Insect Leg Muscles Research Articles

Fiber-type distribution in insect leg muscles parallels similarities and differences in the functional role of insect walking legs.

Previous studies have demonstrated that myofibrillar ATPase (mATPase) enzyme activity in muscle fibers determines their contraction properties. We analyzed mATPase activities in muscles of the front, middle and hind legs of the orthopteran stick insect (Carausius morosus) to test the hypothesis that differences in muscle fiber types and distributions reflected differences in their behavioral functions. Our data show that all muscles are composed of at least three fiber types, fast, intermediate and slow, and demonstrate that: (1) in the femoral muscles (extensor and flexor tibiae) of all legs, the number of fast fibers decreases from proximal to distal, with a concomitant increase in the number of slow fibers. (2) The swing phase muscles protractor coxae and levator trochanteris, have smaller percentages of slow fibers compared to the antagonist stance muscles retractor coxae and depressor trochanteris. (3) The percentage of slow fibers in the retractor coxae and depressor trochanteris increases significantly from front to hind legs. These results suggest that fiber-type distribution in leg muscles of insects is not identical across leg muscles but tuned towards the specific function of a given muscle in the locomotor system.

In situmuscle power differs without varyingin vitromechanical properties in two insect leg muscles innervated by the same motor neuron

The mechanical behavior of muscle during locomotion is often predicted by its anatomy, kinematics, activation pattern and contractile properties. The neuromuscular design of the cockroach leg provides a model system to examine these assumptions, because a single motor neuron innervates two extensor muscles operating at a single joint. Comparisons of the in situ measurements under in vivo running conditions of muscle 178 to a previously examined muscle (179) demonstrate that the same inputs (e.g. neural signal and kinematics) can result in different mechanical outputs. The same neural signal and kinematics, as determined during running, can result in different mechanical functions, even when the two anatomically similar muscles possess the same contraction kinetics, force-velocity properties and tetanic force-length properties. Although active shortening greatly depressed force under in vivo-like strain and stimulation conditions, force depression was similarly proportional to strain, similarly inversely proportional to stimulation level, and similarly independent of initial length and shortening velocity between the two muscles. Lastly, passive pre-stretch enhanced force similarly between the two muscles. The forces generated by the two muscles when stimulated with their in vivo pattern at lengths equal to or shorter than rest length differed, however. Overall, differences between the two muscles in their submaximal force-length relationships can account for up to 75% of the difference between the two muscles in peak force generated at short lengths observed during oscillatory contractions. Despite the fact that these muscles act at the same joint, are stimulated by the same motor neuron with an identical pattern, and possess many of the same in vitro mechanical properties, the mechanical outputs of two leg extensor muscles can be vastly different.

Invertebrate connectin spans as much as 3.5 microm in the giant sarcomeres of crayfish claw muscle.

In crayfish claw closer muscle, the giant sarcomeres are 8.3 microm long at rest, four times longer than vertebrate striated muscle sarcomeres, and they are extensible up to 13 microm upon stretch. Invertebrate connectin (I-connectin) is an elastic protein which holds the A band at the center of the sarcomere. The entire sequence of crayfish I-connectin was predicted from cDNA sequences of 53 424 bp (17 352 residues; 1960 kDa). Crayfish I-connectin contains two novel 68- and 71-residue repeats, and also two PEVK domains and one kettin region. Kettin is a small isoform of I-connectin. Immunoblot tests using antibody to the 68-residue repeats revealed the presence of I-connectin also in long sarcomeres of insect leg muscle and barnacle ventral muscle. Immunofluorescence microscopy demonstrated that the two repeats, the long spacer and the two PEVK domains contribute to sarcomere extension. These regions rich in charged amino acids, occupying 63% of the crayfish I-connectin molecule, may allow a span of a 3.5 microm distance as a new class of composite spring.

Proctolin and octopamine actions on the contractile systems of insect leg muscles

1. The pentapeptide proctolin produced contractions of the coxal depressor muscle of the cockroach, Periplaneta americana. 2. The contraction was dependent upon extracellular calcium and the contraction was completely blocked by a Ca-free EGTA saline. 3. Caffeine elicited transient contractions which were unaffected by manganese treatment. 4. When the muscle was pre-treated with the conditioning solution with different K + concentrations (1–100 mM), the amplitude of proctolin-induced contractions was reduced in the low K + saline as well as in the high K + saline. 5. The results suggest that voltage sensitive calcium channels account for the proctolin-induced contractions. 6. Octopamine (OA) reduced the contractions resulting from brief applications of elevated K + concentration and of caffeine. 7. The effect of OA on the response to elevated K + concentrations was blocked by the α-adrenergic blocker, phentolamine.

Histochemical, biochemical, and contractile properties of red, white, and intermediate fibers.

Histochemical, biochemical, and contractile properties of red, white, and intermediate fibers.

Potentiation of contraction in some insect skeletal muscles—The effect of uranyl acetate

1. 1. Twitch and tetanus responses of locust and stick insect leg muscles were recorded isometrically during perfusion with salines containing 0·5 mM/l uranyl acetate. 2. 2. Uranyl acetate ions caused a potentiation of twitch tension of the order of 200 per cent. Peak tetanus tension was also potentiated, but to a lesser degree. 3. 3. Uranyl acetate ions induced a prolongation of the twitch time course particularly in locust muscle, and the muscles entered a slight contracture which lasted the duration of the uranyl acetate treatment. 4. 4. Uranyl acetate ions caused an increase in the rate of tension development in both insect muscles, but there was no observable effect on tetanus fusion frequency. 5. 5. Removal of calcium ions during uranyl acetate treatment resulted in a reversal of potentiation. From this evidence it is concluded that uranyl acetate ions exert their potentiating effects via the muscle calcium release mechanism. 6. 6. It is argued that uranyl acetate ions may well act by inhibiting or delaying the reactivation of the calcium pump of the sarcoplasmic reticulum.

THE LOCATION OF ADENINE NUCLEOTIDE IN RESTING AMPHIBIAN STRIATED MUSCLE.

Ultra-violet absorption studies of insect leg muscles and of vertebrate muscle (Caspersson & Thorell 1942; Engström 1944) provided the first suggestion that the adenine nucleotide of striated muscle is not dispersed throughout the sarcoplasmic space, but that a large part of it is concentrated in the isotropic band of the muscle. The location of adenine nucleotide in amphibian muscle has also been investigated by autoradiography (Hill 1960) in sections of a muscle which had been labelled with tritiated adenine. A large fraction of the adenine nucleotide was found to be aggregated in narrow transverse 'lines’ in the I -band. The work discussed at the present meeting (and published in detail elsewhere, Hill 1964) is an extension of these autoradiographic studies, and besides confirming the earlier findings with regard to the longitudinal distribution of the adenine nucleotide a new type of autoradiograph (viewed in the electron microscope) has now provided evidence which suggests that a large proportion of the nucleotide which is concentrated in the I -band lies in the inter-fibrillar spaces rather than in the fibrils themselves. In addition, electron micrographs of suitably stained sections have shown the existence (figure 30, plate 86) of ‘vesicles’ (presumably these are components of the sarcoplasmic reticulum) at the relevant site in the inter-fibrillar spaces, and it is suggested that the nucleotide is concentrated within these vesicles.