肾上腺素对离体豚鼠左心室流出道组织自律性电活动的影响

　　作者：陈立锋 徐涛 范凌 陈少峰 孙琳　 尹万斌　赵兰平 作者单位：(1.河北北方学院医学院生理教研室，河北 张家口 075000;2.河北北方学院附属第一医院心血管内科，河北 张家口 075000;3. 河北北方学院附属第一医院血液科，河北 张家口 075000;4.河北北方学院医学院临床医学本科2007级2班,河北 张家口 075000;5.河北北方学院医学院解剖教研室，河北 张家口 075000;6.河北北方学院医学院临床医学本科2006级2班，河北 张家口 075000)

　　【摘要】 目的：观察肾上腺素(E)对离体豚鼠左心室流出道组织自发慢反应电位的影响。方法：采用标准玻璃微电极细胞内记录技术，观察E对离体豚鼠左心室流出道组织自发慢反应电位的影响。观测指标有：最大舒张电位(MDP)，动作电位幅度(APA)，0期最大除极速度(Vmax)，4期自动除极速度(VDD)，自发放电频率(RPF)，复极50%和90%时间(APD50、APD90)。结果：用100μmol/L E灌流，豚鼠左心室流出道自律组织动作电位APA明显增大(P<0.01)，Vmax明显增快(P<0.05)，MDP显著增大(P<0.05)，APD90显著缩短(P<0.01);RPF明显增快(P<0.01)，VDD明显加快(P<0.05)。结论：E对左心室流出道组织自律细胞有兴奋作用。

　　【关键词】 肾上腺素;电生理学技术/心脏;豚鼠;左心室流出通;自律细胞

　　As is a clinical cardiac stimulant,the epinephrine(E)has very important function in the cardiovascular system,but the effects on ventricular outflow tract cells havent been deeply reseached. The ventricular outflow tract used to be thought a hemal outflow path.With the development of clinical electrophysiology examination and radio frequency ablation technique in recent years,it was discovered that some arhythmias had relation with the abnormality of structure,appearance and function of ventricular outflow tract. By using standard intracellular microelectrode technique to record Aps,epinephrine was used to investigate the electrophysiological features of left ventricular outflow tract pacemaker cells of Guineapig.The purpose of our study was to observe the electrophysiological effects of epinephrine on pacemaker cells in left ventricular outflow tract,elucidate the mechanism(s)involved,provide electrophysiologic proof for the nosogenesis of some arrhythmias that originated from ventricular outflow tract.

　　1 MATERIALS AND METHODS

　　1.1 Specimen Preparation

　　Guineapig of either sex(weighing 200～350g,provided by Experiment Animal Research Center of Chinese Academy of Medical Sciences). Guineapigs were killed with a single blow on the head and the hearts were quickly removed and placed in warm(36.0±0.5)℃ improved Locke solution(NaCl 0.157mol/L,KCl 0.56×10-2mol/L,CaCl 0.21×10-2mol/L,NaHCO30.18×10-2mol/L and glycose 0.56×10-2mol/L). It was oxygenated with 95%O2 and 5%CO2 and maintained at(36.0±0.5)℃ with pH of 7.40±0.03.The left ventricular outflow tract were cut from the left ventricle and then pinned on a thin silicon disc at the bottom of a perfusion chamber[1,2]. The preparations were perfused(5mL/min)with warm(36.0±0.5)℃ improved Locke solution. It was oxygenated with 95%O2 and 5%CO2 and maintained at(36.0±0.5)℃ with pH of 7.40.

　　1.2 Potential Recording

　　By using standard intracellular microelectrode technique to record Aps,The transmembrane action potentials were recorded by 3mol/L KClfilled glass microelectrode(a tip resistance of 10～20MΩ)coupled to a high input impedence amplifier(made in Chengdu Instrumeny Factory),The amplified signals were fed to a multichannel physiological signal acquisition system(RM6280C,made in Chengdu Instrumeny Factory)and processed by a microcomputer. The parameters of action potentials were automatically analyzed by the microcomputer.

　　1.3 Electrophysiological Parameters

　　MDP(maximal diastolic potential),APA(amplitude of action potential),Vmax(maximal rate of depolarization),VDD(velocity of diastolic depolarization),APD50 and APD90(50% and 90% of duration of action potential)，RPF(rate of pacemaker firing).

　　1.4 Lab Proc and Grouping

　　APs were recored after equilibrium for 10min. After recording 1 control APs,epinephrine(100μmol/L)were applied.APs were then recorded respectively at 0.5,1,2,3,5 and 10min after application of epinephrine.Experiment grouping:(1)control group(n=7);(2)100μmol/L E(n=7).

　　1.5 Statistics

　　All data were presented as means±SEM(x±s).The differences in the parameters between before and after chemical application were analyzed by paired Students t test.Differences between groups were assessed by oneway ANOVA and unpaired t test.Statistical significance was set at P<0.05.

　　2 RESULTS

　　The results obtained were as follows:Compared with the result of the control group,application of 100μmol/L E resulted in a significant increase in APA(P<0.05)，Vmax(P<0.05),and a notable shorteness in APD90(P<0.01).The above mentioned effects maintained an opposite stability after 5～10min of E superfusion,led to a significant increase in MDP(P<0.01),RPF(P<0.01),and VDD(P<0.01). The above mentioned results occurred after 30～60sec of superfusion of E and reached the peak within 5～10min. After washed 25 min,the abovementioned parameters basically recovered normal(Table 1).Table 1 Effects of E on electrophysiological features of left ventricular outflow tract pacemaker cells

　　3 DISCUSSION

　　The sympathetic nerves excitement can cause sinus tachycardia and premature ventricualr contraction,the increasing of myocardial partial catechol amine(CA)density,and also induce sinus tachycardia[3].In recent years,with the development of clinical electrophysiology examination and radio frequency ablation technique,it was discovered clinically that idiopathetic ventricular tachycardia(IVT)who originate from ventricular outflow tract was very common,but the nosogenesis was still hard to explain currently.

　　The norepinephrine(NE)that the heart sympathetic nerve ending releases and the CA in the body fluid can effect on the adrenergic receptor(AR)of myocardial cell membrane,which has positive chronotropic action,positive inotropic action and positive dromotropic action. In the experiment,Application of E resulted in a significant increase in VDD,RPF and APA，a notable shorteness in APD50 and APD90 in the pacemaker cells. These results suggested that epinephrine(E)could excite the pacemaker cells of left ventricular outflow tract.

　　It is well known that AR is divided into 3 types:α1,α2,β,and each has various subtypes.The AR that distributes in the heart mainly were β1  AR and α1AR[4,5]. The CA mainly combines with βAR(More β1 AR)，and effects many kinds of ion current through the Gproteincoupled receptor pathway,which exerts a negative chronotropic action on pacemaker cells in SA nodes:make it easily excitement and amplitude increasing through decreasing level of threshold of inward sodium currents(If);increase VDD through increasing slow inward calcium currents(ICaL and ICaT);increasing the decaying potassium currents(IK)[3].The previous study had demonstrated that the ion currents at phase 4 of the pacemaker cells of left ventricular outflow tract and that of pacemaker cells in sinoatrial(SA)were similar[6],this results indicate that the significant increase in RPF and VDD may be due to the abovementioned factors. The ion current at phase 0 of the pacemaker cells of left ventricular outflow tract and that of pacemaker cells in sinoatrial(SA)also were similar,It is mainly L type slow inward calcium current(IcaL)[2].E increase IcaL,so it makes APA and Vmax enlargement;E shorten APD90 by promoting potassium efflux of repolarization process. The significant increase in MDP of experiment group may be due to the effect that E incite the generating electricity sodium pump[3].

　　In summary,the observation demonstrates that the pacemaker cells of left ventricular outflow tract is relatively sensitive to CA,it easily causes arrhythmia.The results hint that the organization of left ventricular outflow tract may be one of ablation targets when practise radio frequency ablation technique in clinic.

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