模拟失重大鼠心肌肌浆网Ca ^（2＋）摄取功能的变化

Change of Ca2+Uptake Function of Cardiac Sarcoplasmic Reticulum in Rat after Simulated Weight-lessness

为研究模拟失重对大鼠心肌肌浆网Ｃａ２＋摄取功能的影响，采用差速离心法制备心肌肌浆网（ＣＳＲ）粗制膜，测定ＣＳＲ囊泡膜各种ＡＴＰ酶活性，并用Ｍｉｌｌｉｐｏｒｅ滤过技术测定ＣＳＲ囊泡的Ｃａ２＋摄取功能。结果表明，４周模拟失重大鼠心肌肌浆网膜Ｃａ２＋，Ｍｇ２＋－ＡＴＰ酶活性不变，Ｃａ２＋－激活ＡＴＰ酶活性却较对照组降低６．８％（Ｐ＜０．０５）。模拟失重组心肌肌浆网囊泡ＡＴＰ依赖性Ｃａ２＋摄取的时间动态曲线较对照组降低１９％～３１％（Ｐ＜０．０５或Ｐ＜０．０１）。在测定的Ｃａ２＋浓度范围内，Ｃａ２＋依赖性Ｃａ２＋摄取速率较对照组减低１９％～３９％（Ｐ＜０．０５或Ｐ＜０．０１）。对照组与模拟失重组的Ｃａ／Ｐ耦联比值分别为０．２２±０．０６与０．２０±０．０９，两值间无显著差别（Ｐ＞０．０５）。结果提示，这可能是模拟失重导致心肌等长收缩发展张力幅值降低与达到张力峰值时间（ＴＰＴ）延长的内在机理之一。

Crude cardiac sarcoplasmic reticulum(CSR ) membrane vesicles were prepared by differen-tial centrifugation. Its ATPase activity and Ca2+uptake function were assayed and examined. Ca2+uptake was determined by a Millipore filter technique with Ca2+ as an isotopic tracer. As compared with the controls,Ca2+,Mg2+-ATPase activity didn’t show any significant change,whereas CSR Ca2+-activated ATPase activity showed a 6.8% decrease (P<0.05) in 4-week tail-suspension.Results concerning changes in CSR Ca2+ uptake during simulated weightlessness showed that, the ini-tial rate of Ca2+ uptake of CSR preparation was decreased by 19.0%(P<0.05),the curve of time course of Ca2+ uptake shifted downwards, and the Ca2+-dependent Ca2+ uptake was decreased by 19～39%(P<0.05 or P<0. 01)as compared with that of the control rats.The apparent coupling ratio of Ca2+ uptake to Ca2+ -ATPase activity didn’t show any significant difference(P>0.05) between the two groups. These results suggest that lowered CSR Ca2+ uptake might be one of the underlying mechanisms leading to reduced developed tension and prolonged time to peak tension in isometric con-traction of papillary muscle from 4-week tail-suspended rats.