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1.
The role of troponin-I (the inhibitory subunit of troponin) in the regulation by Ca2+ of skeletal muscle contraction was investigated with resonance energy transfer and photo cross-linking techniques. The effect of Ca2+ on the proximity of troponin-I to actin in reconstituted rabbit skeletal thin filaments was determined. The distance between the cysteine residue at position 133 (Cys133) of troponin-I and Cys374 of actin increases by approximately 15 angstroms on binding of Ca2+ to troponin-C. Also, troponin-I labeled at Cys133 with benzophenone-4-maleimide could be photo cross-linked to actin in the absence of Ca2+, but not in its presence. These results suggest that troponin-I is attached to actin in the Ca2(+)-free or relaxed state of muscle, and that it detaches from actin on Ca2+ activation of contraction. Thus, troponin-I may function as a Ca2(+)-dependent molecular switch in regulation of skeletal muscle contraction.  相似文献   

2.
According to Starling's law of the heart, the force of contraction during the ejection of blood is a function of the end-diastolic volume. To seek the molecular explanation of this effect, a study was made of the effects of length on Ca2+ sensitivity during tension development by isolated demembranated cardiac muscle in which the cardiac form of troponin C was substituted with skeletal troponin C. The results of troponin C exchange were compared at sarcomere lengths of 1.9 and 2.4 micrometers. Enhancement of the myocardial performance at the stretched length was greatly suppressed with the skeletal troponin C compared with the cardiac troponin C. Thus the troponin C subunit of the troponin complex that regulates the activation of actin filaments has intrinsic molecular properties that influence the length-induced autoregulation of myocardial performance and may be a basis for Starling's law of the heart.  相似文献   

3.
Voltage-independent calcium release in heart muscle   总被引：21，自引：0，他引：21  
The Ca2+ that activates contraction in heart muscle is regulated as in skeletal muscle by processes that depend on voltage and intracellular Ca2+ and involve a positive feedback system. How the initial electrical signal is amplified in heart muscle has remained controversial, however. Analogous protein structures from skeletal muscle and heart muscle have been identified physiologically and sequenced; these include the Ca2+ channel of the sarcolemma and the Ca2+ release channel of the sarcoplasmic reticulum. Although the parallels found in cardiac and skeletal muscles have provoked valuable experiments in both tissues, separation of the effects of voltage and intracellular Ca2+ on sarcoplasmic reticulum Ca2+ release in heart muscle has been imperfect. With the use of caged Ca2+ and flash photolysis in voltage-clamped heart myocytes, effects of membrane potential in heart muscle cells on Ca2+ release from intracellular stores have been studied. Unlike the response in skeletal muscle, voltage across the sarcolemma of heart muscle does not affect the release of Ca2+ from the sarcoplasmic reticulum, suggesting that other regulatory processes are needed to control Ca2(+)-induced Ca2+ release.  相似文献   

4.
The three-dimensional structure of favin, the glucose- and mannose-binding lectin of Vicia faba (vetch, broad bean), has been determined at a resolution of 2.8 angstroms by molecular replacement. The crystals contain specifically bound glucose and provide the first high-resolution view of specific saccharide binding in a leguminous lectin. The structure is similar to those of concanavalin A (Con A) and green pea lectin; differences from Con A show that minimal changes are needed to accommodate the cyclic permutation in amino acid sequence between the two molecules. The molecule is an ellipsoidal dimer dominated by extensive beta structures. Each protomer contains binding sites for two divalent metal ions (Mn2+ and Ca2+) and a specific saccharide. Glucose is bound by favin in a cleft in the molecular surface and has noncovalent contacts primarily with two peptide loops, one of which contains several metal ion ligands. The specific carbohydrate-binding site is similar to that of Con A in location and general peptide folding, despite several differences in specific amino acid residues.  相似文献   

5.
The mechanisms underlying the ontogeny of voltage-gated ion channels in muscle are unknown. Whether expression of voltage-gated channels is dependent on mitogen withdrawal and growth arrest, as is generally true for the induction of muscle-specific gene products, was investigated in the BC3H1 muscle cell line by patch-clamp techniques. Differentiated BC3H1 myocytes expressed functional Ca2+ and Na+ channels that correspond to those found in T tubules of skeletal muscle. However, Ca2+ and Na+ channels were first detected after about 5 days of mitogen withdrawal. In order to test whether cellular oncogenes, as surrogates for exogenous growth factors, could prevent the expression of ion channels whose induction was contingent on mitogen withdrawal, BC3H1 cells were modified by stable transfection with oncogene expression vectors. Expression vectors containing v-erbB, or c-myc under the control of the SV40 promoter, delayed but did not prevent the appearance of functional Ca2+ and Na+ channels. In contrast, transfection with a Val12 c-H-ras vector, or cotransfection of c-myc together with v-erbB, suppressed the formation of functional Ca2+ and Na+ channels for greater than or equal to 4 weeks. Potassium channels were affected neither by mitogenic medium nor by transfected oncogenes. Thus, the selective effects of certain oncogenes on ion channel induction corresponded to the suppressive effects of mitogenic medium.  相似文献   

6.
Elevated free Ca2+ concentrations found in adult dystrophic muscle fibers result in enhanced protein degradation. Since the difference in concentrations may reflect differences in entry, Ca2+ leak channels in cultures of normal and Duchenne human myotubes, and normal and mdx murine myotubes, have been identified and characterized. The open probability of leak channels is markedly increased in dystrophic myotubes. Other channel properties, such as mean open times, single channel conductance, ion selectivity, and behavior in the presence of pharmacological agents, were similar among myotube types. Compared to the Ca2+ concentrations in normal human and normal mouse myotubes, intracellular resting free Ca2+ concentrations ([Ca2+]i) in myotubes of Duchenne and mdx origin were significantly higher at a time when dystrophin is first expressed in normal tissue. Taken together, these findings suggest that the increased open probability of Ca2+ leak channels contributes to the elevated free intracellular Ca2+ concentration in Duchenne human and mdx mouse myotubes.  相似文献   

7.
A new superconductor that displays onset behavior near 120 K has been identified as Bi(2)Sr(3-x)Ca(x)Cu(2)O(8+y), with x ranging from about 0.4 to 0.9. Single crystal x-ray diffraction data were used to determine a pseudo-tetragonal structure based on an A-centered orthorhombic subcell with a = 5.399 A, b= 5.414A, and c = 30.904 A. The structure contains copper-oxygen sheets as in La(2)CuO(4) and YBa(2)Cu(3)O(7), but the copper-oxygen chains present in YBa(2)Cu(3)O(7) do not occur in Bi(2)Sr(3-x)Ca(x)Cu(2)O(8+y). The structure is made up of alternating double copper-oxygen sheets and double bismuth-oxygen sheets. There are Ca(2+) and Sr(2+) cations between the adjacent Cu-O sheets; Sr(2+) cations are also found between the Cu-O and Bi-O sheets. Electron microscopy studies show an incommensurate superstructure along the a axis that can be approximated by an increase of a factor of 5 over the subcell dimension. This superstructure is also observed by x-ray diffraction on single crystals, but twinning can make it appear that the superstructure is along both a and b axes. Flux exclusion begins in our samples at about 116 K and is very strong by 95 K. Electrical measurements on a single crystal of Bi(2)Sr(3-x)Ca(x)Cu(2)O(8+y) show a resistivity drop at about 116 K and apparent zero resistivity at 91 K.  相似文献   

8.
The purpose of this research was to study the effect of hypoxia on the Ca^2＋ concentration in broiler＇s cardiac muscle cells （CMCs）. The concentration of Ca^2＋ in the CMC was observed using a laser scanning confocal microscope （LSCM）. The results showed that hypoxia could significantly increase intracellular Ca^2＋（normal oxygen, 99.3 ＋_ 13.1; hypoxia, 129.4 ＋_ 24.3, P 〈 0.01） in CMCs. The Ca^2＋ antagonist （nifedipine, verapamil） could significantly restrain the Ca^2＋ influx across the cell membrane of CMC treated by hypoxia （CMC： hypoxia ＋ verapamil, 100.9± 28.2; hypoxia ＋ nifedipine, 107.6± 27.7; P 〈 0.01）. The results showed hypoxia could increase intracellular Ca^2＋ concentration of CMC, and the Ca^2＋ antagonist could restrain the Ca^2＋ influx across the cell membrane of CMC treated by hypoxia.  相似文献   

9.
【目的】分析粘性卵翘嘴鲌与漂浮性卵翘嘴鲌肌肉品质差异,为翘嘴鲌营养品质鉴定及其养殖提供参考依据。【方法】依据相关标准分别对2种翘嘴鲌肌肉基本营养成分、氨基酸、脂肪酸、质构特性和矿物元素含量进行测定,并评价其营养价值。【结果】粘性卵翘嘴鲌肌肉的灰分含量（1.16 g/100 g）显著低于漂浮性卵翘嘴鲌（1.26 g/100 g）（P<0.05,下同）,而2种翘嘴鲌的水分、粗蛋白和粗脂肪含量无显著差异（P>0.05,下同）。2种翘嘴鲌肌肉中均检测出17种氨基酸,其中粘性卵翘嘴鲌的谷氨酸（Glu）、精氨酸（Arg）含量及鲜味氨基酸总量（∑DAA）显著低于漂浮性卵翘嘴鲌,必需氨基酸指数（EAAI）低于漂浮性卵翘嘴鲌;2种翘嘴鲌的第一限制性氨基酸均为蛋氨酸+胱氨酸（Met+Cys）,第二限制性氨基酸均为缬氨酸（Val）。粘性卵翘嘴鲌肌肉中检测出15种脂肪酸,漂浮性卵翘嘴鲌肌肉中检测出17种脂肪酸,其中粘性卵翘嘴鲌的二十碳一烯酸（C20:1）相对含量（0.85%）显著高于漂浮性卵翘嘴鲌（0.61%）,而α-亚麻酸（C18:3）的相对含量（1.93%）显著低于漂浮性卵翘嘴鲌（2.62%）。质构特性方面,粘性卵翘嘴鲌肌肉硬度、弹性和咀嚼性低于漂浮性卵翘嘴鲌,但回复性高于漂浮性卵翘嘴鲌;粘性卵翘嘴鲌肌纤维长径和短径大于漂浮性卵翘嘴鲌。2种翘嘴鲌肌肉矿物元素含量丰富,粘性卵翘嘴鲌肌肉中硒含量（0.06mg/kg）显著低于漂浮性卵翘嘴鲌（0.11mg/kg）,钙、镁、锌和铁含量在2种翘嘴鲌间无显著差异。【结论】粘性卵和漂浮性卵翘嘴鲌肌肉中氨基酸和脂肪酸含量丰富,具有高蛋白的特点,但漂浮性卵翘嘴鲌肌肉营养价值更高,口感更好。  相似文献   

10.
扶桑绵粉蚧钙调蛋白基因的克隆与生物信息学分析   总被引：1，自引：0，他引：1  
钙调蛋白(calmodulin,CaM)对生物体内多种Ca2+依赖的细胞功能和酶体系都有重要的调节作用。为研究扶桑绵粉蚧的信号转导受体蛋白,首次克隆了扶桑绵粉蚧钙调蛋白基因PsCaM的cDNA全长序列,其开放阅读框(ORF)包含447bp的片段,编码148个氨基酸。PsCaM基因由3个内含子和4个外显子组成。3个内含子的长度分别为73、81、72bp,分隔的4个外显子的长度分别为33、133、183、98bp。功能域分析结果显示:该蛋白具有2个EF-hand结构域,有13个Ca2+结合位点;该蛋白的理论等电点是6.21,属于稳定蛋白,且没有跨膜区域;通过同源建模获得了其蛋白的三维结构。多序列比较显示,PsCaM基因相对较保守。  相似文献   

11.
Free calcium at rest during "catch" in single smooth muscle cells   总被引：2，自引：0，他引：2  
Tension and intracellular free calcium concentration [( Ca2+]i) were measured simultaneously in single smooth muscle cells isolated from the anterior byssus retractor muscle (ABRM) of Mytilus edulis that were loaded with the fluorescent Ca2+ indicator fura-2. Electrical stimulation evoked a transient elevation of [Ca2+]i associated with a "catch" contraction. During the catch state, however, [Ca2+]i was effectively at its resting level and was unaffected by 5-hydroxytryptamine, which induced a rapid relaxation from catch. The results indicate that a maintained high [Ca2+]i is not required for the maintenance of catch tension in intact ABRM and that there was no significant change in [Ca2+]i upon abolition of catch.  相似文献   

12.
Calcium ion (Ca2+) influx through voltage-gated Ca2+ channels is important for the regulation of vascular tone. Activation of L-type Ca2+ channels initiates muscle contraction; however, the role of T-type Ca2+ channels (T-channels) is not clear. We show that mice deficient in the alpha1H T-type Ca2+ channel (alpha(1)3.2-null) have constitutively constricted coronary arterioles and focal myocardial fibrosis. Coronary arteries isolated from alpha(1)3.2-null arteries showed normal contractile responses, but reduced relaxation in response to acetylcholine and nitroprusside. Furthermore, acute blockade of T-channels with Ni2+ prevented relaxation of wild-type coronary arteries. Thus, Ca2+ influx through alpha1H T-type Ca2+ channels is essential for normal relaxation of coronary arteries.  相似文献   

13.
Calcium-induced calcium release (CICR) may function widely in calcium-mediated cell signaling, but has been most thoroughly characterized in muscle cells. In a homogenate of sea urchin eggs, which display transients in the intracellular free calcium concentration ([Ca2+]i) during fertilization and anaphase, addition of Ca2+ triggered CICR. Ca2+ release was also induced by the CICR modulators ryanodine and caffeine. Responses to both Ca2+ and CICR modulators (but not Ca2+ release mediated by inositol 1,4,5-trisphosphate) were inhibited by procaine and ruthenium red, inhibitors of CICR. Intact eggs also displayed transients of [Ca2+]i when microinjected with ryanodine. Cyclic ADP-ribose, a metabolite with potent Ca(2+)-releasing properties, appears to act by way of the CICR mechanism and may thus be an endogenous modulator of CICR. A CICR mechanism is present in these nonmuscle cells as is assumed in various models of intracellular Ca2+ wave propagation.  相似文献   

14.
Confocal laser-scanned microscopy and long-wavelength calcium (Ca2+) indicators were combined to monitor both sustained and rapidly dissipating Ca2+ gradients in voltage-clamped sympathetic neurons isolated from the bullfrog. After a brief activation of voltage-dependent Ca2+ channels, Ca2+ spreads inwardly, and reaches the center of these spherical cells in about 300 milliseconds. Although the Ca2+ redistribution in the bulk of the cytosol could be accounted for with a radial diffusion model, local nonlinearities, suggesting either nonuniform Ca2+ entry or spatial buffering, could be seen. After electrical stimulation, Ca2+ signals in the nucleus were consistently larger and decayed more slowly than those in the cytosol. A similar behavior was observed when release of intracellular Ca2+ was induced by caffeine, suggesting that in both cases large responses originate from Ca2+ release sites near or within the nucleus. These results are consistent with an amplification mechanism involving Ca2(+)-induced Ca2+ release, which could be relevant to activity-dependent, Ca2(+)-regulated nuclear events.  相似文献   

15.
采用RT-PCR技术克隆了凡纳滨对虾肌钙蛋白Ⅰ基因全长编码序列,对其核苷酸序列和编码的氨基酸序列进行了生物信息学分析,并在对虾肌钙蛋白Ⅰ基因的编码区查找了单核苷酸多态性位点。结果显示：本研究克隆获得了凡纳滨对虾肌钙蛋白Ⅰ基因的4个可变剪切体,其编码的蛋白质均具有Troponin超家族结构域特征,同源性比对发现该蛋白的氨基酸序列在节肢动物中高度保守。系统进化分析发现凡纳滨对虾Tn-Ⅰ3和Tn-Ⅰ4与中国对虾和小龙虾的Tn-Ⅰ遗传距离较近,而Tn-Ⅰ1和Tn-Ⅰ2单独聚为一支,且与其他物种Tn-Ⅰ遗传距离较远;通过测序比较不同个体凡纳滨对虾Tn-Ⅰ基因序列发现在Tn-Ⅰ的4种不同剪切体编码区共同序列区第302位和472位碱基分别存在2个（A/G） SNP位点,其中位于第302位碱基的（A/G）错义突变使编码氨基酸由甘氨酸变为了谷氨酸（G/E）。凡纳滨对虾Tn-Ⅰ基因不同剪切体及编码区错义突变的发现为进一步探讨其基因功能奠定了基础。  相似文献   

16.
 为研究日粮不同能量和蛋白质水平对乌金猪肌肉组织能量代谢的影响,试验选取体重约15kg的乌金猪108头,随机分为6组,下设３个重复,每个重复６头,在15～30,＞30～60,＞60～100kg体重阶段分别饲喂不同能量和蛋白质水平日粮,能量水平为：高消化能（HE,1422MJ/kg）、中消化能 (ME,1289MJ/kg)和低消化能 (LE,1174MJ/kg),蛋白水平为：高蛋白质 (HP,18％,16％,14％）、中蛋白质（MP,16％,14％,12％）和低蛋白质（LP,14％,12％和10％）,在体重30,60,100kg体重时分批屠宰,取血液、肝脏及肌肉组织样品,测定血糖、肝糖原、肌糖原和肌肉中乳酸的含量及肌肉中乳酸脱氢酶、钠钾ATP酶（Na+K+ATP酶）和钙镁ATP酶（Ca2+Mg2+ATP酶）的活性。结果表明,乌金猪血糖、肝糖原、肌糖原和肌肉中乳酸的含量及肌肉中乳酸脱氢酶、Na+K+ ATP酶和Ca2+Mg2+ATP酶的活性随日粮能量和蛋白质水平的升高而升高;在60kg体重时,高能量和高蛋白质日粮组乌金猪上述各项指标均明显升高（P<0.05）,在100kg体重时,高能量和高蛋白质日粮组乌金猪血糖、肝糖原和肌糖原的含量及Na+K+ATP酶和Ca2+Mg2+ATP酶的活性明显高于低能量和低蛋白质组（P<0.05）。本次试验结果表明高能量和高蛋白质日粮（HE,1422MJ/kg和HP,18％）可促进乌金猪肝糖原和肌糖原的合成,肌肉组织中糖酵解途径供能增加,能量代谢加强。研究结果对阐明日粮不同营养水平对猪肌肉组织能量代谢的影响机制具有重要科学意义。  相似文献   

17.
A cloned complementary DNA derived from a messenger RNA transiently present at low abundance levels in early chick embryonic skeletal muscle hybridizes to a messenger RNA present at high abundance levels in cardiac muscle. Genomic DNA hybridization and nucleotide sequence identity of complementary DNA's from both heart and skeletal muscle demonstrate that the messenger RNA's from both sources are encoded by the same gene. The encoded polypeptide is a troponin T sequence which is probably a cardiac isoform. This single copy troponin T isogene is governed by different regulatory programs in heart and skeletal muscle differentiation.  相似文献   

18.
A wide variety of nonexcitable cells generate repetitive transient increases in cytosolic calcium ion concentration ([Ca2+]i) when stimulated with agonists that engage the phosphoinositide signalling pathway. Current theories regarding the mechanisms of oscillation disagree on whether Ca2+ inhibits or stimulates its own release from internal stores and whether inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DG) also undergo oscillations linked to the Ca2+ spikes. In this study, Ca2+ was found to stimulate its own release in REF52 fibroblasts primed by mitogens plus depolarization. However, unlike Ca2+ release in muscle and nerve cells, this amplification was insensitive to caffeine or ryanodine and required hormone receptor occupancy and functional IP3 receptors. Oscillations in [Ca2+]i were accompanied by oscillations in IP3 concentration but did not require functional protein kinase C. Therefore, the dominant feedback mechanism in this cell type appears to be Ca2+ stimulation of phospholipase C once this enzyme has been activated by hormone receptors.  相似文献   

19.
Spatially resolved measurements of intracellular free calcium and of the changes produced by excitatory amino acids were made in neurons isolated from adult mammalian brain. Extremely long-lasting (minutes) Ca2+ gradients were induced in the apical dendrites of hippocampal CA1 neurons after brief (1 to 3 seconds), local application of either glutamate or N-methyl-D-aspartate (NMDA). These gradients reflect the continuous flux of Ca2+ into the dendrite. The sustained gradients, but not the immediate transient response to the agonists, were prevented by prior treatment with the protein kinase C inhibitor sphingosine. Expression of the long-lasting Ca2+ gradients generally required a priming or conditioning stimulus with the excitatory agonist. The findings demonstrate a coupling between NMDA receptor activation and long-lasting intracellular Ca2+ elevation that could contribute to certain use-dependent modifications of synaptic responses in hippocampal CA1 neurons.  相似文献   

20.
傅维  孙勇民  王芃 《安徽农业科学》2012,40(3):1476-1478
[目的]测定黑米发芽过程中色素及氨基酸含量的变化。[方法]选取大小一致的黑米粒,采用Ca2+和去离子水进行前处理,在不同温度条件下进行发芽,测定不同发芽温度及前处理方法对黑米芽长的影响,考察黑米色素及氨基酸在发芽过程中的变化规律。[结果]黑米发芽过程中,黑米长芽的趋势,温度较高的要比温度较低的好;采用Ca2+进行前处理的要比用去离子水进行前处理的更为显著。黑米色素提取液色价值与温度的高低呈正相关;提取批次和样品脱脂与否对提取液色价值也有较大影响。整个发芽过程中黑米的氨基酸和必需氨基酸含量有所增加,但不同发芽时期内有差异。[结论]发芽前后,黑米中氨基酸含量升高,黑米的色素色价值也呈上升趋势。  相似文献   

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