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

AIM To investigate the circadian rhythm of vasodilation and related-BK_Ca 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 BK_Ca 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, BK_Ca 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 BK_Ca 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 BK_Ca signaling. Our work provides a novel mechanism underlying the circadian dysfunction in small mesenteric arteries when exposed to microgravity.