模拟失重降低大鼠心肌细胞对异丙肾上腺素的反应性

Depressed responsiveness of cardiomyocytes to isoproterenol in simulated weightlessness rats

本文旨在研究模拟失重对大鼠单个心肌细胞无负荷收缩功能的影响以及对异丙肾上腺素(isoproterenol,ISO)反应性的变化。采用大鼠尾部悬吊法在地面模拟失重状态,4周后以胶原酶Ⅰ消化分离心肌细胞,分别对左、右两心室心肌细胞进行收缩功能测量。结果显示,悬吊4周大鼠(悬吊组)左、右心室心肌细胞的长度和宽度与正常大鼠(对照组)相比均无显著差异。随刺激频率增加,对照组与悬吊组大鼠心肌细胞缩短幅值均逐步增加。在1.0、2.0与4.0 Hz刺激下,对照组大鼠左心室心肌细胞缩短幅值分别为(8.50±1.26)%、(9.00±1.38)%与(9.23±1.83)%,右心室心肌细胞缩短幅值分别为(9.80±2.48)%、(10.03±2.48)%与(10.28±2.27)%:与对照组大鼠相比,在1.0与2.0 Hz刺激下,悬吊组大鼠左心室心肌细胞无负荷缩短幅值分别降低12.2%、10.9%(P<0.05),右心室则分别降低16.5%、16.3%(P<0.05);但是在4.0 Hz刺激下却无显著性改变。与同一频率刺激下的对照组大鼠相比,悬吊组大鼠左、右心室心肌细胞达到缩短峰值的时程(time to peak shortening,TPS)明显缩短(P<0.05);而从缩短峰值至75%舒张的时程(TR_(75))则明显延长(P<0.05)。在各刺激频率下,悬吊组大鼠左、右心室心肌细胞缩短(+dL/dt_(max))与舒张(-dL/dt_(max))速度均未发生明显改变。用1、5、10 nmol/L ISO灌流达稳态水平后,对照组大鼠心肌细胞缩短幅值分别增加了(10.63±0.83)%、(35.06±5.22)%和(71.64±6.83)%;而悬吊组大鼠心肌细胞缩短幅值仅增加(5.75±0.76)%、(23.97±4.50)%和(26.38±8.13)%,均有显著性差异(P<0.05,P<0.01)。用10、50、100 nmol/L forskolin灌流达稳定水平后,对照组大鼠心肌细胞缩短幅值分别增加了(3.04±0.27)%、(9.81±2.66)%、(20.20±3.47)%;而悬吊组大鼠心肌细胞缩短幅值仅增加了(1.42±0.53)%、(3.83±1.71)%、(5.49±4.08)%,均有显著性差异(P<0.05)。以上结果表明,模拟失重4周降低大鼠心肌细胞无负荷缩短幅值以及对ISO的反应性。

The present study aimed to observe the changes of contractile function and responsiveness to isoproterenol （ISO） in tailsuspended rat cardiomyocytes under simulated weightlessness condition. Tail-suspended rat model was used to simulate weightlessness on the ground. Twenty-four male Sprague-Dawley rats were randomly divided into the control and tail-suspended groups. After 4 weeks of suspension, the rats were injected with heparin （100 IU/100 g body weight, i.p.） and anesthetized with pentobarbital sodium （40 mg/kg body weight）. The hearts were removed and the aortas were cannulated rapidly. The cannulated hearts were mounted on a Langendorff perfusion apparatus and perfused with constant flow. The perfusion pressure was monitored. The hearts were digested by 0.08% collagenase I at 37℃. The ventricular tissues were chopped and the single myocytes were dispersed gently by a wide-tipped pipette. The contractile function was measured in the Edge Detector system within 6 h after isolation. The length and width of cardiomyocytes were measured without electric stimulation. Contractile curves of the single cardiomyocytes were recorded at stimulation frequency of 1.0, 2.0 and 4.0 Hz. To observe the responsiveness of cardiomyocytes to ISO, 1, 5 and 10 nmol/L ISO in Kreb＇s solution was perfused at a stimulation frequency of 2.0 Hz. The length and width of the left and right ventricular cardiomyocytes in tail-suspended group had little difference from that in the control group. The unloaded shortening amplitude increased as stimulation frequency elevated in both the control and tail-suspended groups. It was increased by （8.50±1.26）%, （9.00±1.38）%, （9.23±1.83）% in the left ventricular cardiomyocytes, and （9.80±2.48）%, （10.03±2.48）%, （10.28±2.27）% in the right ventricular cardiomyocytes in the control group at stimulation frequency of 1.0, 2.0 and 4.0 Hz. Compared with that in the control group, the unloaded shortening amplitude decreased by 12.2% and 10.9% in the left ventricular cardiomycytes （P〈0.05）, and 16.5% and 16.3% in the right ventricular cardiomyocytes （P〈0.05） at stimulation frequency of 1.0 and 2.0 Hz in tail-suspended group. There was no significant difference in unloaded shortening amplitude at stimulation frequency of 4.0 Hz between the control and tail-suspended groups. Time to peak shortening （TPS） in tail-suspended group significantly reduced in both the left and right ventricular cardiomyocytes （P〈0.05）. Time from peak to 75% relaxation （TR75） in tail-suspended group significantly prolonged in both the left and right ventricular cardiomyocytes （P〈0.05）. No significant differences in shortening and relaxation rate （＋dL/dtmax） were observed between the control and tail-suspended groups. The unloaded shortening amplitude increased by （10.63±0.83）%, （35.06±5.22）% and （71.64±6.83）% in the control cardiomyocytes, but increased by （5.75±0.76）%, （23.97±4.50）% and （26.38±8.13）% in tail-suspended group during perfusion with 1, 5 and 10 nmol/L ISO （P〈0.05, P〈0.01）. The unloaded shortening amplitude increased by （3.04±0.27）%, （9.81±2.66）% and （20.20±3.47）% in the control cardiomyocytes, but increased by （1.42±0.53）%, （3.83±1.71）% and （5.49±4.08）% in tail-suspended group during perfusion with 10, 50 and 100 nmol/L forskolin （P〈0.05）. The results obtained suggest that the unloaded shortening amplitude and responsiveness to ISO decrease in rat cardiomyocytes after 4-week tail-suspension.