大鼠容量超负荷性心肌肥厚时环磷酸腺苷、原癌基因蛋白、微管蛋白的变化及意义

Variation and significance of tubulin, cAMP and c-myc protein in rat cardiac volume-overload hypertrophy

目的 动态观察大鼠容量超负荷性心肌肥厚模型中微管蛋白 (tubulin)的变化以及环磷酸腺苷 (cAMP)、原癌基因蛋白 (c myc蛋白 )对机械信号刺激的应答反应。方法 应用免疫方法、激光共聚焦扫描观察在容量负荷后不同时点大鼠心肌中tubulin、cAMP、c myc蛋白的变化。结果 (1)容量负荷后tubulin光密度及象素分布即刻均低于正常 ,在 6h最为明显 ,在 4d时呈现恢复状况 ,7d、11d、2 0d时微管结构排列呈进行性紊乱趋势 ;(2 )容量负荷后即刻及 4～ 6h ,cAMP明显下降 ,其后逐渐上升 ,1周时超过正常水平 ,2周时下降 ,5月时显著下降 ;4～ 6h ,c myc蛋白表达率最高 ,其后逐渐下降 ,5个月时c myc蛋白表达很低 ;(3)在慢性容量超负荷基础上给予急性容量负荷时cAMP呈现反常反应、c myc蛋白无应答。结论 肥厚心肌存在机械信号跨膜传递障碍。微管结构紊乱可能参与心肌肥厚的形成过程及机械信号的跨膜传递过程。

Objective To investigate the relationship between the function of microtubule and the response of cAMP, and c-myc protein to volume-overload. Methods The pixel intensity and distribution of microtubule image was estimated from laser scanning confocal images of left ventricular cardiocytes immuno-labeled with an antibody to β-tubulin. The content of cAMP was examined by RIA and the expression of c-myc protein was examined by immunohistochemical study. Results The pixel distribution of microtubule image was not even just after the volume-overload, especially at 6 hours, at that time the pixel intensity of microtubule image was decreased (<150) and was the same as the pixel intensity and distribution of the colchicine depolymerized microtubules image (<150). That changes were recovered partly at 4 days (200). The pixel intensity of the control microtubule image was 250 and the distribution of that was even. The structure of microtubule was more disordered along with the development of volume-overload hypertrophy. The content of the cAMP was decreased obviously just after the volume-overload (0.04 pmol/mg) and at 4-6 hours (0 11 pmol/mg), then increased gradually and exceeded the normal content (0 93 pmol/mg) of the rat at 1 week (1 38 pmol/mg), but decreased again at 2 weeks (1 07 pmol/mg) and decreased more obviously at 5 months (aortocaval fistula group versus sham operated group, P < 0 01). The expression of c-myc protein was increased obviously at 4-6 hours (62 73%) than control (45 41%, P < 0 01) after the volume-overload, then decreased gradually along with the development of volume-overload hypertrophy and was decreased extremely at 5 months ( r = -0 514, P < 0 01). Based on chronic volume-overload hypertrophy the content of cAMP had an abnormal response to acute mechanical stress (volume overload), and the expression of c-myc protein had no response. Conclusions There are disorders in the signal transduction pathways in hypertrophic myocardium. Microtubule is one of the members of the signal transduction pathways governing the hypertrophic response of cardiomyocytes.