Biology subjects

Amano, A.

Publications and source records attributed to Amano, A..

5 recordsLinked to original sources

bioRxiv2026

A Theoretical Framework for the Hemodynamic Role of Sarcomere Length Dynamics During the Isovolumic Phases of the Left Ventricle

The left ventricle (LV) exhibits torsional deformation during systole, and mechanical relaxation begins during the isovolumic phase. Recent advances in imaging techniques, such as MRI, have revealed that myocardial tissue deformation and sarcomere length changes occur during the isovolumic relaxation phase, even when the chamber volume remains constant. Although such ventricular deformation during the isovolumic phase is considered important for blood ejection and filling efficiency, its mechanistic contribution to contraction and relaxation remains unresolved. In this study, we hypothesized that sarcomere length dynamics during the isovolumic phase affect the isovolumic contraction and relaxation time (IVCT and IVRT) by regulating the contraction force via the force-velocity relationship of ventricular myocytes. To investigate this hypothesis, we focused on experimentally reported differences in the relationship between sarcomere length and LV volume across the endocardial and epicardial layers, as described by Rodriguez et al. We constructed and compared two types of hemodynamic models within the same integrated framework consisting of a circulation model, a LV model, and a myocardial cell contraction model by Negroni-Lascano et al., which differ only in how sarcomere length is determined: a volume-based length model (VL model), in which sarcomere length is uniquely determined by LV volume, and a volume-force-coupled length model (VFL model), in which sarcomere length is determined by the balance between LV volume and contraction force. Simulation results showed that in the VFL model, compared to the VL model, sarcomere length changed during the isovolumic phase, leading to a decrease in contractile force and shortening of IVRT, which may contribute to improved hemodynamic efficiency. These results indicate that sarcomere length dynamics can mechanically regulate force decay during isovolumic relaxation, even under constant left ventricular volume. This study provides a theoretical framework for understanding the contributions of different layers within the LV wall to diastolic function during the isovolumic relaxation phase.

physiology↗

bioRxiv2023

Mathematical Analysis of Left Ventricular Elastance with respect to Afterload Change During Ejection Phase

Since the left ventricle (LV) has pressure (P{iota}{upsilon}) and volume (V{iota}{upsilon}), we can define LV elastance from the ratio between P{iota}{upsilon} and V{iota}{upsilon}, termed as "instantaneous elastance." On the other hand, end-systolic elastance (Emax) is known to be a good index of LV contractility, which is measured by the slope of several end-systolic P{iota}{upsilon} -V{iota}{upsilon} points obtained by using different loads. The word Emax originates from the assumption that LV elastance increases during the ejection phase and attains its maximum at the end-systole. From this concept, we can define another elastance determined by the slopes of isochronous P{iota}{upsilon} -V{iota}{upsilon} points, that is P{iota}{upsilon} -V{iota}{upsilon} points at a certain time after the ejection onset time by using different loads. We refer to this elastance as "load-dependent elastance." To reveal the relation between these two elastances, we used a hemodynamic model that included a detailed ventricular myocyte contraction model. From the simulation results, we found that the isochronous P{iota}{upsilon} -V{iota}{upsilon} points lay in one line and that the line slope corresponding to the load-dependent elastance slightly decreased during the ejection phase, which is quite different from the instantaneous elastance. Subsequently, we analyzed the mechanism determining these elastances from the model equations. We found that instantaneous elastance is directly related to contraction force generated by the ventricular myocyte, but the load-dependent elastance is determined by two factors: one is the transient characteristics of the cardiac cell, i.e., the velocity-dependent force drops characteristics in instantaneous shortening. The other is the force-velocity relationship of the cardiac cell. We also found that the linear isochronous pressure-volume relation is based on the approximately linear relation between the temporal differential of the cellular contraction force and the cellular shortening velocity that results from the combined characteristics of LV and aortic compliances.

biophysics↗

bioRxiv2022

The gradient-based parameter optimization to determine membrane ionic current composition of human induced pluripotent stem cell-derived cardiomyocytes

1.Premature cardiac myocytes derived from human-induced pluripotent stem cells (hiPSC-CMs) show heterogeneous action potentials (APs), most probably because of different expression patterns of membrane ionic currents. We aim to develop a method of determining expression patterns of functional channels in terms of the whole-cell ionic conductances (Gx) using individual spontaneous AP configurations. However, it has been suggested that apparently identical AP configurations were obtained by different sets of ionic currents in a mathematical model of cardiac membrane excitation. If so, the inverse problem of Gx estimation might not be solved. We computationally tested the feasibility of the gradient-based optimization method. For realistic examination, conventional cell-specific models were prepared by superimposing the model output of AP on each experimental AP record by the conventional manual adjustment of Gxs of the baseline model. Then, Gxs of 4 ~ 6 major ionic currents of the cell-specific models were randomized within a range of {+/-}5 ~ 15% and were used as initial parameter sets for the gradient-based automatic Gxs recovery by decreasing the mean square error (MSE) between the target and model output. When plotted all data points of MSE - Gx relation during the optimization, we found that the randomized population of Gxs progressively converged to the original value of the cell-specific model with decreasing MSE. To confirm the absence of any other local minimum in the global search space, we mapped the MSE by randomizing Gxs over a range of 0.1 ~ 10 times the control. No additional local minimum of MSE was obvious in the whole parameter space besides the global minimum of MSE at the default model parameter.

physiology↗

bioRxiv2021

Fusobacterium nucleatum metabolically integrates commensals and pathogens in oral biofilms

Fusobacterium nucleatum is a common constituent of the oral microbiota in both periodontal health and disease. Previously, we discovered ornithine cross-feeding between F. nucleatum and Streptococcus gordonii, where S. gordonii secretes ornithine via an arginine-ornithine antiporter (ArcD), which in turn supports the growth and biofilm development of F. nucleatum; however, broader metabolic aspects of F. nucleatum within polymicrobial communities and their impact on periodontal pathogenesis have not been addressed. Here, we show that when co-cultured with S. gordonii, F. nucleatum increased amino acid availability to enhance the production of butyrate and putrescine, a polyamine produced by ornithine decarboxylation. Co-culture with Veillonella parvula, another common inhabitant of the oral microbiota, also increased lysine availability, promoting cadaverine production by F. nucleatum. We confirmed that ArcD-dependent ornithine excretion by S. gordonii results in synergistic putrescine production, and mass spectrometry imaging revealed this metabolic capability creates a putrescine-rich microenvironment inside F. nucleatum biofilms. We further demonstrated that polyamines caused significant changes in the biofilm phenotype of a periodontal pathogen, Porphyromonas gingivalis, with putrescine being a potent stimulator of biofilm development and dispersal, and confirmed that F. nucleatum-mediated conversion of ornithine to putrescine enhances biofilm formation by P. gingivalis. Lastly, analysis of plaque samples revealed cooccurrence of P. gingivalis with genetic modules for putrescine production by S. gordonii and F. nucleatum. Overall, our results highlight the ability of F. nucleatum to induce synergistic polyamine production within multi-species consortia, and provide insight into how the trophic web in oral biofilm ecosystems can eventually shape disease-associated communities. Significance StatementPeriodontitis is caused by the pathogenic transition of subgingival microbiota ecosystems, which is accompanied by alterations to microbiome functions including metabolic systems and the establishment of metabolic cross-feeding. While Fusobacterium nucleatum is a major constituent of the periodontal microbiota, its metabolic integration within polymicrobial communities and the impact on periodontal pathogenesis are poorly understood. Here, we report that amino acids supplied by other commensal bacteria induce polyamine production by F. nucleatum, creating polyamine-rich microenvironments. We further show that this trophic web results in enhancement of biofilm formation and dispersal of a periodontal pathogen, Porphyromonas gingivalis. This work provides mechanistic insight into how cooperative metabolism within oral biofilms can tip the balance toward periodontitis.

microbiology↗

bioRxiv2019

Specific decreasing of Na+ channel expression on the lateral membrane of cardiomyocytes causes fatal arrhythmias in Brugada syndrome

One phenotypic feature of Brugada syndrome (BrS) is slowed conduction due to the reduction (loss-of-function) of Na+ channels. In contrast, recent clinical observations in BrS patients highlighted the poor correlation between the phenotype (typical ECG change or lethal arrhythmia) and the genotype (SCN5A mutation). Inspired by our previous theoretical study which showed that reduced Na+ channels in the lateral membrane (LM) of ventricular myocytes caused the slowing of conduction under myocardial ischemia, we hypothesized that a loss-of-function of Na+ channels caused by the decreases in Na+ channel expression within myocytes leads to phase-2 reentry (P2R), the major triggering mechanism of lethal arrhythmias in BrS. We constructed an in silico human ventricular myocardial strand and ring models, and investigated the relationship between the subcellular Na+ channel distribution and P2R. Reducing Na+ channel expression in the LM of each myocyte caused not only the notch-and-dome but also loss-of-dome type action potentials and slowed conduction, both of which are typically observed in BrS patients. Furthermore, we showed that both the reduction in Na+ channels on the LM of each myocyte and tissue-level heterogeneity of Na+ channel expression were essential for P2R as well as P2R-mediated reentrant excitation. Our data suggest that the alteration in subcellular Na+ channel distribution together with a tissue-level heterogeneity of Na+ channels can cause arrhythmogenesis in BrS.

biophysics↗