High -resolution scanning electron-microscopic studies on the three-dimensional structure of mitochondria and sarcoplasmic reticulum in the different twitch muscle fibers of the frog

Summary The three-dimensional structure of the mitochondria and sarcoplasmic reticulum (SR) in the three types of twitch fibers, i.e., the red, white and intermediate skeletal muscle fibers, of the vastus lateralis muscle of the Japanese meadow frog (Rana nigromaculata nigromaculata Hallowell) was examined by high resolution scanning electron microscopy, after removal of the cytoplasmic matrices.The small red fibers have numerous mitochondrial columns of large diameter, while the large white fibers have a small number of mitochondrial columns of small diameter. In the medium-size intermediate fibers, the number and diameter of the mitochondrial columns are intermediate between those of the red and white fibers.In all three types of fibers, the terminal cisternae and transverse tubules form triads at the level of each Z-line. The thick terminal cisternae continue into much thinner flat intermediate cisternae, through a transitional part where a row of tiny indentations can be observed. Numerous slender longitudinal tubules originating from the intermediate cisternae, extend longitudinally or obliquely and form elongated oval networks of various sizes in front of the A-band, then fuse to form the H-band collar (fenestrated collar) around the myofibrils. On the surface of the H-band collar, small fenestrations as well as tiny hollows are seen. The three-dimensional structure of SR is basically the same in all three muscle fiber-types. However, the SR is sparse on the surface of mitochondria, so the mitochondria-rich red fiber has a smaller total volume of SR than the mitochondria-poor white fiber. The volume of SR of the intermediate fiber is intermediate between other the two.     

Capillarization,mitochondrial densities,oxygen diffusion distances and innervation of red and white muscle of the lizard Dipsosaurus dorsalis

Summary The white and red regions of the iliofibularis muscle of the lizard Dipsosaurus dorsalis were analyzed using histologic and morphometric analysis. These regions are composed of fast glycolytic (FG) and both fast oxidative, glycolytic (FOG) and tonic fibers, respectively. Endplate morphology and number of endplates per fiber were estimated from fibers from both areas. Capillary volume densities of the red and white regions were quantified from transverse sections. Mitochondrial volume of fibers from the red and white regions were estimated from electron micrographs.All fibers from the white region of the iliofibularis possessed a single, well defined endplate, as did most red region fibers. The remaining red fibers (28±5%) possessed an average of 14.7±3 endplates each, distributed along the entire length of the fiber at intervals of approximately 1124 m.Red fibers possessed twice the mitochondrial volume of white fibers (7.6±0.4%, red; 3.8±0.3%, white). Mitochondria were distributed uniformly through the fibers from both regions. Capillary anisotropy was low ( = 1.018) in both regions. Capillary densities of the red region (629±35 mm^-2) were much greater than those of the corresponding White region (73±8 mm^-2).The data indicate that capillary densities, mitochondrial volumes and theoretical diffusion distances correlate well with the oxidative capacity of lizard muscle fibers. Tonic fibrs of this species appear oxidative and therefore metabolically capable of functioning during locomotion. The similar mitochondrial volumes and capillary densities of reptilian and mammalian muscles suggest that the greater oxidative capacity of mammalian muscle is due in part to possession of more oxidatively active mitochondria rather than to possession of more mitochondria per se.     

A comparison of quantitative ultrastructural and contractile characteristics of muscle fibre types of the perch,Perca fluviatilis L.

Summary Quantitative ultrastructural and physiological parameters were investigated in three types of muscle fibres ofPerca fluviatilis: white fibres from the m. levator operculi anterior, pink (intermediate) fibres of the m. hyohyoideus and deep red fibres of the m. levator operculi anterior. Times to peak tension and half relaxation times of isometric twitches increased in the mentioned order. The extent of contact between the T system and the sarcoplasmic reticulum and the relative volume and surface area of the terminal cisternae showed an inverse relation with the time to peak tension of the twitch. The maximal isometric tetanic force per unit cross section area was similar for all three investigated types. The inverse relation between the time to peak tension of the twitch and the relative length of contact between T system and SR is in agreement with data obtained for fast- and slow twitch muscle fibres of the carp,Cyprinus carpio L.Abbreviations LOPA musculus levator operculi anterior - HH musculus hyohyoideus - SR Sarcoplasmic reticulum     

Jaw muscle fiber type distribution in Hawaiian gobioid stream fishes: histochemical correlations with feeding ecology and behavior

Differences in fiber type distribution in the axial muscles of Hawaiian gobioid stream fishes have previously been linked to differences in locomotor performance, behavior, and diet across species. Using ATPase assays, we examined fiber types of the jaw opening sternohyoideus muscle across five species, as well as fiber types of three jaw closing muscles (adductor mandibulae A1, A2, and A3). The jaw muscles of some species of Hawaiian stream gobies contained substantial red fiber components. Some jaw muscles always had greater proportions of white muscle fibers than other jaw muscles, independent of species. In addition, comparing across species, the dietary generalists (Awaous guamensis and Stenogobius hawaiiensis) had a lower proportion of white muscle fibers in all jaw muscles than the dietary specialists (Lentipes concolor, Sicyopterus stimpsoni, and Eleotris sandwicensis). Among Hawaiian stream gobies, generalist diets may favor a wider range of muscle performance, provided by a mix of white and red muscle fibers, than is typical of dietary specialists, which may have a higher proportion of fast-twitch white fibers in jaw muscles to help meet the demands of rapid predatory strikes or feeding in fast-flowing habitats.     

Capillary Distribution in the Lateral Muscle of Axolotl (Ambystoma mexicanum Shaw)

The vascular supply of red, intermediate and white fibres in the axial muscle of axolotl (Ambystoma mexicanum Shaw) was visualized with Indian ink-injections and quantified with morphometrical methods on semithin sections. Red fibres were surrounded by 1.4 ± 0.6 capillaries (mean + SD), the intermediate fibres by 1.2 ± 0.9 capillaries and white fibres by 0.3 ± 0.6 capillaries. The mean vascularized surface area per unit volume of fibre was 0.0159, and 0.0068 and 0.0007 (μm²/μm³) for red, intermediate and white fibres, respectively. A unit volume of mitochondria within each type of fibre was supplied by 0.15, 0.17 and 0.08 μm² vascularized surface for red, intermediate and white fibres, respectively. This indicates that there exist a good balance between oxygen demand represented by mitochondrial content and oxygen supply represented by the vascularized surface.     

Organization and fine structure of extraocular muscles in Carassius and Rana

Summary 1. Two types of muscle fibers, red (-slow) and white (-twitch), have been described in the extraocular muscles of Carassius and Rana, respectively. 2. Red and white muscle fibers occupy a definite position in particular eye muscles and occur in almost constant numerical relation. 3. The red fibers in the fish extraocular muscles are supposedly slow. The position of the triads is at the level of the A/I junction, whereas that of the white muscle fibers is at the Z line level. 4. In the frog the extraocular muscles consist of two types of muscle fibers, which have morphological features of slow and fast fibers, respectively, the triads being localized at the Z line level.This work has been supported by the Polish Academy of Sciences.Authors express their thanks to Doc. Dr. J. Kawiak for help in densitometrography.     

Quantitative distribution of muscle fiber types in the scup Stenotomus chrysops

Because the mass-specific power generated by myotomal muscle during swimming varies along the length of the fish, a realistic assessment of total power generation by the musculature requires integrating the product of mass-specific power and muscle mass at each position over the length of the fish. As a first step toward this goal, we examined the distribution of red, pink, and white muscle along the length of Stenotomus chrysops (scup) using histochemical and image analysis techniques. The largest cross-sectional area of red fibers occurs at 60% of total fish length and declines both anteriorly and posteriorly. By contrast, white fibers have the largest cross-sectional area in the anterior and decline dramatically moving posteriorly. The proportion of the fishes' cross-section occupied by red fibers increases from 1.37% to 8.42% moving posteriorly along the length of the fish. In contrast, the proportion of cross-sectional area occupied by pink fibers is constant (1.19%), while the proportional cross-sectional area of white fibers falls from 82.5% to 66.3%. The red, pink, and white fibers comprise 2.09, 0.73, and 51.1%, respectively, of total fish weight. We also compared the distribution of muscle in 10°C-and 200°C-acclimated animals. The value for red fiber volume, though slightly higher (13%) in cold-acclimated fish, is not statistically different. No difference was found in pink or white fibers. Finally, the finding that most of the red muscle is in the posterior half of the fish further supports the notion that most power for steady swimming at moderate speeds comes from posterior rather than anterior musculature. © 1996 Wiley-Liss, Inc.     

Calcium buffering properties of sarcoplasmic reticulum and calcium-induced Ca2+ release during the quasi-steady level of release in twitch fibers from frog skeletal muscle

Experiments were performed to characterize the properties of the intrinsic Ca²⁺ buffers in the sarcoplasmic reticulum (SR) of cut fibers from frog twitch muscle. The concentrations of total and free calcium ions within the SR ([Ca_T]_SR and [Ca²⁺]_SR) were measured, respectively, with the EGTA/phenol red method and tetramethylmurexide (a low affinity Ca²⁺ indicator). Results indicate SR Ca²⁺ buffering was consistent with a single cooperative-binding component or a combination of a cooperative-binding component and a linear binding component accounting for 20% or less of the bound Ca²⁺. Under the assumption of a single cooperative-binding component, the most likely resting values of [Ca²⁺]_SR and [Ca_T]_SR are 0.67 and 17.1 mM, respectively, and the dissociation constant, Hill coefficient, and concentration of the Ca-binding sites are 0.78 mM, 3.0, and 44 mM, respectively. This information can be used to calculate a variable proportional to the Ca²⁺ permeability of the SR, namely d[Ca_T]_SR/dt ÷ [Ca²⁺]_SR (denoted release permeability), in experiments in which only [Ca_T]_SR or [Ca²⁺]_SR is measured. In response to a voltage-clamp step to −20 mV at 15°C, the release permeability reaches an early peak followed by a rapid decline to a quasi-steady level that lasts ∼50 ms, followed by a slower decline during which the release permeability decreases by at least threefold. During the quasi-steady level of release, the release amplitude is 3.3-fold greater than expected from voltage activation alone, a result consistent with the recruitment by Ca-induced Ca²⁺ release of 2.3 SR Ca²⁺ release channels neighboring each channel activated by its associated voltage sensor. Release permeability at −60 mV increases as [Ca_T]_SR decreases from its resting physiological level to ∼0.1 of this level. This result argues against a release termination mechanism proposed in mammalian muscle fibers in which a luminal sensor of [Ca²⁺]_SR inhibits release when [Ca_T]_SR declines to a low level.     

Lactate: a substrate for reptilian muscle gluconeogenesis following exhaustive exercise

Summary The pattern of lactate and glycogen metabolism in red and white muscle fibers was examined in fasted, cannulated lizards (Dipsosaurus dorsalis) run on a treadmill to exhaustion. The white and red portions of the iliofibularis (wIF, rIF) muscle of the hindlimb were analyzed post-exercise and at intervals over 120 min of recovery for lactate and glycogen changes. Five min of exercise resulted in lactate concentrations of from 35 mM (rIF) to 48 mM (wIF) while blood lactate concentrations were elevated to 21 mM from resting levels of 1.8 mM. Glycogen depletion was significant (p<0.05) in whole hindlimb (–30%) and in wIF (–42%) but not in rIF (–25%). Metabolite changes were consistent with a pattern of fiber type recruitment favoring fast-twitch glycolytic (FG) fibers during high intensity locomotion. Glycogen replenishment during recovery was fiber typespecific. After 2 h recovery, whole hindlimb glycogen concentration had increased 24% above pre-exercise levels (p<0.05). Rates of glycogen resynthesis during recovery were significant only in oxidative fibers of the red iliofibularis. Animals were infused with either [U-¹⁴C]-lactate or [U-¹⁴C]-glucose at the point of exhaustion, and label incorporation into muscle glycogen was used to estimate the substrate preference for glycogenesis during recovery. Lactate uptake and incorporation occurred in both wIF and rIF. Glucose uptake and incorporation into glycogen was greatest in the rIF, where it equalled 9% of the rate of lactate incorporation. The rate of lactate incorporation could account for 67% of the rate of glycogen synthesis that occurred in oxidative fibers of the rIF. The data indicate that in contrast to mammalian muscle, reptilian muscle replenishes glycogen while it removes lactate, utilizing lactate directly as a gluconeogenic substrate. The data also suggest that lactate produced by FG fibers during exercise is utilized by oxidative fiber types post-exercise to synthesize glycogen in excess of pre-exercise levels.Abbreviations wIF, rIF white, red portions of iliofibularis muscle - FG fast-twitch, glycolytic muscle fiber - FOG fast-twitch, oxidative, glycolytic muscle fiber - HPLC high performance liquid chromatography - SA specific activity - [LA] lactate concentration - GLU glucose - ANOVA analysis of variance - C.I. confidence interval     

Functional capacities of marsupial hearts: size and mitochondrial parameters indicate higher aerobic capabilities than generally seen in placental mammals

This study of marsupial hearts explored the aerobic capacities of this group of mammals; recent information suggests that marsupials possess higher aerobic abilities than previously accepted. Characteristics such as heart mass, mitochondrial features and capillary parameters were examined. A comprehensive study of the heart of red kangaroos was included because of the high maximum oxygen consumption of this species. Goats were also included as a reference placental mammal. Marsupials have a heart that is generally larger than that of placentals. The allometric equation for the relationship between heart mass and body mass for marsupials was M_h=7.5M_b^0.944 (M_h in g and M_b in kg); the equivalent equation for placental mammals was M_h=6.0M_b^0.97. Mitochondrial volume density and inner mitochondrial surface density do not differ between the two mammal groups; although capillary parameters indicated a lower capillary volume in marsupials. Heart size appears to be the major difference between the two groups. The overall pattern seen in marsupials is similar to that of "athletic" placentals and indicates a relatively high aerobic potential.Abbreviations BMR basal metabolic rate - c(K,0) tortuosity factor - Jv(c,f) capillary length density - M_b body mass - M_h heart mass - N_A(c,f) numerical capillary density - r_c mean capillary radius - S(im,m) total surface area of inner mitochondrial membranes in the heart - Sv(im,m) surface density of the inner mitochondrial membranes - Sv(im,mt) surface density of inner mitochondrial membranes per unit volume of mitochondria - TEM transmission electron microscope - O₂max maximum aerobic capacity - V(mt,m) total mitochondrial volume - Vv(f,m) volume fraction of muscle occupied by muscle fibres - Vv(mt,f) mitochondrial volume densityCommunicated by I.D. Hume     

ULTRASTRUCTURE AND ADENOSINE TRIPHOSPHATASE ACTIVITY OF RED AND WHITE MUSCLE FIBERS OF THE CAUDAL REGION OF A FISH, SALMO GAIRDNERI

Electron microscopy, together with quantitation using a tracing device linked to a digital computer, reveals that the red and white muscle fibers of Salmo gairdneri differ in diameter, organization of myofibrils, dimensions of myofilaments, volumes and surface areas of T system and sarcoplasmic reticulum, morphology of mitochondria, and content of mitochondria, lipid, and glycogen. Biochemical studies show that the ATPase activity of white fibers is three times that of the red fibers. Actomyosin content of red fibers is higher than that of the white fibers. The functional significance of these differences between two fiber types is discussed.     

Measurement of surface potential and surface charge densities of sarcoplasmic reticulum membranes

Summary The binding of the anionic fluorescent probe 1-anilino-8-naphthalene-sulfonate (ANS^–) was used to estimate the surface potential of fragmented sarcoplasmic reticulum (SR) derived from rabbit skeletal muscle. The method is based on the observation that ANS^– is an obligatory anion whose equilibrium constant for binding membranes is proportional to the electrostatic function of membrane surface potential, exp(e₀/kT, where ₀ is the membrane surface potential,e is the electronic charge, andkT has its usual meaning. The potential measured is characteristic of the ANS^– bindings of phosphatidylcholine head groups and is about one-third as large as the average surface potential predicted by the Gouy-Chapman theory. At physiological ionic strength the surface potentials, measured by ANS^–, referred to as the aqueous phase bathing the surface, were in the range –10 to –15 mV. This was observed for the outside and inside surfaces of the Ca²⁺-ATPase-rich fraction of theSR and for both surfaces of theSR fraction rich in acidic Ca²⁺ binding proteins. The inside and outside surfaces were differentiated on the basis of ANS^– binding kinetics observed in stopped-flow rapid mixing experiments. A mechanism by which changes in Ca²⁺ concentration could give rise to an electrostatic potential across the membrane and possibly result in changes in Ca²⁺ permeability.The dependence of the surface potential on the monovalent ion concentration in the medium was used together with the Gouy-Chapman theory to determine the lower limits for the surface charge density for the inside and outside surfaces of the two types ofSR. Values for the Ca²⁺-ATPase richSR fraction were between 2.9×10³ and 3.8×10³ esu/cm², (0.96×10^–6 and 1.26×10^–6 C/cm²) with no appreciable transmembrane asymmetry. A small amount of asymmetry was observed in the values for the inside and outside surfaces of the fraction rich in acidic binding proteins which were ca. 6.6×10³ and ca. 2.2×10³ esu/cm² (2.2×10^–6 and 0.73×10^–6 C/cm). The values could be accounted for by the known composition of negatively-charged phospholipids in theSR. The acidic Ca²⁺ binding proteins were shown to make at most a small contribution to the surface charge, indicating that their charge must be located at least several tens of Å from the membrane surface. The experiments gave evidence for a Donnan effect on the K⁺ distribution in the fraction rich in acidic binding proteins. This could be accounted for by the known concentration of acidic binding proteins in thisSR fraction.The equilibrium constant for ANS^– was shown to be more sensitive to changes in the divalent cation concentration than to changes in the monovalent cation concentration, as predicted by the Gouy-Chapman theory. Use of these findings together with the stopped-flow rapid mixing techniques constitutes a method for rapid and continuous monitoring of changes in ion concentrations in theSR lumen.     

Purification and localization of human carbonic anhydrase

Summary Three different isoenzymes of human carbonic anhydrase are now well characterized. Carbonic anhydrase I and II have been known for several years and are located in high amounts in red blood cells as well as in many other tissues.Carbonic anhydrase III, a protein showing CO₂ hydratase and p-nitrophenylphosphatase activity was isolated from skeletal muscle some years ago. Earlier observations based on enzyme activity and radioimmunoassay studies have suggested that this protein is present in greater quantities in red skeletal muscles than in white ones. We have purified CA III from human soleus muscle and using obtained monospecific polyclonal antibody localized this protein in the same muscle fibers which show acid resistant ATPase activity. Using this protein as a marker for type I muscle fibers, fiber classification into type I and II could now be done also from paraffin embedded sections.This study is supported by the Research Council of Physical Education and Sport, Ministry of Education, Finland     

Effects of Partial Sarcoplasmic Reticulum Calcium Depletion on Calcium Release in Frog Cut Muscle Fibers Equilibrated with 20 mM EGTA

Resting sarcoplasmic reticulum (SR) Ca content ([Ca_SR]_R) was varied in cut fibers equilibrated with an internal solution that contained 20 mM EGTA and 0–1.76 mM Ca. SR Ca release and [Ca_SR]_R were measured with the EGTA–phenol red method (Pape et al. 1995. J. Gen. Physiol. 106:259–336). After an action potential, the fractional amount of Ca released from the SR increased from 0.17 to 0.50 when [Ca_SR]_R was reduced from 1,200 to 140 μM. This increase was associated with a prolongation of release (final time constant, from 1–2 to 10–15 ms) and of the action potential (by 1–2 ms). Similar changes in release were observed with brief stimulations to −20 mV in voltage-clamped fibers, in which charge movement (Q _cm) could be measured. The peak values of Q _cm and the fractional rate of SR Ca release, as well as their ON time courses, were little affected by reducing [Ca_SR]_R from 1,200 to 140 μM. After repolarization, however, the OFF time courses of Q _cm and the rate of SR Ca release were slowed by factors of 1.5–1.7 and 6.5, respectively. These and other results suggest that, after action potential stimulation of fibers in normal physiological condition, the increase in myoplasmic free [Ca] that accompanies SR Ca release exerts three negative feedback effects that tend to reduce additional release: (a) the action potential is shortened by current through Ca-activated potassium channels in the surface and/or tubular membranes; (b) the OFF kinetics of Q _cm is accelerated; and (c) Ca inactivation of Ca release is increased. Some of these effects of Ca on an SR Ca channel or its voltage sensor appear to be regulated by the value of [Ca] within 22 nm of the mouth of the channel.     

The concentration of free Ca(2+) in the sarcoplasmic reticulum of frog cut twitch skeletal muscle fibers estimated with tetramethylmurexide

One aim of this article was to determine the resting concentration of free Ca²⁺ in the sarcoplasmic reticulum (SR) of frog cut skeletal muscle fibers ([Ca²⁺]_SR,R) using the calcium absorbance indicator dye tetramethylmurexide (TMX). Another was to determine the ratio of [Ca²⁺]_SR,R to TMX's apparent dissociation constant for Ca²⁺ (K_app) in order to establish the capability of monitoring [Ca²⁺]_SR(t) during SR Ca²⁺ release – a signal needed to determine the Ca²⁺ permeability of the SR. To reveal the properties of TMX in the SR, the surface membrane was rapidly permeabilized with saponin to rapidly dissipate myoplasmic TMX. Results indicated that the concentration of Ca-free TMX in the SR was 2.8-fold greater than that in the myoplasm apparently due to binding of TMX to sites in the SR. Taking into account that such binding might influence K_app as well as a dependence of K_app on TMX concentration, the results indicate an average [Ca²⁺]_SR,R ranging from 0.43 to 1.70 mM. The ratio [Ca²⁺]_SR,R/K_app averaged 0.256, a relatively low value which should not depend on factors influencing K_app. As a result, the time course of [Ca²⁺]_SR(t) in response to electrical stimulation is well determined by, and approximately linearly related to, the active TMX absorbance signal.     

Development of ionic currents of zebrafish slow and fast skeletal muscle fibers

Voltage-gated Na+ and K+ channels play key roles in the excitability of skeletal muscle fibers. In this study we investigated the steady-state and kinetic properties of voltage-gated Na+ and K+ currents of slow and fast skeletal muscle fibers in zebrafish ranging in age from 1 day postfertilization (dpf) to 4-6 dpf. The inner white (fast) fibers possess an A-type inactivating K+ current that increases in peak current density and accelerates its rise and decay times during development. As the muscle matured, the V50s of activation and inactivation of the A-type current became more depolarized, and then hyperpolarized again in older animals. The activation kinetics of the delayed outward K+ current in red (slow) fibers accelerated within the first week of development. The tail currents of the outward K+ currents were too small to allow an accurate determination of the V50s of activation. Red fibers did not show any evidence of inward Na+ currents; however, white fibers expressed Na+ currents that increased their peak current density, accelerated their inactivation kinetics, and hyperpolarized their V50 of inactivation during development. The action potentials of white fibers exhibited significant changes in the threshold voltage and the half width. These findings indicate that there are significant differences in the ionic current profiles between the red and white fibers and that a number of changes occur in the steady-state and kinetic properties of Na+ and K+ currents of developing zebrafish skeletal muscle fibers, with the most dramatic changes occurring around the end of the first day following egg fertilization.     

Oxygen consumption and the composition of skeletal muscle tissue after training and inactivation in the European woodmouse (Apodemus sylvaticus)

Summary In European woodmice the amount and intensity of daily activity was compared to oxygen uptake and to the potential for oxidative metabolism of heart and skeletal muscle. One group of animals was inactivated by exposition to light during night time; another group of animals was trained by enforced running on a treadmill. The oxidative potential of the muscle tissue was assessed by morphometry of capillaries and mitochondria. A novel sampling technique was used which allowed us to obtain morphological data related to single muscles, to muscle groups, and finally to whole body muscle mass.Reducing the spontaneous activity by ten fold had no effect on oxygen uptake nor on capillaries or mitochondria in locomotory muscles. Mitochondrial volume was reduced, however, in heart and diaphragm. Enforced running increased the weight specific maximal oxygen uptake significantly. It also increased the mitochondrial volume in heart and diaphragm as well as in M. tibialis anterior. Capillary densities were neither affected by training nor by inactivation. A significant correlation was found between the capillary density and the volume density of mitochondria in all muscles analysed morphometrically. For the whole skeletal muscle mass of a European woodmouse the inner mitochondrial membranes were estimated to cover 30 m². The oxygen consumption per unit time and per unit volume of muscle mitochondrion was found to be identical in all groups of animals (4.9 ml O₂ min^–1 cm^–3).Symbols S _v (im,m) surface area of inner mitochondrial membranes per unit mitochondrial volume - V _v (mt, f) volume density of mitochondria (mitochondrial volume per fiber volume) - V (mt) total mitochondrial volume - V (f) muscle volume - N _A (c, f) capillary density - (f) mean fiber cross-sectional area     

Assessing the capacity for compensatory growth in growth‐hormone transgenic coho salmon Oncorhynchus kisutch

The effect of feed cycling (consisting of periods of starvation followed by periods of refeeding to satiation) on compensatory growth was evaluated in growth hormone transgenic and non‐transgenic wild‐type coho salmon Oncorhynchus kisutch. The specific growth rate (G_SR) of feed‐restricted non‐transgenic O. kisutch was not significantly different from the G_SR of fully‐fed non‐transgenic O. kisutch during two refeeding periods, whereas the G_SR of feed‐restricted transgenic O. kisutch was significantly higher in relation to the G_SR of fully‐fed transgenic O. kisutch during the second refeeding period, but not during the first, indicating that growth compensation mechanisms are different between non‐transgenic and growth‐hormone (GH)‐transgenic O. kisutch and may depend on life history (i.e. previous starvation). Despite the non‐significant growth rate compensation in non‐transgenic O. kisutch, these fish showed a level of body mass catch‐up growth not displayed by transgenic O. kisutch.     

AMP-deaminase in elasmobranch fish: a comparative histochemical and enzymatic study

AMP-deaminase activity was measured in white muscle from a wide range of fish, including one cyclostome, 13 chondrosteans, and one teleost to elucidate the pattern of the AMP-deaminase activity in white muscle of fish. Compared to a mammalian (rat) muscle extract, low enzyme activities are found in the cyclostome and two elasmobranchs from two families (Scyliorhinidae, Hexanchidae). In contrast, higher AMP-deaminase activities, similar to mammals, are expressed in Squalidae, all families of skates, Chimaeridae and in the teleostean fish. We then compared AMP-deaminase activities in red and white muscles from two representative elasmobranch fish, the dogfish (Scyliorhinus canicula) and the thornback ray (Raja clavata). The fibre type composition and distribution of the locomotory musculature were determined in these two elasmobranchs to establish a relationship between the morphology, the type of fibres of the locomotion-implicated muscles and the AMP-deaminase activity. Experimental data are discussed with respect to the layout of fibres in the myotome. In both species, three fibre types were identified. In the two fish myotomes, most of the axial muscles are white fibres while red fibres constitute a thin sheet. Some differences were observed between the two species in the distribution of intermediate fibres: in dogfish, these are located between the red and white fibres; in thornback ray, some are dispersed within the white fibre region, while others form an intermediary layer like in dogfish. These results suggest that in the course of evolution, an amplification of the AMP-deaminase activity in muscle was coupled with increase of complexity of the muscular structure.