变温过程中大鼠心肌等长收缩发展张力呈双相变化

A BIPHASIC RESPONSE APPEARS IN DEVELOPED TENSION OF RAT MYOCARDIUM DURING TEMPERATURE CHANGE

本实验旨在探明变温过程对心肌的影响，以及可能的内在机理。采用阶梯方式降、复温，测定３０℃、２５℃、２０℃、１５℃与１０℃条件下，大鼠乳头肌等长收缩的各参数值的变化。结果表明：在降温过程中，心肌发展张力（ＤＴ）呈双相变化，即从３０℃降温到２５℃，ＤＴ增大，而后ＤＴ逐渐下降；温度降到２０℃时，静息张力（ＲＴ）保持不变，而降至１５℃以后ＲＴ明显上升。乳头肌等长收缩的时间参数如ＴＰＰ、ＴＰＮ、ＴＰＴ、Ｔ１／２Ｒ均随温度的降低而逐渐延长。在复温过程中，与降温过程中相同温度点相比，２０℃、２５℃、３０℃点发展张力明显降低，而１５℃、２０℃、２５℃点静息张力显著增高。这提示在降温过程中，心肌细胞肌钙蛋白Ｃ对Ｃａ２＋敏感性可能呈现双相变化，且低温造成的心肌细胞内游离Ｃａ２＋浓度增高，可能引起心肌细胞损伤。因而，心冷停搏液保护心肌功能的关键环节，应是如何防止在降温过程中心肌细胞内游离Ｃａ２＋浓度一过性增高。

? The purpose of present study was to examine the influence of temperature on myocardial contractility and its underlying mechanism. The parameters of myocardial twitch in left ventricular papillary muscle were measured at 30℃, 25℃, 20℃, 15℃, and 10℃. The developed tension (DT) increased significantly when the temperature of perfusion solution dropped from 30℃ to 25℃ (2.9±0.4g/mm2 at 30℃, 3.4±0.6g/mm2 at 25℃, P<0.01), then progressively decreased from 20℃ to 10℃ (3.3±0.6g/mm2 at 20℃, P>0.05; 1.6±0.3g/mm2 at 15℃, P<0.01; 0.2±0.1g/mm2 at 10℃, P<0.01; as compared with the value at 30℃). The resting tensions (RT) at 15℃ and 10℃ were higher than the value at 30℃ (2.0±0.2g/mm2 at 30℃; 2.4±0.3g/mm2 at 15, P<0.01;2.7±0.2g/mm2 at 10℃ P<0.01). There was a similar changing profile in the DT and RT when the temperature rose from 10℃ to 30℃, but the DTs in the rising phase were lower than the corresponding values in the dropping phase at 20℃, 25℃ or 30℃ points. The time to peak tension and half relaxation of papillary muscle twitch were prolonged with the drop in the temperature of perfusion solution from 30℃ to 10℃. Those results suggest that the sensitivity of troponin C to calcium ion is increased when temperature drops from 30℃ to 25℃, then progressively to 10℃. The low temperature might cause an intracellular Ca2+ increase that might impair the cardiomyocytes.