等渗溶液Ca2+浓度改变对去神经主动脉平滑肌生物张力及兴奋性作用研究

目的 研究等渗高Ca2+环境对去神经主动脉平滑肌膜电流的影响,以及不同前负荷状态和Ca2+通道阻滞剂干预下去神经主动脉平滑肌的肌源性自主舒缩变化.方法 平滑肌标本取自昆明小鼠主动脉平滑肌层.标本在松弛状态下被两端固定并浸润于任氏液中,待稳定后于显微镜下将玻璃微电极吸附于平滑肌肌膜并高阻封接,观察生理渗透压环境下的膜电流状态.将任氏液中Ca2+浓度由0.9 mol/L提高至1.2 mol/L,观察渗透压改变后的即刻膜电流变化.增加标本前负荷至1 g,观察前负荷增加后标本在同等渗透压环境下膜电位的改变,并记录此时的标本自主舒缩曲线.结果 平滑肌标本处于松弛状态时,在等渗环境下将Ca2+浓度由0.9 mol/L提高至1.2 mol/L后,膜电流改变幅度由(10.25±1.34)pA增至(24.91±3.27)pA,差异具有统计学意义(P＜0.05);前负荷增加后标本在等渗高Ca2+及低Ca2+环境下的膜电流改变幅度较松弛状态时均有所增加(低Ca2+浓度时(15.33±4.33) pA比(10.25±1.34) pA,高Ca2+浓度时(33.31±7.25) pA比(24.91±3.27) pA),差异均具有统计学意义(均P＜0.05).低Ca2+浓度为0.9 mol/L时,若仅增加前负荷,标本肌源性自主舒缩幅度可增加175％;而Ca2+浓度增至1.2 mol/L时,标本自主舒缩幅度可进一步增长40％.经Ca2+通道阻滞剂(质量浓度为0.5 g/L尼群地平)预处理后,高Ca2+环境下的膜电流及肌源性自主舒缩均明显减弱,结果表明膜电位及自主舒缩均由Ca2+主导.结论 细胞外Ca2+浓度的增加既提高了主动脉平滑肌细胞膜的兴奋性,又使平滑肌产生较明显的自主性舒缩,可在前负荷改变时有效地改善平滑肌组织顺应性.Ca2+通道阻滞剂抑制了Ca2+主导的跨膜电流,降低了肌源性自主舒缩,增加了平滑肌的僵直度,这可能会对改善弹性储器血管的功能产生负面影响.     

不同强度周期性动态力学载荷对微重力下骨质疏松的影响

目的探讨生理性周期动态力学载荷与过载对微重力致骨质疏松的作用及影响,为宇航员长时间外太空活动发生的相关骨科疾病寻找一种简便的预防或治疗方案。方法利用尾吊的方法模拟太空微重力环境,建立小鼠骨质疏松模型。32只C57BL/6J正常小鼠随机分为正常组、尾吊组、生理性载荷组和过载组;尾吊的同时对两施加力学载荷组小鼠左侧胫骨进行周期性动态力学加载。实验4周后对比分析各组小鼠后肢胫骨力学性能、骨小梁微观参数、生化指标以及成骨相关基因表达结果。结果与正常组相比,尾吊组小鼠胫骨松质骨大量流失,胫骨生物力学性能明显降低,骨微观结构严重破坏、成骨活性显著减弱。生理性载荷可使骨力学性能及骨小梁微观结构有明显的改善,成骨活性增强、相关基因表达显著上调(P0.05)。过载也能改善微重力下骨质疏松的状况,但改善效果不明显(P0.05)。结论尾吊可成功模拟微重力环境,复制骨质疏松模型;生理性载荷可有效对抗微重力致骨质疏松的发生与发展;过载也能使得微重力所致骨质疏松有所改善,但是结果与尾吊组相比没有显著性差异。     

Forces and moments delivered by novel,thinner PET-G aligners during labiopalatal bodily movement of a maxillary central incisor: An in vitro study

Objective:To evaluate whether overloading of teeth can be avoided by utilizing aligners with reduced thicknesses of 0.4 mm or 0.3 mm.Materials and Methods:The experimental setup included an acrylic maxillary jaw model with tooth 11 separated and fixed via a 3-D force-moment transducer to a hexapod for experimental movement. Aligners tested were fabricated on duplicate stone models using commercially available polyethylene terephthalate glycol (PET-G) foils with thicknesses between 0.5 and 0.75 mm, and novel 0.4-mm- and 0.3-mm-thick foils. With the test aligner seated, 11 was bodily displaced in a labiopalatal direction in the range of ±0.25 mm while all six force-and-moment components exerted on this tooth were registered.Results:With the thinnest commercially available 0.5-mm aligner, median forces of −7.89 N and 8.37 N were measured for the maximum 0.25-mm movement of 11 in a labial and palatal direction, respectively. In comparison, force values were 35% and 71% lower for the novel aligners with a thickness of 0.4 mm and 0.3 mm, respectively.Conclusions:Novel “leveling” aligners with reduced thickness may reduce overloading of individual teeth during aligner therapy. Due to form instability of 0.3-mm aligners, we suggest a novel sequence of 0.4–0.5–0.75 mm for aligner systems using several foil thicknesses for load graduation within single setup steps. This would combine low stiffness of the initial aligner and relatively constant load increases throughout the treatment.     

The acute structural changes of loaded articular cartilage following meniscectomy or ACL-transection

Objective Meniscectomy and anterior cruciate ligament (ACL) rupture have been identified as precursors of osteoarthrosis (OA) in clinical reviews and animal experiments. In this study, the acute effects of these injuries on articular cartilage matrix deformation, preserved in a loaded state using a cryopreservation technique, were studied by scanning electron microscopy (SEM).Method Whole knee joints from adult White New Zealand rabbits (N=87) were loaded ex vivo, using a simulated quadriceps pull under static and cyclic loading conditions, following medial meniscectomy or transection of the ACL. Specimens were plunge-frozen while under load, or following a recovery period, and prepared for SEM by cryofixation. Using SEM and photographic images, the medial tibial plateau cartilage was assessed both qualitatively and quantitatively.Results After meniscectomy, significantly increased bending and crimping of radial collagen fibers occurred with static loading. Compared to intact knees, the area of tibial cartilage showing an indentation was increased by 80% (P< 0.05), the articular cartilage thickness was significantly more reduced when under load (for high force long duration static loading, intact joints had 53%±3 reduction in cartilage thickness compared to 39%±4 after meniscectomy, P< 0.05), and it took nearly twice as long for the cartilage thickness to recover following loading. These post-meniscectomy differences were either not present or were minimal when the joint was allowed to extend when loaded. ACL-transection slightly increased collagen deformation in the deeper zones, but only with cyclic loading.Conclusion The findings indicate that, with static loading, significantly increased deformation of articular cartilage collagen structure can occur following meniscectomy, but is minimized by joint motion. This increased deformation may be relevant to the etiology and progression of joint degeneration.