| Objective: To investigate the changes of potassium channel of left ventrucularmyocytes in rats after myocardial infarction and the intervention effect of apocynin.Methods:1.90healthy male Sprague Dawley rats weighing230-260g were usedand anesthesiaed by intraperitoneal injection of chloral hydrate(10%). After endotrachealintubation, thoracotomy was performed, myocardial infarction(MI) was produced byligation of anterior descending coronary artery, the sham group underwent the sameprocedure without coronary artery ligation. The rats of MI were assigned randomly tointragastrically receive apocyinin (10mg/kg/d), named MI intervention group or saline,named MI group,24hours after surgery for5weeks. Itraperitoneal anesthesia was doneafter the rats were weighed on the sixth week, and the hearts were taken out after openingchest rapidly, patch clam technique was used to record the potassium currents by isolatingsingle ventricular myocyte cells through Langendoff enzymatic perfusion. Total of32ratssurvived on the sixth week,there was5rats in sham group,6rats in MI group,and6rats inMI intervention group. The other rats were used for genetic expression test, which weremade after weighing left ventricular weigh and taking cardiac muscle tissue ofnon-infarcted area.There were5rats in each group.2. Single ventricular myocytes were isolated through Langendoff enzymaticperfusion. Currents were recorded using whole-cell patch clamp technique for cellcapacitance(Cm) and current densities of transient outward potassium current(Ito),steady-state outward potassium current(Iss), inward rectifier potassium current(Ik1)separately, and then depicted I-V(current density to each clamp voltage) curve for eachcurrent.The activation and inactivation time constant of Itowere measured.3. The expression level of Kv4.2α-subunits encoding Itowere detected with RT-qPCR.Results:1. Left ventricular mass index (LVMI) was (3.19±0.25) mg/g in MIgroup, sham group was (2.61±0.32) mg/g, there was significant difference between thetwo groups(P<0.01). MI intervention group was (2.72±0.22) mg/g, reduced significantlythan MI group(P<0.01), but without significance compared with sham group (P>0.05).Left ventricular weight and body weight were not statistically significant among MI group,sham group and MI intervention group (P>0.05).2. There was significant difference in membrane capacitance of ventricular myocytesbetween sham group[(189.91±26.53)pF(n=12)] and MI group[（248.54±28.13）pF（n=8）](P<0.01); There was significant difference in membrane capacitance ofventricular myocytes between MI intervention group[（203.68±19.33）pF（n=9）] and MIgroup[（248.54±28.13）pF（n=8）](P<0.01), but without significcant difference betweenMI intervention group(P>0.05).3. The current density of Ito(+60mv) was significantly decreased in MI group[(15.55±1.63)pA/pF(n=8)] compared with sham group[(28.26±2.26)pA/pF(n=12)](P<0.01),thedensity in MI intervention group was[(23.72±2.55)pA/pF(n=9)], significantly increasedthan MI group(P<0.01),decreased than sham group(P<0.01).Activation voltage of Itowereall at-30mv in three groups, the activation time constant in three groups separately were:（1.41±0.52）ms,（1.57±0.34）ms and（1.21±0.32）ms, the inactivation time constantseparately were:（17.82±4.33）ms,（20.54±2.95）ms和（19.12±4.58）ms, there were nosignificant difference in activation voltage, activation and inactivation time constant amongthree groups(P>0.05).4. The current densities of Issat+60mv in three groups separately were: Sham groupwas[(8.45±0.68)pA/pF(n=12)], MI group was [(8.38±0.35)pA/pF(n=8)], MI interventiongroup was [(9.05±0.32)pA/pF(n=9)]. There were no statistical significance among threegroups(P>0.05).5. The current densities of Ik1at-120mv in three groups separately were: Sham groupwas[(16.29±1.18)pA/pF(n=12)], MI group was [(16.87±0.65)pA/pF(n=8)], MIintervention group was [(17.34±0.72)pA/pF(n=9)]. There was no significant differenceamong three groups(P>0.05). 6. The expression level of Kv4.2mRNA in sham group was (5.35±0.53) times thanMI group, significantly different between the two groups(P<0.01), it was（1.47±0.14）times than MI intervention group(p＜0.05). The expression levels of Kv4.2mRNA in MIintervention group was (2.82±0.47）times than MI group, there was statistical difference（p＜0.01）.Conclusion:1. The LVMI and membrane capacitance of left ventricular myocytesin non-infarcted area of rats in MI group was significantly higher than that of Sham group,and the above indexes decreased significantly after using apocynin, this indicates that leftventricular myocytes hypertrophy after myocardial infarction can be relieved by supressingNADPH oxidase.2. Itocurrent density in MI group significantly reduced compared with control group,and the I-V curve moved downward, meanwhile, the Kv4.2mRNA expression level of Itodecreased prominently compared with Sham group, this suggests that the decrease of Itodensity results from the decrease of gene expression. while, Ik1and Isscurrent densities arenot influenced.3. Both expression of Kv4.2mRNA and Itocurrent rose notably after being intervenedby apocynin,which proposed that apocynin can lead to Kv4.2mRNA expressionup-regulation by restraining NADPH oxidase, and then Itodensity increased also. |
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