Submitted on November 8, 2006
Accepted on February 19, 2007
Differential regulation of CaL in cerebral and mesenteric arteries after 3- and 28-d simulated microgravity in rats and its intervention by 1 h/d standing
Jun-Hui Xue1, Li-Fan Zhang1*, Jin Ma2, and Man-Jiang Xie2
1 Department of Aerospace Physiology, Fourth Military Medical University, Xi'an, Shaanxi, China
2 Xi'an, Shaanxi, China; Department of Aerospace Physiology, Fourth Military Medical University, Xi'an, Shaanxi, China
* To whom correspondence should be addressed. E-mail: zhanglf{at}fmmu.edu.cn.
This study was designed to clarify whether simulated microgravity can induce differential changes in the current and protein expression of L-type calcium channel (CaL) in cerebral and mesenteric arteries and whether these changes can be prevented by daily short- duration -Gx gravity exposure. Tail-suspension (HU) for 3 and 28 days was used to simulate short- and medium-term microgravity-induced deconditioning effects. Daily standing (STD) for 1 h was used to provide -Gx gravitation as a countermeasure. Whole-cell patch-clamp experiments revealed an increase in current density of CaL of the vascular smooth muscle cells (VSMCs) isolated from cerebral arteries of rats subjected to HU, but a decrease was found in the VSMCs from mesenteric arteries. Western blot analysis revealed a significant increase and decrease of CaL channel protein expression in cerebral and small mesenteric arterial VSMCs respectively only after a 28-d HU. Daily 1-h STD did not prevent the increase of CaL current density in cerebral arterial VSMCs, but it prevented completely (within 3 days) and partially (28 days) the decrease of CaL current density in small mesenteric arterial VSMCs. Consistent with the changes in CaL current, 1-h/d STD did not prevent the increase of CaL expression in cerebrovascular myocytes, but it prevented the reduction of CaL expression in mesenteric arterial VSMCs that would occur due to a 28-d HU alone. These data indicate that simulated microgravity up- and down-regulates the current and expression of CaL in cerebral and hindquarter VSMCs respectively. The intervention of 1h/d-STD showed differential effects in counteracting the changes of CaL function and expression in cerebral and hindquarter arterial VSMCs of HU rats, suggesting the complexity of the underlying mechanisms of the effectiveness of intermittent artificial gravity in the prevention of postflight cardiovascular deconditioning which needs further clarification.
