Study Of Sarcoplasmic Reticulum Ca～(2+) Uptake Function Of Immature Myocardium During Ischemia-reperfusion

There are laboratory evidences of greater tolerance with ischemia and hypoxia in immature heart, but clinical myocardial protection strategies and cardioplegic solution that are effective in adult hearts are less effective in infant or neonatal hearts. Mortality of cardiac surgeries in infant and neonate is higher than that in adult. This is largely due to inadequate cardiac protection. Calcium overload is one of important reasons leading to ischemia/reperfusion injury, but the mechanism of calcium overload in immature heart is not completely clear. During ischemia/reperfusion, the role of sarcoplasmic reticulum (SR) in mature heart is clear, sarcoplasmic reticulum role in immature heart is not reported. To answer the question that is about the role of SR' calcium pump, this experiment is carried outPart I Study of sarcoplasmic reticulum Ca2+ uptake function of immature myocardium during ischemia-reperfusionMethods: Thirty immature rabbits (14 days old), randomly-6-divided into two groups, established Langendoff models. Group I : perfused for 30 minutes with KHBB; group II: perfused for 30 minutes with KHBB, underwent cardioplegic arrest for 60 minutes with St.Thomas' II, followed by 30 minutes of reperfusion. Thirty mature rabbits (4 months old) randomly divided into group III and group IV. Group III underwent the same treatment with group I ; group IV underwent the same treatment with group II. At the time of perfusion 30 minutes group I , III; at the time of perfusion 30 minutes and at the end of the experiment group II, IV, their heart rate (HR), coronary flow (CF) in 1 minute were recorded and the blood gas of KHBB, coronary flow were evaluated and myocardial oxygen consumption ( MvO₂) were figured out. At the end of experiment, 6 hearts were randomly chosen from every group, isolated single cell with collagenase I and evaluated density of intracellular free calcium ([Ca2+]i) with MRC-1024 laser scanning confocal microscope. After SR produced,SR Ca2+桝TPase activity and 45Ca2+ uptake were evaluated.Results: With 30 minutes perfusion, HR of group II is 223.33 ?5.68/min, the recovering rate after ischemia/reperfusion is 93.54 + 9.88%; With 30 minutes perfusion, HR of group IV is 136.83 ?9.52/min, the recovering rate after ischemia/reperfusion is 86.87 ?7.20 %. With 30 minutes perfusion, CF of group II is 6.00?.12mL/min, the recovering rate after ischemia/reperfusion is 88.17 + 6.38%; With 30 minutes perfusion, CF of group IV is 34.42 + 2.75mL/min, the recovering rate after ischemia/reperfusion is 90.55?.66%. There are no significant differences for HR and CF between group Hand group IV-7-(P>0.05)With 30 minutes perfusion, MvO2 of group His 94.40 + 3.86 min^-1穏^-1, after ischemia/reperfusion the recovering rate is 93.42+4.84%. With 30 minutes perfusion, MvCh of group IV is 102.64 + 4.11 ulQzç©–in ^-1穏^-1, after ischemia/reperfusion the recovering rate is 80.84 + 10.11%. The recovering rate of MvC>2 of group II is significant higher than that of group IV(p<0.05).[Ca2+]i of group II is higher than that of group I by 126.39 + 9.42nmol稬-1; [Ca2+]i of group IV is higher than that of group III by 138.54 + 7.32nmol稬-1. There is no significant difference between the increasing amount of mature and immature myocardium (P>0.05).With 30 minutes perfusion, SR Ca2+-ATPase activity of immature myocardium is 43.93 + 1.55 mol pi穏-1穐-1, after ischemia/reperfusion the recovering rate is 82.08 + 1.70 % . With 30 minutes perfusion, SR Ca2+桝TPase activity of mature myocardium is 47.73 ?1.36 mol pi 'g^'h'1, after ischemia/reperfusion the recovering rate is 76.36?.07%. The recovering rate of SR Ca2+-ATPase activity of immature myocardium is significant higher than that of maturemyocardium (.PO.01) .With 30 minutes perfusion, the initial 45Ca2+ uptake of immature myocardium is 32.19 + 2.57 祄ol稬-1, the recovering rate is 84.15 ?.70 %; the maximum 45Ca2+ uptake of immature myocardium is 109.67 + 5.49 nmol稬-1, the recovering rate is 88.56 + 2.33 %. With 30 minutes pe...