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J M Squire

Publications and source records attributed to J M Squire.

At least 37 records · Page 2Linked to original sources
PubMed1992

Evidence for structurally different attached states of myosin cross-bridges on actin during contraction of fish muscle.

Using data from fast time-resolved x-ray diffraction experiments on the synchrotrons at Daresbury and (Deutsches Elektronen Synchrotron [DESY]), it is shown that during contraction of fish muscle there are at least two distinct configurations of myosin cross-bridges on actin, that they appear to have different tension producing properties and that they probably differ in the axial tilt of the cross-bridges on actin. Evidence is presented for newly observed myosin-based layer lines in patterns from active fish muscle, together with intensity changes of the actin layer lines. On the equator, the 110 reflection changes much faster (time for 50% change t1/2 = 21 +/- 4 ms after activation) than the 100 reflection (t1/2 = 35 +/- 8 ms) and tension (t1/2 = 41 +/- 3 ms) during the rising phase of tetanic contractions. These and higher order reflections have been used to show the time course of mass attachment at actin during this rising phase. Mass arrival (t1/2 = 25 ms) precedes tension by approximately 15 ms. Analysis has been carried out to evaluate the effects of changes in sarcomere length during the tetanus. It is shown that any such effects are very small. Difference "equatorial" electron density maps between active muscle at a time when mass arrival at actin is just complete, but the tension is still rising, and at a later time well into the tension plateau, show that the structural difference between the lower and higher force states corresponds to mass movement consistent with axial swinging of heads from a nonstereospecific actin attached state (low force) to a more stereospecific (high force) state.

Actins↗
PubMed1991

Crossbridge states in isometrically contracting fish muscle: evidence for swinging of myosin heads on actin.

We have previously shown that time-resolved X-ray diffraction studies of the 2-D pattern from isometrically contracting flatfish (turbot) fin muscle have considerable advantages over similar studies of other vertebrate muscles due to the simple lattice and the better long-range order in these muscles (5, 24). Here we show not only that two structurally different myosin head to actin attached states must exist in the crossbridge cycle but that we are also able to define the likely crossbridge configurations in these states. A non-force producing "weak-binding" state is evident from the lead of the (11) equatorial reflections (and actin mass) time-course relative to that of tension (and the (10) equatorial reflection decrease) by about 30 msec. The first myosin layer line at 429 A has a weakened but altered intensity distribution, with no change in axial spacing, in patterns from active muscle. We show this to be consistent with myosin heads binding in the non-specific manner envisaged for the "weak-binding" state. Evidence for the second force-producing attached state, or series of states, comes from the observation of only a small increase in the intensity of the 360 A actin layer line between resting and active muscle patterns. It might be thought that a substantial increase in this layer line would be expected if myosin heads were even transiently attached to the thin filaments in a force-producing state. However, this is not so because internal changes in the structure of the thin filaments in active muscle have the opposite effect of causing this layer line to decrease in intensity. Observation of a small net intensity increase is therefore evidence for myosin head attachment with the symmetry of the actin helix. From the equatorial diffraction pattern, Fourier synthesis maps were computed at 10 msec intervals throughout the isometric tetanus, enabling changes in the mass distribution to be visualised between the force- and non-force producing populations of crossbridges. This difference map shows that in the force-producing state myosin heads have their centres of mass on average at a smaller radius from the thin filament axis compared to the case for non-force producing myosin heads. Since there is good evidence that there is no substantial change in myosin head shape during contraction (30) these observations are consistent with myosin heads swinging on actin as fairly rigid structures.

Actins↗
PubMed1991

X-ray diffraction testing for weak-binding crossbridges in relaxed bony fish muscle fibres at low ionic strength.

Equatorial X-ray diffraction patterns from single skinned fibres from bony fish muscle (turbot) were obtained with the fibres at 6 degrees C bathed in relaxing solutions of 170 down to 26 mM ionic strength. Diffraction patterns from rigor fibres were also obtained as controls. Unlike fibres from rabbit muscle, which show very clear evidence of substantial crossbridge formation at low ionic strength in what is mechanically a rapid equilibrium ("weak-binding") state (Brenner et al., 1982), diffraction patterns from bony fish fibres showed only a small change in relative peak intensities at low ionic strength (26 mM) compared with normal (170 mM) ionic strength. However, there was a slight ordering of the filament lattice at low ionic strength. The specimen temperature used (about 6 degrees C) was not far from the normal physiological temperature of the fish. Likewise, only a small change was seen by Xu et al. (1987) in patterns from frog fibres at low ionic strength at 2 to 6 degrees C. (Rabbit fibres previously studied, where large changes were seen at temperatures of 5 to 20 degrees C, were about 17 to 32 degrees C below physiological.) The I11/I10 ratio for fish fibres at 26 mM ionic strength was actually lower than that for rabbit even at normal ionic strength. This may be associated with an intrinsic structural difference between these muscles or alternatively with the disordering of the crossbridge helix in rabbit muscle found at low temperature by Wray (1987), and could support the view that rabbit fibres at 5 degrees C and normal ionic strength may already have a significant population of weak-binding crossbridges.

Animals↗
PubMed1991

Cryoultramicrotomy of muscle: improved preservation and resolution of muscle ultrastructure using negatively stained ultrathin cryosections.

Ultrathin sections of rapidly frozen, briefly pre-treated muscle tissue are cut and thereafter are thawed and contrasted using a negative staining technique. The method has provided micrographs in which the in-vivo order in the muscle fibres has been preserved well enough to enable both a more complete interpretation of X-ray diffraction evidence from muscle, and also a gain of new ultrastructural information on aspects of myofibril and myofilament architecture in different types of fibre. Examples here are taken from chicken, rabbit and fish muscles and show both the M-band and the bridge region of the A-band in great detail. To enhance the detail in the original images, one-dimensional (1-D) and 2-D averaging techniques (lateral smearing and step averaging, respectively) are used. Although there is major shrinkage in section thickness to about one-third of its original value, demonstrated here for the first time is the fact that the characteristic A-band lattice planes are preserved in these sections in 3-D. This confirms the usefulness of cryosections not just for 1-D and 2-D image processing, but also for 3-D reconstruction. Thus, in combination with techniques of image processing, cryoultramicrotomy can give the muscle morphologist the detailed data that are needed to match the molecular biologists, biochemists and immunologists in the interpretation of their data about physiological and pathophysiological events in muscle fibres at the macromolecular level.

Animals↗
PubMed1990

The three-dimensional structure of the nemaline rod Z-band.

In nemaline myopathy and some cardiac muscles, the Z-band becomes greatly enlarged and contains multiple layers of a zigzag structure similar to that seen in normal muscle. Because of the additional periodicity in the direction of the filament axis, these structures are particularly favorable for three-dimensional analysis since it becomes possible to average the data in all three dimensions and thus improve the reliability of the reconstruction. Individual views of the structure corresponding to tilted longitudinal and transverse sections were combined by matching the phases of common reflections. Examination of the tilted views strongly suggested that to the available resolution, the structure possesses fourfold screw symmetry along the actin filament axes. This symmetry could be used both in establishing the correct alignment for the combination of individual tilted views and to generate additional views not readily accessible in a single tilt series. The reconstruction shows actin filaments from one sarcomere surrounded by an array of four actin filaments with opposite polarity from the adjacent sacormere. The actin filaments show a right-handed twist and are connected by a structure that links adjacent filaments with the same polarity at the same axial level, then runs parallel to the filaments, and finally forms a link between two actin filaments whose polarity is opposite to that of the first pair. The connecting structure is probably composed of alpha-actinin which is located in Z-bands and cross-links actin filaments. The connecting structure may consist of two alpha-actinin molecules linking actin filaments of opposite polarity.

Actin Cytoskeleton↗
PubMed1989

Maternal behavior of SHR rats and its relationship to offspring blood pressures.

In Part I of this study maternal behavior of 15 spontaneously hypertensive (SHR) and 11 Wistar-Kyoto (WKY) rat mothers was recorded throughout the preweaning period. SHR mothers were observed: 1) in arched-and blanket-nursing postures more often, and in passive-nursing posture less often, 2) licking their pups more often, and 3) resting less often. Further, SHR mothers retrieved their pups more quickly than did WKY. In the second part of this study we found that a composite maternal behavior score, derived from summing occurrences of mother/pup contact, arched-nursing, and pup-licking, was positively correlated with the offspring blood pressures. This relationship, which accounted for 43.5% of the variance in adult blood pressure, suggests that certain types of interactions between mothers and their pups may contribute to individual differences in cardiovascular system development.

Animals↗
PubMed1989

Relationships between maternal behavior of SHR and WKY dams and adult blood pressures of cross-fostered F1 pups.

In this experiment SHR and WKY dams reared genetically identical F1 pups derived from SHR x WKY matings. We found that a composite maternal behavior score was positively correlated with adult blood pressures of the fostered offspring. This replicated a similar finding from our previous study in which SHR and WKY mothers reared their own pups. Unlike this previous study, WKY dams rearing F1 pups exhibited maternal behavior patterns similar to SHR dams. Finally, we found there was no effect of the strain of foster mother upon adult blood pressures of the F1 offspring. These results indicate that some aspects of maternal behavior may change as a function of pup characteristics, and support our hypothesis that the cardiovascular system may be shaped by experiences of early life which are embedded in mother/young behavioral interactions.

Age Factors↗
PubMed1988

Structural diversity in muscle fibres of chicken breast.

Chicken breast muscle is usually considered to be a relatively homogeneous white muscle and has therefore been widely used for studies of muscle proteins. In a previous study, however, we have found different M-region structures in different fibres from this muscle. Because of this result, we have now carried out a combined histochemical and ultrastructural survey of this muscle. In particular, we have made use of large transverse cryo-sections that include most of the muscle cross-section. Although the white region is fairly homogeneous in fibre content according to normal histochemical criteria (mATPase), we have found that there is a gradation of fibre structure across the muscle. The bulk of the muscle stains conventionally for Type-II fibres according to mATPase tests (the "white" part) but, in the small "red" part of the muscle, there are also Type-I fibres together with the Type-II fibres. Superimposed on this division into Type-I and Type-II fibres are variations in fibre size, oxidative and glycolytic staining properties, and variations of Z-band width and M-band structure; there is no strict correlation among any of these parameters. The apparently uniform staining across most of the muscle when tested for myofibrillar ATPase may be a misleading indicator of fibre properties.

Adenosine Triphosphatases↗
PubMed1988

Actin filament organization and myosin head labelling patterns in vertebrate skeletal muscles in the rigor and weak binding states.

The structures of vertebrate skeletal muscles (particularly from frog and fish) in the rigor state are analysed in terms of the concept of target areas on actin filaments. Assuming that 100% of the heads are to be attached to actin in rigor, then satisfactory qualitative low-resolution modelling of observed X-ray diffraction data is obtained if the outer ends of these myosin heads can move axially (total range about 200A) and azimuthally (total range less than 60 degrees) from their original lattice sites on the myosin filament surface to attach in defined target areas on the actin filaments. On this basis, each actin target area comprises about four actin monomers along one of the two long-pitched helical strands of the actin filament (about 200 A) or an azimuthal range of actin binding sites of about 100 degrees around the thin filament axis. If myosin heads simply label in a non-specific way the nearest actin monomers to them, as could occur with non-specific transient attachment in a 'weak binding' state, then the predicted X-ray diffraction pattern would comprise layer lines at the same axial spacings (orders of 429 A) as those seen in patterns from resting muscle. It is shown that actin target areas in vertebrate skeletal muscles are probably arranged on an approximate 62 (right-handed) helix of pitch (P) of about 720 A, subunit translation P/6 and near repeat P/2. Troponin position need not be considered in defining the labelling pattern of cross-bridges on this 62 helix of target areas; the target areas appear to be defined solely by the azimuthal position of the actin binding sites. The distribution of actin filament labelling patterns could be regular in fish muscle which has a 'crystalline' A-band, but will be irregular in higher vertebrate muscles such as frog sartorius muscle.

Actin Cytoskeleton↗
PubMed1988

Fine structure of the A-band in cryo-sections. Diversity of M-band structure in chicken breast muscle.

Electron micrographs of longitudinal ultrathin cryo-sections and plastic sections of chicken pectoralis muscle together with their average images have been used to study in detail the axial structure of the M-band. It was found that M-band structure could vary markedly in different fibres, even within the white part of the muscle. Strong M-band density ("M-bridges") could be seen at M4 and M4' in all fibres. On the other hand the density at M1 or M6 could vary systematically. Some fibres (probably fast) had M1 strong, M6 weak (a "3-line" M-band), and the Z-band was narrow. Other fibres, especially (but not exclusively) in the red part of the muscle and probably slow, had M6 strong, M1 weak (a "4-line" M-band), and the Z-band was broad. However, the majority of fibres ranged in structure between those two extremes and had a more or less "5-line" M-band with M1 and M6 both strong and a Z-band of intermediate width. Since they were such a constant feature, the M4 lines may be the sites of the primarily structural component of the M-band, whereas the different proteins at M1 and M6 may vary in quantity according to the physiological needs of the fibre. Finally, detailed analysis sometimes revealed substructure within the strong M-bridge lines. This substructure may represent additional unknown M-band proteins or may be an indication of the shape of single proteins at these positions.

Animals↗
PubMed1987

Comparative histochemistry of a flatfish fin muscle and of other vertebrate muscles used for ultrastructural studies.

Because of the high degree of filament order in the myofibrils of fish skeletal muscles, and the resulting usefulness of such preparations (particularly flatfish fin muscles) in structural studies of muscular contraction, the fibre type composition of plaice fin muscle has been determined by conventional histochemical tests. As controls, and for comparison, fibre type distributions have also been studied in several other vertebrate skeletal muscles which are widely used for ultrastructural and mechanical studies. In view of the importance of single fibres in such studies and because much of the published information on fibre types is rather difficult to collate, we summarize here the fibre compositions of several muscles; comparable enzyme tests have been carried out on cryostat sections of rabbit psoas muscle, frog sartorius and semitendinosus muscles and plaice fin muscles. On this basis all four muscles are composed of more than one fibre type. We confirm that frog sartorius muscle is mainly a random mixture of two fast fibre types and show that there is also a third group of fibres which are small, metabolically rich and dark under acid m-ATPase tests. We confirm that the semitendinosus is composed of three fibre types, in three non-exclusive, concentric regions and that rabbit psoas muscle contains a mixture of at least three fibre types. The principal new findings of this work are that plaice fin muscle can be divided into four regions, some of which are composed of more than one fibre type, on the basis of its histochemical reactions. This division into regions changes seasonally. The system of classification devised by Dubowitz & Brooke (1973) for mammalian muscle, and which can be applied approximately to frog muscle, can also be applied to the fibres of plaice fin muscle provided that the test for lactate dehydrogenase is carried out in the presence of polyvinyl alcohol. These fibres do not easily fit the division into red, white and intermediate types normally used for fish myotomal muscles. Since none of these muscles is homogeneous, their complex nature must be borne in mind if they are to be used satisfactorily in structural and mechanical studies of muscular contraction involving the use of single fibres.

Adenosine Triphosphatases↗
PubMed1987

Dichotic listening following idiopathic precocious puberty: speech processing capacity and temporal efficiency.

Eleven right-handed adolescent females with a history of idiopathic precocious puberty (IPP) were compared to 11 pair-matched normal controls of similar maturational status. They were tested on a dichotic consonant-vowel (CV) discrimination task in which syllables were presented simultaneously to the two ears or with an interaural delay of 30 or 60 msec. The IPP and control groups did not differ: (1) in right-ear advantages; (2) in double-correct or total correct measures of accuracy; or (3) in "lag effects." The findings provide further evidence that timing of puberty--maturation rate--is not related to verbal ability or lateralization in adolescent females.

Adolescent↗
PubMed1987

Cardiovascular responses to exercise and stress in the borderline hypertensive rat.

This report demonstrates the effect of voluntary exercise in attenuating increases in heart rate (HR) caused by chronic stress in an animal model of stress-induced hypertension, the borderline hypertensive rat (BHR). Exercise training also protected against the hypertensive effects of stress in 16-wk-old, but not 10-wk-old animals. In the first experiment, adult borderline hypertensive rats were subjected to 1 wk of signaled shock followed by 6 wk of signaled, unsignaled, or no shock. Half of these animals also had free access to a running wheel. Blood pressure (BP) and HR were measured before and after treatments by the tail cuff method. Exercise was found to significantly attenuate the rise in BP by 56% and HR by over 100%, as compared to non-exercised animals. In a second study, borderline hypertensive rats were subjected daily to anticipation of shock or handling for 6 wk. Half of these animals could exercise voluntarily. BP and HR, measured weekly under light ether anesthesia, increased over time due to both stressors alone. Exercise attenuated stress-induced increases in HR by 50%, but did not attenuate BP. These studies demonstrate that voluntary exercise can reliably attenuate increases in HR regardless of age or concurrent stress, but the protective effects of exercise on stress-induced hypertension may interact with the age of the subject.

Animals↗
PubMed1983

Three-dimensional structure of the insect (Lethocerus) flight muscle M-band.

The oval myosin filament profiles in transverse sections through the M-band of Lethocerus flight muscle are arranged in one of three orientations 60 degrees apart and point along the 11 directions of the hexagonal filament lattice. Relative orientations are not systematically related to give a superlattice structure, but neither are the orientations arranged completely randomly. In fact there is a nearly random structure with a slight bias towards adjacent filaments being identically oriented. This form of M-band structure is explained in terms of interactions between quasi-equivalent M-bridges. Its implications with regard to myosin crossbridge arrangement depend on the rotational symmetry of the crossbridge helix. For 6-stranded helices, 60 degrees rotations have no noticeable effect. However, in the case of the more likely 4-stranded structure, our results show that the crossbridge origins in the insect flight muscle A-band would be highly disordered. This disorder must be accounted for in interpreting both the flared-X crossbridge interactions seen in transverse sections of rigor insect flight muscle and the beautiful X-ray diffraction patterns from the same preparation. It is likely that in rigor insect muscle, some flared-Xs have the two heads of single myosin molecules interacting with two different actin filaments, whereas other flared-Xs have both of the myosin heads in one molecule interacting with the same actin filament.

Animals↗
PubMed1980

Direct observation of a transverse periodicity in collagen fibrils.

Collagen fibrils have been extensively studied by electron microscopy, but only scant evidence has yet been obtained about their transverse structure. A transverse pediodicity of about 40 or 80 A might be expected if the microfibril model (until recently the common preference) is correct, but little direct evidence for such a periodicity has been obtained so far. We have studied electron micrographs of longitudinal cryosections of rat tail tendon. These appear very fibrous when studied by eye, but they produce at best only diffuse equatorial peaks in optical diffraction patterns. Nevertheless, we show here that like other fibrous protein structures, they do possess a strong transverse periodicity as revealed by their self-convolution functions (or auto-correlation functions). The observed periodicity is consistent with the presence of an 80 A structural unit in collagen fibrils in vivo.

Animals↗