Myosin and tropomyosin-troponin complementarily regulate thermal activation of muscles.

Contraction of striated muscles is initiated by an increase in cytosolic Ca2+ concentration, which is regulated by tropomyosin and troponin acting on actin filaments at the sarcomere level. Namely, Ca2+-binding to troponin C shifts the "on-off" equilibrium of the thin filament state toward the "on" state, promoting actomyosin interaction; likewise, an increase in temperature to within the body temperature range shifts the equilibrium to the on state, even in the absence of Ca2+. Here, we investigated the temperature dependence of sarcomere shortening along isolated fast skeletal myofibrils using optical heating microscopy.

Effects of omecamtiv mecarbil on the contractile properties of skinned porcine left atrial and ventricular muscles.

Omecamtiv mecarbil (OM) is a novel inotropic agent for heart failure with systolic dysfunction. OM prolongs the actomyosin attachment duration, which enhances thin filament cooperative activation and accordingly promotes the binding of neighboring myosin to actin. In the present study, we investigated the effects of OM on the steady-state contractile properties in skinned porcine left ventricular (PLV) and atrial (PLA) muscles.

Heat-hypersensitive mutants of ryanodine receptor type 1 revealed by microscopic heating.

Thermoregulation is an important aspect of human homeostasis, and high temperatures pose serious stresses for the body. Malignant hyperthermia (MH) is a life-threatening disorder in which body temperature can rise to a lethal level. Here we employ an optically controlled local heat-pulse method to manipulate the temperature in cells with a precision of less than 1 °C and find that the mutants of ryanodine receptor type 1 (RyR1), a key Ca release channel underlying MH, are heat hypersensitive compared with the wild type (WT).

Modulation of Local Cellular Activities using a Photothermal Dye-Based Subcellular-Sized Heat Spot.

Thermal engineering at the microscale, such as the regulation and precise evaluation of the temperature within cellular environments, is a major challenge for basic biological research and biomaterials development. We engineered a polymeric nanoparticle having a fluorescent temperature sensory dye and a photothermal dye embedded in the polymer matrix, named nanoheater-thermometer (). When is illuminated with a near-infrared laser at 808 nm, a subcellular-sized heat spot is generated in a live cell.

Synchrony of sarcomeric movement regulates left ventricular pump function in the in vivo beating mouse heart.

Sarcomeric contraction in cardiomyocytes serves as the basis for the heart's pump functions. It has generally been considered that in cardiac muscle as well as in skeletal muscle, sarcomeres equally contribute to myofibrillar dynamics in myocytes at varying loads by producing similar levels of active and passive force. In the present study, we expressed α-actinin-AcGFP in Z-disks to analyze dynamic behaviors of sequentially connected individual sarcomeres along a myofibril in a left ventricular (LV) myocyte of the in vivo beating mouse heart.

Nanoscopic changes in the lattice structure of striated muscle sarcomeres involved in the mechanism of spontaneous oscillatory contraction (SPOC).

Muscles perform a wide range of motile functions in animals. Among various types are skeletal and cardiac muscles, which exhibit a steady auto-oscillation of force and length when they are activated at an intermediate level of contraction. This phenomenon, termed spontaneous oscillatory contraction or SPOC, occurs devoid of cell membranes and at fixed concentrations of chemical substances, and is thus the property of the contractile system per se.

Tug-of-war between actomyosin-driven antagonistic forces determines the positioning symmetry in cell-sized confinement.

Symmetric or asymmetric positioning of intracellular structures including the nucleus and mitotic spindle steers various biological processes such as cell migration, division, and embryogenesis. In typical animal cells, both a sparse actomyosin meshwork in the cytoplasm and a dense actomyosin cortex underneath the cell membrane participate in the intracellular positioning. However, it remains unclear how these coexisting actomyosin structures regulate the positioning symmetry.

Single-cell temperature mapping with fluorescent thermometer nanosheets.

Recent studies using intracellular thermometers have shown that the temperature inside cultured single cells varies heterogeneously on the order of 1°C. However, the reliability of intracellular thermometry has been challenged both experimentally and theoretically because it is, in principle, exceedingly difficult to exclude the effects of nonthermal factors on the thermometers. To accurately measure cellular temperatures from outside of cells, we developed novel thermometry with fluorescent thermometer nanosheets, allowing for noninvasive global temperature mapping of cultured single cells.

Thermal Activation of Thin Filaments in Striated Muscle.

In skeletal and cardiac muscles, contraction is triggered by an increase in the intracellular Ca concentration. During Ca transients, Ca-binding to troponin C shifts the "" equilibrium of the thin filament state toward the "" sate, promoting actomyosin interaction. Likewise, recent studies have revealed that the thin filament state is under the influence of temperature; , an increase in temperature increases active force production.

Real-Time In Vivo Imaging of Mouse Left Ventricle Reveals Fluctuating Movements of the Intercalated Discs.

Myocardial contraction is initiated by action potential propagation through the conduction system of the heart. It has been thought that connexin 43 in the gap junctions (GJ) within the intercalated disc (ID) provides direct electric connectivity between cardiomyocytes (electronic conduction). However, recent studies challenge this view by providing evidence that the mechanosensitive cardiac sodium channels Na1.

On the on-line journal "Biophysics and Physicobiology (BPPB)".

This Commentary describes the history and current status of the international journal run by the Biophysical Society of Japan known as Biophysics and Physicobiology (BPPB).

Microscopic heat pulses activate cardiac thin filaments.

During the excitation-contraction coupling of the heart, sarcomeres are activated via thin filament structural changes (i.e., from the "off" state to the "on" state) in response to a release of Ca from the sarcoplasmic reticulum.

Functional significance of HCM mutants of tropomyosin, V95A and D175N, studied with motility assays.

The majority of hypertrophic cardiomyopathy (HCM) is caused by mutations in sarcomere proteins. We examined tropomyosin (Tpm)'s HCM mutants in humans, V95A and D175N, with motility assay using optical tweezers to evaluate the effects of the Tpm mutations on the actomyosin interaction at the single molecular level. Thin filaments were reconstituted using these Tpm mutants, and their sliding velocity and force were measured at varying Ca concentrations.

Processive Nanostepping of Formin mDia1 Loosely Coupled with Actin Polymerization.

Formins are actin-binding proteins that construct nanoscale machinery with the growing barbed end of actin filaments and serve as key regulators of actin polymerization and depolymerization. To maintain the regulation of actin dynamics, formins have been proposed to processively move at every association or dissociation of a single actin molecule toward newly formed barbed ends. However, the current models for the motile mechanisms were established without direct observation of the elementary processes of this movement.

Optimization of Fluorescent Labeling for Nanoimaging of Sarcomeres in the Mouse Heart.

The present study was conducted to systematically investigate the optimal viral titer as well as the volume of the adenovirus vector (ADV) that expresses -actinin-AcGFP in the Z-disks of myocytes in the left ventricle (LV) of mice. An injection of 10 L ADV at viral titers of 2 to 4 × 10 viral particles per mL (VP/mL) into the LV epicardial surface consistently expressed -actinin-AcGFP in myocytes , with the fraction of AcGFP-expressing myocytes at ~10%. Our analysis revealed that SL was ~1.

Sarcomeric Auto-Oscillations in Single Myofibrils From the Heart of Patients With Dilated Cardiomyopathy.

Background: Left ventricular wall motion is depressed in patients with dilated cardiomyopathy (DCM). However, whether or not the depressed left ventricular wall motion is caused by impairment of sarcomere dynamics remains to be fully clarified.

Methods And Results: We analyzed the mechanical properties of single sarcomere dynamics during sarcomeric auto-oscillations (calcium spontaneous oscillatory contractions [Ca-SPOC]) that occurred at partial activation under the isometric condition in myofibrils from donor hearts and from patients with severe DCM (New York Heart Association classification III-IV).

Estimation of actomyosin active force maintained by tropomyosin and troponin complex under vertical forces in the in vitro motility assay system.

The interaction between actin filaments and myosin molecular motors is a power source of a variety of cellular functions including cell division, cell motility, and muscular contraction. In vitro motility assay examines actin filaments interacting with myosin molecules that are adhered to a substrate (e.g.

Radial stiffness characteristics of the overlap regions of sarcomeres in isolated skeletal myofibrils in pre-force generating state.

We have studied the stiffness of myofilament lattice in sarcomeres in the pre-force generating state, which was realized by a relaxing reagent, BDM (butane dione monoxime). First, the radial stiffness for the overlap regions of sarcomeres of isolated single myofibrils was estimated from the resulting decreases in diameter by osmotic pressure applied with the addition of Dextran. Then, the radial stiffness was also estimated from force-distance curve measurements with AFM technology.

Biphasic Effect of Profilin Impacts the Formin mDia1 Force-Sensing Mechanism in Actin Polymerization.

Formins are force-sensing proteins that regulate actin polymerization dynamics. Here, we applied stretching tension to individual actin filaments under the regulation of formin mDia1 to investigate the mechanical responses in actin polymerization dynamics. We found that the elongation of an actin filament was accelerated to a greater degree by stretching tension for ADP-G-actin than that for ATP-G-actin.

Optical visualisation of thermogenesis in stimulated single-cell brown adipocytes.

The identification of brown adipose deposits in adults has led to significant interest in targeting this metabolically active tissue for treatment of obesity and diabetes. Improved methods for the direct measurement of heat production as the signature function of brown adipocytes (BAs), particularly at the single cell level, would be of substantial benefit to these ongoing efforts. Here, we report the first application of a small molecule-type thermosensitive fluorescent dye, ERthermAC, to monitor thermogenesis in BAs derived from murine brown fat precursors and in human brown fat cells differentiated from human neck brown preadipocytes.