scholarly journals Nonlinear calcium ion waves along actin filaments control active hair–bundle motility

Biosystems ◽  
2018 ◽  
Vol 173 ◽  
pp. 181-190 ◽  
Author(s):  
Jack A. Tuszynski ◽  
Miljko V. Sataric ◽  
Dalibor L. Sekulic ◽  
Bogdan M. Sataric ◽  
Slobodan Zdravkovic
Keyword(s):  
Calcium Ion ◽  
Actin Filaments ◽  
Hair Bundle ◽  
Ion Waves

scholarly journals Nonlinear calcium ion waves along actin filaments control active hair–bundle motility

2018 ◽  
Author(s):  
J. A.Tuszynski ◽  
M. V. Sataric ◽  
D. L. Sekulic ◽  
B. M. Sataric ◽  
S. Zdravkovic
Keyword(s):  
Nonlinear Dynamics ◽  
Inner Ear ◽  
Hair Cells ◽  
Calcium Ion ◽  
Actin Filaments ◽  
Characteristic Time ◽  
Biophysical Model ◽  
Myosin Motors ◽  
Ion Waves

AbstractActin filaments are highly dynamic semiflexible cellular biopolymers with diverse functions, such as cell motility. They also play the role of conduits for propagation of calcium ion waves. In this paper, we propose a new biophysical model that describes how actin filaments with their polyelectrolyte properties serve as pathways for calcium ion flows in hair cells. We show this can be utilized for the tuning of force–generating myosin motors. In this model, we unify the calcium nonlinear dynamics involved in the control of the myosin adaptation motors with mechanical displacements of hair– bundles. The model shows that the characteristic time scales fit reasonably well with the available experimental data for spontaneous oscillations in the inner ear. This model offers promises to fill a gap in our understanding of the role of calcium ion nonlinear dynamics in the regulation of processes in the auditory cells of the inner ear.

Fragmin: a calcium ion sensitive regulatory factor on the formation of actin filaments

Biochemistry ◽  
1980 ◽  
Vol 19 (12) ◽  
pp. 2677-2683 ◽  
Author(s):  
Takayuki Hasegawa ◽  
Sho Takahashi ◽  
Hiroshi Hayashi ◽  
Sadashi Hatano
Keyword(s):  
Calcium Ion ◽  
Actin Filaments ◽  
Regulatory Factor

scholarly journals Stereocilia Rootlets: Actin-Based Structures That Are Essential for Structural Stability of the Hair Bundle

2020 ◽  
Vol 21 (1) ◽  
pp. 324 ◽  
Author(s):  
Itallia Pacentine ◽  
Paroma Chatterjee ◽  
Peter G. Barr-Gillespie
Keyword(s):  
Inner Ear ◽  
Hair Cells ◽  
Actin Filaments ◽  
Hair Bundle ◽  
Sensory Hair ◽  
Sensory Hair Cells ◽  
Associated Proteins ◽  
Unique Manner ◽  
Electrical Impulses ◽  
Mechanical Movement

Sensory hair cells of the inner ear rely on the hair bundle, a cluster of actin-filled stereocilia, to transduce auditory and vestibular stimuli into electrical impulses. Because they are long and thin projections, stereocilia are most prone to damage at the point where they insert into the hair cell’s soma. Moreover, this is the site of stereocilia pivoting, the mechanical movement that induces transduction, which additionally weakens this area mechanically. To bolster this fragile area, hair cells construct a dense core called the rootlet at the base of each stereocilium, which extends down into the actin meshwork of the cuticular plate and firmly anchors the stereocilium. Rootlets are constructed with tightly packed actin filaments that extend from stereocilia actin filaments which are wrapped with TRIOBP; in addition, many other proteins contribute to the rootlet and its associated structures. Rootlets allow stereocilia to sustain innumerable deflections over their lifetimes and exemplify the unique manner in which sensory hair cells exploit actin and its associated proteins to carry out the function of mechanotransduction.

scholarly journals The contractile basis of ameboid movement. II. Structure and contractility of motile extracts and plasmalemma-ectoplasm ghosts.

1976 ◽  
Vol 70 (1) ◽  
pp. 123-143 ◽  
Author(s):  
D L Taylor ◽  
J A Rhodes ◽  
S A Hammond
Keyword(s):  
Calcium Ion ◽  
Actin Filaments ◽  
Amoeba Proteus ◽  
Ion Concentration ◽  
Micromolar Concentration ◽  
Low Calcium ◽  
Relaxation Solution ◽  
Calcium And Magnesium ◽  
Calcium Ion Concentration

The role of calcium and magnesium-ATP on the structure and contractility in motile extracts of Amoeba proteus and plasmalemma-ectoplasm "ghosts" of Chaos carolinensis has been investigated by correlating light and electron microscope observations with turbidity and birefringence measurements. The extract is nonmotile and contains very few F-actin filaments and myosin aggregates when prepared in the presence of both low calcium ion and ATP concentrations at an ionic strength of I = 0.05, pH 6.8. The addition of 1.0 mM magnesium chloride, 1.0 mM ATP, in the presence of a low calcium ion concentration (relaxation solution) induced the formation of some fibrous bundles of actin without contracting, whereas the addition of a micromolar concentration of calcium in addition to 1.0 mM magnesium-ATP (contraction solution) (Taylor, D. L., J. S. Condeelis, P. L. Moore, and R. D. Allen. 1973. J. Cell Biol. 59:378-394) initiated the formation of large arrays of F-actin filaments followed by contractions. Furthermore, plasmalemma-ectoplasm ghosts prepared in the relaxation solution exhibited very few straight F-actin filaments and myosin aggregates. In contrast, plasmalemmaectoplasm ghosts treated with the contraction solution contained many straight F-actin filaments and myosin aggregates. The increase in the structure of ameba cytoplasm at the endoplasm-ectoplasm interface can be explained by a combination of the transformation of actin from a less filamentous to a more structured filamentous state possibly involving the cross-linking of actin to form fibrillar arrays (see above-mentioned reference) followed by contractions of the actin and myosin along an undetermined distance of the endoplasm and/or ectoplasm.

Electron Microscopy of Cytoplasmic Contractile Proteins

1978 ◽  
Vol 36 (3) ◽  
pp. 606-614 ◽  
Author(s):  
T.D. Pollard ◽  
P. Maupin
Keyword(s):  
Electron Microscopy ◽  
Actin Filaments ◽  
Three Dimensional ◽  
Uranyl Acetate ◽  
Contractile Proteins ◽  
Dimensional Structure ◽  
X Ray Diffraction ◽  
Cytoplasmic Matrix ◽  
Computer Image Processing ◽  
Nonmuscle Cells

In this paper we review some of the contributions that electron microscopy has made to the analysis of actin and myosin from nonmuscle cells. We place particular emphasis upon the limitations of the ultrastructural techniques used to study these cytoplasmic contractile proteins, because it is not widely recognized how difficult it is to preserve these elements of the cytoplasmic matrix for electron microscopy. The structure of actin filaments is well preserved for electron microscope observation by negative staining with uranyl acetate (Figure 1). In fact, to a resolution of about 3nm the three-dimensional structure of actin filaments determined by computer image processing of electron micrographs of negatively stained specimens (Moore et al., 1970) is indistinguishable from the structure revealed by X-ray diffraction of living muscle.

Lead aspartate: a new en bloc stain for electron microscopy

1978 ◽  
Vol 36 (2) ◽  
pp. 34-35
Author(s):  
J.R. Walton
Keyword(s):  
Electron Microscopy ◽  
Calcium Ion ◽  
Enzyme Reaction ◽  
Lead Citrate ◽  
Reaction Products ◽  
En Bloc ◽  
Thin Sections ◽  
Lead Salts ◽  
Thin Sectioning ◽  
High Alkalinity

In electron microscopy, lead is the metal most widely used for enhancing specimen contrast. Lead citrate requires a pH of 12 to stain thin sections of epoxy-embedded material rapidly and intensively. However, this high alkalinity tends to leach out enzyme reaction products, making lead citrate unsuitable for many cytochemical studies. Substitution of the chelator aspartate for citrate allows staining to be carried out at pH 6 or 7 without apparent effect on cytochemical products. Moreover, due to the low, controlled level of free lead ions, contamination-free staining can be carried out en bloc, prior to dehydration and embedding. En bloc use of lead aspartate permits the grid-staining step to be bypassed, allowing samples to be examined immediately after thin-sectioning.Procedures. To prevent precipitation of lead salts, double- or glass-distilled H20 used in the stain and rinses should be boiled to drive off carbon dioxide and glassware should be carefully rinsed to remove any persisting traces of calcium ion.

Destruction of Actin Filaments by Osmium Tetroxide

1977 ◽  
Vol 35 ◽  
pp. 466-467
Author(s):  
P. Maupin-Szamier ◽  
T. D. Pollard
Keyword(s):  
Actin Filaments ◽  
Time Course ◽  
Osmium Tetroxide ◽  
Rabbit Muscle ◽  
Muscle Actin ◽  
Sodium Phosphate Buffer ◽  
Transmission Electron ◽  
The Difference ◽  
Rates Of Decay ◽  
Short Time

We have studied the destruction of rabbit muscle actin filaments by osmium tetroxide (OSO4) to develop methods which will preserve the structure of actin filaments during preparation for transmission electron microscopy.Negatively stained F-actin, which appears as smooth, gently curved filaments in control samples (Fig. 1a), acquire an angular, distorted profile and break into progressively shorter pieces after exposure to OSO4 (Fig. 1b,c). We followed the time course of the reaction with viscometry since it is a simple, quantitative method to assess filament integrity. The difference in rates of decay in viscosity of polymerized actin solutions after the addition of four concentrations of OSO4 is illustrated in Fig. 2. Viscometry indicated that the rate of actin filament destruction is also dependent upon temperature, buffer type, buffer concentration, and pH, and requires the continued presence of OSO4. The conditions most favorable to filament preservation are fixation in a low concentration of OSO4 for a short time at 0°C in 100mM sodium phosphate buffer, pH 6.0.

Structure of Myosin Subfragment-1 from Electron Microscopy and Crystallography

1988 ◽  
Vol 46 ◽  
pp. 156-157
Author(s):  
Donald A. Winkelmann
Keyword(s):  
Electron Microscopy ◽  
Molecular Weight ◽  
Actin Filaments ◽  
Light Chains ◽  
Myosin Filament ◽  
Primary Role ◽  
Heavy Chains ◽  
Myosin Subfragment ◽  
Myosin Subfragment 1 ◽  
Globular Head

The primary role of the interaction of actin and myosin is the generation of force and motion as a direct consequence of the cyclic interaction of myosin crossbridges with actin filaments. Myosin is composed of six polypeptides: two heavy chains of molecular weight 220,000 daltons and two pairs of light chains of molecular weight 17,000-23,000. The C-terminal portions of the myosin heavy chains associate to form an α-helical coiled-coil rod which is responsible for myosin filament formation. The N-terminal portion of each heavy chain associates with two different light chains to form a globular head that binds actin and hydrolyses ATP. Myosin can be fragmented by limited proteolysis into several structural and functional domains. It has recently been demonstrated using an in vitro movement assay that the globular head domain, subfragment-1, is sufficient to cause sliding movement of actin filaments.The discovery of conditions for crystallization of the myosin subfragment-1 (S1) has led to a systematic analysis of S1 structure by x-ray crystallography and electron microscopy. Image analysis of electron micrographs of thin sections of small S1 crystals has been used to determine the structure of S1 in the crystal lattice.

Orientation of actin filaments during motion in motility assay

1995 ◽  
Vol 53 ◽  
pp. 52-53
Author(s):  
J. Borejdo ◽  
S. Burlacu
Keyword(s):  
Actin Filaments ◽  
Thin Filament ◽  
Striated Muscle ◽  
Myosin Head ◽  
Classical Method ◽  
Polarization Of Fluorescence ◽  
Single Protein ◽  
Intracellular Organelles ◽  
Change Orientation ◽  
Active Entity

Polarization of fluorescence is a classical method to assess orientation or mobility of macromolecules. It has been a common practice to measure polarization of fluorescence through a microscope to characterize orientation or mobility of intracellular organelles, for example anisotropic bands in striated muscle. Recently, we have extended this technique to characterize single protein molecules. The scientific question concerned the current problem in muscle motility: whether myosin heads or actin filaments change orientation during contraction. The classical view is that the force-generating step in muscle is caused by change in orientation of myosin head (subfragment-1 or SI) relative to the axis of thin filament. The molecular impeller which causes this change resides at the interface between actin and SI, but it is not clear whether only the myosin head or both SI and actin change orientation during contraction. Most studies assume that observed orientational change in myosin head is a reflection of the fact that myosin is an active entity and actin serves merely as a passive "rail" on which myosin moves.

Modulated polarization microscopy displays the dynamics of cytoskeletal structures in living, motile cells

1995 ◽  
Vol 53 ◽  
pp. 902-903
Author(s):  
J. R. Kuhn ◽  
M. Poenie
Keyword(s):  
Mitotic Spindle ◽  
Actin Filaments ◽  
Cell Shape ◽  
Dynamic Structure ◽  
Living Cells ◽  
Cytoskeletal Proteins ◽  
Polarization Microscopy ◽  
Video Enhancement ◽  
Ultrastructural Studies ◽  
Motile Cells

Cell shape and movement are controlled by elements of the cytoskeleton including actin filaments an microtubules. Unfortunately, it is difficult to visualize the cytoskeleton in living cells and hence follow it dynamics. Immunofluorescence and ultrastructural studies of fixed cells while providing clear images of the cytoskeleton, give only a static picture of this dynamic structure. Microinjection of fluorescently Is beled cytoskeletal proteins has proved useful as a way to follow some cytoskeletal events, but long terry studies are generally limited by the bleaching of fluorophores and presence of unassembled monomers.Polarization microscopy has the potential for visualizing the cytoskeleton. Although at present, it ha mainly been used for visualizing the mitotic spindle. Polarization microscopy is attractive in that it pro vides a way to selectively image structures such as cytoskeletal filaments that are birefringent. By combing ing standard polarization microscopy with video enhancement techniques it has been possible to image single filaments. In this case, however, filament intensity depends on the orientation of the polarizer and analyzer with respect to the specimen.

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