scholarly journals Evidence from Insect Fibrillar Muscle about the Elementary Contractile Process

1967 ◽  
Vol 50 (6) ◽  
pp. 139-156 ◽  
Author(s):  
J. W. S. Pringle
Keyword(s):  
Ionic Strength ◽  
Atpase Activity ◽  
Striated Muscle ◽  
Contractile Activity ◽  
High Elasticity ◽  
Flight Muscles ◽  
The Cross ◽  
Cross Bridges ◽  
Low Ionic Strength ◽  
Water Bugs

Bundles of myofibrils prepared from the dorsal longitudinal flight muscles of giant water bugs show oscillatory contractile activity in solutions of low ionic strength containing ATP and 10-8-10-7 M Ca2+. This is due to delay between changes of length and changes of tension under activating conditions. The peculiarities of insect fibrillar muscle which give rise to this behavior are (1) the high elasticity of relaxed myofibrils, (2) a smaller degree of Ca2+ activation of ATPase activity in unstretched myofibrils and extracted actomyosin, and (3) a direct effect of stretch on ATPase activity. It is shown that the cross-bridges of striated muscle are probably formed from the heads of three myosin molecules and that in insect fibrillar muscle the cycles of mechanochemical energy conversion in the cross-bridges can be synchronized by imposed changes of length. This material is more suitable than vertebrate striated muscle for a study of the nature of the elementary contractile process.

Cross bridge-dependent activation of contraction in cardiac myofibrils at low pH

1999 ◽  
Vol 276 (5) ◽  
pp. H1460-H1467 ◽  
Author(s):  
D. R. Swartz ◽  
D. Zhang ◽  
K. W. Yancey
Keyword(s):  
Atpase Activity ◽  
Calcium Binding ◽  
Striated Muscle ◽  
Contractile Activity ◽  
Low Ph ◽  
Myofibrillar Atpase ◽  
Peak Activity ◽  
Cross Bridge ◽  
Myofibrillar Atpase Activity ◽  
Cross Bridges

Striated muscle contracts in the absence of calcium at low concentrations of MgATP ([MgATP]), and this has been termed rigor activation because rigor cross bridges attach and activate adjacent actin sites. This process is well characterized in skeletal muscle but not in cardiac muscle. Rigor cross bridges are also thought to increase calcium binding to troponin C and play a synergistic role in activation. We tested the hypothesis that cross bridge-dependent activation results in an increase in contractile activity at normal and low pH values. Myofibrillar ATPase activity was measured as a function of pCa and [MgATP] at pH 7.0, and the data showed that, at pCa values of ≥5.5, there was a biphasic relationship between activity and [MgATP]. Peak activity occurred at 10–50 μM MgATP, and [MgATP] for peak activity was lower with increased pCa. The ATPase activity of rat cardiac myofibrils as a function of [MgATP] at a pCa of 9.0 was measured at several pH levels (pH 5.4–7.0). The ATPase activity as a function of [MgATP] was biphasic with a maximum at 8–10 μM MgATP. Lower pH did not result in a substantial decrease in myofibrillar ATPase activity even at pH 5.4. The extent of shortening, as measured by Z-line spacing, was greatest at 8 μM MgATP and less at both lower and higher [MgATP], and this response was observed at all pH levels. These studies suggest that the peak ATPase activity associated with low [MgATP] was coupled to sarcomere shortening. These results support the hypothesis that cross bridge-dependent activation of contraction may be responsible for contracture in the ischemic heart.

scholarly journals Substructure and accessory proteins in scallop myosin filaments.

1989 ◽  
Vol 109 (2) ◽  
pp. 539-547 ◽  
Author(s):  
P Vibert ◽  
L Castellani
Keyword(s):  
Ionic Strength ◽  
Striated Muscle ◽  
Rotational Symmetry ◽  
Thick Filament ◽  
Accessory Proteins ◽  
Myosin Filaments ◽  
Cross Bridges ◽  
Low Ionic Strength ◽  
Muscle Myosin

Native myosin filaments from scallop striated muscle fray into subfilaments of approximately 100-A diameter when exposed to solutions of low ionic strength. The number of subfilaments appears to be five to seven (close to the sevenfold rotational symmetry of the native filament), and the subfilaments probably coil around one another. Synthetic filaments assembled from purified scallop myosin at roughly physiological ionic strength have diameters similar to those of native filaments, but are much longer. They too can be frayed into subfilaments at low ionic strength. Synthetic filaments share what may be an important regulatory property with native filaments: an order-disorder transition in the helical arrangement of myosin cross-bridges that is induced on activation by calcium, removal of nucleotide, or modification of a myosin head sulfhydryl. Some native filaments from scallop striated muscle carry short "end filaments" protruding from their tips, comparable to the structures associated with vertebrate striated muscle myosin filaments. Gell electrophoresis of scallop muscle homogenates reveals the presence of high molecular weight proteins that may include the invertebrate counterpart of titin, a component of the vertebrate end filament. Although the myosin molecule itself may contain much of the information required to direct its assembly, other factors acting in vivo, including interactions with accessory proteins, probably contribute to the assembly of a precisely defined thick filament during myofibrillogenesis.

Filament Formation by Slime Mould Myosin Isolated at Low Ionic Strength

1974 ◽  
Vol 15 (1) ◽  
pp. 113-129
Author(s):  
H. HINSSEN ◽  
J. D'HAESE
Keyword(s):  
Ionic Strength ◽  
Striated Muscle ◽  
Divalent Cations ◽  
Filament Formation ◽  
Selective Precipitation ◽  
Slime Mould ◽  
Preparation Conditions ◽  
Filament Structure ◽  
Low Ionic Strength

Myosin was isolated and purified from plasmodia of the slime mould Physarum polycephalum by a new method. This method is based on actomyosin extraction at low ionic strength after extensive washing, followed by the selective precipitation of myosin at pH 6.1 under relaxing conditions. The yield of myosin was 3-5 times higher than reported for other methods. In contrast to earlier studies a remarkably strong tendency to filament formation was found for slime mould myosin, probably due to a better preservation of some structural properties during preparation. Conditions were worked out under which numerous filaments up to 4 µm in length can be produced. It was established that not only a gradual decrease of ionic strength may influence filament formation, but also pH, ATP concentration and the presence of divalent cations. Compared to the current filament models a difference exists in the structure of the filaments. No central bare zone can be found, and thus, they lack an apparent bipolarity. Along the entire filament there are lateral projections representing the head portion of myosin molecules. A clear periodicity with an axial repeat of about 14 nm was observed, indicating a highly ordered arrangement of these projections. In this paper it is shown for the first time that myosin from one of the primitive motile systems is able to form aggregates of high structural order, indicating that the contraction of non-muscular actomyosin systems is not necessarily effected with oligomeric or randomly aggregated myosin. The possible role of myosin aggregation in vivo and the similarity of filament structure to that recently reported for myosin from vertebrate smooth muscle and striated muscle are discussed.

scholarly journals Activation of the Adenosine Triphosphatase of Limulus polyphemus Actomyosin by Tropomyosin

1972 ◽  
Vol 59 (4) ◽  
pp. 375-387 ◽  
Author(s):  
William Lehman ◽  
Andrew G. Szent-Györgyi
Keyword(s):  
Ionic Strength ◽  
Atpase Activity ◽  
Adenosine Triphosphatase ◽  
Limulus Polyphemus ◽  
Muscle Tropomyosin ◽  
Low Ionic Strength ◽  
Full Activation

Purified actin does not stimulate the adenosine triphosphatase (ATPase) activity of Limulus myosin greatly. The ATPase activity of such reconstituted preparations is only about one-fourth the ATPase of myofibrils or of natural actomyosin. Actin preparations containing tropomyosin, however, activate Limulus myosin fully. Both the tropomyosin and the actin preparations appear to be pure when tested by different techniques. Tropomyosin combines with actin but not with myosin and full activation is reached at a tropomyosin-to-actin ratio likely to be present in muscle. Tropomyosin and actin of several different animals stimulate the ATPase of Limulus myosin. Tropomyosin, however, is not required for the ATPases of scallop and rabbit myosin which are fully activated by pure actin alone. Evidence is presented that Limulus myosin, in the presence of ATP at low ionic strength, has a higher affinity for actin modified by tropomyosin than for pure actin.

scholarly journals THE DOUBLE ARRAY OF FILAMENTS IN CROSS-STRIATED MUSCLE

1957 ◽  
Vol 3 (5) ◽  
pp. 631-648 ◽  
Author(s):  
H. E. Huxley
Keyword(s):  
Striated Muscle ◽  
The Other ◽  
Thin Sections ◽  
Alternative Models ◽  
Double Array ◽  
The Cross ◽  
Cross Bridges

The conditions under which one might expect to see the secondary filaments (if they exist) in longitudinal sections of striated muscle, are discussed. It is shown that these conditions were not satisfied in previously published works for the sections were too thick. When suitably thin sections are examined, the secondary filaments can be seen perfectly easily. It is also possible to see clearly other details of the structure, notably the cross-bridges between primary and secondary filaments, and the tapering of the primary filaments at their ends. The arrangement of the filaments and the changes associated with contraction and with stretch are identical to those already deduced from previous observations and described in terms of the interdigitating filament model in previous papers. There are therefore excellent grounds for believing that this model is correct. The alternative models which have been proposed appear to be incompatible both with the present observations and with much of the other available evidence.

Basis of passive tension and stiffness in isolated rabbit myofibrils

1997 ◽  
Vol 273 (1) ◽  
pp. C266-C276 ◽  
Author(s):  
M. L. Bartoo ◽  
W. A. Linke ◽  
G. H. Pollack
Keyword(s):  
Ionic Strength ◽  
Dynamic Stiffness ◽  
Passive Tension ◽  
Passive Force ◽  
Force Response ◽  
Weakly Bound ◽  
Strain Limit ◽  
Sinusoidal Oscillations ◽  
Cross Bridges ◽  
Low Ionic Strength

By examining the mechanical properties of isolated skeletal and cardiac myofibrils in calcium-free, ATP-containing solution, we attempted to separate the stiffness contribution of titin filaments from that of weakly bound cross bridges. Efforts to enhance weak cross-bridge binding by lowering ionic strength were met by clear contractile responses. Even at low temperature, myofibrils bathed in low-ionic-strength relaxing solution generated increased force and exhibited sarcomere shortening, apparently caused by active contraction. At normal ionic strength, myofibril stiffness, estimated from the force response to rapid sinusoidal oscillations, increased steadily with sarcomere extension up to a strain limit. No obvious stiffness contribution from weak cross bridges was detectable. Instead, the stiffness response, which was frequency dependent at all sarcomere lengths, was apparently generated by the viscoelastic titin filaments. During imposed stretch-hold ramps, both peak force/stiffness and the amount of subsequent stress relaxation increased with higher stretch rates, larger stretch amplitudes, and longer sarcomere lengths. We conclude that, for a truly relaxed myofibril, both passive force and dynamic stiffness principally reflect the intrinsic viscoelastic properties of the titin filaments.

scholarly journals A 72,000-mol-wt protein from tomato inhibits rabbit acto-S-1 ATPase activity.

1983 ◽  
Vol 96 (6) ◽  
pp. 1761-1765 ◽  
Author(s):  
M Vahey
Keyword(s):  
Skeletal Muscle ◽  
Ionic Strength ◽  
Atpase Activity ◽  
Rabbit Skeletal Muscle ◽  
Ion Concentration ◽  
Actin Binding ◽  
Molar Ratio ◽  
Reversible Inhibitor ◽  
Skeletal Muscle Myosin ◽  
Low Ionic Strength

Tomato activation inhibiting protein (AIP) is a molecule of an apparent molecular weight of 72,000 that co-purifies with tomato actin. In an assay system containing rabbit skeletal muscle F-actin and rabbit skeletal muscle myosin subfragment-1 (myosin S-1), tomato AIP dissociated the acto-S-1 complex in the absence of Mg+2ATP and inhibited the ability of F-actin to activate the low ionic strength Mg+2ATPase activity of myosin S-1. At a molar ratio of 5 actin to 1 AIP, a 50% inhibition of the actin-activated Mg+2ATPase activity of myosin S-1 was observed. The inhibition can be reversed by raising the calcium ion concentration to 1 X 10(-5) M. The AIP had no effect on the basal low ionic strength Mg+2ATPase activity of myosin S-1 in the absence of actin. The protein did not bind directly to actin nor did it cause depolymerization or aggregation of F-actin but appeared, instead, to interact with the actin binding site on myosin S-1. Since AIP is a potent, reversible inhibitor of the rabbit acto-S-1 ATPase activity, it is postulated that it may be responsible for the low levels of actin activation exhibited by tomato F-actin fractions containing the AIP.

Actomyosin-like protein of arterial wall

1963 ◽  
Vol 205 (6) ◽  
pp. 1247-1252 ◽  
Author(s):  
Ronald S. Filo ◽  
J. Caspar Ruegg ◽  
David F. Bohr
Keyword(s):  
Ionic Strength ◽  
Atpase Activity ◽  
Arterial Wall ◽  
Structural Protein ◽  
High Solubility ◽  
Viscosity Change ◽  
Relaxing Factor ◽  
Contractile System ◽  
Crude Preparation ◽  
Low Ionic Strength

A structural protein is extractable from hog carotids in solutions of low ionic strength (0.05 m KCl + 0.02 m histidine buffer). The following procedures cause precipitation of this protein: 1) standing 12 hr at 2–4 C, 2) dialysis against 0.05 m KCl, or 3) addition of 10 mm CaCl2. The crude preparation obtained by any of these precipitation procedures fails to show superprecipitation on the addition of ATP, but when dissolved in 0.6 m KCl it does demonstrate a viscosity change on the addition of ATP and is capable of ATPase activity. If this crude preparation is purified by repeated calcium precipitation and dialysis against 0.05 m KCl, it then shows the following characteristics typical of actomyosin: 1) superprecipitation, 2) reversible viscosity change on addition of ATP, and 3) ATPase activity characteristically influenced by calcium, or magnesium, or ionic strength. We conclude that this structural protein from hog carotid is an actomyosin-like protein involved in a standard contractile system, and its initial high solubility at low ionic strength may be due either to a reduction in bound calcium or to the presence of an unusually effective solubilizing factor which, like relaxing factor, can be inhibited by calcium.

Correlation between Ca2+-ATPase activity of rat islet cells and insulin secretion

1992 ◽  
Vol 134 (2) ◽  
pp. 221-225 ◽  
Author(s):  
C. M. Gronda ◽  
G. B. Diaz ◽  
J. P. F. C. Rossi ◽  
J. J. Gagliardino
Keyword(s):  
Enzyme Activity ◽  
Insulin Secretion ◽  
Ionic Strength ◽  
Atpase Activity ◽  
Islet Cells ◽  
Experimental Conditions ◽  
Physiological Regulation ◽  
Enhancing Effect ◽  
Cellular Targets ◽  
Low Ionic Strength

ABSTRACT Using medium with a low ionic strength, a low concentration of Ca2+ and Mg2+ and devoid of K+, we have measured Ca2+-ATPase activity in the homogenates of rat islets preincubated for 3 min with several hormones in the presence of 3·3 mmol glucose/l. Insulin secretion was also measured in islets incubated for 5 min under identical experimental conditions. Islets preincubated with glucose (3·3 mmol/l) and glucagon (1·4 μmol/l) plus theophylline (10 mmol/l), ACTH (0·11 nmol/l), bovine GH (0·46 μmol/l), prolactin (0·2 μmol/l) or tri-iodothyronine (1·0 nmol/l) have significantly lower Ca2+-ATPase activity than those preincubated with only 3·3 mmol glucose/l. All these hormones increased the release of insulin significantly. Dexamethasone (0·1 μmol/l) and somatostatin (1·2 μmol/l) enhanced the Ca2+-ATPase activity while adrenaline (10 μmol/l) did not produce any significant effect on the activity of the enzyme. These hormones decreased the release of insulin significantly. These results demonstrated that islet Ca2+-ATPase activity was modulated by the hormones tested. Their inhibitory or enhancing effect seemed to be related to their effect on insulin secretion; i.e. those which stimulated the secretion of insulin inhibited the activity of the enzyme and vice versa. Hence, their effect on insulin secretion may be due, in part, to their effect on enzyme activity and consequently on the concentration of cytosolic Ca2+. These results reinforce the assumption that Ca2+-ATPase activity participates in the physiological regulation of insulin secretion, being one of the cellular targets for several agents which affect this process. Journal of Endocrinology (1992) 134, 221–225

scholarly journals Effect of cross-bridge kinetics on apparent Ca2+ sensitivity.

1982 ◽  
Vol 79 (6) ◽  
pp. 997-1016 ◽  
Author(s):  
P W Brandt ◽  
R N Cox ◽  
M Kawai ◽  
T Robinson
Keyword(s):  
Ionic Strength ◽  
Phosphate Concentration ◽  
Hill Coefficient ◽  
Cross Bridge ◽  
Left Shift ◽  
Hill Coefficients ◽  
Tension Curve ◽  
The Cross ◽  
Cross Bridges ◽  
The Hill

Three different ways of shifting the pCa/tension curve on the pCa axis have been studied and related to changes in the rate constants of the cross-bridge cycle. The curve midpoint shifts to higher pCa's when the substrate (Mg-ATP) is reduced from 5 to 0.25 mM, when the phosphate concentration is reduced from 7.5 mM to 0, and when the ionic strength is reduced from 0.200 to 0.120. The Hill coefficients of the pCa/tension curve in our standard saline (5 mM substrate, 5 mM free ATP, 7.5 mM phosphate, ionic strength 0.200, 15 degree C) are between 5.1 and 5.6 and fall to 3.0 with the left shift of the curve brought about by reducing both substrate and phosphate. Left shifts of the curve produced by reduction in the ionic strength do not result ina lower Hill coefficient. Reducing eigher substrate or phosphate is associated with a reduction in the optimal frequency for oscillatory work, but reduction in ionic strength is not so associated. Maximum tension increases with the left shift of the curve brought about by reducing phosphate concentration or ionic strength, but tension decreases with the left shift of the curve accompanying substrate concentration reduction in phosphate-free saline. We argue that one mechanism for the observed shift of the curve along the pCa axis is the relationship between the time a cross-bridge takes to complete a cycle and the time Ca2+ stays bound to troponin C (TnC). If the cycle rate is decreased, a smaller fraction to TnC sites must be occupied to keep a given fraction of cross-bridges active. To illustrate this concept, we present a simplified model of the cross-bridge cycle incorporating the kinetics of Ca binding to TnC.

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