大鼠心肌素慢病毒RNA干扰载体的构建及其对血管平滑肌细胞分化的影响

目的: 构建大鼠心肌素(myocardin)慢病毒RNA干扰(RNAi)重组质粒,分析该RNAi质粒的干扰效果及其对血管平滑肌细胞(VSMCs)分化的影响。方法: 设计并合成3对针对大鼠myocardin的shRNA片段,退火后将双链oligo-DNA克隆入慢病毒质粒载体pGCSIL- GFP获得重组干扰质粒pGCSIL- GFP-shMyocd。以pEGFP-N1 / X124G表达载体构建含Flag标签的myocardin表达质粒pEGFP-N1- Myocd。将重组干扰质粒和过表达质粒共转染293T细胞,Western blotting分析Flag标签蛋白的表达,筛选出干扰效率最好的干扰质粒并大量扩增。干扰质粒转染大鼠主动脉VSMCs,RT-PCR和Western blotting检测myocardin及分化标志物SM22α的表达。结果: 成功构建大鼠myocardin的慢病毒干扰质粒pGCSIL- GFP-shMyocd和过表达质粒pEGFP-N1-Myocd。上述2种质粒共转染293T细胞后,1号干扰质粒转染组Flag标签蛋白表达下降最显著。将1号质粒进行大包装,获得滴度为1×10¹² TU/L的慢病毒颗粒,该病毒转染VSMCs后,myocardin表达明显下调并伴随分化标志物SM22α表达的显著下降。结论: 成功构建大鼠myocardin慢病毒重组干扰质粒pGCSIL- GFP-shMyocd;抑制基因myocardin表达后伴随VSMCs分化的表达下降,提示myocardin在VSMCs分化过程中的重要性。pGCSIL- GFP-shMyocd重组质粒的成功构建为后续研究特定病理条件下(如动脉粥样硬化)VSMCs表型转变的分子机制奠定了基础。     

Beclin1基因siRNA慢病毒载体构建和鉴定

本研究通过慢病毒载体(pRNAT-U6.2/Lenti)构建靶向Beclin1基因的RNA干扰(RNAi)重组体,用以建立Beclin1基因稳定沉默的非小细胞肺癌(NSCLC)A549细胞株。PCR鉴定结果显示3个扩增的阳性片段均已插入pRNAT-U6.2/Lenti载体;测序结果证明3个重组慢病毒载体pRNAT-U6.2/Lenti-si356、pRNAT-U6.2/Lenti-si423和pRNAT-U6.2/Lenti-si684的插入序列完全正确;重组慢病毒载体感染A549细胞后,RT-PCR和Westernblot检测结果均证实3组重组体感染的细胞内Beclin1mRNA和蛋白表达都受到不同程度的抑制,Beclin1mRNA的沉默效率分别为35.56%、89.22%和66.78%。结果显示成功构建了Beclin1基因的RNAi病毒重组载体,并建立了其稳定表达的NSCLC A549细胞株,为探讨Beclin1基因对NSCLCA549细胞生物学行为的影响提供了新的细胞模型。     

小鼠水通道蛋白1基因shRNA慢病毒载体构建与鉴定

目的 应用RNA干扰技术,构建小鼠水通道蛋白1(AQP1)基因重组慢病毒载体并鉴定.方法 对小鼠AQP1 mRNA分析,设计合成的单链引物经退火形成双链寡核苷酸序列,连接入经Age Ⅰ和EcoR Ⅰ双酶切线性化的pLKO.1-TRC慢病毒质粒载体中,菌液PCR鉴定并经测序验证.测序正确后与慢病毒包装辅助质粒共转染293T细胞,收集病毒上清经高速离心浓缩后感染小鼠小胶质细胞BV-2,Western blot法分析筛选有效shRNA序列.结果 成功退火合成3对发夹shRNA序列并将其克隆到pLKO.1-TRC载体中,构建重组质粒pLKO-AQP1-SH1、2、3,经菌液PCR鉴定和测序验证载体构建成功.Real-time PCR检测发现重组质粒pLKO-AQP1-SH2感染BV-2细胞后AQP1 mRNA表达最低,Western blot结果进一步验证结果的准确性.结论 成功构建出AQP1基因shRNA慢病毒载体.     

SPARC基因RNAi慢病毒载体的构建及其在SKM-1细胞中的表达

目的:构建SPARC基因RNAi慢病毒载体获得稳定产毒的细胞,并观察其对人MDS细胞株SKM-1细胞的转染效率及其对SPARC基因的抑制效率。方法:针对已经筛选确定的SPARC基因RNAi有效靶序列,合成靶序列的OligoDNA,退火形成双链DNA,与经AgeⅠ和EcoRⅠ双酶切后的pGCSIL-GFP载体连接产生GC-shSPARC慢病毒载体,PCR筛选阳性克隆并进行测序鉴定。用GC-shSPARC、pHelper1.0和pHelper 2.0载体共转染包装细胞293T细胞,包装产生慢病毒,以293T细胞GFP蛋白的表达水平测定病毒滴度,并将获得的重组慢病毒GC-shSPARC转染SKM-1细胞,通过荧光显微镜检测转染后GFP表达情况,测定转染效率;RT-PCR和Western blot分别验证转染后SKM-1细胞SPARC mRNA及蛋白的表达。结果:经测序证实,构建出了SPARC shRNA的慢病毒载体GC-sh SPARC。包装、浓缩病毒悬液的滴度为1×109TU/mL。荧光显微镜下能直接观察到转染组细胞的GFP表达,转染效率为70%,RT-PCR、Western blot技术分别检测到GC-shSPARC慢病毒转染SKM-1细胞SPARC mRNA、SPARC蛋白表达水平较空白组明显降低(P<0.05)。结论:成功构建SPARC基因RNAi慢病毒载体,其能高效干扰SKM-1细胞SPARC基因的表达。     

SIRT1基因shRNA慢病毒载体构建及干扰效应检测

背景：SIRT1基因在细胞能量代谢、凋亡及衰老过程中发挥极重要的作用,另有研究发现SIRT1可能在炎症反应方面起着调控作用。 目的：构建SIRT1特异性的shRNA慢病毒载体,并初步检测其对THP-1细胞SIRT1基因的抑制效应。 方法：设计SIRT1靶点特异性的寡核苷酸序列,连接到经Age Ⅰ和EcoR Ⅰ酶切线性化的pGCSIL-GFP载体,包装293T细胞产生慢病毒,再转染THP-1细胞,通过实时荧光定量PCR实验及Western Blot检测对SIRT1靶基因的抑制情况。 结果与结论：阳性克隆PCR及测序证实SIRT1基因shRNA慢病毒载体构建成功,实时荧光定量PCR及Western Blot检测该载体在mRNA和蛋白水平能抑制THP-1细胞的SIRT1表达。     

Slug基因RNAi慢病毒载体的构建与鉴定

目的构建Slug基因RNA干扰(RNA interference,RNAi)慢病毒表达载体。方法针对人Slug基因的序列,设计出RNA干扰的靶序列,合成靶序列Oligo DNA,退火形成双链DNA,通过Age I和EcoR I酶切后的pGCSIL-GFP载体连接产生shRNA慢病毒载体,质粒转化感受态细菌,筛选阳性克隆并用插入鉴定引物进行PCR鉴定阳性克隆并测序,同时应用Real-time PCR和Western blot方法检测HCT116结肠癌细胞中Slug基因mRNA和蛋白的表达情况。结果 PCR鉴定与DNA测序证实合成的含Slug shRNA慢病毒载体寡核苷酸链插入正确。Western blot证实Slug RNAi慢病毒载体能够抑制Slug的表达。结论成功构建Slug基因RNAi慢病毒表达载体,为后续感染结肠癌细胞,为探索在结直肠癌发生和发展中的作用奠定基础。     

Siglec-1小干扰慢病毒载体的构建和干扰效率验证

目的 构建小干扰唾液酸黏附素(sialic acid-binding immunoglobulin-like lectin 1,Siglec-1)的慢病毒载体,并体外筛选出具有干扰效果的病毒载体.方法 利用软件设计3条Siglec-1 siRNA片段,并克隆到慢病毒pGCSIL-GFP质粒载体,再与pHelper 1.0载体和pHelper 2.0载体共转染293T细胞,培养48 h后,收集并浓缩富含慢病毒颗粒的细胞上清液.逐孔稀释法测定慢病毒滴度并转导原代培养的骨髓巨噬细胞(BMM),流式细胞术和实时荧光定量PCR筛选具有干扰效果的病毒载体.结果 成功构建3个vshRNA质粒载体和一个阴性对照质粒载体,并经测序验证序列正确.包装的慢病毒滴度介于1×108 ～ 1×109 TU/ml之间,适合体外转导及体内试验.体外转导BMM筛选出Lv-1能靶向抑制Siglec-1表达.结论 成功构建并筛选出具有体外干扰效果的小干扰Siglec-1慢病毒载体,为体内应用该病毒载体进行基因敲除实验奠定了基础.     

细胞因子信号转导抑制因子1 RNA干扰慢病毒载体的构建与鉴定*☆

背景：以往关于细胞因子信号转导抑制因子1的研究多用脂质体或其他载体转染的技术,但存在效率低和安全性差等问题。 目的：构建细胞因子信号转导抑制因子1 RNA干扰慢病毒载体并进行鉴定。 方法：实验设计3组针对细胞因子信号转导抑制因子1的短发夹RNA序列,应用基因重组技术插入pPll3.7载体,测序正确的重组病毒质粒与包装质粒通过共转染293T细胞,培养48 h后,收集细胞培养上清液,感染A549细胞,western blot检测目的蛋白细胞因子信号转导抑制因子1在靶细胞中的表达。 结果与结论：实验通过对重组载体进行测序分析证实短发夹RNA插入慢病毒载体,慢病毒载体上清成功转染A549细胞后western blot检测结果显示该载体抑制了细胞因子信号转导抑制因子1蛋白在A549细胞有表达。说明实验成功构建了细胞因子信号转导抑制因子1 RNA干扰慢病毒载体。 关键词：细胞因子信号转导抑制因子1;慢病毒载体;RNA干扰;A549细胞;组织构建 doi:10.3969/j.issn.1673-8225.2012.07.030     

Beclin1 基因慢病毒表达载体的构建和鉴定

背景：Beclin1基因是哺乳动物的自噬调控基因。 目的：实验拟构建Beclin1 基因慢病毒过表达载体。 方法：聚合酶链反应扩增目的基因Beclin1 后插入慢病毒表达载体pLenex中,构建重组载体pLenex-Beclin1。使用聚合酶链反应、双酶切和DNA的测序方法对其进行鉴定,并与辅助包装质粒共感染293T细胞。慢病毒颗粒转染非小细胞肺癌A549细胞后,用蛋白质印迹法检测Beclin1 基因的过表达效率。 结果与结论：聚合酶链反应鉴定结果显示扩增的阳性片段已插入pLenex载体,聚合酶链反应、双酶切和DNA测序结果表明,重组慢病毒载体pLenex-Beclin1 的插入序列完全正确,重组慢病毒载体感染A549细胞后,细胞内Beclin1蛋白高效表达。结果证实,实验成功构建了Beclin1 基因慢病毒过表达载体。     

NSBP1基因干扰RNA慢病毒载体的构建及效应检测

目的 构建和鉴定NSBP1基因RNA干扰慢病毒表达载体。 方法 针对NSBP1 mRNA设计了3条siRNA,并构建pGCSIL-GFP-NSBP1慢病毒质粒,测序鉴定。用pGCSIL-GFP-NSBP1 、pHelper1.0和 pHelper2.0质粒共转染293T细胞包装产生慢病毒,测定病毒滴度。将慢病毒转染前列腺癌DU145细胞,Western-blot检测NSBP1表达, MTT法检测细胞生长活性,用转染细胞种植裸鼠成瘤,观察抑瘤效果。结果 PCR和测序证实,成功构建LV-shNSBP1的慢病毒载体,病毒滴度达2×108TU/ml。转染细胞中NSBP1蛋白表达显著降低,且MTT检测细胞生长活性明显减慢,转染细胞在裸鼠体内成瘤率没有影响,但对肿瘤的生长有明显抑制作用。结论 人NSBP1基因RNA干扰慢病毒载体的成功构建,且NSBP1对前列腺癌激素非依赖DU145细胞的生长具有重要作用。     

Expression of cell cycle regulators during smooth muscle cell proliferation after balloon catheter injury of rat artery

Intimal hyperplasia is defined as the abnormal migration and proliferation of vascular smooth muscle cells (VSMCs) with deposition of extracellular matrix. However, the cell cycle regulatory mechanisms of injury-induced VSMC proliferation are largely unknown. To examine the expression kinetics of cell cycle regulatory factors which is known to be worked positively or negatively, we used rat balloon injury model. Marked induction of proliferating cell nuclear antigen (PCNA), G1/S cyclin-dependent kinase (cdk2), and its regulatory subunit (cyclin E) occurred between 1 and 3 days after balloon arterial injury, and this was sustained for up to 7 days and then declined. However, the induction of the negative regulators, p21 and p27, occurred between 3 and 5 days of injury, peaked after 7 and 14 days and was then sustained. VSMC proliferation after balloon catheter injury of the rat iliac artery is associated with coordinated expression of positive (cdk2, cyclin E and PCNA) and negative (p21, p27) regulators. Cell cycle regulators such as cdk2, cyclin E, p21, p27 may be suitable targets for the control of intimal hyperplasia.     

犬阴道上皮细胞和平滑肌细胞可在体外长期稳定培养

背景：体外分离培养获得足够活性良好的种子细胞是构建阴道组织工程的关键。文献报道阴道上皮细胞体外纯化培养和传代较为困难,尤其是体外长期培养犬等大动物的阴道种子细胞尚未见报道。 目的：建立体外稳定培养犬阴道上皮细胞和平滑肌细胞方法。 方法：获取犬小块阴道组织,机械分离阴道黏膜上皮,Dispase酶和胰蛋白酶分步消化收集上皮细胞,接种于无血清角化细胞培养液中培养和传代;机械分离阴道平滑肌组织后采用Ⅱ型胶原酶消化获得平滑肌细胞,在含体积分数10%胎牛血清的DMEM培养液中连续培养传代。动态观察上皮细胞和平滑肌细胞生长增殖情况,分别采用特异性抗体行细胞免疫化学染色鉴定。 结果与结论：原代培养的上皮细胞24-36 h后开始贴壁铺展,四五天后呈对数生长,七八天可达70%融合,为单一的上皮细胞,呈典型铺路石样,未见成纤维细胞混杂。每四五天可传代1次,连续传代六七次,细胞免疫化学染色角蛋白AEl/AE3抗体阳性。平滑肌细胞原代培养24 h后贴壁呈梭形,此后呈对数生长,4 d后融合呈典型的“峰和谷”样,每三四天可传代1次,连续传代七八次,细胞免疫化学染色示α-肌动蛋白染色阳性。结果证实,犬阴道上皮细胞和平滑肌细胞可在体外长期稳定培养,可为体外构建组织工程化阴道提供足够的种子细胞。中国组织工程研究杂志出版内容重点：干细胞;骨髓干细胞;造血干细胞;脂肪干细胞;肿瘤干细胞;胚胎干细胞;脐带脐血干细胞;干细胞诱导;干细胞分化;组织工程全文链接：     

Effects of polyamines on contractility of guinea-pig gastric smooth muscle

This study was designed to investigate the effects of polyamines on mechanical contraction and voltage-dependent calcium current (VDCC) of guinea-pig gastric smooth muscle. Mechanical contraction and calcium channel current I(Ba) were recorded by isometric tension recording and whole-cell patch clamp technique. Spermine, spermidine and putrescine inhibited spontaneous contraction of the gastric smooth muscle in a concentration-dependent manner. Spermine (2 mM) reduced high K+ (50 mM)-induced contraction to 16+/-6.4% of the control (n=9), and significantly inhibited I(Ba) in a reversible manner (p<0.05; IC50=0.8 mM). Pre- and post-treatment of tissue with spermine (2-5 mM, n=10) also inhibited acetylcholine (10 microM)-induced phasic contraction to 5+/-6.4% of the control. Inhibitory effect of spermine on I(Ba) was observed at a wide range of test potentials of current/voltage (I/V) relationship (p<0.05), and steady-state activation of I(Ba) was shifted to the right by spermine (p<0.05). Spermidine and putrescine (1 mM each) also inhibited I(Ba) to 51+/-5.7% and 81+/-5.3% of the control, respectively. And putrescine (1 mM) inhibited I(Ba) at whole tested potentials (p<0.05) without significant change of kinetics (p<0.05). Finally, 5 mM putrescine also inhibited high K+-induced contraction to 53+/-7.1% of the control (n=4). These findings suggest that polyamines inhibit contractions of guinea-pig gastric smooth muscle via inhibition of VDCC.     

人KLK1和EGFP双顺反子重组腺病毒构建及其在血管平滑肌细胞中的表达

目的：构建携EGFP为报告基因和人组织激肽释放酶1(hKLK1)基因双顺反子的重组腺病毒（Ad-hKLK1-IRES-EGFP）,并观察在自发性高血压大鼠（SHR）血管平滑肌细胞（VSMCs）中的表达变化。方法:通过双酶切质粒pBluescritII KS-hKLK1，将hKLK1基因定向克隆至带有IRES-EGFP的腺病毒穿梭质粒pDC316中，构建成重组穿梭质粒 ，将其与腺病毒骨架质粒BHGloxE1，3Cre共转染293A细胞，经包装并获得重组腺病毒，用PCR、酶切及测序方法对其进行鉴定，测定病毒滴度；用重组腺病毒感染VSMCs，用荧光显微镜下观察到的绿色荧光来测定感染率，用RT－PCR和Western blotting法测定hKLK1基因在VSMCs中的表达。结果:PCR、酶切和测序表明携EGFP的重组穿梭质粒pDC316-hKLK1-IRES-EGFP构建正确，并与骨架质粒在293A细胞中成功包装出重组腺病毒Ad-hKLK1-IRES-EGFP，其滴度为4.5×10¹¹/L。重组腺病毒感染VSMCs后，在荧光显微镜下观察到明亮绿色荧光蛋白表达，感染率高达90％以上，可检测到hKLK1基因的mRNA及蛋白表达，并与感染时间(1 d-7 d) 有显著依赖关系，峰值感染复数为100 MOI。结论:成功构建并包装了携EGFP和hKLK1基因的双顺反子重组腺病毒载体系统Ad-hKLK1-IRES-EGFP；感染VSMCs可检测到基因hKLK1和EGFP的独立共同高表达，该系统为一直观、安全、高效的基因转移系统。     

Alterations of excitation-contraction coupling by platelet-derived growth factor in enzymatically isolated and cultured vascular smooth muscle cells

We studied stimulus-specific alterations of the excitation-contraction coupling pathway in freshly isolated contractile and subcultured non-contractile vascular smooth muscle cells. Using the calcium indicator aequorin, we detected physiological increases in cytoplasmic free calcium ([Ca²⁺]_i) in subcultured smooth muscle cells subjected to angiotensin or 33 mM potassium depolarization. These increases were qualitatively identical to those previously measured in intact vascular strips. Platelet-derived growth factor (PDGF) induced a slow, sustained [Ca²⁺]_i increase when applied to the subcultured smooth muscle cells at low picomolar concentrations. Freshly isolated, contractile vascular smooth muscle cells, prepared by a novel technique, exhibited a slow shortening of 20% of resting length in response to PDGF. PDGF also markedly potentiated smooth muscle cell shortening in response to an ED₅₀ dose of phenylephrine. This effect was PDGF concentration dependent. The time course of shortening induced by PDGF alone was consistent with the time course of the PDGF-induced [Ca²⁺]_i increase in the cultured smooth muscle cells. These data suggest that agonists which induce [Ca²⁺]_i changes in contractile smooth muscle cells may retain this ability with respect to cultured smooth muscle cells. PDGF, a peptide mitogen for proliferative smooth muscle cells, may also serve to modulate vascular tone by modestly raising [Ca²⁺]_i in contractile smooth muscle cell and, therefore, sensitizing the cells to alpha adrenergic agonists.     

血管紧张素转换酶抑制剂抑制血管平滑肌细胞增殖的机制

目的: 探讨血管紧张素转换酶抑制剂(ACEI)抑制动脉平滑肌细胞增殖及向内膜迁徙的机理。方法: 球囊导管损伤Wistar大鼠颈总动脉, 实验组于术前2 d开始给与ACEI(temocapril-HCl 10 mg·kg^-1·d^-1), 术后2 d、3 d、5 d分批处死。用抗人PDGF-A、-B及其受体, 抗人MMP-1、MMP-9等抗体以ABC法行免疫染色。动脉组织行放射自显影乳剂原位酶谱分析。电镜下观察细胞质内小器官及细胞周围弹性、胶原纤维的密度。结果: 给ACEI后, PDGF及其受体、MMP-1、-9蛋白阳性细胞率及明胶酶活性显著降低, 并抑制了中膜平滑肌细胞的表型转换。结论: ACEI可能通过继发地抑制PDGFs、MMPs蛋白表达, 阻碍细胞表型转换, 从而阻止中膜平滑肌细胞增殖及向内膜迁徙。     

改良植块贴壁法建立大鼠主动脉平滑肌细胞体外培养模型

目的：建立大鼠主动脉平滑肌细胞体外培养模型。 方法： 参照传统的主动脉平滑肌细胞培养方法，在动物体重、中膜的取材、植块贴壁过程、培养基选择、细胞传代等多个关键环节进行改进，成功建立了大鼠主动脉平滑肌细胞体外培养模型；用倒置相差显微镜对培养细胞进行形态学观察，用特异性α-SM-actin单克隆抗体免疫组织化学对培养细胞进行鉴定。 结果： 台盼蓝检查传代细胞的存活率大于96%；培养细胞排列呈梭形及“峰”“谷”状的结构特征；免疫组织化学染色鉴定培养细胞中的平滑肌细胞的纯度为97%。 结论： 此培养方法可作为研究血管平滑肌细胞生物学行为和移植血管再狭窄机制的有效模型。     

Induction of endothelin-1 expression by oxidative stress in vascular smooth muscle cells

Atherosclerosis is based on endothelial dysfunction leading to impaired vasomotor function. This is partially due to nitric oxide (NO) depletion caused by oxidative stress. Since the vasoconstrictor endothelin-1 (ET-1) might also be involved in endothelial dysfunction, we investigated whether oxidative stress regulates ET-1 expression in vascular smooth muscle cells (VSMC). Human aortic VSMC were treated with H₂O₂ (200 μM) for up to 8 h. mRNA expression of preproendothelin (prepro-ET) was analyzed by RT-PCR. ET-1 protein and the marker for oxidative stress, 8-isoprostane, were determined by ELISA. Activity of cytosolic phospholipase A2 (cPLA₂) as an indicator of ET-1 autocrine activity was measured photometrically. Stimulation of VSMC with H₂O₂ resulted in increased expression of prepro-ET mRNA after 1 h with a maximum after 6 h (fourfold), similar to treatment with angiotensin II. ET-1 protein was significantly increased by H₂O₂ treatment with a maximum after 8 h (P<.05). This effect was inhibited by the antioxidants resveratrol (100 μM) and quercetin (50 μM). In quiesced VSMC, incubation with H₂O₂-conditioned medium resulted in increased cPLA₂ activity compared to the controls (P<.05). This activity was partially inhibited by the ET_A-receptor antagonist, PD 142893 (10 μM), indicating functional ET-1 in the conditioned medium. The presence of oxidative stress in H₂O₂-treated VSMC was associated by significantly increased formation of 8-isoprostane (P<.05). The data indicate for the first time that oxidative stress increases ET-1 generation and autocrine ET-1 activity in VSMC, a mechanism that might contribute to endothelial dysfunction in atherosclerosis.     

腺病毒介导的反义AT1R转染对血管平滑肌细胞迁移的影响

目的:观察腺病毒介导的反义AT1基因转染对培养的大鼠动脉平滑肌细胞(VSMCs)迁移的影响。方法:用定向克隆和同源重组方法构建携带人反义AT1基因的复制缺陷型重组腺病毒(AdCMV/ahAT1),转染体外培养的VSMCs,用RT-PCR半定量法和免疫组化法检测AT1R的表达,用改良趋化小室法检测细胞迁移。结果:与对照组相比转染AdCMV/ahAT1后48h的VSMCs,AT1RmRNA表达少50%,AT1R的蛋白表达也显著低下(P＜0.01);迁移距离为(41.7±9.7)μm,显著短于空白对照组(77.5±12.7)μm和Ad/CMV.LacZ组(77.2±10.6)μm,均为P＜0.01。结论:腺病毒介导的反义hAT1R转染,通过抑制AT1R的表达,明显抑制了大鼠VSMCs的迁移。     

Dynamics of length-force relations in airway smooth muscle

We tested the plasticity hypothesis that isometric force could optimize to similar levels, independent of muscle length after repeated contractions in bovine airway smooth muscle. In constant length experiments in which muscle lengths were held constant, we found that total force remained significantly length-dependent during repeated contractions, and changed by tenfold between 40 and 100% optimal length (L(o)). Passive force contributed to < 10% of total force. In sequential length experiments, total force increased by fourfold between 38 and 75% L(o), but changed insignificantly between 75 and 100% L(o), suggesting limited force plasticity near L(o). Force became attenuated after each length change, but remained length-dependent during redevelopment. Changing length from L(o) to 150% L(o) induced proportional decrease in active force and increase in passive force, with insignificant change in total force. Furthermore, post-stretch force redeveloped at L(o) was substantially attenuated, resulting in the shifting of the length-total force relation toward longer length. The observed complex dynamics of length-force relations could explain the complex lung mechanics in vivo.