Muscle systems

The distinction between a- and P-adrenergic receptors was first proposed by Ahlquist in 1948 based on experiments with various catecholamine derivatives to produce excitatory (a) or inhibitory (P) responses in isolated smooth muscle systems. Initially, a further subdivision into presynaptic a2- and postsynaptic oq-receptors was proposed. However, this anatomical classification of a-adrenergic recqrtor subtypes was later abandoned. 

The situation concerning a possible role for free radicals in fatigue of skeletal muscle therefore remains unclear. Antioxidants may have some inhibitory role in fatigue of a diaphragm preparation but our experiments using a similar intact skeletal muscle system have not supported these conclusions. It is therefore possible that antioxidants are only beneficial where tissue viability is compromised. Further work is required to clarify this area. 

A complex of linked variables is associated with the elaboration of TF, the main features being the depth of tongue-tip division (its forkedness), relative tine and tongue lengths, plus the circular muscle system which controls the extent of its protrusion (Cooper, 1997b). Functionally, the tips of the fork play the most significant part in delivery of particulates [Fig. 7.3(b)] to the VN duct (Clarke, 1981). 

The model of electric field-controlled artificial muscles has been described in 1972 [5], Fragala et al. fabricated an electrically activated artificial muscle system which uses a weakly acidic contractile polymer gel sensitive to pH changes. The pH changes are produced through electrodialysis of a solution. The response of the muscle as a function of pH, solution concentration, compartment size, certain cations, and gel fabrication has been studied. The relative change in length was about 10%, and the tensile force was 1 g/0.0025 cm2 under an applied electric field of 1.8 V and 10 mA/cm2. It took 10 min for the gel to shrink. 

Fig. 8.5 The polyp and medusa body forms characteristic of phylum Cnidaria are structurally similar, (a) The polyp form as seen in Hydra, (b) The medusa form is basically an upside-down polyp. The mouths are a primitive muscle system. Note the separation of organs.

That myosin, a structural protein, also had enzyme activity as an ATPase, had been shown by Engelhardt and Ljubimova (1939-1941). ATP was now found to dissociate actomyosin producing a marked fall in viscosity the ATP was split to ADP and Pj. Contrasting properties of ATP in muscle systems were also observed. The rigor seen at postmortem occurred as ATP levels fell. The ATPase activity of myosin could be inhibited by mercurials (which block SH groups on cysteine) with ATPase blocked, ATP caused muscle fibers to relax (Weber and Portzehl, 1952). 

By 1950, Hogeboom and Schneider had prepared relatively pure mitochondria (Chapter 9) which could be used as the oxidizing system rather than crude particulate preparations like the heart muscle system of Keilin and Hartree. The problem still remained for the extraction and identification of the components from the (inner) mitochondrial membrane without denaturation. 

A synthetic muscle system would have a broad range of uses. A recent article " hypothesized that the future of heart restoration would be the replacement of a damaged heart chamber with a synthetic muscle. Implantable circulatory-assist... 

Synthetic muscle systems were first mentioned by Flory in 1953 and defined in the context of this chapter by Kuhn et al. 5° Flory described the effect of temperature on a polyacrylic acid-polyvinyl alcohol blend. Kuhn studied pH, temperature, and ionic strength stimuli. Tanaka et al. made a significant contribution to the technology in an experiment that combined the contraction-relaxation phenomenon with stimuli developed indirectly by an electric current. Their work resulted in a patent. ... 

FaRP immunostaining patterns in flatworms have been widely reported and are consistent between the classes in that all major central and peripheral nerve elements appear to contain these peptides (see Halton et al., 1994 Halton and Gustafsson, 1996 Shaw et al., 1996 Day and Maule, 1999 Halton and Maule, 2004). Another key feature of FaRP distribution is its occurrence in nerves that innervate muscle systems, from attachment organs to feeding apparatus and reproductive ducts (see Halton and Maule, 2004). The localization data alone implicate FaRPs in pivotal brain functions including motor modulation. 

Ward, S.M., McKerr, G. and Allen, J.M. (1986) Structure and ultrastructure of muscle systems within Grillotia erinaceus metacestodes (Cestoda Trypanorhyncha). Parasitology 93, 587-597. 

In summary, interaction between actin and myosin in vertebrate and invertebrate muscle systems requires a critical level of calcium. It is tentatively suggested that interaction between myosin and actin is prevented by blocking sites on actin in the case of vertebrate muscles, whereas in the case of molluscan muscles it is the sites on myosin which are blocked in the absence of calcium. The acidic amino acids seem to be of utmost importance in the regulation process. 

Blaxter, J.H.S., Wardle, C.S. and Roberts B.L. (1971). Aspects of the circulatory physiology and muscle systems of deep-sea fish. Journal of the Marine Biological Association UK SI, 991-1006. 

The cyclophyllidean oncosphere is well supplied with musculature and the general pattern of muscles appears to be similar in most species. So in both Hymenolepis citelli (which penetrates an invertebrate gut) and E. granulosus (which penetrates a vertebrate gut) there are 16 somatic muscle cells (146, 839). However, E. granulosus has 16 hook muscle cells but H. citelli has only 13. In E. granulosus, the hook muscles have been shown to insert at the collar and base of the hooks and at the basal lamina of the embryonic epithelium. Each pair of hooks has three muscle systems associated with it (a) a protractor system, for hook extensions (b) an abductor system, which draws the hooks together and (c) a retractor system which pulls the hooks into the body (839). 

Echinococcus granulosus hook-muscle systems and cellular organization of infective oncospheres. International Journal for Parasitology, 13 289-99. 

Figure 2.16. The effect of change in flux through the glycolytic path (low vs high work rates) for two (A trout muscle B rat gastrocnemius) skeletal muscle systems in vivo (modified from Hochachka, 1994) and (C) for perfused rat heart preparations in vitro (modified from Kashiwaya et al., 1994). One of the instructive insights arising from these kinds of studies is the so-called [s] stability paradox remarkably stable concentrations of pathway intermediates during changes in pathway fluxes that can approach or exceed 100-fold. See text for other details.

Evidence of the involvement of proctolin in the regulatory mechanisms of insect nerve-muscle systems has continued to grow and the remainder of this section discusses these more recent developments and their significance. Proctolin-like immunoreactive (PLI) neurons have been detected in the blowfly, Calliohora ervthrocephala (27) the Colorado potato beetle, Leptinotarsa decemlineata (28) and the fruitfly larvae, Drosophila melanomaster (29). In the blow fly, 80-90 neurons in the brain-suboesophageal complex were fo md to be PLI. The thoracic ganglia, by comparison, contained 100-130 PLI neurons, while the abdominal section had only... 

Actuators based on the swelling and shrinking of gels are the subject of much research. They can be regarded as modeling muscle systems. However, the response times of such systems are limited, because actuator motion occurs with molecular diffusion in the gel. If each molecule could expand and shrink instead, motional response times would significantly improve. Carbon nanotubes are known to expand or shrink upon injections of electrons or... 

Skeletal muscle phosphorylase has also been used for the assay of cyclic AMP [135]. The muscle system is even more tedious than that with liver phosphorylase because of the high concentrations of phosphorylase b which must be used. This is necessitated by the stimulation of muscle phosphorylase b activity by 5 -AMP, the major catabolite of cyclic AMP. 

The superficial muscle system. Illustration by Argosy. The Gale Group. 

---