Actin isoforms of insect muscles: Two-dimensional electrophoresis studies

1. Two-dimensional electrophoresis was carried out to determine the isoelectric points of actins from thoracic and leg muscles of various kinds of insects (Coleoptera, Orthoptera, Odonata, Hemiptera, Lepidoptera, Hymenoptera and Diptera).2. The isoelectric points of insect muscle actin ranged from 5.6 to 5.9, appreciably more basic than rabbit skeletal muscle actin (α-actin).3. There was usually one predominant isoform of insect muscle actin except that two isoforms were detected in fly and wasp thoracic muscles.4. In a cicada, the isoelectric points of actins from thoracic, leg and sound organ were 5.65, 5.68 and 5.57, respectively.5. Actins from spider thoracic muscle, and crab claw and crayfish claw muscles also showed the isoelectric points of 5.5–5.7.6. Thus arthropod muscle actins appear to have more basic isoelectric points than vertebrate skeletal muscle ones.     

Further studies on single fibres of bovine muscles.

Young & Davey (1981) (Biochem. J. 195, 317-327) identified numbers of polymorphs of myofibrillar proteins by sodium dodecyl sulphate/polyacrylamide gel electrophoresis of single muscle fibres isolated from three bovine muscles. Fibres were classed according to the distribution of polymorphs. The study has now been extended to eight diverse bovine muscles. The previous distinction made between fast and slow fibres is valid without exception in the extended study. Within these classes, variations in myofibrillar expression are examined within and between fibres, muscles and animals. Two slow muscles are contrasted; masseter is homogeneous in fibre type, whereas diaphragm is subtly heterogeneous, possibly arising from greater physiological demands. Of the myofibrillar polymorphs, attention is concentrated on two variants of fast-muscle myosin heavy chain. Both are present in all fast and mixed muscles examined, except sternomandibularis, and each is respectively associated with certain unidentified proteins. Within a muscle the fast-muscle myosin light-chain expression is the same irrespective of the heavy-chain variant. Histochemical techniques demonstrated that the variants are respectively associated with types IIA and IIB as defined by other investigators.     

How the choice of method influence on the results in electrophysiological studies of insect olfaction

In identifying the volatiles that insects use to locate suitable host plants, electrophysiological recordings of olfactory responses to plant volatiles may give important information. However, divergent results may be obtained with different recording techniques. To illustrate these differences, the results of a previous investigation using single cell recordings linked to a gas chromatograph (SCR-GC) are compared with the results obtained with an electroantennogram linked to a gas chromatograph (EAG-GC). Testing insects of the same species (Hylobius abietis) for the same test sample, 30 potent volatile compounds were identified by SCR-GC and 18 by EAG-GC. Of the 34 different compounds, 14 were identified by both techniques. Furthermore, when the same compound elicited detectable responses by both techniques, the response strength was usually not the same relative to the strongest response recorded by each technique. This shows that both EAG-GC and SCR-GC are important techniques in the identification of potent plant volatiles for insects. However, by using SCR-GC more information was obtained, information that can be crucial for understanding the insect-plant relationship.     

Estimation of nektonic insect populations

SUMMARY 1. A water column sampler is described for obtaining absolute population estimates of nektonic insects in shallow waters.
2. Relative population estimates were obtained for Corixidae (Hemip-tera) and Buenoa (Hemiptera: Notonectidae) using a standardized sweep net procedure and compared to absolute estimates from column samples. These two types of estimates were highly correlated among lakes.
3. Simultaneous prediction and tolerance intervals for predictions from linear regressions indicated that reliable absolute population estimates generally cannot be expected from relative estimates     

Endocrine regulation of terminal muscle differentiation: Atrophy and degeneration of the intersegmental muscles of Lepidoptera

The intersegmental muscles of the Lepidoptera pass through three separate, sequential differentiated states during pharate adult development: status quo; atrophy; degeneration. Each of these developmental programs is characterized by a distinct morphology, physiology and endocrine responsiveness. The factors responsible for regulating these differentiative changes are ecdysteroids. In Manduca sexta, the haemolymph ecdysteroid titre declines in a circadian-modified fashion during the last three days of adult development, which parallels the maturation of the intersegmental muscles. Abdomen-ligation, which causes a precipitous decline in the ecdysteroid titre, causes the precocious atrophy and degeneration of these muscles, whereas injection of, or infusion with, 20-hydroxyecdysone greatly delays such changes. While the terminal differentiation of the epidermis and nervous system is also regulated by ecdysteroids, endocrine manipulations have suggested that the development of the intersegmental muscles is independent of these tissues.In the silkmoth Antheraea polyphemus, ecdysteroids are also responsible for regulating intersegmental muscle differentiation, but eclosion hormone (a peptide) acts as the proximal trigger for the activation of the degeneration program. The declining ecdysteroid titre initiates the atrophy program and subsequently determines the timing of both release of eclosion hormone and intersegmental muscle sensitivity to the peptide. Eclosion hormone then acts directly on the muscles, via cGMP, to activate the degeneration program. Ecdysteroids appear to prevent premature muscle degeneration by regulating a biochemical step distal to both the eclosion hormone receptor and the rise in cGMP.     

Slow and fast fatigable frog muscle fibres: electrophysiological and histochemical characteristics

Continuous activity of isolated frog gastrocnemius muscle fibres provoked by repetitive stimulation of 5 Hz was used as an experimental model for fatigue development in different fibre types. Parameter changes of the elicited intracellular action potentials and mechanical twitches during the period of uninterrupted activity were used as criteria for fatigue evaluation. Slow fatigable muscle fibre (SMF) and fast fatigable muscle fibre (FMF) types were distinguished depending on the duration of their uninterrupted activity, which was significantly longer in SMFs than in FMFs. The normalized changes of action potential amplitude and duration were significantly smaller in FMFs than in SMFs. The average twitch force and velocity of contraction and relaxation were significantly higher in FMFs than in SMFs. Myosin ATPase (mATPase) and succinate dehydrogenase activity were studied by histochemical assessment in order to validate the fibre type classification based on their electrophysiological characteristics. Based on the relative mATPase reactivity, the fibres of the studied muscle were classified as one of five different types (1-2, 2, 2-3, 3 and tonic). Smaller sized fibres (tonic and type 3) expressed higher succinate dehydrogenase activity than larger sized fibres (type 1-2, 2), which is related to the fatigue resistance. The differences between fatigue development in SMFs and FMFs during continuous activity were associated with fibre-type specific mATPase and succinate dehydrogenase activity.     

细胞电生理技术在昆虫抗药性研究中的应用

害虫几乎对所有化学农药及Bt等生物农药都产生了抗性。离子通道是多种杀虫剂的作用靶,因此作为研究离子通道基本手段的电压钳与膜片钳技术在害虫抗性检测与抗性机理研究中越来越受到重视。该文综述了细胞电生理技术在害虫抗性机理、杀虫剂作用机理以及药物筛选中的应用。     

Differences in electrophysiological properties of motor and sensory nerve fibres

Differences in the electrophysiological properties of amphibian motor and sensory nerve fibres are reviewed. It is concluded that the differences are mainly due to an altered K-conduction system which suggests the presence of different K channels in the two types of nerve fibres.     

Stability of environment and of insect populations

The abundance of moths was monitored with light-traps in two sites in southern Bohemia, České Budějovice for 22 years and in Černiš for 9 years. In these sites, that are vastly different in environmental stability and predictability, stability of insect populations was studied. The amplitude of fluctuations in abundance of the insect populations, as measured by the coefficient of variation (CV), varied a great deal between species so that there was a large overlap between the two sites. Nevertheless there was a highly significant tendency for species at Černiš, the more stable site, to have smaller values of CV, i.e., to be less fluctuating. Also in species co-occurring in the two sites, the CV at Černiš tended to be smaller. Trends in abundance of individual species over time, both increases and decreases, were common in both sites and did not differ between habitats. Environmental stability begets insect population stability in terms of the amplitude of the fluctuations, but trends in time occur irrespective of stability of the habitat.     

Cross-bridge conformation as revealed by x-ray diffraction studies on insect flight muscles with ATP analogues.

The effects of three ATP analogues, alpha,beta-methylene-ATP [ATP(alpha,beta-CH1)], adenosine 5'-0-(3-thiotrophosphate) [ATP(gamma-S)], and beta,gamma-amino-ATP [ATP(beta,gamma-NH)] at various concentrations and temperatures on the X-ray fiber diagrams of glycerinated flight muscles from a water bug (Lethocerus maximus) have been investigated. It is shown that the "relaxed" state can be obtained with all three analogues at high concentrations, the result being particularly clear with ATP(gamma-S). It is inferred that the binding of an ATP-like molecule suffices to produce the relaxed state. At low concentrations ATP(beta,gamma-NH) produces state intermediate between rigor and relaxed which is not simply a mixture of the two. The possible nature of the intermediate is discussed.     

Mechanical models for insect locomotion: active muscles and energy losses

 We extend the analysis of simple, energy-conserving models for the dynamics of insect locomotion in the horizontal plane developed in Schmitt and Holmes (2000a,b, 2001), where gaits characteristic of steady cockroach running and turning were evoked. In this paper, we include dissipation and energy inputs via active “muscles” in three forms: via prescribed torques at the “hip” pivot, via an active spring element of variable length, and via a pair of Hill-type muscle models representing an extensor/flexor system. Due to mechanical feedback of passive elastic forces, the stable gaits of the conservative models are preserved, and now energy input and absorption balances to additionally stabilize a preferred speed, with only modest neural sensing and feedback being required. However, these bipedal models still cannot simultaneously match observed moment-yaw magnitudes and fore-aft dynamics. Received: 17 September 2001 / Accepted: 20 February 2003 / Published online: 20 May 2003 Correspondence to: P. Holmes (e-mail: pholmes@math.Princeton.EDU) Acknowledgements. This work was supported by DARPA/ONR: N00014-98-1-0747 and DoE: DE-FG02-95ER25238. John Schmitt was partially supported by a DoD Graduate Fellowship, a Wu Fellowship of the School of Engineering and Applied Science, and a George Van Ness Lothrop Honorific Fellowship of the Graduate School at Princeton University. We thank Kenneth Meijer for allowing us to use his muscle model in Sect. 4 and Bob Full and Dan Koditschek for numerous helpful suggestions.     

The chloride conductance of intermediate fibres from frog muscles

Sheets of muscle fibres dissected from surface portions of frog ileofibularis and semitendinosus muscles were soaked in solutions with elevated K and Cl concentrations. The KCl-loaded muscles were then bathed in low [Cl-] solutions, whereby the membrane potential became transiently inside positive. The repolarization of the twitch fibres from the tonus bundle ("intermediate fibres") was faster than that of the fibres adjacent to it ("fast fibres") when the preceding exposure to high KCl was brief (7-15 min), and it was slower than that of the fast fibres when KCl was applied for 4 hours. Measurements of the voltage displacement at constant current and of the current in a point voltage clamp showed that inwardly rectifying K channels were present in the membranes of both types of fibres. The ionic conductance ratio, gK/gCl, was 191/523 in fast fibres and 335/230 in "intermediate" fibres. The different repolarization rates may thus be explained by differences in the chloride conductance of the fast and intermediate fibre membranes. The smaller diameter of the latter fibres may be another factor.     

Characteristics of insect populations on habitat fragments: A mini review

Modern human-dominated landscapes are typically characterized by intensive land-use and high levels of habitat destruction, often resulting in sharply contrasted habitat mosaics. Fragmentation of remaining habitat is a major threat to biodiversity. In the present paper, we focus on the different features of habitat fragmentation. First we discuss the importance of pure habitat loss, fragment size, fragment isolation and quality, edge effects, and the importance of landscape structure. Second, we characterize life-history features of fragmentation-sensitive species, showing that rare, specialized, little dispersing species are most affected, as well as species characterized by high population variability and a high trophic position, while the effect of body size is unclear. Third, we discuss the conservation value of habitat fragments. The question arises how to relate studies on population survival to those of community structure and studies on biodiversity to those on ecologicalal functions. Despite the general superiority of large to small reserves, only small or medium-sized reserves are available in many human-dominated landscapes. A great number of small habitats covering a wide range of geographic area should maximize beta diversity and spreading of risk and may be very important for the regional conservation of biodiversity, in contrast to the prevailing arguments in favor of large habitats. Finally, landscape context influences community structure of fragments, and communities are composed of species that experience the landscape on a broad range of spatial scales. Spatial arrangement of habitat fragments in a landscape appears to be important only in simple, not complex landscapes.