模拟失重可通过BKCa信号调控大鼠肠系膜小动脉血管功能的昼夜节律变化

Simulated microgravity decreased diurnal oscillation in vasodilation of rat mesenteric small arteries by altering circadian regulation of BKCa signaling

目的探讨模拟失重对大鼠肠系膜小动脉舒张功能昼夜节律的影响以及血管舒张调控分子大电导钙激活钾离子(BKCa)信号的时间节律特征。方法采用1周尾部悬吊大鼠模型,检测大鼠肠系膜小动脉的舒张功能,继而在一天24 h内不同的6个授时因子时间点(Zeitgeber time,ZT)(ZT 0、4、8、12、16和20)以膜片钳电生理学方法记录BKCa通道的全细胞电流,以Western blot分析和RT-PCR检测BKCa通道α亚基的蛋白和mRNA表达水平。结果对照组大鼠肠系膜小动脉的舒张功能表现为白天升高(ZT4,中午12:00)、夜晚(ZT16,凌晨12:00)降低的趋势;而悬吊组大鼠后肠系膜小动脉舒张功能在白天与夜晚均显著下降(P<0.05),且其昼夜波动幅度明显降低(P<0.05)。对照组大鼠肠系膜小动脉血管平滑肌细胞BKCa通道电流密度、亚基的蛋白与mRNA表达水平均呈现"昼高夜低"的节律特征;而悬吊组可显著降低BKCa通道在白天与夜晚的电流密度、亚基的蛋白与mRNA表达水平,而且其通道活性和蛋白表达的昼夜波动幅度也显著降低(均P<0.05),但mRNA表达水平的昼夜波动幅度没有明显变化,提示存在转录后修饰调控。结论模拟失重可通过BKCa信号调控大鼠肠系膜小动脉血管的昼夜节律变化,深入研究BKCa通道昼夜节律特征,对揭示航天飞行后心血管功能失调和血管疾病的发生机制均有深远的意义。

AIM To investigate the circadian rhythm of vasodilation and related-BKCa channel in mesenteric small arteries of simulated microgravity rats. METHODS Sprague-Dawley rats were subjected to 7-day hindlimb unweighting to simulate the effects of microgravity on vasculature. The dilation of mesenteric small arteries was estimated by investigating vascular relaxation. The circadian regulation of BKCa channel(the primary determinant of vascular dilation) was determined by recording whole-cell currents and evaluating protein and mRNA expressions at six different time points(ZT 0, 4, 8, 12, 16 and 20). RESULTS Simulated microgravity significantly decreased the diurnal oscillation in vascular dilation of rat mesenteric small arteries(P<0.05). In addition, BKCa activities, expressions of protein and mRNA levels exhibited a circadian regulation responsible for vasodilation in rat mesenteric small arteries. However, simulated microgravity decreased the diurnal oscillation in BKCa activities(P<0.05) and protein expression levels(P<0.05), but not mRNA expression levels, which suggested a posttranscriptional regulation. CONCLUSION Simulated microgravity decreases the diurnal oscillation in vasodilation of rat mesenteric small arteries by altering the circadian regulation of BKCa signaling. The present investigation provides a novel mechanism underlying circadian dysfunction in small mesenteric arteries when exposed to microgravity.