| Background and objective: Sphincter of Oddi ( S0)is the structure of muscle which has refined division of labor. Under the action of hormone and nerves, SO and gallbladder could contract and relax coordinately, through these movements SO could maintain the hydraulic pressure of biliary tract and regulate biliary and pancreatic flow. Sphincter of Oddi dysfunction (SOD) may be one of the causes in inducing biliary tract and other disorders. There are many literatures about the influence of cholesterol on gallbladder motility, however, few data were reported about the effect of cholesterol on Oddi's sphincter muscles.In this study, rabbits fed with hypercholesterol diet, cells culture,transmissional electron microscope and laser scan confocal microscope were performed to investigate the effect of hypercholesterolemia on ultrastructure, Ca2+ transport and Character of calcium sparks of Oddi's sphincter muscle cells in rabbits, in order to exploring the relationship between the mechanisms of Oddi's sphincter dysfunction and the regulation of Ca2+.Methods: 32 New Zealand rabbits were equally divided into two groups randomly and fed for 8 weeks: control group (n=16) and experimental group (ri=16) , normal diet and cholesterol. Then, Sphincter of Oddi's muscle cells dissociated from both the treated and control rabbits were slided using normal methods to observe by transmissional electron microscope, and primarily cultured respectively, loaded with Fluo-3/AM. By using Laser scanning confocal microscopy, changes in intracellular Ca2+ concentration and character of calcium sparks were measured under the resting state and the action of MgSO4 (3.6mmol ?L"1) . Results:1 Disorder of the cellular skeleton, uneven in distribution and reduction in amount of dense body > dense patch, loosening and disarrangement of myofilament, swelling of mitochondria and dilation of endoplasmic reticulum, a few of smooth muscle cells in synthetic phenotype and myofibroblasts were observed in some myocyte of experimental group under electron microscope.2 Comparing with the control group, the intensity of the intracellular Ca2+ fluorescence was significantly increased at resting state in the experimental group [control vs. experimental: (13.56+1.22) vs (21.07?.82), P<0.05]. When treated with MgSO4 (3.6 mmol -L-1), the rate of descent [(0.87 + 0.14) -s'1vs (1.38?.22) ?*,? <0.05] and amplitude of descent[(23.59+1.22) % vs (50.77 + 2.56) %, P<0.05] in intracellular Ca2+ fluorescence were decreasedcomparing with the control group. Moreover, the lowest value of intracellular Ca2+ was higher in the experimental group than in the control group [(16.81 ± 0.05) vs (6.40 ± 0.16), P <0.05]. On the other hand, recovery rate of intracellular Ca2+ concentration was slower in the experimental group than inthe control [(0.01±0.00) s"1 vs. (0.41 ?.04) s-1, P<0.05]. Character ofcalcium sparks: At. resting state, comparing with the frequency(1.24 ± 0.03 s-1 cell-1), amplitude(3.9+0.32), duration(260ms) of calcium sparks in the control group, the frequency( 1.28 ±0.02 s"1 cell-1), amplitude (3.820.26), duration(260ms) of calcium sparks in the experimental group were not significant difference(/>>0.05); When treated with MgSO.4, the frequency of calcium sparks were slower in the experimental group( 1.39 ?.02 s-1 cell-1) than in the control( 1.61 ± 0.02 s-1 cell-1). The amplitude(0.41 ± 0.26), duration(260ms) of calcium sparks in the experimental group were similar to the amplitude(0.40± 0.21), duration(260ms) of calcium sparks in the control group (p>0.05). Conclusions:1 Hypercholesterolemia affected the ultrastructure of Oddi's sphincter in rabbits by damaging the structure and function of plasma membrane, changing the configuration and quantity of cellular skeleton, which may be induce SO dysfunction.2 Hypercholesterolemia caused disorder of transport of Ca2+, unbalance of homeostasis and overloading of [Ca2+]i in muscle cells of SO, which was related to SOD.3 In the c...
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