Changes in vitamin A status following prolonged immobilization (simulated weightlessness).

A study was conducted to investigate the effects of a simulated weightlessness induced by chronic immobilization on vitamin A status. To simulate the stress condition of weightlessness, rats were suspended for 10 days in a special jacket to which metal chains were attached. Animals received a commercial stock diet. Control rats were pair-fed in reference to the suspended rats. As compared with the control, prolonged immobilization resulted in a decrease in body weight gain and an increase in adrenal weight occurred. In the suspended rats, serum concentrations of retinol and retinol-binding protein (RBP) declined. Hepatic retinyl palmitate content increased, and the hepatic retinol level was decreased. The prolonged immobilization led to significantly reduced retinyl palmitate levels in the testis and lung as well as lowered testicular retinol levels. The results suggest that the stress state induced by prolonged immobilization caused accumulation of hepatic retinyl palmitate, decreasing the serum retinol concentration and retinyl ester content in the extrahepatic tissues.     

两种骨丢失动物模型骨质,甲状旁腺激素和降钙素的变化比较

本文观察了模拟失重１４天、２１天大鼠和卵巢切除（ＯＶＸ）３０天、６０天大鼠第６胸椎（Ｔ６）、第３腰椎（Ｌ３）和股骨干骨量、骨生物力学特性,血ＰＴＨ和ＣＴ变化特点。实验结果显示,悬吊１４天大鼠Ｔ６和Ｌ３矿盐密度显著增加,２１天Ｔ６矿盐密度显著增加,但Ｌ３矿盐密度显著降低。ＯＶＸ大鼠Ｔ６矿盐密度无变化,但Ｌ３矿盐密度显著降低。悬吊１４天、２１天大鼠股骨干近侧１／３段矿盐含量显著降低,ＯＶＸ６０天大鼠股骨干近侧１／３段矿盐含量显著降低。悬吊大鼠骨力学特性降低较ＯＶＸ大鼠严重。悬吊大鼠血ＰＴＨ无变化,但ＣＴ显著增加,ＯＶＸ大鼠ＰＴＨ、ＣＴ显著降低。实验结果提示,模拟失重大鼠有骨矿盐再分布现象发生,ＯＶＸ大鼠无此现象。悬吊模拟失重大鼠骨质量的降低较ＯＶＸ大鼠严重。在两个动物模型中,皮质骨和松质骨均受影响。     

The effects of simulated weightlessness on bone biomechanical and biochemical properties in the maturing rat

Histomorphometric and biomechanical changes in bone resulting from hypogravity (simulated weightlessness) were examined in this study. Using a head-down hindlimb suspension model, three groups of six male rats underwent simulated weightlessness for periods of one, two and three weeks while a fourth recovery group was suspended for two weeks followed by two weeks of normal activity. Biomechanical data were collected during static and dynamic bending and torsion tests on intact femora. Histomorphometric values were determined from midshaft bone cross sections and material properties were obtained using ash and calcium assays. The experimental groups exhibited significantly lower geometric and material properties than the controls, resulting in structural hypotrophy; geometric and material changes contributed equally to the structural changes. Recovery following a return to normal activity was indicated, although full recovery may take longer than the weightlessness period. In the rat, altered maturation and reduced bone strength were the sequelae of weightlessness.     

The effect of chronic food and water restriction on open-field behaviour and serum corticosterone levels in rats

In operant conditioning experiments, two methods are commonly used to motivate laboratory rats to perform designated tasks. The first is restricting food so that rats are forced to lose 20% of body weight within one week, followed by maintenance at 80% of the baseline weight for the remainder of the experiment. The second is restricting access to water to 15 min in each 24 h period. These methods are effective in motivating the animals. There is, however, little information available on the effects on performance in tests of behaviour that are not related to operant conditioning. In addition, it is not clear if these commonly used methods of food and water restriction will lead to physiological stress as indicated by an elevation of serum corticosterone. Male rats were either food-restricted to reduce and maintain their weight at 80% of baseline weight, or were restricted to 15 min access to water every 24 h. Activity in the open field was significantly greater in food-restricted rats than in water-restricted or control rats, but freezing behaviour was similar in all experimental groups. Food-restricted rats had a higher mean serum corticosterone level than water-restricted and control rats 37 days after the start of the experimental period. These data suggested that chronically restricting food and maintenance of body weight at 80% of baseline body weight led to significant behavioural changes and physiological stress. In contrast, water restriction did not lead to changes in behaviour or corticosterone levels. A second experiment was conducted to compare the effects of food restriction to 80% of baseline body weight, as described above, with a less stringent protocol in which test rats were initially reduced to 80% of baseline weight, but were then maintained at 80% of an ad libitum fed control rat's weight. Serum corticosterone levels and adrenal gland weights were measured after the initial week of forced weight loss and after maintenance for 21 days. Forced loss of 20% of body weight in the first week led to significantly increased serum corticosterone levels and adrenal gland weights compared to ad libitum fed controls. Serum corticosterone levels and adrenal gland weights in rats maintained at 80% of their initial body weight for 21 days remained higher than ad libitum fed control rats. However, rats maintained at 80% of an ad libitum fed control rat's weight did not differ from control rats in serum corticosterone levels or adrenal gland weights at the end of the 21-day study period. Adjustment of the feeding regimen in this manner eliminated physiological evidence of chronic stress.     

Energy expenditure and blood flows in thermoregulatory organs during microgravity simulation in rat. Emphasis on the importance of the control group

Rat tail suspension is commonly used to mimic human physiology in space. However, energy metabolism adaptation and related autonomic responses are unknown. To give new insights in energy homeostasis, we determined total energy expenditure (TEE) and blood flow redistribution in thermoregulatory organs during suspension using two control groups of animals widely accepted in the literature: the individually housed (isolated) and restraint rats (horizontally attached to the suspension device). Rats (n=33) were randomly assigned during 14-days to three experimental groups: isolated, suspended, or attached. TEE was assessed by a doubly labeled water method throughout the 14 days, and regional blood flow by radiolabeled microsphere procedure at the end of the protocol. Attachment vs. suspension resulted in a significant decrease in TEE (25%), skin (54%), adrenal (55%) and kidney (42%) blood flows, cardiac index (33%), and plasma corticosterone (50%), whereas total peripheral resistances increased (50%). Isolation vs. attachment triggered an inverse response, of similar amplitude, for all above variables. By comparing isolation and suspension, no overall effect was observed. The striking conclusion of this study is that no clear conclusion can be drawn. The choice of the isolated or attached animals as control profoundly influences the outcome results regarding the effects of simulated weightlessness. Further studies are needed but we favor the attached group as the true control since, from a theoretical point of view, a suspended rat is attached plus suspended. In such conditions, TEE decreases to the same extent in rat and humans during simulated microgravity. When reviewing published experiments, we recommend special attention to the control group used rather than on the effects of suspension as compared to an undefined control.     

Vasopressin, corticosterone levels, and gastric ulcers during food-restriction stress.

Corticosterone levels and ulcers were compared in vasopressin-containing (LE) and vasopressin-deficient (DI) rats under ad lib and food-restricted conditions. In the ad lib situation, DI and LE rats had similar corticosterone levels and no ulcers. After 1 day of food restriction, the corticosterone levels were elevated in DI and LE rats, with a significantly higher level in LE rats. No ulcers were present in either strain. After 2 days of food restriction, the corticosterone levels were similar in DI and LE rats. The level in DI rats was comparable to that of the preceding day, but the level in LE animals dropped significantly from the previous day. Significant ulceration was evident in DI rats, but absent in LE rats. Following 3 days of food restriction, the corticosterone level in LE rats had returned to the ad lib level, whereas, for DI rats, an elevated level was maintained. There were no ulcers in LE rats, but they were present in DI rats. Thus LE and DI rats responded differently to the stress of food restriction. The mechanism underlying the response is most likely related to changes in the hypothalamic-pituitary-adrenocortical axis and its reaction to stress.     

Influences of chemical sympathectomy and simulated weightlessness on male and female rats.

Maximum oxygen consumption (VO2max) has been shown to be reduced after periods of simulated weightlessness. To assess the role of the sympathetic nervous system in these reductions, Sprague-Dawley rats were either chemically sympathectomized (SYMX) or injected with saline (SHAM) and assigned to head-down suspension (HDS), horizontal restraint with the hindlimbs weight bearing (HWB), or cage-control (CC) conditions. VO2max, run time (RT), and mechanical efficiency (ME) were measured before suspension and on days 7 and 14. Male and female SHAM HDS groups exhibited reduced measures of VO2max (12-13%) after 7 and 14 days, and this decrease was attenuated in the SYMX and HWB rats. HDS resulted in a significant reduction in RT (9-15%) in both the male and female rats, and ME was significantly reduced after HDS in male and female SYMX and male SHAM rats (23-33%) but not in the female SHAM rats. Lesser reductions in ME were observed in the HWB rats. HDS and HWB were associated with lower body, fat-free, and fat masses, which were similar in male and female rats as well as for the SHAM and SYMX conditions. In a related HDS experiment with normal rats, plasma norepinephrine and epinephrine were increased by 53 and 42% after 7 days, but only epinephrine returned to baseline after 14 days. It was concluded that chemical sympathectomy and/or a weight-bearing stimulus will attenuate the loss in VO2max associated with simulated weightlessness in rats despite similar changes in body mass and composition. The mechanism(s) remains unclear at this time.     

Changes in myocardial contractility and contractile proteins after four weeks of simulated [correction of simulate] weightlessness in rats

The interaction between the gravitational field, the position of the body, and the functional characteristics of the blood vessels determines the distribution of intravascular volume. In turn, this distribution determines cardiac pump function. One of the most profound circulatory changes that occurs in man during exposure to weightlessness is a cephalad redistribution of fluid caused by the lack of hydrostatic pressure in this microgravitative environment. The cephalad redistribution of fluid results in a loss of blood volume and then induces a decrease in preload. Recently, a decrease in sensitivity of arteriole to catecholamine has reported in rats of simulated weightlessness. This change in arteriole may reduce afterload. As a result, cardiovascular system may be shifted to a hypokinetic state during weightlessness condition for long-term. Echocardiographic data from astronauts during space flight showed an increase in heart rate, a 12 % decrease in stroke volume, and a 16 % decrease in left end diastolic volume. Electron-microscopic studies have shown changes in cardiac morphology in rats after exposure to microgravity for 7-12.5 days. After the COSMOS 2044 flight for 14 days, the light-microscopic studies have shown an atrophy of papillary muscles in rats left cardiac ventricle. It is not clear whether the function of atrophic myocardium is impaired. The data in three aspects as mentioned above suggest that weightlessness or simulated weightlessness may decrease the myocardial function. However, definite changes in cardiac performance have been hard to prove due to many limits. This studies were to answer two questions: Is the myocardial contractility depressed in rats subjected to simulated weightlessness for four weeks? What are the underlying mechanisms of the changing contractility?     

Salt-loading and simulated microgravity on baroreflex responsiveness in rats

Cardiovascular adaptations observed during exposure to microgravity results in impairment of baroreflex activity partially as a result of fluid and electrolyte shifts. The head-down tilt rat model mimics some of the physiological observations that have been made in astronauts. We examined the effects of salt-loading on baroreflex activity after 7 day simulated microgravity (30 degrees tail-suspension) and the subsequent 6 hr post-suspension in Sprague-Dawley (SD) rats, using low salt (0.3% NaCl) and high salt (8% NaCl) diets. In suspended animals on a low salt diet, the baroreflex response curve was shifted to the left, while the heart rate (HR) range and MAP50 values were reduced compared to their parallel tethered, non-suspended controls. For non-suspended animals, salt-loading shifted the curve to the right with a reduced HR range. In salt-loaded, suspended animals, the curve and its parameters resemble those of non-suspended animals on a low salt diet. In summary, these data have demonstrated that a short-term (seven days) simulated weightlessness may elicit cardiovascular deconditioning in rats after release from the simulation manifested as an altered responsiveness in baroreceptor-heart rate reflex and a lowered blood pressure while the rats are tethered and horizontal. Our results also suggest the counteracting effect of salt loading on cardiovascular deconditioning.     

Rats with passive coping strategy have average,but not low social range

Social ranks were determined in rats with different degrees of activity-passivity in coping style. The dominance status of rats was assessed by their behavior during social interaction and during competition for food and water. Coping styles were determined during initial trials of acquisition of active avoidance in a two-way shuttle box. Animals with passive behavior in a shuttle box had average scores of social ranks. Both dominant and subordinate rats displayed significantly more active behavior than subdominant animals. In additional experiment, the rats were caged as a one male-one female pairs. Two weeks later, the social ranks of males were determined during agonistic interactions. Males were caged in triads, and corticosterone levels were assayed in blood samples taken from the tail veins during the first five days. The corticosterone level was significantly higher in subdominants than in dominants. There was no significant difference between the dominants and subordinates in corticosterone levels. The obtained evidence suggests the passive coping in subdominant rats, whereas the dominant and subordinate animals were more "active" under aversive stimulation.     

钙蛋白酶介导模拟失重大鼠心肌肌钙蛋白抑制亚基的降解

本文旨在观察尾部悬吊模拟失重大鼠心肌钙蛋白酶(calpain)与钙蛋白酶抑素(calpastatin)表达的变化,以探讨心肌肌钙蛋白抑制亚基(cardiac troponin I,cTnI)降解的可能机制。采用尾部悬吊模拟失重大鼠模型,Western blotting技术观测心肌calpain-1、calpain-2与calpastatin的表达;PD150606抑制calpain活性,分析cTnI降解程度的变化。结果显示:与同步对照组相比,悬吊2周与4周组大鼠心肌calpastatin表达呈显著性降低(P0.05),calpain-1表达未改变,calpain-2表达略有降低;但是,心肌calpain-1/calpastatin及calpain-2/calpastatin的比值在悬吊2周与4周组明显增高(P0.05,P0.01)。悬吊4周组cTnI降解显著高于对照组(P0.01);然而,用calpain非特异性抑制剂PD150606处理后,对照组及悬吊组cTnI的降解均被显著抑制(P0.01)。这些结果提示模拟失重大鼠心肌calpain活性增高可能增加cTnI的降解。     

Modulation of {beta}-adrenoceptor signaling in the hearts of 4-wk simulated weightlessness rats.

The modulation of beta-adrenoceptor signaling in the hearts of hindlimb unweighting (HU) simulated weightlessness rats has not been reported. In the present study, we adopted the rat tail suspension for 4 wk to simulate weightlessness; then the effects of simulated microgravity on beta-adrenoceptor signaling were studied. Mean arterial blood pressure (ABP), left ventricular pressure (LVP), systolic function (+dP/dtmax), and diastolic function (-dP/dtmax) were monitored in the course of the in vivo experiment. Single rat ventricular myocyte was obtained by the enzymatic dissociation method. Hemodynamics, myocyte contraction, and cAMP production in response to beta-adrenoceptor stimulation with isoproterenol or adenylyl cyclase stimulation with forskolin were measured, and Gs protein was also determined. Compared with the control group, no significant changes were found in heart weight, body weight and ABP, while LVP and +/-dP/dtmax were significantly reduced. The ABP decrease, LVP increase, and +/-dP/dtmax in response to isoproterenol administration were significantly attenuated in the HU group. The effects of isoproterenol on electrically induced single-cell contraction and cAMP production in myocytes of ventricles in the HU rats were significantly attenuated. The biologically active isoform, Gsalpha (45 kDa) in the heart, was unchanged. Both the increased electrically induced contraction and cAMP production in response to forskolin were also significantly attenuated in the simulated weightlessness rats. Above results indicated that impaired function of adenylyl cyclase causes beta-adrenoceptor desensitization, which may be partly responsible for the depression of cardiac function.     

Temporal changes in prolactin and corticosterone response during chronic treatment with d-fenfluramine

In order to elucidate the mechanism of development of tolerance to the anorectic effect during chronic treatment with d-fenfluramine (d-F), we examined the temporal changes induced by d-F in food intake and prolactin (PRL) and corticosterone secretion. Male Sprague-Dawley rats were treated for 14 days with d-F (2.5 mg/kg i.p.) or saline twice daily and were given free access to food and water. Groups of 8 rats were sacrificed 30 min after d-F or saline injection at days 1, 4 and 14 for measurements of serum PRL and corticosterone. Food intake and weight gain were reduced significantly by d-F during the first 2-3 days of treatment but not thereafter. Compared with saline, d-F initially increased PRL (57 +/- 9 vs. 7 +/- 0.7 ng/ml) and corticosterone (42 +/- 2 vs. 14 +/- 3 micrograms/dl) serum concentrations. At 4 days, PRL was still significantly increased (43 +/- 5 vs. 10 +/- 4 ng/ml) but corticosterone returned to basal levels. At 14 days, PRL and corticosterone concentrations in the d-F group were not different from corresponding values in the saline group. To verify whether the loss of corticosterone and PRL responses to d-F was not due to a depletion of hormone stores, direct stimulation of corticosterone with corticotrophin and of PRL with metoclopramide were made at days 4 and 14, respectively. Corticotrophin (0.25 mg/kg i.p.) increased corticosterone concentrations similarly in d-F-treated (45 +/- 8 micrograms/dl) and in saline-treated rats (51 +/- 7 micrograms/dl).(ABSTRACT TRUNCATED AT 250 WORDS)     

Interactions of insulin, corticosterone and prolactin in promoting milk-fat synthesis by mammary explants from pregnant rabbits

1. The rate of fatty acid synthesis by mammary explants from rabbits pregnant for 16 days or from rabbits pseudopregnant for 11 days was stimulated up to 15-fold by culturing for 2-4 days with prolactin. This treatment initiated the predominant synthesis of C(8:0) and C(10:0) fatty acids, which are characteristic of rabbit milk. 2. Inclusion of insulin in the culture medium increased the rate of synthesis of these medium-chain fatty acids. By contrast the inclusion of corticosterone led to the predominant synthesis of long-chain fatty acids. When explants were cultured for 2-4 days with insulin, corticosterone and prolactin, the rate of fatty acid synthesis increased up to 42-fold, but both medium- and long-chain fatty acids were synthesized. 3. These results show that the stimulus to mammary-gland lipogenesis and the initiation of synthesis of medium-chain fatty acids observed between days 16 and 23 of pregnancy in the rabbit can be simulated in vitro by prolactin alone. 4. When mammary explants from rabbits pregnant for 23 days were cultured for 2 days with insulin, corticosterone and prolactin, the rate of fatty acid synthesis increased fivefold, but there was a preferential synthesis of long-chain fatty acids. Culture with prolactin alone had little effect on the rate or pattern of fatty acids synthesized. 5. The results are compared with findings in vivo on the control of lipogenesis in the rabbit mammary gland, and are contrasted with the known effects of hormones in vitro on the mammary gland of the mid-pregnant mouse.     

Daily Changes of Plasma Corticosterone by an 8-h Daytime Feeding Occur Without Body Weight Loss or Severe Food Restriction in the Rat

Different studies have reported that daytime feeding entrains the circadian rhythm of corticosterone secretion in rats. However, it remained unclear whether calorie restriction or daytime feeding access have an effect. The aim of our study is to evaluate the effect of an 8-h daytime feeding access on the circadian rhythm of plasma corticosterone. Eleven adult male Wistar rats were assigned to two different conditions of access to food: ad lib feeding for one week and daytime feeding for the following two weeks. On the 7th, 14th and 21st day, blood samples were collected every 4 h from 08:00 to 04:00. Food intake and body weight were recorded daily. During daytime feeding, rats ingested 88% of the amount of food ingested over 24 h in the ad lib feeding period. However, body weight increased significantly from the first day to the end of experiment. Peak plasma corticosterone was 12 h shifted during daytime feeding period compared to the ad lib condition. This study showed that an 8-h daytime feeding entrained the circadian rhythm of plasma corticosterone without body weight loss or severe food restriction.     

Daily Changes of Plasma Corticosterone by an 8-h Daytime Feeding Occur Without Body Weight Loss or Severe Food Restriction in the Rat

Different studies have reported that daytime feeding entrains the circadian rhythm of corticosterone secretion in rats. However, it remained unclear whether calorie restriction or daytime feeding access have an effect. The aim of our study is to evaluate the effect of an 8-h daytime feeding access on the circadian rhythm of plasma corticosterone. Eleven adult male Wistar rats were assigned to two different conditions of access to food: ad lib feeding for one week and daytime feeding for the following two weeks. On the 7th, 14th and 21st day, blood samples were collected every 4 h from 08:00 to 04:00. Food intake and body weight were recorded daily. During daytime feeding, rats ingested 88% of the amount of food ingested over 24 h in the ad lib feeding period. However, body weight increased significantly from the first day to the end of experiment. Peak plasma corticosterone was 12 h shifted during daytime feeding period compared to the ad lib condition. This study showed that an 8-h daytime feeding entrained the circadian rhythm of plasma corticosterone without body weight loss or severe food restriction.     

Short-term simulated weightlessness enhances response of L-type calcium channel to angiotensin II in cerebral vascular smooth muscle cells in rats

Some studies suggest that the calcium channels and rennin-angiotensin system (RAS) play pivotal roles in the region-specific vascular adaptation due to simulated weightlessness. This study was designed to clarify if angiotensin II (Ang II) was involved in the adaptational change of the L-type calcium channel (Ca(L)) in the cerebral arterial vascular smooth muscle cells (VSMCs) under simulated weightlessness. Tail suspension (SUS) for 3 d was used to simulate immediate early cardiovascular changes to weightlessness. Then VSMCs in cerebral basilar artery were enzymatically isolated using papain, and Ca(L) current (barium instead of calcium as current carrier) in VSMCs was measured by whole-cell patch-clamp techniques. The results showed that 3-day simulated weightlessness significantly increased current density of Ca(L). However, I-V relationships of normalized peak current densities and steady-state activation curves of Ca(L) were not affected by simulated weightlessness. Although Ang II significantly increased current densities of Ca(L) in both SUS and control rats, the increase of Ca(L) current density in SUS rats was much more than that in control rats. These results suggest that 3-day simulated weightlessness induces the adaptational change of Ca(L) in cerebral VSMCs including increased response to Ang II, indicating that Ang II may play an important role in the adaptational change of cerebral arteries under microgravity.     

Altered gravity downregulates aquaporin-1 protein expression in choroid plexus.

Aquaporin-1 (AQP1) is a water channel expressed abundantly at the apical pole of choroidal epithelial cells. The protein expression was quantified by immunocytochemistry and confocal microscopy in adult rats adapted to altered gravity. AQP1 expression was decreased by 64% at the apical pole of choroidal cells in rats dissected 5.5-8 h after a 14-day spaceflight. AQP1 was significantly overexpressed in rats readapted for 2 days to Earth's gravity after an 11-day flight (48% overshoot, when compared with the value measured in control rats). In a ground-based model that simulates some effects of weightlessness and alters choroidal structures and functions, apical AQP1 expression was reduced by 44% in choroid plexus from rats suspended head down for 14 days and by 69% in rats suspended for 28 days. Apical AQP1 was rapidly enhanced in choroid plexus of rats dissected 6 h after a 14-day suspension (57% overshoot, in comparison with control rats) and restored to the control level when rats were dissected 2 days after the end of a 14-day suspension. Decreases in the apical expression of choroidal AQP1 were also noted in rats adapted to hypergravity in the NASA 24-ft centrifuge: AQP1 expression was reduced by 47% and 85% in rats adapted for 14 days to 2 G and 3 G, respectively. AQP1 is downregulated in the apical membrane of choroidal cells in response to altered gravity and is rapidly restored after readaptation to normal gravity. This suggests that water transport, which is partly involved in the choroidal production of cerebrospinal fluid, might be decreased during spaceflight and after chronic hypergravity.     

模拟失重大鼠心肌与血管组织的热应激诱导HSP70表达

为研究模拟失重是否可以引起大鼠心肌与血管组织HSP70的诱导表达发生改变,用尾部悬吊大鼠模型模拟失重,以研究失重对生理的影响,用Northern杂交与Western印迹分析检测4周模拟失重大鼠热应激后并在室温下恢复1h(SUS-H1)或2h(SUS-H2_心肌,血管组织HSP70表达的变化,结果表明,热应激后,各组大鼠心肌组织的HSP72 mRNA表达的均显著增加,但SUS－H2大鼠心肌组织的表达显著低于CON－H2组;各组大鼠心肌组织HSP72表达也均显著增加,但SUS－H1与SUS－H2大鼠的表达与相应对照组相比,则仅呈降低趋势,其底动脉血管组织的HSP72 mRNA与HSP72诱导表达均显著增高,而在股动脉则两者仅呈降低趋势,上述结果提示,模拟失重可导致大鼠心肌发生类似衰老的心肌改变;身体前,后部血管组织HSP70的诱导表达变化可能与血管的分化性适应方向一致。     

模拟失重大鼠肠系膜小动脉平滑肌细胞电压依赖性钙离子通道电流的改变

本工作旨在探讨短、中期模拟失重下人鼠肠系膜小动脉血管平滑肌细胞(vascular smooth muscle cells,VSMCs)电压依赖性钙离子通道(voltage-dependent calcium channels,VDC)功能的改变。以尾部悬吊大鼠模型模拟失重对不同部位血管的影响。采用全细胞膜片钳实验技术,以Ba^2 作为载流子,测定1周及4周模拟失重人鼠肠系膜小动脉VSMCs的VDC电流密度、稳态激活与失活曲线及有关参数,并与对照组结果进行比较。研究表明,本实验所记录到的内向电流主要为钡离子通过长时程VDC(L-VDC)所形成的电流。与对照组相比,1周模拟失重大鼠肠系膜小动脉VSMCs的L-VDc电流密度仪呈降低趋势;但4周模拟失重人鼠肠系膜小动脉VSMCs的L-VDC电流密度则已显著降低。此外,与对照组相比,1、4周模拟失重大鼠肠系膜小动脉VSMCs的膜电容、翻转电位与L-VDC的一些动力学特征值,如通道的开放与关闭速率,通道电流稳态激活与火活曲线及其特征拟合参数V0.5与K的值,均末见有显著改变。结果提示：模拟失重下后身小动脉VSMCs的VDC功能降低可能是模拟失重引起人鼠后身动脉收缩反应性降低及适应性萎缩变化的电生理机制之一。