| Background : Acute myocardial infarction is one of the common clinical cardiovascular diseases, and serious threat to human health. We can save the ischemic myocardial tissue through reperfusion timely with the application of reperfusion,such as thrombolytic therapy and percutaneous coronary artery stent angioplasty. In most cases, reperfusion can not only reduce tissue injury, but also can cause ischemia reperfusion injury, such as increased infarct size, decreased cardiac function and caused reperfusion cardiac arrhythmia, these reperfusion injuries greatly reduced the benefit of reperfusion therapy. Therefore, we have been committed to finding drugs thatcan prevent reperfusion injury. As the endogenous ligand of angiotensin receptor-like protein J(APJ),Apelin play an important roal in physiological regulation?APJ is a G protein coupled receptor, its structure is very similar to type I receptor(ATl) of angiotensin II(Ang II),but not combine with Ang II. Previous studies showedthat Apelin/APJ system had a certain role in the occurrence and development of hypertension, heart failure, atherosclerosis and other diseases. Recently studies showed that Apelin also had cardioprotective effects in the animal model of myocardial infarction(MI) and ischemia/reperfusion(I/R) injuries,but there are no reports about Apelin on calcium current during myocardial ischemia reperfusion. Objective:1. The current study is aimed to study the effects of Apelin-13 on ischemia reperfusion through establishing Langendorff rates model, and compare with I-post C. 2. To observe the effects of Apelin-13 on L- type calcium channel at the cellular level when simulated ischemia-reperfusion state.Method: 1. Groups in Langendorff rates model :Wistar male rats(260-300g)were randomly divided into 5 groups: normal group(N), Apelin-13 group(A), ischemia reperfusion group(I-R), Apelin-13 + I-R group(A/I-R) and classical ischemia post conditioning group(I-post C). N group: Continued perfusion for 150 min with KH liquidwithout any treatment. A group: Continued perfusion for 150 min with KH liquid containing aqelin-13(500nmol/L) without any other treatment. I-R group:Stable perfusion for 30 min followed by ligating LAD 30 min, then reperfusion for 90 min with KH liquid. A/I-R group: Stable perfusion for 30 min followed by ligating LAD 30 min, then reperfusion with Apelin-13(500nmol/L) for 20 minfollowed by reperfusionwith KH liquid for 70 min. I-post C group: Stable perfusion for 30 min followed by ligating LAD 30 min, then reperfusion for 30 s, ligation for 30 s, and 3 cycles in all before reperfusion with KH liquid for 90 min. Recorded and observed RA, LVDP by 16 physiological recorder and calculated myocardial infarct size. Observe the expression of voltage-gated Ca2+ channel protein with Western Blot. 2. Groups in cellular level: Wistar male rats(260-300g) were scarified by decapitation after anesthesiaed to isolate the hearts. normal group(N), ischemia-reperfusion group(I-R), Apelin-13 + I-R group(A/I-R)(n=8). N group: Continued perfusion with ICa,L electrode liquid,normal membrane currents of the isolated rat ventricular myocytes were recorded by the whole cell patch clamp technique after the intracellular and extracellular fluid were adequate exchanged. I-R group: Continued perfusion with ICa, L electrode liquid for 2min, then exchangednormal liquid with simulated ischemia liquid. Ischemiamembrane currents were recorded by the whole cell patch clamp technique when the liquid exchanged adequately. After 15 min of ischemia, weexchanged simulated ischemia liquid with normal ICa,L electrode liquid or contained Apelin-13, and then recorded the membrane currents which stand for the calcium current of I/R group or A/I-R group. Data for each group were used for statistical analysis, comparing the standard peak currents, membrane potential at 50% maximal activation(V1/2)and offsetting of activation curve(k).Results:1. About the LVDP:Compared with N group, LVDP was significantly increased in Apelin-13 administration group(A group)(P<0.05), but a steady decline was arisen in groups which treated with I-R. The depression was attenuated by Apelin-13 and I-Post C. A/I-R and I-Post C group had no significant difference in LVDP at the same time(P>0.05). 2. About RA score: RA score in A/I-R group was lower than I-R group(P<0.005), A/I-R and I-Post C group had no significant difference in RA score(P>0.005). 3. About myocardial infarct size:Myocardial infarct size in A/I-R was smaller than I-R group(37.45±3.53 VS 54.27± 3.88, P<0.05), A/I-R and I-Post C group had no significant difference in myocardial infarct area(P>0.05). 4. The expression of myocardial voltage-gated Ca2+ channel protein had no significant difference(P>0.05).5. About ICa,L:Compared with N group, the standard peek currents were significantly increased in I-R group and A/I-R group, but the increase was attenuated by Apelin-13. The standard peek currents were increased from 0.93 ± 0. 26 to 1.38 ± 0. 14 after ischemia(P<0.01), and from 0.71 ± 0. 10 to 1.29 ± 0. 15(P<0.01) after reperfusion. Apelin-13 can make the peek currents back to 1. 08 ± 0. 12(P<0.01). Compared with N group, the calcium activation curves were left shift, V1/2 changed from-3.73±5.51to-14.62±3.88(P<0. 01). But Apelin-13 can make the changes back to-9.58±3.28(P<0.05). But the k value(mv)had no significant difference in groups(P>0.05).Conclusions: Apelin-13 can reduce myocardial ischemia reperfusion injury, improve cardiac pump function, reduce the incidence of RA, and decrease infarct area. Apelin-13 can inhibit the activation of ICa,L and attenuate by the increase of ICa,L after I-R. But the expression of?1C subunit had no significant difference in groups. The inhibitory effect of ICa,L by Apelin-13 may be one of the mechanisms of protective role in ischemia reperfusion injury. |
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