Insect Muscle Research Articles

Bicarbonate ions and the resting potential of cockroach muscle: Implications for the development of suitable salinem media

1. 1. The efficacy of different buffering systems in maintaining the resting potential of cockroach muscle, when included in the bathing saline, has been tested. HCO 3 −-buffered saline proved particularly suitable. 2. 2. Although it has been tested less exhaustively in the present experiments, Tris (hydroxymethyl) methylammonium carbonate may also prove to be a very useful buffering system for experiments with insect muscle, especially where exposure is prolonged. 3. 3. The resting potential of cockroach muscle apparently contains a HCO 3 −-sensitive, hyperpolarizing component which accounts for approximately one third of the normal transmembrane potential and which is inhibited by treatment with 5 mM acetazolamide. This component may be implicated in the transport of ions across the muscle membrane. Comparisons are made with other HCO 3 −-dependent transport systems. 4. 4. It is suggested that in studies on the electrochemistry of the muscles of other insects the buffering system of the saline should be checked by comparing it with the insect's own haemolymph in its ability to maintain the resting potential over periods of 2—3 hr.

Excitatory Transmission in Insect Neuromuscular Systems

Many, but not all, visceral muscles in insects are innervated by neurosecretory axons. The neurosecretory junctions with the heart muscle of the American cockroach, Periplaneta americana , show ultrastructural and electrophysiological evidence of chemically transmitting synapses, and cytochemical evidence for the presence of monoamines. Electron microscopy of nerve terminals shows that synaptic vesicles may be formed directly from electron-dense “neurosecretory” granules Neurotomy of motor axons to skeletal muscles in insects leads to aggregation and clumping of synaptic vesicles after 48 hours. Treatment of in vitro nerve-muscle preparations with various respiratory poisons caused aggregation similar to that developed in neurotomized animals. This suggested that vesicle aggregation in both cases may have resulted from a decrease in available adenosine triphosphate in the nerve terminal with subsequent alteration in the normal charge density which supports a repulsive force between the vesicles.

Function of Peripheral Inhibitory Axons in Insects

There are now many examples in insects of axons which elicit hyperpolarizing junctional potentials in the muscle fibers they innervate. With the muscles bathed in haemolymph, electrical stimulation of these axons causes a decrease in the magnitude of slow contractions. This property allows them to be defined as inhibitory. Although inhibitory axons have the ability to regulate the magnitude of maintained slow contractions, there is little evidence that this is their normal function. The inhibitory axons supplying at least three insect muscles function to increase the rate of relaxations following each contraction of a rhythmic sequence. Moreover, when the haemolymph potassium concentration is high, some inhibitory axons probably ensure complete relaxation between rhythmic contractions by preventing potassium contractions in tonic muscle fibers. There is no convincing evidence that inhibitory axons can facilitate muscular contractions by becoming active immediately before the excitatory input.

Musculature and innervation of the neck of the desert locust, Schistocerca gregaria (Forskål).

The innervation of each of the muscles involved in mediating head movement in the desert locust Schistocerca gregaria is described in detail. The number of motor neurones to each muscle and the neutral pathway and ganglion of origin of each are deduced from both histological and electrophysiological evidence. Only two of the muscles are, on histological evidence, innervated by as few as four different neurones, while several receive more than ten, and one at least 13. Individual muscles are shown physiologically to receive, in a few cases, as many as six different motor neurones. At least six muscles are innervated by motor neurones originating in more than one ganglion. One group of four muscles consisting in total of less than 100 muscle fibres receives more than 20 different motor neurones from three different ganglia through three or four different nerve roots. In these muscles, many single muscle fibres receive innervation from at least two different ganglia. It is concluded that the segmental nature of an insect muscle can not be deduced solely from a knowledge of the ganglion of origin of the motor innervation to that muscle. The innervation patterns that exist today must reflect past evolutionary development, but changes in the peripheral distribution of motor neurones, or migration of motor neurone cell bodies from one ganglion to another, or the development of additional motor neurones, or several of these factors together, must have formed a part of that development.

The effects of calcium ions on the activities of trehalase, hexokinase, phosphofructokinase, fructose diphosphatase and pyruvate kinase from various muscles.

1. The effects of Ca(2+) on the activities and regulatory properties of trehalase, hexokinase, phosphofructokinase, fructose diphosphatase and pyruvate kinase from vertebrate red and white muscle and insect fibrillar and non-fibrillar muscle have been investigated. These muscles were selected because of the possible difference in the role of glycolysis in energy production in the vertebrate muscles, and the possible difference in the role of Ca(2+) in the control of contraction in the two types of insect muscle. An increase in Ca(2+) concentration from 0.001mum to 10mum did not modify the activities nor did it modify the regulatory properties of these enzymes from these various muscles. 2. Concentrations of Ca(2+) above 0.1mm inhibited the activities of hexokinase and phosphofructokinase from the different muscles. It has been suggested that this inhibition may provide the basis for a theory of regulation of glycolysis (Margreth et al., 1967). If phosphofructokinase is located within the sarcoplasmic reticulum, its activity will be inhibited when the muscle is at rest, but the release of Ca(2+) from the reticulum during contraction will lead to a stimulation of its activity and hence an increase in glycolytic flux. The distribution of hexokinase and phosphofructokinase in the various cell fractions of these muscles was very variable. In particular, both enzymes were present almost exclusively in the 100000g supernatant fraction in the extracts of insect flight muscles. Thus there is no correlation between the properties of the enzymes and their distribution in muscle. 3. It is concluded that Ca(2+) does not control the activities of the important regulatory enzymes of glycolysis in muscle. It is suggested that in some muscles the sensitivity of the control mechanism at the level of phosphofructokinase to changes in the concentration of AMP may be increased by a process known as ;substrate-cycling'.

Functional development of the reticular system in an insect muscle with synchronously differentiating cells.

ABSTRACT In contrast to many developing muscles which contain a spectrum of cells at different stages of differentiation, cell development in the locust abdominal intersegmental muscle tends to be synchronous, so that at any stage of development the cells are at the same stage of differentiation. This makes it feasible to relate the properties of the developing tissue as a whole to changes occurring within the cells. Muscle contraction in the abdominal dorsal muscles of locust embryos and young hoppers has been related to ultra-structural changes within the muscle. Early in development both contraction and relaxation rates are very slow and the muscle shortens very little. The maximum registered tension is achieved relatively early while the rates of contraction and relaxation remain slow. Contraction and relaxation become more rapid as the embryo develops. These changes can be related to the development of the reticular system, various components of which mature at different rates. When the muscle is first able to develop tension the myofibres contain scattered clusters of myofilaments while the transverse tubule system (T-system), the cisternae and the sarcoplasmic reticulum (SR) are not well developed. The myofibres reach their final size and the filaments are fully formed while the T-system is still irregular and the SR is sparse. The T-system and the cisternae become well developed before the SR. During the time that the relaxation time decreases the SR becomes increasingly prominent.

The Structure and Function of Insect Muscle

The Structure and Function of Insect Muscle

General model of myosin filament structure: II. Myosin filaments and cross-bridge interactions in vertebrate striated and insect flight muscles

Details are given of a proposed geometry of cross-bridge interaction in rigor insect flight muscle based on the general model of myosin filament structure (Squire, 1971). It is shown that on the basis of this model the symmetry of the myosin filaments in insect muscle must be that of a six-stranded helix of pitch 2310 Å and repeat 1155 Å. The flared-X appearances of cross-bridges in thin transverse sections of rigor insect muscle (Reedy, 1967) are explained in terms of the proposed geometry of interaction. The mass transference involved in the change from a relaxed to a rigor state of a vertebrate striated muscle is also considered in terms of the probable geometry of cross-bridge interaction in this muscle. It is shown that there are three types of filament symmetry which satisfy all the data available at present about myosin filaments in vertebrate striated muscle.

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.

Effects of enervation on the ultrastructure of insect muscle.

ABSTRACT The structure of normal and denervated muscle fibres in the metathoracic retractor unguis muscle of the locust (Schistocerca gregaria) has been examined. Section of the 2 motor neurons which innervate this muscle results initially in muscle hypertrophy but this is followed about 4 days post neurotomy by progressive atrophy. Atrophy of the retractor unguis muscle is characterized by a decrease in muscle volume and degeneration of muscle organelles, e.g. mitochondria, sarcoplasmic reticulum, transverse tubular system, protein filaments, etc. During its later stages the degeneration of the denervated muscle is possibly assisted by the phagocytic action of haemocytes which invade the muscle.

The ionic requirements for the initiation of action potentials in insect muscle fibers.

Electrical properties of locust leg muscle fibers were studied by means of intracellular electrodes. In most fibers, a depolarizing current pulse initiated a local response. A delayed decrease in membrane resistance appeared with more than about 10 mv depolarization. In some fibers a regenerative response also was found. Membrane constants were measured, applying the short cable model. The value of the space constant lambda was 1.6 mm and the calculated value of R(m) was about 1750 ohm cm(2). Action potentials could be elicited when the bathing fluid contained more than 2-5 mM Ba or Sr. Similar responses were seen with 2 mM Ca in the presence of tetraethylammonium (TEA). The overshoot of these action potentials increased with increasing [Ca(++)](o), [Sr(++)](o), or [Ba(++)](o), the increment for a 10-fold increase being about 29 mv for Ca and Sr and between 40 and 50 mv for Ba. These action potentials were inhibited by Mn ions but were not affected by tetrodotoxin or procaine. In solutions containing Ba or Sr, action potentials generated were suppressed by addition of Ca. The removal of Na ions did not change the configuration of the action potential. The results suggest that an increase in permeability to Ca, Ba, or Sr ions makes a major contribution to the initiation of action potentials in this tissue.

Evidence for peripheral inhibition in an arachnid muscle

Blectrophysiological investigations on the promotor tibiae muscle in the tarantulaDugesiella hentzi showed for the first time the existence of peripheral inhibition in an arachnid. The observed effects of GABA and picrotoxin are similar to those in crustacean and insect muscle.

Enhancement of acid phosphatase detection by viewing stained insect muscle with polarized light.

Enhancement of acid phosphatase detection by viewing stained insect muscle with polarized light.

The Chloride Conductance and its pH Sensitivity in Insect Muscle

The effects of the replacement of chloride with methyl sulfate and of changes in the pH of the extracellular solution on the membrane conductance of locust leg muscle fibers were studied with intracellular electrodes. The contribution of chloride to the membrane conductance varied with the extracellular pH. The membrane conductance was sensitive to change in pH in the standard (chloride) saline, being high in alkaline solution and low in acid solution. However, after replacement of chloride by methyl sulfate the membrane conductance showed little change when pH was altered. It was concluded that chloride ions are mainly concerned in the pH sensitivity of the resting conductance.

Ultrastructure of the respiratory and non-respiratory dorso-ventral muscles of the larva of a dragonfly

The respiratory and non-respiratory dorso-ventral muscles of the dragonfly larva have certain features in common. Nevertheless they differ in a number of ways. Thus the respiratory muscle is heavily tracheated and has nine to ten actins surrounding each myosin filament, a poorly developed sarcoplasmic reticulum, numerous mitochondria regularly arranged on each side of the Z lines and abundant glycogen. On the other hand the non-respiratory muscle has ten to twelve actin filaments in each array, both tubular systems are well developed, there are fewer mitochondria and glycogen is less abundant. The significance of these differences and a possible scheme for classifying insect muscles are discussed.

High Density Display and Recording of Pulse Activity

Entomologists are becoming increasingly involved in research on insect nerve and muscle physiology. Instrumentation can be almost prohibitively expensive, especially where analyses of large numbers of action potentials are required. A simple method, utilizing standard electrophysiological instrumentation, may be employed for recording and analysis of such data; e.g., changes in spontaneous firing rates of nerve and muscle in response to insecticides.

Ultrastructure of stick insect and locust skeletal muscle in relation to excitation-contraction coupling

The subcellular structures involved in excitation-contraction coupling have been examined in locust metathoracic extensor tibialis muscle and stick insect prothoracic flexor tibialis muscle. In both muscles the sarcomeres are of similar resting length (4·5 μm) and the fibres are invaded by sarcolemmal invaginations and an extensive transverse tubular system is present. Locust muscle has a much more extensive sarcoplasmic reticulum and more frequent dyads per unit area than stick insect muscle. The myofilament array is fairly similar in both muscles; in locust, each myosin filament is surrounded by nine to eleven actin filaments, while in stick insect twelve actin filaments usually surround each myosin filament. The striking differences in speed of contraction and relaxation between these muscles can almost certainly be ascribed to differences in development of the sarcoplasmic reticulum and the dyads, which are areas of active calcium uptake and release during the excitation-contration coupling cycle.

A study of the different types of action potentials and miniature potentials in insect muscles

1. 1. Three different types of postsynaptic potentials were found in the muscle fibres of the m. adductor anterior of the metathoracic coxa of Schistocerca gregaria. Two different types of depolarizing potentials, E 1- and E 2-potentials, could be distinguished in addition to a hyperpolarizing I-potential. 2. 2. Marked differences in the distribution of these potentials in male and female locusts in different stages of development were observed. 3. 3. Miniature hyperpolarizing potentials were observed showing a number of characteristics which would classify them as miniature inhibitory post-synaptic potentials ( mipsp's). 4. 4. Nerve 3c innervating the m. adductor coxae anterior contains at least three axons with a cross-section of more than 5 μ 2. 5. 5. In two roaches, a stick insect and a moth, E 1-, E 2- and I-potentials have been found in one and the same fibre of one or more thoracic muscles.

Regulation of Glycogen Metabolism in Insect Flight Muscle: PURIFICATION AND PROPERTIES OF PHOSPHORYLASES IN VITRO AND IN VIVO

Abstract The mechanism for controlling the rapid rate of glycogenolysis in flight muscle of the blowfly, Phormia regina, was studied by isolating phosphorylase a and b from the muscle and determining the physical and kinetic properties of the purified enzymes and the relative amounts of the two forms of the enzymes in the muscle of the insect at rest and during flight. A method is described for the purification of phosphorylase a and b from flight muscle. Sedimentation velocity and disc gel electrophoresis studies indicate homogeneous preparations. The molecular weights of both phosphorylase b and a are about 100,000. p-Chloromercuribenzoate has no effect on the sedimentation coefficient. Amino acid analyses of the insect muscle enzyme show high contents of half-cystine and lysine and a low content of arginine, relative to the amounts of these residues found previously in mammalian muscle preparations. Other properties of the flight muscle enzyme, including pH optimum, stability, and pyridoxal phosphate content are described. The apparent Km of phosphorylase a and b for glycogen, Pi, or AMP has been determined at various concentrations of cosubstrate and activator. From these kinetic data, plus previously determined concentrations of metabolites in flight muscle, conditions in vivo were simulated. The level of glycogen in the muscle is sufficient to saturate the enzymes. The apparent Km of phosphorylase b for Pi, at 0.1 mm AMP, is about 100 mm, well above the concentration found in the muscle. The apparent Km for AMP, at 8 mm Pi, is about 1.0 mm, approximately 10-fold that in the muscle, at rest. ATP strongly inhibits phosphorylase b at low concentrations of AMP. The concentration of AMP in the muscle is 100-fold its apparent Km for phosphorylase a. The apparent Km for Pi at simulated conditions in vivo is 8 mm, approximately the concentration found in the muscle. ATP does not inhibit the a form of the enzyme. Thus, at the levels in vivo of substrates, activators, and inhibitors, phosphorylase a retains about 50% of its potential activity. The activity of phosphorylase b is too low to account for the rate of glycogenolysis during flight. The activity of phosphorylase a is adequate, if at least 50% of the total enzyme is in the a form. Measurements of the relative amounts of phosphorylase a and b at rest and during flight show that the conversion of the b to the a form is of this order of magnitude. It is concluded that in blowfly flight muscle the mechanism for controlling the intense rate of glycogenolysis concomitant with the initiation of flight is the conversion of phosphorylase b to phosphorylase a.

Carbohydrate metabolism in flight muscle of the tsetse fly ( Glossina) and the blowfly ( Sarcophaga)

1. 1. Estimations of the glycogen content of blowflies and tsetse flies confirmed earlier observations that only minute amounts of carbohydrates could be detected in the latter, although considerable amounts are present in the former. 2. 2. The activities of enzymes involved in carbohydrate breakdown in the supernatant fraction of homogenates of flight muscle of both insects have been determined. In the case of trehalase, phosphorylase, phosphoglucomutase, glucosephosphate isomerase, phosphofructokinase and aldolase, activities were found to be considerably greater in blowfly than in tsetse fly muscle. 3. 3. Considerable trehalase activity was detected in the mitochondrial fraction of blowfly flight muscle, but none was detected in the case of the tsetse. 4. 4. No glucose-6-phosphatase or fructose-1,6-diphosphatase could be detected in either insect. 5. 5. Succinic dehydrogenase activity in the mitochondria was found to be similar in the two insects. 6. 6. The findings outlined above are consistent with the hypothesis that the energy required for tsetse flight is derived from different metabolites than in the case of most other Diptera.