Fibrillar Flight Muscle Research Articles

Phosphate starvation and the nonlinear dynamics of insect fibrillar flight muscle.

The nonlinear mechanical dynamics of glycerinated insect fibrillar flight muscle are investigated. The most striking nonlinearity reported previously, which often resulted in oscillatory work being limited to frequencies below those of natural flight, disappears if 5 mM or more orthophosphate is added to the experimental solutions. We show that two further asymmetric nonlinearities, which remain even though phosphate is present, are predicted by cross-bridge theory if one takes account of the expected distortion of attached cross-bridges as filament sliding becomes appreciable. Adenosine triphosphate and adenosine diphosphate have opponent effects upon the mechanical rate constants, suggesting a scheme for the sequential ordering of the events comprising the cross-bridge cycle.

Structure of insect fibrillar flight muscle in the presence and absence of ATP

Low-angle X-ray diffraction pictures were taken of Lethocerus flight muscle in one or other of its two inactive states, relaxation and rigor. They showed more detail than previous pictures and the parameters of the actin and myosin helices could be deduced from the spacings of the observed layer lines. Subunits consisting of actin monomers and of myosin heads were arranged on helices so as to conform to these parameters, and the diffraction patterns from these models were calculated. When these model systems resembled the structures observed in the electron microscope, the calculated diffraction patterns had layer Unes similar in radial distribution and relative intensity to those observed, with certain exceptions. The fit was quite critical, in that variation of the size and orientation of the subunits affected it considerably. The results support the idea that in rigor (i.e. without ATP) all of the myosin heads attach to actin monomers in a regular angled configuration. In contrast, on relaxation (i.e. on addition of ATP but no Ca 2+) most or all of the myosin heads detach from the actin and are arranged with a specific symmetry around the myosin filament. It is not necessary, however, to assume that they change shape or move far from the actin filament in this process. Features of the X-ray diffraction pattern which remained unaccounted for by this model can be explained on the basis of an arrangement of actin helices on a further helix around a thick filament. Types of extended lattices containing actin helices in statistical axial or azimuthal positions are discussed.

The formation of ‘giant’ mitochondria in the fibrillar flight muscles of the house fly, Musca domestica L.

Mitochondria in the fibrillar flight muscles of higher insects are of unusually large size and are reported to undergo age-related changes in size and number. Fibrillar flight muscles of adult male house flies ranging from 1 to 9 days of age were examined by electron microscopy in order to study the mitochondrial changes with age. In longitudinal sections of the muscle from 1-day-old flies mitochondria are elongated, 2 μ or less in length, and lie parallel to the longitudinal axis of the myofibrils. In cross-sectioned muscles of 1-day-old flies, 3–6 ovoid mitochondria surround each myofibril. Several profiles representing mitochondrial fusion are observed in flies 2 days of age. Longitudinal sections of the muscle in 9-day-old flies reveal highly elongated mitochondria ranging up to 15 μ in length. In cross sections, mitochondria form broad sleeve like structures in close apposition with the myofibrils. The bulky mitochondria in 9-day-old flies seem to be formed by the end-to-end, as well as side-to-side, fusion of smaller mitochondria. Histometric comparison indicated that the mitochondria in the flight muscle of 9-day-old flies are significantly larger in size and fewer in number than those of 1-day-old flies. It is suggested that the “giant” mitochondria in the flight muscles of the house fly arise primarily by an age-related fusion of smaller mitochondria.

Fine Structural Damage in the Somatic Tissues of Gamma-Irradiated House Fly. 1. 1 Flight Muscles

Irradiation of male Musca domestica L. with gamma rays induced considerable changes in the fine structure of the fibrillar flight muscles. Within 4 hrs after irradiation with 10,000 rads, the sarcoplasmic and transverse tubular system showed vacuolation. The extent of vacuolation increased with increase in dose. These vacuoles disappeared in the 10,000- and 20,000-rads-irradiated groups by the 6th and 10th day, respectively, but remained in the flight muscles of flies irradiated with 40,000 rads. Damage to the flight muscle mitochondria became evident 2 days after irradiation with 20,000 and 40,000 rads. Disruption of the cristae was followed by loss of material from the matrix. Eighteen days after irradiation most of the mitochondria in the 20,000-rads-irradiated group appeared to have repaired this damage, whereas in the 40,000-rads-irradiated group the damage persisted, and many mitochondria contained whorllike structures. Moreover, the mitochondria showed accumulation of glycogen granules. The significance of these findings with respect to aging in the house fly is discussed.

Bound lipid in the tissues of mammal and insect: a new histochemical method.

ABSTRACT ‘Bound’ lipids persist in ester wax sections of tissues fixed in glutaraldehyde. They do not take up Sudan black B. They are unmasked by dilute sodium hypochlorite and then stain readily with the Sudan dye and are extractable in warm chloroform and methanol. Bound lipids have been studied in tissues from the mouse and from the insects Rhodnius, Periplaneta and Calliphora. They are so widely distributed that Sudan staining alone gives an informative histological picture. They occur in nucleoli and the nuclear envelope, in the nuclear matrix and in the cytoplasm (especially when rich in endoplasmic reticulum), in plasma membranes and their invaginations and évaginations (microvilli), in septate desmosomes, and particularly in mitochondria, dictyosomes and myelin. In erythrocytes they are not only concentrated in the surface membrane but are distributed throughout the interior of the cell. In muscle fibrils (papillary muscle of the ventricle and fibrillar flight muscle of Calliphora) bound lipid occurs in small amounts in the dark regions of the unstained muscle (‘A’-bands) but is normally absent from the ‘Z’-line and from the ‘I’-bands. In highly contracted muscle this relation is reversed: lipid is concentrated around the ‘Z’-line. The elastic layers and fibrils in arteries are rich in bound lipid. Bound lipids are presumably lipoproteins. Purified lipoprotein from egg yolk examined histochemically has the same properties.

Evidence of Crossbridge Movement during Contraction of Insect Flight Muscle

THE myosin crossbridges which project from the thick filaments of striated muscle are known to bend and attach to the thin filaments in the absence of their enzymatic substrate, ATP1. Huxley and Brown have produced evidence that crossbridges are displaced during tetanic contraction of frog sartorius muscle2. We have sought evidence of such motion during the oscillatory contraction of insect fibrillar flight muscle.

Distributed Representations for Actin-Myosin Interaction in the Oscillatory Contraction of Muscle

In this paper we suggest and test a specific hypothesis relating the attachment-detachment cycle of cross bridges between actin (I) and myosin (A) filaments to the measured length-tension dynamics of active insect fibrillar flight muscle. It is first shown that if local A-filament strain perturbs the rate constants in the cross-bridge cycle appropriately, then exponentially delayed tension changes can follow imposed changes of length; the latter phenomenon is sufficient for the work-producing property of fibrillar muscle, as measured with small-signal forcing of length and at low Ca(2+) concentration, and possibly for related effects described recently in frog striated muscle. It is not clear a priori that the above explanation of work production by fibrillar muscle will remain tenable when the viscoelastic complexity of the heterogeneous sarcomere is taken into account. However, White's (1967) recent mechanical and electron microscope study of the passive dynamics of glycerinated fibrillar muscle has produced a model of the distributed viscoeleastic structure sufficiently explicit that alternative schemes for cross-bridge force generation in this muscle can now be tested more critically than previously. Therefore, we derive and solve third-order partial-differential equations which relate local interfilament shear forces associated with the perturbed cross-bridge cycles to the over-all length-tension dynamics of an idealized sarcomere. We then show (a) that the starting hypothesis can account approximately for the small-signal dynamics of glycerinated muscle in the work-producing state over two decades of frequency and (b) that the rate constants for cross-bridge formation and breakage, restricted solely by fitting of the model to the mechanical data, determine a cycling rate of cross bridges in the model compatible with recent measurements of ATP hydrolysis rate vs. stretch in this muscle. Finally, the formulation is extended tentatively to the large-signal nonlinear case, and shown to compare favorably with previous suggestions for the origin of the work-producing dynamics of fibrillar flight muscle.

On the contractile mechanism of insect fibrillar flight muscle. 3. The phenomenon of stress relaxation.

On the contractile mechanism of insect fibrillar flight muscle. 3. The phenomenon of stress relaxation.

Changes of adenosine triphosphatase activity and tension with fibre elongation in glycerinated insect fibrillar flight muscle

1. The relationship between fibre elongation and the CA2+-activated ATPase of glycerinated insect fibrillar muscle has been studied. 2. The A-filaments in insect fibrillar muscle are directly strained in a Ca2−-free solution in the absence of permanent actin-myosin interactions. Strain increases the sensitivity of the fibres to low levels of Ca2+. 3. Both ATPase and tension increase up to a fibre extension of 10%; above this fibre length no further strain can be applied to the A-filaments. Between 10% and 20% stretch both tension and ATPase reach a plateau. 4. At fibre elongations greater than 20% both fibre tension and ATPase activity decrease again corresponding to the reduction in the overlap between the A-and I-filaments.

On the contractile mechanism of insect fibrillar flight muscle. II. Passive muscle--a visco-elastic system.

On the contractile mechanism of insect fibrillar flight muscle. II. Passive muscle--a visco-elastic system.

On the contractile mechanism of insect fibrillar flight muscle. I. The dynamics and energetics of the linearized system.

Zur Erfassung der dynamischen Vorgange bei der Muskelkontraktion wurde das System des fibrillaren Insektenflugmuskels unter Bedingungen, die eine Linearisierung zulassen, untersucht. Um die Frequenzantwort als das Systemverhalten im sinusformigen stationaren Zustand zu erhalten, wurden die durch aufgepragte sinusformige Langenanderungen erzeugten Spannungsanderungen gemessen. Die Frequenzganganalysen beziehen sich auf die Annahme eines zeitinvarianten Systems mit konzentrierten Elementen. Die dominanten passiven Strukturen des Muskels, die Verbindungs-filamente und die Myosinbrucken, konnen in dem Frequenzbereich, der den Arbeitsfrequenzen des Insektenflugmuskels entspricht, durch ein aus drei Elementen bestehendes viscoelastisches System des Maxwell-Typs mit Zeitkonstanten vergleichbarer Grose beschrieben werden. Fur die Frequenzantwort des aktivierten Muskels wurde mit hinreichender Genauigkeit die Ubertragungsfunktion eines Phasenminimum-systems ermittelt. Eine theoretische Ubertragungsfunktion fur aktive Seite der Kontraktion ist durch Differenzbildung experimentell erhaltener Ortskurven bestatigt worden. Auf der Grundlage dieser theoretischen Differenzkurve wurde eine Beziehung zwischen oscillatorischer Arbeit und enzymatischer Hydrolyse des Adenosintriphosphates (ATP) als Energiequelle hergestellt. Bis zur optimalen Frequenz der Oscillation unter den benutzten Bedingungen wird eine Proportionalitat zwischen diesen Grosen festgestellt, die durch einen konstanten mechanochemischen Kopplungsfaktor bestimmt ist.

The calcium sensitivity of ATP ase activity of myofibrils and actomyosins from insect flight and leg muscles

Myofibrils and actomyosin suspension were prepared from the fibrillar flight and non-fibrillar leg muscles of the water-bug, Lethocerus maximus , and their ATP ase activity measured in solutions of various ionic strength containing Mg ATP . Leg muscle showed a low ATP ase in the absence of Ca 2+ , and a large increase of ATPase over a narrow range of Ca 2+ concentration. Flight muscle had a greater ATPase in the absence of Ca 2+ but showed a much smaller increase over a wider range of Ca 2+ concentration. A similar difference between flight and leg muscle was found in the honey-bee, Apis mellifera , and the beetle, Oryctes rhinoceros , both of which have fibrillar flight muscles, but was not found in the locust, Locusta migratoria , which has non-fibrillar flight muscle. Tryptic digestion raised the ATP ase in the absence of Ca 2+ , and abolished the Ca 2+ -activation, in both flight and leg-muscle preparations from the water-bug; addition of ‘native tropomyosin5 prepared from rabbit muscle partially reversed the effect. These results are discussed in relation to the structural peculiarities and oscillatory mechanical activity of fibrillar flight muscle.

The effect of glycerination on the fibrillar flight muscles of belostomatid water-bugs.

The progressive effects of glycerol extraction on the myofibrils and membranous structures of insect flight muscle were examined. The myofibrils appear to be intact after extraction for several months. The mitochondria are completely disrupted within 3 days, but later the fragments come together to form mitochondrion-like bodies. The sarcoplasmic reticulum around the Z-lines is preserved for many months, but the T-system and dense bodies of the dyads disappear after about 7 days extraction.

The fibrillar flight muscles of giant water-bugs: an electron-microscope study.

Abstract The fibrillar flight muscles of several species of tropical water-bugs of the family Belosto-matidae have been examined in the electron microscope. The myofibrils are very similar to those of the other fibrillar flight muscles which have been studied. The membrane systems, however, display features which appear to be peculiar to this family. The sarcoplasmic reticulum can be divided into three parts : a series of interconnecting vesicles surrounding the Z-lines, randomly scattered small vesicles around the myofibrils, and flattened cisternae which lie along the transverse tubular system, and form the dyads. These three components of the sarcoplasmic reticulum do not appear to be interconnected. The cisternae of the dyads contain an electron-dense substance. The narrow tubules of the transverse tubular system or T-system penetrate deep into the fibre from the cell mémbrane. They follow a course roughly perpendicular to the myofibrils at the level of the M-lines. The dyads are scattered along their length, and may not be near a myofibril. Another system of very large vesicles is found in the muscle fibres, interspersed among the mitochondria. These vesicles usually appear to be empty; their nature and function are not at present known. Numerous mitochondria are present among the myofibrils. The peculiarities of the water-bug fibrillar flight muscle are discussed in relation to the flight muscles of other insects and the physiological properties of fibrillar flight muscle.

The effect of Ca 2+ and fibre elongation on the activation of the contractile mechanism of insect fibrillar flight muscle

1. The relationship between fibre length and the Ca 2+-activated ATPase (ATP phosphohydrolase, EC 3.6.1.3) of insect fibrillar muscle has been studied. 2. Low levels of Ca 2+ and small degrees of fibre extension have been found to increase the ATPase activity. Either factor influences the sensitivity of the material to the other factor. 3. In insect fibrillar muscle, where the A filaments are continuous with the Z line, it is possible to strain the A filaments directly in the absence of permanent actin-myosin interactions. 4. The higher ATPase activity as a result of fibre elongation is accompanied by an increase in Ca 2+ binding. 5. Small maintained length changes do not affect the rate of ATP breakdown catalyzed by glycerinated fibres from frog sartorius or rabbit psoas muscle. 6. The relevance of the findings to the mechanism of oscillatory contraction of insect fibrillar muscle is discussed.

The mass of myosin per cross-bridge in insect fibrillar flight muscle

The myofibrillar proteins in the flight muscle of the tropical water-bug Lethocerus cordofanus were fractionated to obtain a measure of the myosin content of the muscle fibres. The number of myofilaments present in each muscle fibre was calculated from optical and electron micrographs of transverse sections and related to the number of cross-bridges per myosin filament. The results suggest that there are three myosin molecules of molecular weight 5 × 10 5 present in each cross-bridge.

Mechanical factors affecting the ATPase activity of glycerol-extracted insect fibrillar flight muscle.

The ATP split by glycerol-extracted fibrillar flight muscle of the tropical water bug Lethocerus cordofanus was measured in the presence of an inhibitor of mitochondrial ATP ase in a calciumbuffered solution at pH 7.1 and under controlled mechanical extension and oscillation. In the absence of calcium (pCa > 8.5) the ATP ase activity of the fibres was low ( ca . 10 nmole ATP split (mg protein) -1 min -1 ) and was not significantly changed by oscillating or stretching the muscle by a few percent of its rest length. When the calcium concentration was raised to 10 -7 to 10 -6 M in an unstretched muscle the ATP ase increased, and on stretching the muscle by up to 5 % of its rest length the calcium-activated ATP ase rose again, to 30 to 90 nmole (mg protein ) -1 min -1 . Further extension of the muscle did not increase the ATP ase. The effect of extension on ATP ase was found whether or not calcium was present during the extension. Oscillation of the stretched muscle by up to 3 % of its rest length at a frequency of 3 to 5 c/s produced a further increase of the calcium-activated ATP ase, apparently proportional to the work done by the muscle (mechanochemical coefficient = 1.0 to 2.4 kcal/mole). Oscillation at higher or lower frequencies produce less increase of ATP ase. Evidence is presented to show that these changes were effects of the mechanical events on the myofibrillar enzymic activity in a constant chemical environment, and were not caused by variation in the diffusion of ATP within the fibres.

Indication for an allosteric effect of adenosine diphosphate in actomyosin gels from insect fibrillar flight muscle

Actomyosin can be extracted as the intact contractile complex from insect fibrillar flight muscle at high ionic strength. The ATPase activity is activated by calcium concentrations above 10 −8 m and reaches an initial maximum at 7.5 × 10 −7 m Ca ++. This Ca ++-activated actomyosin ATPase is under cooperative inhibition by ADP. In presence of inhibitory levels of ADP, the Ca ++-activated enzyme also exhibits cooperative effects with respect to the substrate. A structural transition can be observed in presence of ADP. Both the cooperative effects of ADP on the enzyme activity and the structural changes induced by ADP are lost as a result of various desensitizing treatments, although the enzyme activity either increases or remains unaffected. An allosteric model and its possible implication for the oscillatory contractile activity of insect flight muscle is discussed.

The activating effects of calcium ions on the contractile systems of insect fibrillar flight muscle

The Ca2+ induced activation of the ATP-ase and contraction of myofibrils and actomyosin from fibrillar insect flight muscle, the sensitivity to Ca2+ and conditions for the Ca2+ activation have been investigated. 1. Ca2+ activate the ATP-ase of the myofibrils and of the actomyosin but not that of mitochondria (in presence of Mg2+). 2. 50% activation of ATP-ase is produced by about 10−7 M Ca2+. 3. The degree of ATP-ase activation by Ca2+ (10−6 M) is five to ten times less than in non-oscillating insect muscle or in vertebrate-skeletal muscle. 4. The low ATP-ase activity of isolated myosin and the superprecipitation of an actomyosin gel in the relaxing medium suggest that the relativly high ATP-ase of myofibrils and actomyosin gels is not a myosin ATP-ase but an actomyosin ATP-ase or an additional ATP-ase. 5. The relaxation of glycerinated fibres and isolated actomyosin by removal of Ca2+ requires the presence of Mg2+. But the inhibitory effect on the ATP-ase activity produced by removal of Ca2+ is decreased by addition of Mg2+. 6. Contraction induced by addition of Ca2+ is associated with an increased ATP-ase activity, contraction induced by removal of Mg2+ in the absence of Ca2+ is associated with a decreased ATP-ase activity. This difference may suggest that both types of contraction depend on different mechanisms.

Functional aspects of flight in belostomatid bugs (Heteroptera)

1. There are four pairs of fibrillar muscles in the mesothorax of the Belostomatidae. The dorsal longitudinal muscles provide power for the downstroke and automatic pronation of the wings. The dorso-ventral muscles provide upstroke power and automatic supination. The oblique dorsal muscles act mainly as wing supinators; they are also important in the wing unlocking process. The fourth pair of fibrillar flight muscles are basalars which act indirectly via an insertion on the pre-episterna; their action is that of an accessory wing depressor and pronator. The only direct flight muscles in the mesothorax are the tonic wing-folding muscles which insert on the third axillary sclerites. There are no fibrillar flight muscles in the metathorax. 2. The pterothorax contains a fused meso- and metathoracic ganglion. The most anterior nerve trunk from this ganglion provides the motor supply to the dorsal longitudinal and oblique dorsal muscles. There are no recurrent nerves between pro- and pterothoracic ganglia, yet some of the motor neurons of the dorsal longitudinal and oblique dorsal muscles are located anterior to the pterothoracic ganglion. This is not true of the motor neurons of any of the other pterothoracic muscles. There are at least three motor units in each oblique dorsal muscle and five or more in each dorsal longitudinal muscle. The anterior nerve trunk of the pterothoracic ganglion also supplies a sensory nerve to the wings and a small nerve which sup­plies the mesothoracic scolopophorous organ which probably monitors the flight rhythm. The second nerve trunk of the pterothoracic ganglion supplies all of the other mesothoracic muscles and sends one nerve to the mesothoracic legs. 3. Wing-beat frequency for a specimen ofL. maximus105 mm long and weighing 23·4 g was 21-25/s at 23-24°C. ForHydrocyrius57 mm long and weighing 2·9 g wing beat was 30/s. ForL. uhleritypical values are 42 mm long, 1·7 g weight and wing-beat frequency of 38/s. 4. The fibrillar muscles all display strong spike activity coincident with wing opening. The wings may be held open indefinitely without flight and fibrillar muscle activity then subsides to a lower level within a few seconds. Once open, the wings may be held open in the absence of any muscle activity. When flight is initiated directly from closed wings a phasic burst of spikes is recorded initially from the fibrillar muscles but this subsides quickly to a lower level characteristic of steady flight. When flight is initiated from open wings and these muscles are already active electrically there is no change in pattern of spike activity signalling start of flight. In steady flight the pattern of spike activity is irregular and bears no temporal rela­tionship to the regular wing beat. The activity of motor units from each muscle of a pair or from different fibrillar muscles also show random temporal relationships.