The ultrastructure and vascular supply of the different fibre types in the axial muscle of the sturgeon Acipenser stellatus,Pallas

Summary The ultrastructure and vascular supply of the different fibre types in the lateral muscles of the sturgeon Acipenser stellatus were studied by light- and electron microscopy and morphometry. Three fibre types form separate layers without intermingling. The red fibres are superficial, the white fibres deep and the intermediate fibres between them. From morphometric analyses, the mitochondrial volume fraction in red fibres is 30%, in intermediate fibres 3.7% and in white fibres 0.7%. Z lines are most fuzzy in the red fibres. Triads of the sarcotubular system are always situated at the level of the Z discs. In red fibres the three elements are arranged in a series along the myofibrils, whereas in white fibres they are arranged transversely and in the intermediate fibres they are aligned obliquely. The number of capillaries surrounding each fibre is 2.3, 0.9 and 0.2 for the red, intermediate and white fibres, respectively. In red fibres 16% of the surface is directly covered by capillaries. The corresponding percentages for intermediate and white fibres are 5 and 1, respectively. Per unit volume of the fibre, the directly vascularised fibre surface in red fibres is about ten times larger than that of white fibres.The degree of vascularisation of the fibre types is directly related to the volume fraction of mitochondria, and thus to their aerobic capacities.     

Vascularization of the lateral muscle of some elasmobranchiomorph fishes

The vascular bed of the locomotor muscle in three shark species and in a holocephalan is investigated and the capillarization quantified by morphometrical methods. The red muscle fibres of Scyliorhinus, Galeus, Etmopterus and Chimaera are well vascularized having respectively 25, 18, 23 and 5 per cent of fibre surface covered by capillaries. The white muscle fibres of Scyliorhinus are far better vascularized than white muscle fibres of Galeus, Etmopterus and Chimaera . The fibre surface covered by capillaries are 9, 1.4, 0.2 and 1.3 per cent, respectively. The intermediate muscle fibres have a vascular supply between that of red and white muscle fibres in all species. If the capillary contact area to the fibres are related to the mitochondrial volume, more similar values are obtained for the vascular supply to all fibres types in all animals. This parameter indicates that there is a definite relation between the capacity of the oxygen transport system and the aerobic metabolic machinery.     

Quantitative analyses of ultrastructure and vascularization of the slow muscle fibres of the anchovy

A quantitative study has been made of the ultrastructure and vascularization of slow fibres in the lateral muscles of the European anchovy (Engraulis encrasicolus). Mitochondria and myofibrils occupy 45.5 and 44.3% of total fibre volume respectively. More than 95% of all myofibrils are adjacent to mitchondria. A total of 51 % of the sarcolemma is in direct contact with capillaries with a mean of 12.9 capillaries per fibre. In transverse sections anchovy slow fibr es are considerably flattened (long to short axis 12:1) such that the surface to volume ratio is more than twice that of a cylindrical fibre of the same area (1115 μm²). The capillary surface required to supply l μm³ of mitochondria is 0.18 μm² and the maximum distance between any capillary and mitochondrion 8 μm. T-system and sarcoplasmic reticulum occupy 0.43 and 2.7% of fibre volume respectively. Adaptations for increasing the capacity of skeletal muscle for aerobic work are discussed.     

On the heterogeneity of capillaries of pigeon pectoralis muscle: a histoenzymatic and ultrastructural study

Synopsis Earlier studies had failed to show the presence of capillaries between the white fibres of pigeon pectoralis muscle. In this paper, data are reported for the first time documenting that these capillaries occur in both intra- and inter-fasicular areas of the muscle. Fresh frozen sections of pigeon pectoralis major muscle were incubated for alkaline ATPase reaction following pretreatment with different EDTA solutions (4.3 mM, pH 4.3). The results showed the existence of an inherent heterogeneity of capillaries. The capillaries of white fibres stained intensely for K^–/Mg^2–-EDTA or Mg²⁺-EDTA pre-incubated ATPase; the capillaries of red fibres stained poorly. Both white fibre and red fibre capillaries were examined ultrastructurally in the non-perfused pigeon pectoralis muscle. It is suggested that a possible correlation exists between the distinctive metabolic and mechanical characteristics of the Type II white, glycolytic, fast-twitch fast-fatigue muscle fibres and the high ATPase activity of their capillaries.     

Quantitative analysis of muscle breakdown during starvation in the marine flatfish Pleuronectes platessa

Summary The present study describes the effects of starvation for a duration of four months on the ultrastructure of skeletal muscles from the marine flatfish (Pleuronectes platessa L.). Starvation is associated with a decrease in resting metabolic rate from 20.1±2.2 to 11.6±1.5mg-O₂/kg/h (P<0.05) and muscle wasting. Median fibre size fell from 700 m² to 500 m² in intermediate (fast oxidative) and from 1,800 m² to 600 m² in starved, white (fast-glycolytic) muscle fibres. In contrast, median fibre size in red (slow oxidative) muscle remained within the range 300–400 m². The fraction of red fibre volume occupied by myofibrils (58.6%) and mitochondria (24.5%) did not change significantly with starvation. There was, however, a decrease in stored lipid (10.7% to 3.2%) and an alteration in the structure of the cristae in mitochondria from red muscle.Atrophy of white muscle fibres is associated with a decrease in both the diameter and fractional volume occupied by myofibrils (85.7% to 61.9% P < 0.01). In a high proportion of white fibres peripheral degeneration of Z-discs is evident causing an unravelling of the thin filament lattice. It is suggested that this allows a partial decrease in myofibril diameter and hence the maintenance of contractile function in muscle from starved fish. In severely degenerating white fibres, disorganised thick and thin filaments and numerous multimembrane lysosome-like vesicles are observed.Starvation results in an increase in the average content of mitochondria in white fibres from 2.2 to 6.7% (P<0.01). In fed plaice mitochondria constitute less than 1% of the volume of the white fibre in 43.5% of the fibres. The proportion of white fibres containing more than 6% mitochondria increases from 6.5% to 58% with starvation.     

The distribution of capillaries in the somatic musculature of two vertebrate types with particular reference to teleost fish

The distribution of capillaries in teleost and rat striated muscles was investigated using a number of different methods. A new method for directly viewing capillaries was developed. Teleost white muscle has a capillary: fibre (C:F) ratio of between 0.2 and 0.3; and 0.6 to 1.0 peripheral capillaries per muscle fibre. 26-49% of fibres had no peripheral capillaries. Values for the rat gastrocnemius were 1.2, 2.6 and 4.8% respectively which compares well with literature values. Flathead red muscle had a C:F ratio of between 1.9 and 2.5; and between 5.3 and 6.6 peripheral capillaries per muscle fibre depending on the method used. Values for rat soleus were 1.8 and 4.1 respectively. Teleost pink fibres had an intermediate number of capillaries. Rat striated muscle, particularly the gastrocnemius, was found to be heterogeneous with respect to the distribution of capillaries. Flathead red muscle was homogeneous whilst teleost white muscle was only slightly variable. Flathead red muscle fibres are well suppled with subsarcolemmal mitochondria. These show a clumped distribution corresponding to the position of capillaries. In contrast teleost white fibres are almost totally devoid of these and all other mitochondria. No differences were observed in the vascularisation of either muscle type along the length of the fish. The results are discussed in relation to the division of labour between fibre types during swimming.     

Renal vasculature and uriniferous tubules in the common iguana

The pattern of vascular supply and the histology of uriniferous tubules of the kidney in the common iguana were studied by light microscopy of semithin sections and by scanning electron microscopy of microcorrosion casts. The corrosion casts showed a strongly developed renal portal system that forms an extensive capillary network throughout the kidney. Glomeruli are numerous and have a capillary pattern consisting of three to six loose coils of capillaries intercalated between afferent and efferent arterioles. Glomeruli are ovoid in shape and relatively small (mean diameter of the casts: 67 ± 19 μm in short axis and 79 ± 18 μm in long axis). Each glomerulus has a single afferent arteriole and efferent arteriole. The length and volume of the glomerular capillaries per unit volume of renal corpuscle are 0.0029 ± 0.0008 μm/μm³ and 0.321 ± 0.077, respectively. A short neck segment consisting of low epithelial cells is interposed between Bowman's capsule and the proximal tubule. A close association between the distal tubule and the glomerular hilus can be interpreted as a juxtaglomerular apparatus. © 1996 Wiley-Liss, Inc.     

Expression of titin isoforms in red and white muscle fibres of carp (Cyprinus carpio L.) exposed to different sarcomere strains during swimming

Titin (also known as connectin) is a striated-muscle-specific protein that spans the distance between the Z- and M-lines of the sarcomere. The elastic segment of the titin molecule in the I-band is thought to be responsible for developing passive tension and for maintaining the central position of thick filaments in contracting sarcomeres. Different muscle types express isoforms of titin that differ in their molecular mass. To help to elucidate the relation between the occurrence of titin isoforms and the functional properties of different fibre types, we investigated the presence of different titin isoforms in red and white fibres of the axial muscles of carp. Gel electrophoresis of single fibres revealed that the molecular mass of titin was larger in red than in white fibres. Fibres from anterior and posterior axial muscles were also compared. For both white and red fibres the molecular mass of titin in posterior muscle fibres was larger than in anterior muscle fibres. Thus, the same fibre type can express different titin isoforms depending on its location along the body axis. The contribution of titin to passive tension and stiffness of red anterior and posterior fibres was also determined. Single fibres were skinned and the sarcomere length dependencies of passive tension and passive stiffness were determined. Measurements were made before and after extracting thin and thick filaments using relaxing solutions with 0.6 mol · l⁻¹ KCl and 1 mol · l⁻¹ KI. Tension and stiffness measured before extraction were assumed to result from both titin and intermediate filaments, and tension after extraction from only intermediate filaments. Compared to mammalian skeletal muscle, intermediate filaments developed high levels of tension and stiffness in both posterior and anterior fibres. The passive tension-sarcomere length curve of titin increased more steeply in red anterior fibres than in red posterior fibres and the curve reached a plateau at a shorter sarcomere length. Thus, the smaller titin isoform of anterior fibres results in more passive tension and stiffness for a given sarcomere strain. During continuous swimming, red fibres are exposed to larger changes in sarcomere strain than white fibres, and posterior fibres to larger changes in strain than anterior fibres. We propose that sarcomere strain is one of the functional parameters that modulates the expression of different titin isoforms in axial muscle fibres of carp. Accepted: 7 May 1997     

Morphological and histochemical characterization of the pectoral fin muscle of the stripped weakfish,Cynoscion guatucupa

The fibres of superficial and deep abductor muscles of the pectoral fins of the stripped weakfish, Cynoscion guatucupa have been studied using histochemical techniques: succinic dehydrogenase (SDH) for mitochondria, periodic acid–Schiff (PAS) for glycogen, myosin‐adenosintriphosphatase (mATPase) to identify different fibre types based on the contraction speed and modified ATPase to identify capillaries. The fibre diameters were measured, and the capillaries of the main fibre types – red, pink and white— were counted. The two muscles showed both macroscopically and microscopically two well‐differentiated zones with predominant white fibres. The area of insertion of muscles into the fin rays had red, pink and white fibres. The origin zone of the muscle into the bone was composed by white fibres only. Both zones of white muscle evidenced a mosaic of small, medium and large polygonal white fibres. Red, pink and white muscles showed a wide histochemical diversity of fibre subtypes. The area per peripheral capillary increased from the red to the white muscles. Due to the predominance of white fibres, the pectoral fins of C. guatucupa were mainly involved in rapid movements to stop/discontinue and stabilize the body during swimming.     

Allometric dependences of oxygen transport parameters in skeletal muscles during ontogenesis of domestic fowl

In domestic fowl, from day 10 of embryogenesis to six month of postnatal life, investigation into the white glycolytic pectoral and red oxidative gastrocnemius muscles allometric dependences of the structural and functional parameters providing muscular fibres by oxygen: speed of breath of an isolated muscular fibre, size of a surface of an external membrane of mitochondria in a fibre, its permeability to oxygen, density of the capillaries located around of a fibre and in all muscle, volumetric speed of a muscular blood flow, and connection of speed of breath of muscular fibres with weight of a body of a bird.     

Routine oxygen consumption and characteristics of the myotomal muscle in tench: Effects of long-term acclimation to hypoxia

Summary Tench (Tinca tinca) were acclimated to either aerated (P _{O 2} 17.6 KPa) or hypoxic water (P _{O 2} 1.5 KPa) at 15° C. Fish acclimated to P _{O 2} 17.6 KPa had a routine oxygen consumption (mls O₂/Kg bodyweight/h) of 32.7 in aerated water. Upon acute exposure to P _{O 2} 1.5 KPa oxygen consumption decreased to 10.8 and 15.6 in fish acclimated to aerated and hypoxic water, respectively.On the basis of staining for glycogen and for the activities of myofibrillar ATPase and succinic dehydrogenase, three main fibre types can be differentiated in the myotomal muscle.Fibres have been classified as slow, fast aerobic and fast glycolytic. Fast aerobic fibres can be distinguished histochemically by their alkaline-stable Ca²⁺-activated myofibrillar ATPase activity and their intermediate levels of staining for glycogen and succinic dehydrogenase activity.The patterns of innervation of the fibre types have been investigated by staining neuromuscular endplates and peripheral axons for acetylcholinesterase activity. Motor axons to slow fibres branch extensively giving rise to a number of diffuse endplate formations on the same and adjacent fibres. Fast glycolytic fibres also have a complex pattern of innervation with 8–20 endplates per fibre. A large proportion of the endplates belonged to separate axons.Cross-sectional areas and perimeters of fibres, the number of capillaries/fibre and the lengths of contacts between capillaries and fibres were determined from low-magnification electron micrographs.Acclimation to hypoxia resulted in a decrease in the number of capillaries per fibre for both slow (1.8 to 1.0) and fast (0.8 to 0.2) muscles. The capillary perimeter supplying 1 m² of fibre cross-sectional area decreased by 43 % and 76 % for slow and fast fibres, respectively.     

Endothelial cells of the meningeal capillaries in the rainbow trout: A freeze-fracture study

Meningeal capillaries are unfenestrated. They are made up of endothelial cells that have a pinocytotic caveolae density of 41 ± 11/μm² and 89 ± 21/μm² on the abluminal and luminal sides respectively. The total density of intramembrane particles is not significantly different between the luminal and the abluminal membranes; however, the coefficients of partition are significantly different (P< 0.001). One or two strands of tight junctions occur between adjacent cells but no gap junctions nor desmosomes exist. The density of nuclear pores is less than 3.2/μm². An abundance of intermediate filaments and free vesicles, some of which are seriated, characterize the cytoplasm. The functional significance of these findings is discussed.     

Effect of in vivo cold-exposure on intracellular glycogen reserves in the "Starling type" avian pectoralis

The pectoralis muscle of the grackle ($\text{Quiscalus}$$\text{quiscula}$), as an example of the “Starling Type” of avian pectoralis whose fibre composition is characterized as consisting of “red” and “intermediate” fibres, was studied in order to determine the respective roles of the fibre types in shivering thermogenesis. Exposure of partially-defeathered grackles to cold (?25°C; 30 min) elicited an overt shivering-response in which a rapid depletion of the glycogen reserves in the intermediate fibres, but not in the red, was demonstrated histochemically. It is concluded that the intermediate fibres are chiefly, if not solely, responsible for effecting shivering thermogenesis in the grackle, as are the white fibres in the pigeon under indentical conditions of cold stress.     

The effect of starvation on the ultrastructure of the red and white myotomal muscles of the crucian carp (Carassius carassius)

Summary The effect of 16 weeks total starvation on the ultrastructure of the red and white myotomal muscles of the crucian carp (Carassius Carassius) has been investigated. In the white fibres the amount of myofibrillar material fell from 89.6% to 70.7% of the total fibre volume whilst in the red fibres the fall was from 72.2% to 70.3%. The sarcoplasmic reticulum appeared to have become swollen during starvation in both fibre types. In the white fibres the terminal cisternae of some triads seem to have fused. The volume of the red fibres occupied by mitochondria was reduced from 16.2 % to 5.9 %. The concentration of mitochondria in the white fibres was too low to detect any quantitative changes. A marked reduction in the amount of euchromatin material was observed in most white fibre nuclei and many red fibre nuclei. Many of the ultrastructural changes noted in the present study can be correlated with biochemical changes known to occur in the red and white myotomal muscles of fish during starvation. This work was supported by a grant from the Natural Environmental Research Council.     

RESPONSE OF PROROCENTRUM MARIAE-LEBOURIAE (DINOPHYCEAE) TO LIGHT OF DIFFERENT SPECTRAL QUALITIES AND IRRADIANCES: GROWTH AND PIGMENTATION1

Growth and pigment concentrations of the, estuarine dinoflagellate, Prorocentrum mariae-lebouriae (Parke and Ballantine) comb. nov., were measured in cultures grown in white, blue, green and red radiation at three different irradiances. White irradiances (400–800 nm) were 13.4, 4.0 and 1.8 W · m^?2 with photon flux densities of 58.7 ± 3.5, 17.4 ± 0.6 and 7.8 ± 0.3 μM quanta · m^?2· s^?1, respectively. All other spectral qualities had the same photon flux densities. Concentrations of chlorophyll a and chlorophyll c were inversely related to irradiance. A decrease of 7- to 8-fold in photon flux density resulted in a 2-fold increase in chlorophyll a and c and a 1.6- to 2.4-fold increase in both peridinin and total carotenoid concentrations. Cells grown in green light contained 22 to 32% more peridinin per cell and exhibited 10 to 16% higher peridinin to chlorophyll a ratios than cells grown in white light. Growth decreased as a function of irradiance in white, green and red light grown cells but was the same at all blue light irradiances. Maximum growth rates occurred at 8 μM quanta · m^?2· s^?1 in blue light, while in red and white light maximum growth rates occurred at considerably higher photon flux densities (24 to 32 μM quanta · m^?2· s^?1). The fastest growth rates occurred in blue and red radiation. White radiation producing maximum growth was only as effective as red and blue light when the photon flux density in either the red or blue portion of the white light spectrum was equivalent to that of a red or of blue light treatment which produced maximum growth rates. These differences in growth and pigmentation indicate that P. mariae-lebouriae responds to the spectral quality under which it is grown.     

Bacterial attachment on optical fibre surfaces

Optical fibres have received considerable attention as high-density sensor arrays suitable for both in vitro and in vivo measurements of biomolecules and biological processes in living organisms and/or nano-environments. The fibre surface was chemically modified by exposure to a selective etchant that preferentially erodes the fibre cores relative to the surrounding cladding material, thus producing a regular pattern of cylindrical wells of approximately 2.5 μm in diameter and 2.5 μm deep. The surface hydrophobicity of the etched and non-etched optical fibres was analysed using the sessile pico-drop method. The surface topography was characterised by atomic force microscopy (AFM), while the surface chemistry was probed by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Six taxonomically different bacterial strains showed a consistent preference for attachment to the nano-scale smoother (R _q = 273 nm), non-etched fibre surfaces (water contact angle, θ = 106° ± 4°). In comparison, the surfaces of the etched optical fibres (water contact angle, θ = 96° ± 10°) were not found to be amenable to bacterial attachment. Bacterial attachment on the non-etched optical fibre substrata varied among different strains.     

Three muscle fibre types in the axial muscle of axolotl (Ambystoma mexicanum Shaw) A quantitative lightand electron microscopic study

Morphometric analysis by light microscopy of p-phenylene-diamine stained semithin sections of axolotl tail muscle revealed differences in the cross-sectional area of the fibres and in the number of mitochondria and of lipid inclusions per fibre, and indicated the presence of three distinct types of fibres. The tripartition was found to be statistically highly significant. Representative fibres from each group established by light microscopic morphometry were subjected to an ultrastructural morphometric analysis. The volume content of mitochondria amounted to 9.8% of the fibre volume for red, 4.0% for intermediate and 0.8% for white fibres. The myofibrils composed 60%, 70% and 83% in the same fibres. The volume of the sarcotubular system (t-tubuli and sarcoplasmic reticulum) was 2.5% in red, 4.5% in intermediate and 11.7% in white fibres. The three fibre types also demonstrated differences in myofibrillar cross-striation pattern and number of triads. The reliability of the light microscopic morphometry was tested by correlation with EM montages of the representative fibres.     

Capillarisation,oxygen diffusion distances and mitochondrial content of carp muscles following acclimation to summer and winter temperatures

Summary Many species of fish show a partial or complete thermal compensation of metabolic rate on acclimation from summer to winter temperatures. In the present study Crucian carp (Carassius carassius L.) were acclimated for two months to either 2° C or 28° C and the effects of temperature acclimation on mitochondrial content and capillary supply to myotomal muscles determined.Mitochondria occupy 31.4% and 14.7% of slow fibre volume in 2°C- and 28° C-acclimated fish, respectively. Fast muscles of coldbut not warm-acclimated fish show a marked heterogeneity in mitochondrial volume. For example, only 5 % of fast fibres in 28° C-acclimated fish contain 5 % mitochondria compared to 34 % in 2° C-acclimated fish. The mean mitochondrial volume in fast fibres is 6.1 % and 1.6 % for coldand warm-acclimated fish, respectively.Increases in the mitochondrial compartment with cold acclimation were accompanied by an increase in the capillary supply to both fast (1.4 to 2.9 capillaries/fibre) and slow (2.2 to 4.8 capillaries/fibre) muscles. The percentage of slow fibre surface vascularised is 13.6 in 28° C-acclimated fish and 32.1 in 2° C-acclimated fish. Corresponding values for fast muscle are 2.3 and 6.6 % for warm and cold-acclimated fish, respectively. Maximum hypothetical diffusion distances are reduced by approximately 23–30 % in the muscles of 2° C-compared to 28° C-acclimated fish. However, the capillary surface supplying 1 ³ of mitochondria is similar at both temperatures.Factors regulating thermal compensation of aerobic metabolism and the plasticity of fish muscle to environmental change are briefly discussed.     

Comparative aspects of fibre types,areas, and capillary supply in the pectoralis muscle of some passerine birds with differing migratory behaviour

Summary Fibre types, fibre areas and capillary supply in the pectoralis muscle of fifteen passerines with four different patterns of migratory behaviour have been studied. The predominant fibre type was a fast-twitch oxidative-glycolytic which was the only fibre type present in all species, except in the robin and the blackbird where a fast fibre with intermediate oxidative capacity and a fast glycolytic fibre were also found. There was a significant difference in fibre areas between birds with different migratory strategies, with the long-distance migratory group having the smallest fibres. This also led to higher capillary densities, shorter diffusion distances and, consequently, more capillaries around the fibres relative to fibre area in this group. This indicates an adaptation in the morphology of the pectoralis muscle to differences in migration strategies. In the robin, the proportion of the intermediate fibre was significantly greater during the breeding season than during migration. Seasonal differences in fibre areas and capillary supply within a species were also seen, but no definite trends were detectable.Abbreviations CC capillary/fibre contacts - CCA mean number of capillaries in contact with a fibre relative to fibre cross-sectional area - MD mean diffusion length - CD capillary density - FG fast-twich glycolytic - FOG fast-twitch oxidative-glycolytic     

Technetium-99m-labeled proteins for imaging inflammatory foci

Polyclonal human IgG (IgG), antinuclear antibody (TNT-1), and human serum albumin (HSA), were labeled with ^99mTc by a method recently developed in our laboratory, and administered i.v., each to a separate group of five mice, bearing inflammatory foci induced by an i.m. injection of 40μL turpentine or 5 × 10⁸E. coli and 5 × 10⁸ Entercocci. TNT-1 labeled with ¹²⁵I served as a control and ⁶⁷Ga-citrate as a “gold standard”. At 4 or 24 h post injection, animals were imaged and sacrificed for tissue distribution studies. At 4 h in the turpentine group, the abscess-to-muscle ratios were: ⁶⁷Ga, 4.8 ± 2.1, ¹²⁵I-TNT-1, 4.3 ± 1; ^99mTc-TNT-1, 3.5 ± 1.8; ^99mTc-IgG, 3.9 ± 0.6; and ^99mTc-HSA, 4.3± 1. In the microorganism group, these ratios were 2.6 ± 0.6, 3.3 ± 0.5, 3.4 ± 0.08, 3± 1.1 and 4.1 ± 0.6, respectively. Autoradiographic examination of infected tissues indicated that leakage of labeled proteins into interstitial space due to increased capillary permeability may be one of the major mechanisms of uptake.