Irreversible Structural Alterations Research Articles

Minimizing the Ion/Electron Pathway through Ultra-Thin Conformal Holey Graphene Encapsulation on Li- and Mn-Rich Layered Oxide Cathode for High-Performance Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are increasingly favored due to their attractive features. The design of the cathode in LIBs plays a critical role in determining cell capacity, operating voltage, and overall cost. Lithium- and manganese-rich (LMR) cathode materials stand out as promising candidates for the next generation of cathode materials due to their ability to operate at high voltages and provide capacity exceeding 250 mAh g-1. However, despite these appealing characteristics, LMR faces challenges in commercialization due to factors such as poor rate capability and rapid capacity and voltage decay during cycling. These are closely associated with the fundamental structural issues arising from the two distinct phases of LMR materials, slow reaction kinetics, and structural degradation occurring through side reactions between the electrode and electrolyte. In this study, we introduce a carbon encapsulation technique that integrates polyethylenimine (PEI) and holey graphene onto the LMR surface, aiming not only to augment electrical conductivity but also to facilitate ionic conductivity. Despite its low carbon content of 0.1 wt%, the suggested PEI/holey graphene-encapsulated LMR demonstrates enhanced cycle stability and rate performance for the LMR electrode. Moreover, the thin and uniform PEI/holey graphene encapsulation layer serves a dual purpose by easing the movement of Li+/e- on the LMR surface and providing a protective barrier against physical and chemical aggressions. Throughout cycling assessments, the PEI/holey graphene-encapsulated LMR mitigates the leaching of transition metals, mitigating microcrack formation and irreversible structural alterations compared to bare LMR. Consequently, the proposed PEI/holey graphene encapsulation emerges as an attractive technology for high-performance LIB design, concurrently elevating the cycle stability and rate performance of LMR electrodes.

Fecal microbiome extract downregulates the expression of key proteins at the interface between airway remodelling and lung cancer pathogenesis in vitro

Lung cancer (LC) is the leading cause of cancer-related mortality, and it is caused by many factors including cigarette smoking. Despite numerous treatment strategies for LC, its five-year survival is still poor (<20 %), attributable to treatment resistance and lack of early diagnosis and intervention. Importantly, LC incidence is higher in patients affected by chronic respiratory diseases (CRDs) such as asthma and chronic obstructive pulmonary disorder (COPD), and LC shares with other CRDs common pathophysiological features including chronic inflammation, oxidative stress, cellular senescence, and airway remodelling. Remodelling is a complex process resulting from the aberrant activation of tissue repair secondary to chronic inflammation, oxidative stress, and tissue damage observed in the airways of CRD patients, and it is characterized by irreversible airway structural and functional alterations, concomitantly with tissue fibrosis, epithelial-to-mesenchymal transition (EMT), excessive collagen deposition, and thickening of the basement membrane. Many processes involved in remodelling, particularly EMT, are also fundamental for LC pathogenesis, highlighting a potential connection between CRDs and LC. This provides rationale for the development of novel treatment strategies aimed at targeting components of the remodelling pathways. In this study, we tested the in vitro therapeutic activity of rat fecal microbiome extract (FME) on A549 human lung adenocarcinoma cells. We show that treatment with FME significantly downregulates the expression of six proteins whose function is at the forefront between airway remodelling and LC development: Snail, SPARC, MUC-1, Osteopontin, MMP-2, and HIF-1α. The results of this study, if confirmed by further investigations, provide proof-of-concept for a novel approach in the treatment of LC, focused on tackling the airway remodelling mechanisms underlying the increased susceptibility to develop LC observed in CRD patients.

Exploring the anti-inflammatory and anti-fibrotic activity of NFκB decoy oligodeoxynucleotide-loaded spermine-functionalized acetalated nanoparticles

Chronic inflammation, oxidative stress, and airway remodelling represent the principal pathophysiological features of chronic respiratory disorders. Inflammation stimuli like lipopolysaccharide (LPS) activate macrophages and dendritic cells, with concomitant M1 polarization and release of pro-inflammatory cytokines. Chronic inflammation and oxidative stress lead to airway remodelling causing irreversible functional and structural alterations of the lungs. Airway remodelling is multifactorial, however, the hormone transforming growth factor-β (TGF-β) is one of the main contributors to fibrotic changes. The signalling pathways mediating inflammation and remodelling rely both on the transcription factor nuclear factor-κB (NFκB), underlying the potential of NFκB inhibition as a therapeutic strategy for chronic respiratory disorders. In this study, we encapsulated an NFκB-inhibiting decoy oligodeoxynucleotide (ODN) in spermine-functionalized acetalated dextran (SpAcDex) nanoparticles and tested the in vitro anti-inflammatory and anti-remodelling activity of this formulation. We show that NF-κB ODN nanoparticles counteract inflammation by reversing LPS-induced expression of the activation marker CD40 in myeloid cells and counteracts remodelling features by reversing the TGF-β-induced expression of collagen I and α-smooth muscle actin in human dermal fibroblast. In summary, our study highlights the great potential of inhibiting NFκB via decoy ODN as a therapeutic strategy tackling multiple pathophysiological features underlying chronic respiratory conditions.

Chronic Child Malnutrition in Ecuador and Associated Risk Factors

Chronic child malnutrition worldwide is responsible for 45% of deaths in children under 5 years of age. In Ecuador, 27.2% of children suffer from any type of malnutrition. This problem has alarming consequences since it affects the country's productivity and has an impact throughout the individual's life, since at this stage the greatest impact is suffered by the child's brain, in which irreversible metabolic and structural alterations occur. However, child malnutrition is not only a problem of lack of food, it is a deeper social conflict that must be considered when providing solutions. A nationally representative sample of children under 5 years of age from the National Health and Nutrition Survey 2018 (ENSANUT) was used. A binary logistic linear regression model was used where Odds Ratio (OR) with their 95% confidence intervals (95% CI) were estimated for each of the independent variables. Our results reveal that family income reduces the probability of child malnutrition by 2.03 times. In addition, micronutrient intake during 6 months to 2 years of age reduces the probability of child malnutrition by 2.32 times (OR= -1.91 ; -3.02). This result is statistically significant (p&lt;0.05). On the other hand, unemployment, being out of the labor force (in the mother) having a greater number of children at home, working more hours and being a migrant mother also positively predicts the probability of suffering from chronic child malnutrition. Malnutrition is one of the main health problems in Ecuador. It affects a significant percentage of the population and, associated with other factors, is responsible for most of the avoidable mortality and considerable damage to children's health. For this reason, strategies should include epidemiological surveillance, promotion.

Topology of anisotropic glasses from persistent homology analysis

Glasses are typically isotropic, but permanent or transient anisotropy can be induced by tensile strain. We use persistent homology (PH) analysis to explore the topological effects of such anisotropy in SiO2Na2O glass ensembles with variable alkali concentration as a function of frozen-in anisotropic strain. Statistical information was extracted on ring (H1) and cavity (H2) features, whereby anisotropic stretching was found to induce strong variations in the ring topology of the –O-Si-O- backbone, but only minor changes in the overall cavity statistics or in the Na distribution (the Na distribution was found to be governed by H2 persistence). Tensile fracture led to total recovery of network topology relative to the pristine (isotropic) glass. In revealing such reactions, PH and persistence similarity analysis may help to differentiate purely entropic orientation and irreversible structural alterations leading to glass anisotropy.

Subjective memory complaints, white matter hyperintensities, and cognitive decline in a population‐based cohort study

AbstractBackgroundSubjective memory complaints (SMCs) are associated with a faster cognitive decline and dementia; whether this relationship results from irreversible structural brain alterations, such as white matter hyperintensities (WMH), requires investigation. We aimed to determine the association of SMCs with WMH and cognitive decline and investigate the role of WMH on the relationship between SMCs and cognitive decline.MethodWe studied 917 participants (63% African Americans and 60% women) from the population‐based Chicago Health and Aging Project (CHAP), who responded to questions about SMCs, underwent magnetic resonance imaging of the brain, and had valid cognitive data on two or more visits during the follow‐up period. SMCs were obtained by self‐report questionnaire, and based on frequency and severity of concerns, we categorized participants into three groups: not concerned, moderately concerned, and very concerned.ResultOf 917 participants eligible for the study, 158 (17.2%) had no SMCs concerns, 671 (73.2%) had moderate concerns, and 88 (9.6%) were very concerned. SMCs were associated with larger WMH volumes and faster cognitive decline. Compared to participants with no concerns, those very concerned had 0.833 (95%CI 0.203, 1.463) units higher WMH volumes and 174% faster cognitive decline (‐0.049; 95%CI ‐0.076, ‐0.022). The association between SMCs and cognitive decline was statistically significant only among individuals with large WMH volumes; that is, very concerned individuals with large WMH volumes had 428% faster cognitive decline annually (‐0.077; 95%CI ‐0.144, ‐0.011) than participants with no concerns. In participants with low volumes of WMH, SMCs were not associated with a faster cognitive decline (P‐value = 0.595).ConclusionOur study suggests that SMCs, frequently reported by the elderly, are an important sign of cognitive impairment, especially in people with brain atrophies, such as large WMH volumes.

Commercial soft contact lenses engineered with zwitterionic silver nanoparticles for effectively treating microbial keratitis

The introduction of various drugs onto commercial soft contact lenses (CLs) has emerged as a potentially effective strategy for treating microbial keratitis (MK) because drug-loaded CLs can maintain a controlled drug concentration which leaded to enhanced drug bioavailability and reduced side effects in ocular tissues. In this study, silver nanoparticles modified with zwitterionic poly (carboxybetaine-co-dopamine methacrylamide) copolymer (PCBDA@AgNPs) as novel anti-infective therapeutics were prepared and firmly immobilized onto soft CLs through mussel-inspired surface chemistry. The obtained PCBDA@AgNPs coated CL (PCBDA@AgNPs-CL) remained the excellent transparency of commercial CLs and exhibited strong and broad-spectrum antimicrobial activities. We systematically explored the mechanism and found that the functional CLs can effectively inhibit the growth of microbial biofilms via a synergic “resist–kill–remove” strategy due to the zwitterionic surface and sustained release of silver ions. Significantly, in vitro cell cytotoxicity and in vivo subcutaneous implantation experiments proved the significant biosafety of PCBDA@AgNPs-CL. Furthermore, PCBDA@AgNPs-CL was successfully employed for the in vivo treatment of MK rabbit models, demonstrating excellent abilities to eradicate microbe-induced ocular infections and to prevent the destruction and irreversible structural alterations of corneal tissues. Collectively, PCBDA@AgNPs-CL is therefore a highly promising therapeutic device to significantly boost the efficacy for MK treatment.

Commercial Soft Contact Lenses Engineered with Zwitterionic Silver Nanoparticles for Effectively Treating Microbial Keratitis

The introduction of various drugs onto commercial soft contact lenses (CLs) has emerged as an effective strategy for treating microbial keratitis (MK) because drug-loaded CLs can maintain a controlled drug concentration which leads to enhanced drug bioavailability and reduced side effects in ocular tissues. In this study, silver nanoparticles modified with zwitterionic poly (carboxybetaine-co-dopamine methacrylamide) copolymer (PCBDA@AgNPs) as novel anti-infective therapeutics were prepared and firmly immobilized onto soft CLs through mussel-inspired surface chemistry. The obtained PCBDA@AgNPs-CL remained the excellent transparency of commercial CLs and exhibited strong and broad-spectrum antimicrobial activities. We systematically explored the mechanism and found that the functional CLs can effectively inhibit the growth of microbial biofilms via a synergic “resist–kill–remove” strategy due to the zwitterionic surface and sustained release of silver ions. Significantly, in vitro cell cytotoxicity and in vivo subcutaneous implantation experiments proved the outstanding biosafety of PCBDA@AgNPs-CL. Furthermore, PCBDA@AgNPs-CL was successfully employed for the in vivo treatment of MK rabbit models, demonstrating excellent abilities to eradicate microbe-induced ocular infections and to prevent the destruction and irreversible structural alterations of corneal tissues. Collectively, PCBDA@AgNPs-CL is therefore a highly promising therapeutic device to significantly boost the efficacy for MK treatment.

Reversible and the irreversible structural alterations on brain after resolution of hypercortisolism in Cushing’s disease

The adverse effects of hypercortisolism on the human brain have been highlighted in previous studies of Cushing’s disease (CD). However, the reversibility of brain damage after the resolution of hypercortisolism remains unclear. Thus, we studied the potential volumetric reversibility in biochemically remitted CD patients. Cross-sectional analysis demonstrated the active CD patients (n = 61) had the smallest gray matter (GM) volumes (553.33 ± 45.90 CM3) among four groups. While the GM volumes of short-term remitted CD patients (586.62 ± 46.89 CM3, n = 28) and long-term remitted CD patients (596.58 ± 45.95 CM3, n = 35) were between those of the active CD patients and healthy control subjects (628.14 ± 46.88 CM3, n = 74). Moreover, significant positive correlations between remitted time and GM volumes were only found in short-term remitted CD patients. On the contrary, the alterations of white matter (WM) in CD patients seem to be independent of concomitant hypercortisolism, persisting after remission. A preliminary longitude analysis also demonstrated similar results. Volumetric reversibility of GM, but not WM is highly prevalent in short-term after resolution of hypercortisolism in Cushing disease. Our study enhances our understanding of the reversible and the irreversible structural alterations in the human brain due to hypercortisolism.

Effect of maternal iron status on placenta, fetus and newborn

Maternal anemia (hypoferriemia) results in increased pre-term and low birth weight deliveries and higher rate of stillbirths. There are irreversible structural alterations in placenta. The transfer of iron to fetus is reduced in spite of gradient in relation to severity of maternal hypoferriemia. The fetal hepatic and brain iron contents were reduced. The brain iron reduction was irreversible on rehabilitation and was associated with irreversible neurotransmitter and their receptor alterations. Key words: Maternal anemia, stillbirths, placenta.

Transient receptor potential channels (TRPC) contribute to an enhanced endothelial cell proliferation and irreversible vascular remodeling associated with the development of pulmonary arterial hypertension (PAH)

Disordered pulmonary arterial endothelial cell (PAEC) growth underlies the formation of angio‐proliferation and intimal lesions, obliterating the small pulmonary arteries (PAs), resulting in irreversible structural alterations, or pulmonary vascular remodeling in pulmonary arterial hypertension (PAH) patients.ObjectiveTo demonstrate that transient receptor potential channel (TRPC6) contributes to PAEC proliferation and in the development of PAH.ResultsPAEC isolated from Idiopathic PAH (IPAH) patients showed an enhanced VEGF‐induced [Ca2+]cyt and proliferation. In parallel, TRPC6 (mRNA and protein) expression was markedly up regulated in IPAH compared to normal subjects. Interestingly, knockdown of TRPC6 in IPAH‐PAEC using siRNA significantly attenuated VEGF‐induced rise in [Ca2+]cyt and proliferation. Deletion of either TRPC6 (TRPC6−/−) or TRPC4 (TRPC4−/−) abolished thapsigargin‐induced store Ca2+ release‐activated Ca2+ entry (SOCE) in mice PAEC. In addition, TRPC6−/− mice showed significant abrogation of hypoxia‐induced changes in the right ventricular systolic pressure and right ventricular hypertrophy suggesting its role in vascular remodeling associated with PAH.ConclusionOur studies provide a comprehensive picture of TRPC6‐mediated Ca2+ entry mechanisms in contributing to an increased PAEC proliferation and vascular remodeling associated with PAH.

From chronic liver disorders to hepatocellular carcinoma: Molecular and genetic pathways

Hepatocarcinogenesis is a process attributed to progressive genomic changes that alter the hepatocellular phenotype producing cellular intermediates that evolve into hepatocellular carcinoma (HCC). During the preneoplastic phase, the liver is often the site of chronic hepatitis and/or cirrhosis, and these conditions induce liver regeneration with accelerated hepatocyte cycling in an organ that is otherwise proliferatively at rest. Hepatocyte regeneration is accelerated by upregulation of mitogenic pathways involving molecular and genetic mechanisms. Hepatic growth factors, inhibitors and triggers may also play a role. This process leads to the production of monoclonal populations of aberrant and dysplastic hepatocytes that have telomerase re-expression, microsatellite instability, and occasionally structural aberrations in genes and chromosomes. Development of dysplastic hepatocytes in foci and nodules and the emergence of HCC are associated with the accumulation of irreversible structural alterations in genes and chromosomes even if the genomic basis of the malignant phenotype is largely heterogeneous. Therefore, a malignant hepatocyte phenotype may be produced by changes in genes acting through different regulatory pathways, thus producing several molecular variants of HCC. On these bases, a key point for future research will be to determine whether the deletions are specific, due to particular loci in the minimally deleted regions of affected chromosome arms, or whether they are non-specific with loss of large portions of chromosomes or entire chromosome arms leading to passive deletion of loci. The final aim is the possibility of identifying a step where carcinogenetic processes could be terminated.

Local setting of magnetic anisotropy in amorphous films by Co ion implantation

The local setting of magnetic anisotropy by low fluence Co ion implantation in amorphous magnetic thin films is demonstrated. For a wide range of ion fluences no structural changes occur and the adjustment of anisotropy is reversible. A quantitative relationship between the anisotropy change and the atomic displacements is found. Magnetic domain investigations of the purely magnetically patterned stripes reveal an effective quasi-cubic anisotropy below a critical width for orthogonal magnetic anisotropy alignment. The method of ion-annealing allows for a local setting of anisotropy without irreversible structural and magnetic alterations.

The Natural History and Complications of Eosinophilic Esophagitis

Eosinophilic esophagitis is a chronic disease limited to the esophagus and has a persistent or spontaneously fluctuating course. So far it does not seem to limit life expectancy, but it often substantially impairs the quality of life. To date, there has been no association with malignant conditions, but there is concern that the chronic, uncontrolled inflammation will evoke irreversible structural alterations of the esophagus, leading to tissue fibrosis, stricture formation, and impaired function. This esophageal remodeling may result in several disease-inherent and procedure-related complications.

Alginate/Polymethacrylate Copolymer Microparticles for the Intestinal Delivery of Enzymes

Proteins administered orally must pass through the gastric environment in order to reach their site of absorption in the intestine. How to protect these exogenously administered proteins from the damaging effects of gastric acid and pepsin proteolytic activity, which often induce irreversible structural and functional alterations to the molecules, is an intriguing challenge. Another problem is the physical and chemical instability of proteins during some technological processes, which often involve the use of organic solvents or high temperatures. In this study we investigated the use of alginate microparticles containing one of two enzymes, an enteric polymer and a lyoprotectant for the intestinal delivery of proteins. The two enzymes tested in this protein delivery system were lactate dehydrogenase and alpha-amylase: the former was chosen because of its sensitivity to denaturation, the latter for its relevance in nutrition and medicine. A sodium alginate aqueous solution containing the enteric polymer, a lyoprotectant and the enzyme was either extruded or sprayed into a calcium chloride solution, with the resultant formation of beads and microspheres which were freeze-dried. About 90% of the enzyme activity was maintained during the process of loading the proteins into the microparticles and the subsequent freeze-drying process. The stability of the encapsulated enzyme in an acid medium and the enzymatic activity in an intestinal environment were then investigated by a dissolution test. This consisted of exposing the microparticles to simulated gastric fluid (pH 1.2) for 2 hours and to simulated intestinal fluid (pH 7.5+/-0.1) for 1 hour. The morphology of the microparticles did not change in the acid environment, whereas they completely dissolved within 3 min in the simulated intestinal fluid. Residual enzymatic activity after the test remained satisfactory for both enzymes. In conclusion, these microparticle systems offer promise for applications in human and veterinary medicine as well as in human and animal nutrition.

A variant of the myosin light chain kinase gene is associated with severe asthma in African Americans

Asthma is a complex phenotype influenced by environmental and genetic factors for which severe irreversible structural airway alterations are more frequently observed in African Americans. In addition to a multitude of factors contributing to its pathobiology, increased amounts of myosin light chain kinase (MLCK), the central regulator of cellular contraction, have been found in airway smooth muscle from asthmatics. The gene encoding MLCK (MYLK) is located in 3q21.1, a region noted by a number of genome-wide studies to show linkage with asthma and asthma-related phenotypes. We studied 17 MYLK genetic variants in European and African Americans with asthma and severe asthma and identified a single non-synonymous polymorphism (Pro147Ser) that was almost entirely restricted to African populations and which was associated with severe asthma in African Americans. These results remained highly significant after adjusting for proportions of ancestry estimated using 30 unlinked microsatellites (adjusted odds ratio: 1.76 [95% confidence interval, CI: 1.17-2.65], p = 0.005). Since all common HapMap polymorphisms in approximately 500 kb contiguous regions have low-to-moderate linkage disequilibrium with Pro147Ser, we speculate that this polymorphism is causally related to the severe asthma phenotype in African Americans. The association of this polymorphism, located in the N-terminal region of the non-muscle MLCK isoform, emphasizes the potential importance of the vascular endothelium, a tissue in which MLCK is centrally involved in multiple aspects of the inflammatory response, in the pathogenesis of severe asthma. This finding also offers a possible genetic explanation for some of the more severe asthma phenotype observed in African American asthmatics.

Probing the change of enzymatic activity of horseradish peroxidase induced by membrane permeation using tryptophan fluorescence

Changes in the molecular structure of horseradish peroxidase (HRP-4C) induced by membrane ultrafiltration, as well as its impact on the enzymatic activity, were monitored using three complementary fluorescence techniques: steady-state fluorescence, fluorescence anisotropy and picosecond time-resolved fluorescence. Ultrafiltration experiments were performed using membranes of polyethersulfone (PES) with 30 and 100 kDa and membranes of regenerated cellulose (RC) with 10 and 30 kDa. The results obtained clearly shows HRP-4C structural changes during ultrafiltration, which were essentially controlled by hydrophobic and electrostatic protein–membrane interactions. The structural changes observed depend on the affinity of the membrane material to ions, such as Fe 3+ and Ca 2+, which have a substantial structural and functional relevance to this enzyme. Additionally, it was found that the impact of the ultrafiltration process on the enzymatic activity was a direct consequence of the depletion of iron from the protein structure, causing irreversible structural alterations on HRP-4C, and thus inducing severe changes in its enzymatic activity.

Molecular pathogenesis of human hepatocellular carcinoma.

Hepatocarcinogenesis is a slow process during which genomic changes progressively alter the hepatocellular phenotype to produce cellular intermediates that evolve into hepatocellular carcinoma. During the long preneoplastic stage, in which the liver is often the site of chronic hepatitis, cirrhosis, or both, hepatocyte cycling is accelerated by upregulation of mitogenic pathways, in part through epigenetic mechanisms. This leads to the production of monoclonal populations of aberrant and dysplastic hepatocytes that have telomere erosion and telomerase re-expression, sometimes microsatellite instability, and occasionally structural aberrations in genes and chromosomes. Development of dysplastic hepatocytes in foci and nodules and emergence of hepatocellular carcinoma are associated with the accumulation of irreversible structural alterations in genes and chromosomes, but the genomic basis of the malignant phenotype is heterogeneous. The malignant hepatocyte phenotype may be produced by the disruption of a number of genes that function in different regulatory pathways, producing several molecular variants of hepatocellular carcinoma. New strategies should enable these variants to be characterized.

The Japanese Experience with Tendonitis in Racehorses.

Superficial digital flexor tendon (SDFT) injury leading to tendonitis is the most frequent soft tissue injury in racehorses. As tendonitis has been noted to heal slowly and imperfectly, injured tendons require long periods of rest, and the rate of recurrence of tendonitis upon return to training is high. Between 1, 100 and 1,200 of the 6,400 to 7,000 racehorses currently registered with the Japan Racing Association (JRA) suffer from tendonitis, and some 70% of these return to racing without making a comeback in a single race. In view of this statistic, the JRA has conducted investigational and clinical research from various perspectives. This paper will review the results of these studies, thus providing insight into practical methods of treating and preventing tendonitis. The study results are summarized under the following headings: 1) Introduction; 2) Impacts and loads on the lower limb at the track; 3) Occurrence of tendonitis at JRA training centers; 4) The hoof and tendonitis; 5) Ultrasonic diagnostic criteria; 6) Therapeutic regimens; 7) Conclusion. We concluded that tendon injuries represent irreversible structural alterations that are unlikely to be significantly altered by therapy, so that the best outcome may be achieved by minimizing the damage done by the original injury. From this viewpoint, research efforts will be directed toward prevention and early diagnosis, rather than therapy of established lesions.

Sarcomere Length–tension Relationship of Rat Cardiac Myocytes at Lengths Greater than Optimum

The study was aimed at determining both passive and Ca2+-activated forces of single skinned rat cardiac cells. Particular attention was paid to the descending limb of the active length–tension curve while the sarcomeric order of stretched cells was investigated before and during contraction. To analyse sarcomere length and sarcomere-length inhomogeneity, a fast Fourier transform (FFT) was employed. The fundamental frequency in the FFT spectrum is a measure of sarcomere length. The full-width-half-maximum of the first-order line is a measure of sarcomere-length inhomogeneity. In relaxing buffer, the sarcomere-length inhomogeneity of skinned cells increased linearly with mean sarcomere length. Upon Ca2+-dependent activation of skinned cells contracting isometrically, mean sarcomere length decreased slightly and inhomogeneity increased; both effects were greater at higher Ca2+concentrations. Maximum activation was reached at sarcomere lengths between 2.2 and 2.4 μ m, whereas the descending limb of the active length–tension curve approached zero force already at 2.8 μ m. This steep force decline could not be explained by overly inhomogeneous sarcomere lengths in very long, contracting cells. Rather, the results of mechanical measurements on single cardiac myofibrils implied that high stretching is accompanied by irreversible structural alterations within cardiac sarcomeres, most likely thick-filament disarray and disruption of binding sites between myosin and titin due to changes in titin's tertiary structure. Loss of a regular thick-filament organization may then impair active force generation. We conclude that the descending limb of the cardiac length–tension curve is determined both by the degree of actin–myosin overlap and by the intrinsic properties of titin filaments.