| Although there are laboratory evidences for greater tolerance to ischemia and hypoxia in immature hearts, clinical myocardial protection strategies and cardioplegic solutions that are effective in adult hearts have been less effective in immature infant or neonatal hearts. Mortality of cardiac surgeries is higher in infant and neonatal hearts than that in adult hearts .This is largely due to inadequate understanding the mechanism of Ca + overload after ischemia/reperfusion and inadequate cardiac protection measure of immature myocardium. To solve the problems , we carried out the experiment study on the alteration of calcium-release function in immature myocardial sarcoplasmic reticulum after ischemia/reperfusion compared with mature myocardium so that we can explore the mechanism of Ca2+ overload after ischemia/reperfusion in sub-cellular level.The study is as follows.Isolated Langerdorff heart model was established using 32 adult rabbits (1.8-2.2 kg) and 32 immature rabbits (10-14 days) which were randomized into one of four groups by using cardioplegia or not. A: control group of adult rabbits ( n =16); B: I/R group of adult rabbits( n = 16); C: control group of immature rabbits( n=16); D: I/R group of immature rabbits( n = 16 ). Cardiac functions were assessed by alteration of heart rate (HR),coronary flow (CF),and myocardial oxygen consuption (MVO2) after ischemia/reperfusion.. Then 6 hearts were chosen in every group from which single cell was isolatd for evaluating cytosolic Ca2+ concentration by MRc-1024 laser scanning confocal microscope. After the above protocols, the others was removed from the perfusion system and was placed in ice-cold 0.9% NaCl for trimming of large vessels, arium and fat, remaining cardiac muscle was dried with filler paper for assessment of dry weight and then was frozen in liquid nitrogen to store, we minced and homogenized all examples, then the myocardial sarcoplasmic reticulum membranes isolated by discontinuous sucrose centrifugation were used for measuring the protein concentration of the homogenates by the method of Lowry, we measured the SR Ca2+ uptake rate depended on ATP with Milliporefiltration technique and the percent increment SR Ca2± uptake rate by using ruthelium red which block Ryanodine receptor and using low molecular weight heparin which block IP3 receptor in order to compare the Ca2± release function alteration of SR after I/R between adult myocardium and immature myocardium.Results: The alteration of HR, CF and MVO2: HR, CF and MVO2 of group A and group B are as follows: 174.78±15.97 beats/min, 154.22±19.61 beats/min, P<0.05; 32.78±12.24 ml/min, 20.52±10.49 ml/min, P<0.05; MVO2 76.12±26.491/g.min,43.91 ±29.051/g.min, P<0.05.So there are significant differences of MVO2 , HR and CF between group A and group B. The HR, CF and MVO2 of group C and group D are as follows: 211.40±24.30 beats/min, 206.50±25.51 beats/min, P>0.05; 7.41±3.93 ml/min, 6.15 ±2.46 ml/min, P>0.05, MVO2 88.13±46.831/g.min, 80.97± 53.881/g. min, P>0.05.So there are no significant differences of MVO2, HR and CF between group C and group D.The change of [Ca2±]i: after I/R, the [Ca2±]i of mature hearts increased from 158.23±31.25 nmol/L to 286.95±26.55 nmol/L, P< 0.01; after I/R, the [Ca2±]i of immature hearts increased from 140.75±42.36 nmol/L to 263.47±38.61 nmol/L, P<0.01.But there are nodifference of the increments of [Ca ]i between mature hearts and immature hearts after I/R..The alteration of Ca2± release function in cardiac SR: after I/R, There are no significant changes of the percent increment SR Ca2± uptake rate which reflect Ca2± release function in cardiac SR with ruthelium red in either mature hearts (Control group, 35.6±4.1%,I/R group, 39.2±6.2%, P>0.05) or immature hearts ( Control group, 66.6±4.5%, I/R group, 69.8±5.7%, P>0.05) and with heparin which block IP3 receptor in mature hearts ( Control group, 11.2±4.9%, I/R group, 13.7±4.2%, P>0.05) after I/R. There are differences of thepercent increment of...
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