into three groups:control(1ml/kg NaCl),ischemic/reperfusion (1ml/kg NaCl), Fosinopril(10 mg/kg).Every drug were injected venous before treatment 24 hours. Single ventricular myocyte was obtained by enzymatic dissociation method. Ischemic solution was treated to ventricular cell for mimic ischemic.After 30 minutes ischemic , myocytes were incubated with shortage solution in order to reperfusion. Only rod-shaped cells with a clear margin and striation were used. Using whole-patch clamp method to record the membrane channel current,the date was input computer and analysis.Analysis of statistics Data were presented as mean±s. The significance of group differences was determined by the Student's t- test.The result display as follow: (1) Recordings of the action potential was performed in parallel using the whole-cell current clamp technique at room temprerature. Under the condition of reperfusion,myocytes resting membrane potential is heighten than control( -84.86±3.80 mV vs–72.00±6.66 mV,P<0.01,n=7) ,and action potential duration (APD50,APD90)is shorten (226.43±9.91 mS vs 207.43±10.21mS, 249.71±9.80 mS vs 222.71±9.23mSrespectively, n=7,P<0.01).Fosinopril preconditioning can alleviate this change(-79.22±7.21 mV, 212.77±17.24mS, 238.32±20.62mS respectively,n=7,P>0.05)。Fosinopril late preconditioning can prolong ventricular cell action potential duration during ischemic/reperfusion,the electrophysiology was stable.(2) L-type Ca2+ current (IcaL )were recorded using the whole-cell voltage clamp technique at room temprerature.The IcaL peak current of ventricular cell is measured as the membrane potential at 0 mV. Result show that IcaL peak current of ischemic/reperfusion myocyte significantly decrease compare to control myocyte(-286.00±21.15pA vs -237.71±17.70pA,p<0.01,n=7),Current-voltage relationships curve shift to upper,but the curve shape is not change.Fosinopril preconditioning can increase the IcaL peak current,has significant difference compare to ischemic/reperfusion myocytes(-265.57±20.20pA vs -237.71±17.70pA ,p<0.05),Current-voltage relationships curve shift to under .(3)Membrane conductance was obtained from function G＝Ipeak／Ere-V. Conductance at each membrane poteneial was notmalized by the maximal conductance to obtain the activation curve.Experimental points were then fitted to a Boltzmann function: G/Gmax＝(1+exp[(V 1/2 – V )/ K])-1, where V1/2 is the membrane potential producing half-maximal activation and k is a slope factor.Result show that curve of ischemic/reperfusion myocyte significant shift to positive membrane potential, V 1/2 was -17.63±1.44mV vs -14.78±1.69mV (p<0.01,n=7),this change means myocytes calcium channel activate is delay.Fosinopril preconditioning can shift curve towards to negative potential, V 1/2 was -17.18±0.95mV vs -14.78±1.69mV(p<0.01,n=7).Compare to control, V 1/2 was not different for -17.63±1.44mV vs -17.18±0.95 mV (p﹥0.05,n=7).The parameter k was not different amon...