Ultrastructure of motor nerve terminals on different types of muscle fibers in the atlantic hagfish (Myxine glutinosa,L.)

Summary White and intermediate parietal muscle fibers of Myxine are innervated focally at one end. Most synaptic vesicles are empty. These terminals also contain 1–2% large 800–1.100 Å dense-core vesicles. Red fibers of parietal and craniovelar muscle are innervated in a distributed fashion, and the presynaptic profiles contain a higher number of large dense-core vesicles (averaging 9% and 15%, respectively; up to 37%). For all terminals the synaptic gap is 450–600 Å wide, and postsynaptic folds are absent.Empty synaptic vesicles exist as round or elongated profiles. The proportion of elongated profiles increases by formation from round ones when increasing the molarity of the buffer in the aldehyde fixative. Furthermore, the proportion of elongated vesicle profiles in terminals on Myxine white fibers at different buffer molarities, is identical with that in mammalian motor terminals at similar molarities. On this basis the significance and mode of formation of elongated vesicle profiles is discussed. The conclusion is made that the susceptibility of flattening depends on the osmotic pressure of the vesicle contents once the aldehyde has influenced the vesicle membrane.The different vesicle populations in terminals on different types of muscle fibers are significant. Terminals on red fibers probably contain serotonin (5-HT) either as sole transmitter or in addition to acetylcholine.The author is indebted to Dr. Finn Walvig, Biological Station, University of Oslo, Drøbak, for supply of hagfishes, and to Mrs. Jorunn Line Vaaland for expert technical assistance.     

γδ T-cell receptor repertoire in human peripheral blood and thymus

T-cell clones expressing the T-cell receptor (Tcr) were generated from peripheral blood lymphocytes (PBLs) and from a thymus sample. In the panel of ten thymus-derived clones, four Tcr phenotypes [as defined by the reaction of monoclonal antibodies (mAbs) directed against known V and V regions] were identified. All the clones lacked expression of the V3 V region, while seven clones were V1+ . V1 was found in combination with V9 or with undefined VVregions. In addition, two other Tcr phenotypes were identified on these clones: V9⁺ V1^– V3^– and V9^– V1^– V3^– One of the clones expressed CD4 and another was CD8positive. The remaining clones were CD4^– CD8^–. In the panel of 76 PBL-derived, Tcr-bearing clones, five Tcr phenotypes could be identified. In contrast to the thymus-derived clones, 30% of the clones were V3⁺ whereas V1 was expressed by a minority of the clones only. One clone was CD4-positive and approximately 30% of the clones were CD8-positive. Four of the five mAb-defined Tcr phenotypes could be identified on both thymus and PBL-derived T-cell clones. However, biochemical analysis of the Tcrs demonstrates differences in the usage of Ct- and C2-encoded y chains by T cells derived from the thymus and PBLs. The results therefore indicate that, at the clonal level, similarities and differences exist between the Tcr repertoires expressed in the thymus and by PBLs. Furthermore, they indicate that combinatorial Tcr heterogeneity is larger than has so far been described. The receptor diversity, combined with the potential of Tcr+ cells to express CD4 or CD8, indicates that these cells are a heterogeneous population that might mediate a number of immune functions.     

Some characteristics of anion transport at the tonoplast of oat roots,determined from the effects of anions on pyrophosphatedependent proton transport

The effects of anions on inorganicpyrophosphate-dependent H⁺-transport in isolated tonoplast vesicles from oat (Avena sativa L.) roots were determined. Both fluorescent and radioactive probes were used to measure formation of pH gradients and membrane potential in the vesicles. Pyrophosphate hydrolysis by the H⁺-translocating pyrophosphatase was unaffected by anions. Nonetheless, some anions (Cl^-, Br^- and NO₃-) stimulated H⁺-transport while others (malate, and iminodiacetate) did not. These differential effects were abolished when the membrane potential was clamped at zero mV using potassium and valinomycin. Stimulation of H⁺-transport by Cl^- showed saturation kinetics whereas that by NO₃- consisted of both a saturable component and a linear phase. For Cl^- and NO₃-, the saturable phase had a K _m of about 2 mol·m^-3. The anions that stimulated H⁺-transport also dissipated the membrane potential (.) generated by the pyrophosphatase. It is suggested that the stimulatory anions cross the tonoplast in response to the positive generated by the pyrophosphatase, causing dissipation of and stimulation of pH, as expected by the chemiosmotic hypothesis. The work is discussed in relation to recent studies of the effects of anions on ATP-dependent H⁺-transport at the tonoplast, and its relevance to anion accumulation in the vacuole in vivo is considered.Abbreviations and symools BTP 1,3-bis[tris(hydroxymethyl)-methylamino]-propane - EGTA ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid - Hepes 4-(2-hydroxyethyl)-1-piperazine ethanesulphonic acid - IDA iminodiacetate - membrane potential - pH pH gradient - PPase inorganic pyrophosphatase - PPi morganic pyrophosphate     

Ultrastructure of four types of striated muscle fibers in the atlantic hagfish (Myxine glutinosa,L.)

Summary Four types of striated muscle fibers with distinctive ultrastructure were defined in the Atlantic hagfish (Myxine glutinosa, L.): white, intermediate, and red fibers of m. parietalis, and red fibers of m. craniovelaris.White fibers are thick, contain very few mitochondria and fat vacuoles, and possess distinct and separate myofibrils with thin Z-disks and distinct M-lines. Intermediate fibers are thinner, possess largely similar myofibrils that often are even better separated due to a higher content of fat vacuoles and especially mitochondria and glycogen granules. Red fibers of m. parietalis contain large amounts of mitochondria, fat vacuoles, and glycogen granules. Their myofibrils possess M-lines, and although branching more, the myofibrils of red fibers conform with a Fibrillenstruktur pattern like those of white and intermediate fibers. Red fibers of m. craniovelaris are very thin, possess many smaller fat vacuoles, and large amounts of mitochondria and glycogen granules. The myofibrils are significantly thinner than in m. parietalis fibers, run as quite independent well separated units, possess thicker Z-disks, and lack M-lines. Large amounts of myosatellite cells are associated with these red fibers.Triads are located near A/I-junctions in all four fiber types and occur irregularly, the density of triads being different in the various fiber types.We are indebted to Dr. Finn Walvig, Biological Station, University of Oslo, Drøbak, for supply of hagfishes, and we also wish to thank Dr. Jan K. S. Jansen, Institute of Physiology, University of Oslo, for valuable suggestions during this study.     

The mitochondrially encoded "phantom ATPase" of S. cerevisiae. II. A heterogeneous mitochondrial ATPase population in situ.

Summary The mitochondrial ATPase from a PHO 1 mutant (OLI 2, PHO 1, OLI 4 region on mit DNA of S. cerevisiae) was further examined. A new purification method using Lysolecithin instead of Triton allowed us to solubilize and separate a heterogeneous ATPase population from PHO 1-mitochondria: the major abnormal fraction had extremely low oligomycin-sensitivity (but normal specific immunological reactivity), while a minor normal fraction (representing about 20% of the initial mitochondrial ATPase activity) had high sensitivity and affinity for oligomycin.Moderate urea treatment of PHO 1-mitochondria leads to partial loss of ATPase activity and a concomitant increase of oligomycin-sensitivity, suggesting that a heterogeneous ATPase population exists in situ in the mitochondrial membrane: part of the major abnormal ATPase fraction is selectively inactivated by urea, producing a concomitant enrichment in the initially minor normal ATPase fraction.If the minor normal ATPase fraction is the only one capable of in vivo ATP synthesis, the deficient but oligomycin-sensitive cell growth and oxidative phosphorylation in vitro are readily explained.Further structural studies are under way to ascertain whether the minor normal ATPase fraction is strictly identical to the wild type, in which case PHO 1 is a regulatory gene, or not, in which case PHO 1 is a structural gene.     

Dense-core vesicles in motor nerve terminals

Summary Motor nerve terminals on white and intermediate muscle fibers of the Atlantic hagfish (Myxine glutinosa, L.) contain translucent synpatic vesicles and about 1–2% dense-core vesicles. Terminals on red muscle fibers contain up to 40% dense-core vesicles with diameter 800–1100 Å. Examinations for formaldehyde-induced fluorescence indicate yellow fluorescence (5-HT ?) apparently corresponding with terminal axons on red muscle fibers in craniovelar muscles. Possibly red muscle fibers of Myxine receive monoaminergic innervation.The author is indebted to Dr. Finn Walvig, Biological station, University of Oslo, Drøbak, for supply of hagfishes.     

Synaptic junction development in the spinal cord of an amphibian embryo: An electron microscope study

Summary An electron microscopical study has been made of the cervical spinal cord of Xenopus laevis embryos, from the time that the neural tube closes until the larvae were hatched and could swim. Sections of the whole cord were searched for intercellular junctions during this period. Two nonsynaptic types were found, the first were widely distributed puncta adherentia, the second were rare and similar to gap junctions. Membrane specializations with synaptic vesicles were first found when the neural folds had fused; membrane-vesicle clusters which looked like the presynaptic half of a synaptic junction were present, together with synaptic junctions lacking any postsynaptic membrane thickening or cytoplasm density. About four hours later, mature synaptic junctions with full thickening of the postsynaptic membrane, dense cytoplasm and striated or dense material in the synaptic cleft were present. Presynaptic mitochondria, dense-cored and flattened vesicles, fibre to fibre and fibre to cell body synapses were present from the first, as were synapses onto very fine dendrites which might be filopodia from dendritic growth cones. Synaptogenesis may start with the accumulation of vesicles in dense cytoplasm near a thickened cell membrane; the postsynaptic element becomes associated with this membrane-vesicle cluster and matures by increasing cleft and cytoplasmic density, and by membrane thickening.     

On the structure of the human striate area. Lamina IVcβ

Summary Layer IVc of the human striate area consists mainly of a great number of small spinous local circuit neurons which store numerous characteristic lipofuscin granules. Since the neurons of the neighbouring layers are almost devoid of pigment deposits the boundaries of lamina IVc are easily traceable. Hence, the pigment granules can be used as internal markers to unequivocally identify these small pigmented spinous local circuit neurons of lamina IVc in ultrathin sections. They have a large spherical nucleus surrounded by a narrow cytoplasmic rim poor in organelles, and very scarcely receive axosomatic symmetric synapses.Within layer IVc four types of synaptic boutons can be distinguished. Type-1-boutons are large, contain a few and loosely arranged round vesicles and make asymmetric synaptic contacts with dendrites and dendritic spines. The type-2-boutons which are also large are filled with densely packed round vesicles which accumulate at the presynaptic membrane. The large type-3-boutons are characterized by elongated vesicles and symmetric synaptic contact zones. These boutons generate several fingerlike protrusions. Small profiles which contain elongated vesicles and form symmetric synaptic contacts, are most probably parts of these protrusions. The large amount of small boutons with round vesicles and asymmetric synaptic contact zones are tentatively described as type-4-boutons although it is far from certain that they represent a uniform class. The presumable origins of the different types of boutons are discussed.Supported by the Deutsche Forschungsgemeinschaft (Br. 634/1)Dedicated to Prof. Dr. med. H. Leonhardt in honor of his 60th birthday     

Carbohydrates of influenza virus. Structure of the oligosaccharides linked to asparagines 406 and 478 in the hemagglutinin of fowl plague virus,strain dutch

Fowl plague virus, strain Dutch, was metabolically labeled withd-[2-³H]mannose, or withd-[6-³H]glucosamine, and the small subunit (HA₂; 0.8 mg in total) of the viral hemagglutinin was isolated by preparative sodium dodecylsulfate-polyacrylamide gel electrophoresis. After proteolytic digestion, the radioactive oligosaccharides were sequentially liberated from the glycopeptides by treatment with different endo--N-acetylglucosaminidases and with peptide:N-glycosidase or, finally, by hydrazinolysis. In this manner, four groups of glycans could be obtained by consecutive gel filtrations and were subfractionated by HPLC. The structures of the individual oligosaccharides were analyzed by micromethylation, by acetolysis or by digestion with exoglycosidases. The major species amongst the high mannose glycans at Ans-406 of the viral glycopolypeptide were found to be Man1-2Man1-3(Man1-2Man1-6)Man1-6(Man1-2Man1-2Man1-3)Man1-4GlcNac1-4GlcNAc and Man1-3(Man1-2Man1-6)Man1-6(Man1-2Man1-2Man1-3)Man1-4GlcNAc1-4GlcNAc, while the complex glycans at Asn-478 are predominantly GlcNAc1-2Man1-3(GlcNAc1-2Man1-6)Man1-4GlcNAc1-4GlcNAc (lacking, in part, one of the outerN-acetylglucosamine residues) and GlcNAc1-2Man1-3(Gal1-4GlcNAc1-2Man1-6)Man1-4GlcNAc1-4GlcNAc.Abbreviation BSA bovine serum albumin - endo D (F,H) endo--N-acetyl-d-glucosaminidase D (F,H) - HA hemagglutinin (HA₁, large subunit of HA - HA₂ small subunit - FPV fowl plague virus - PNGase F peptide:N-glycosidase F - SDS sodium dodecylsulfate     

Intra- and extraganglionic nerve endings formed by neurosecretory cells of the cerebral ganglion of the earthworm (Lumbricus terrestris L.)

Summary In the cerebral (= supraesophageal, suprapharyngeal) ganglion of the earthworm, a number of neurosecretory Gomori-positive perikarya are bipolar; others are unipolar, or multipolar. Some of the neurosecretory cell processes project centrally into a fibrous zone; peripheral processes enter small nerves which leave the dorsocaudal aspect of the ganglion.In the central fibrous zone, the neurosecretory fibers form varicose Gomoripositive terminals. Here, also zinc-iodine-osmium (ZIO)-positive fibers and monoamine fluorescent fibers are found. With the electron microscope, nerve terminals containing synaptic vesicles and either large neurosecretory peptidergic granular vesicles (diameter more than 1500 Å), or smaller granular vesicles (diameter about 1300 Å, or 900 Å) are observed. These axon endings mainly form axo-dendritic synapses. Peptidergic profiles are both pre- and postsynaptic. Some of the extraganglionic peptidergic fibers appear to terminate around vessels, but most of them form terminals on the visceral muscle cells which surround the ganglion.We think that the central neurosecretory processes communicate with the fibers of the synaptic zone of the ganglion. The peripheral neurosecretory peptidergic fibers are supposed to form a primitive neurohemal area and/or to function as vasomotor nerves. The fibers innervating the visceral muscle cells may represent vegetative nerves.     

Protoplasmic streaming in the giant unicellular green algaAcetabularia mediterranea

Summary Protoplasmic Streaming inAcetabularia mediteranea has been studied by microcinematography in 1. germinating zygotes, 2. germlings before the differentiation of rhizoids and apices, 3. young cells with rhizoids and apices, 4. vegetative cells-several centimeters in length, 5. cells with a maximum sized cap, containing secondary nuclei, and 6. cells after cyst formation. Intracellular transport is found to occur at a network-system of thin filaments and at a different system of headed streaming bands. At the network of filaments chloroplasts are found to move at a velocity of 1–2 m/sec. Headed streaming bands move along the filaments and may lead without interruption from the rhizoid to the apex of the cell andvice versa. The front zone of the streaming bands is occupied by a leading cytoplasmic head-structure. Small vesicles, polyphosphate granula and secondary nuclei are the predominant moving structures in headed streaming bands. The velocity of these particles is found to be 3–11 m/sec. The filament system is found during all developmental stages. Headed streaming bands are undetectable in germinating zygotes and develop from small cytoplasmic droplets in germlings to broad heavily loaded bands in the huge vegetative cell.Transport of secondary nuclei by headed streaming bands is not observed during mitotic divisions and after cyst formation, though moving bands are still present for several weeks after cyst formation.     

Plant regeneration via somatic embryogenesis in Styrian pumpkin: cytological and biochemical investigations

Somatic embryo formation was induced from cotyledon explants of Styrian pumpkin (Cucurbita pepo L. subsp. pepo var. styriaca Greb.) by using a solid MS medium supplemented with 16.11M NAA and 4.44M BA or 26.85M NAA and 13.32M BA. The callus proliferation was more efficient on medium supplemented with 26.85M NAA and 13.32M BA. In contrast, the embryogenic response was higher on medium with lower concentrations of growth regulators (16.11M NAA and 4.44M BA). The time needed for embryo induction did not depend on medium composition. Embryos in globular stage were transferred to three different maturation media, containing 2.89M GA₃ in combination with 0.54M NAA, 11.42M IAA and growth regulator-free medium. The germination rate was the highest when embryos were cultured on medium with 11.42M IAA. Plantlets grown on this medium achieved maturity suitable for transplantation into soil within 9 to 10weeks. The regenerated plants were successfully transferred into field and developed fertile flowers and set fruits. Biochemical analysis showed significant lower total glutathione levels among in vitro grown plantlets compared to seedlings grown in soil. When the plantlets were transferred into soil, they reached a normal size within a month and the glutathione concentration was comparable to seed-derived plants at the same developmental stage. Transmission electron microscopy was used to investigate possible differences in the ultrastructure of cells from callus cultures, and leaf cells of regenerated and seed-derived plants. Differences in the ultrastructure were found within chloroplasts which contained only single thylakoids, large starch grains and small plastoglobuli in callus cells in comparison to leaf cells, which possessed a well developed thylakoid system, small starch grains and large plastoglobuli.     

On the disposition of a phosphorylated protein (“synapsin I”) and its associated kinases in synaptosomes from rat brain

Endogenous phosphorylation of synapsin I (protein I), a phosphoprotein located on the surface of synaptic vesicles, was studied in vesicles prepared from synaptosomes lysed in the absence (control) or presence of 50 M-cyclic AMP (cAMP-treated). Compared to synaptic plasma membrane (SPM) fractions prepared in parallel, and confirming previous work, the vesicle fractions were highly enriched on a unit protein basis in Ca²⁺-calmodulin-dependent kinase activity towards synapsin I. In contrast, with control vesicles the magnitude of the total phosphorylation of synapsin I in the presence of cyclic AMP was similar to that observed in SPM, but regulation by cyclic AMP was only partial. In cAMP-treated vesicles, however, synapsin I phosphorylation was highly enriched compared to SPM and the activity was virtually independent of cyclic AMP. The results show that while the free catalytic subunit of the cyclic AMP-dependent kinase remains associated with synapsin I during vesicle isolation the holoenzyme remains bound to membrane fragments, probably through its regulatory subunit.Dedicated to Henry McIlwain.     

The innervation of the myometrium of the cynomolgus monkey (Macaca fascicularis)

Summary The autonomic innervation of the myometrium of Macaca fascicularis consists of bundles of unmyelinated nerve fibres running between the smooth muscle cells, and is therefore considered to be of the fascicular (= unitary) type. Close contacts between nerve fibres and smooth muscle fibres were not found. Modification of the chromaffin method according to Tranzer and Richards made it possible to visualize the heterogeneity of the nerve fibres in a single bundle. The following fibre types were found to coexist: (1) noradrenergic fibres containing synaptic vesicles with a dense granule, (2) cholinergic fibres containing empty synaptic vesicles, and (3) non-adrenergic noncholinergic (NANC) fibres containing only or predominantly large dense-cored vesicles, which do not react with this method. Noradrenergic fibres are the most numerous (around 60%), followed by NANC fibres (30%) and cholinergic elements (around 10%). The distribution of these three types is similar in the cervix, the isthmus and the body of the uterus in pregnant and non-pregnant females.     

Detection and partial characterization of two antigenically distinct β-amylases in developing kernels of wheat

A -amylase (EC 3.2.1.2) was identified in the outer pericarp (P) of developing seeds of wheat (Triticum aestivum L.) and compared with the well known -amylase which is synthesized during seed development in the starchy endosperm (E). The enzyme P already exists in the tissues before anthesis and vanishes at the time when E starts to accumulate. The isoelectric-focusing patterns of P and E are very similar. The relative molecular weight (M_r) of P is slightly higher than that of E (66 and 64.5 kDa, respectively). Both P and E exhibit common epitopes in addition to epitopes specific for each of them. The two enzymes were identified in small amounts in the green tissues of the developing seeds (inner pericarp and testa). No antigenic difference was detected between P and the -amylases of roots and leaves.Abbreviations P pericarp -amylase - E endosperm -amylase - IS1 anti--amylase immune serum - IS2 anti- and anti- amylase immune serum - IS3 anti- amylase immune serum - IEF isoelectric focusing - IgG immunoglobulin G The authors thank Dr. P. Ziegler (Universität Bayreuth, FRG) for stimulating discussion and for useful suggestions during the writing of the text. The authors thank Miss C. Mayer for her skillful technical assistance.     

Wall morphogenesis in diatoms: Deposition of silica by cytoplasmic vesicles

Summary Several TEM and SEM techniques were applied to examine developing structures in valves of the centric diatomThalassiosira eccentrica (Ehrenb.) Cleve after cytokinesis. It was possible to confirm that in each stage of the silicification process there is a distinction between a growing zone with a loose assemblage of silica spheres and a compacting zone in an older phase of development. The spherical structure of the silica in the growing zone results from the addition of silica by small cytoplasmic vesicles of about 300 to 400 Å in diameter. The vesicle membrane fuses with the silicalemma and the vesicle content is released into the silica-deposition vesicle. The origin of these vesicles, named STV, is still unknown.     

Shuttle-like movements of Golgi vesicles in the tip of growingChara rhizoids

Summary In tip-growingChara rhizoids, the in-vivo saltatory movements of Golgi vesicles were recorded. The movements in radial direction back and forth between the ER aggregate and the plasma membrane occurred three times more often than movements passing the ER aggregate tangentially. The mean velocity of the class of Golgi vesicles observed (0.4–1 m in diameter) was approx. 0.3 m/s. Higher speed of 1–1.5 m/s occurred only in radial directions. Possibly, the ER aggregate is involved in guidance of the Golgi vesicles.Abbreviations DIC differential interference contrast - ER endoplasmic reticulum - OsFeCN osmium tetroxide-potassium ferricyanide Dedicated to the memory of Professor O. Kiermayer     

Effects of the expression of bovine growth hormone on the testes and male accessory reproductive glands in transgenic mice

The effects of physiological and excessive levels of growth hormone (GH) on reproductive functions are poorly understood, and impairment of fertility is frequently observed in transgenic animals overexpressing GH genes. The present study was undertaken to determine the effects of chronic exposure to heterologous bovine GH (bGH) on the testes and accessory reproductive glands in transgenic mice. Endocrine function of the testes was evaluated by measuring the activities of two steroidogenic enzymes, 5-3-hydroxysteroid dehydrogenase (5-3-HSD) and 17-hydroxysteroid dehydrogenase (17-HSD). The activities of acid phosphatase, alkaline phosphatase and -glucuronidase, important hydrolytic enzymes of lysosomal origin, were measured in testes, seminal vesicles and ventral prostates in normal and transgenic mice. Testicular 5-3-HSD activity was higher in transgenic than in normal mice, while testicular 17-HSD activity in transgenic mice was not altered. Acid phosphatase activity was elevated in both seminal vesicles and ventral prostates of transgenic mice, while alkaline phosphatase activity was increased only in the prostate. The activity of -glucuronidase was elevated in the testes, seminal vesicles and ventral prostate gland of transgenic mice. These results suggest that chronic exposure to bGH is associated with significant stimulation of some hydrolytic enzymes in the testes and in the accessory reproductive glands of transgenic mice.     

On the fine structure of the aglomerular renal tubule in Lophius piscatorius

Summary The fine structure of the secretory tubules in the kidney of the aglomerular goose-fish (Lophius piscatorius) is described. The cells have a pyramidal shape, are joined together by multiple desmosomes, and share as main characteristics: abundant and deep inflections of the basal and lateral cell membranes; coated luminal plasma membranes forming multiple microvilli or a genuine brush border; moderate numbers of comparatively small mitochondria, usually unassociated with the basal and lateral plasma membrane specializations; numerous multivesicular bodies occuring in the apical cytoplasm; abundant large lysosome-like bodies in the intermediate regions of the cytoplasm; and comparatively poor development of endoplasmic reticulum and Golgi apparatus.The observations suggest that the cells perform both absorptive and secretory functions and are metabolically unusually active in autolytic and heterolytic work. Comparisons with other aglomerular species indicate that the ability for active secretory function is not necessarily dependent on a close association between plasma membrane and mitochondria; however, this ability does appear to require a markedly increased basal and/or lateral cell surface created by multiple invaginations of the plasma membrane. The abundance of desmosomes and associated structures appears to represent a unique structural specialization of the goosefish tubule, and indicates that the cells must be firmly anchored to one another to supply a rigid and mechanically continuous lining of the tubule. The multivesicular bodies probably represent endocytic vacuoles which fuse with apical vesicles and invaginate their outer membrane to form the internal vesicles; they appear to transform to ambilysosomes via a function as heterophagosomes and — later — combined hetero- and autophagosomes.Supported by grants from Karolinska Institutet, Fonden til Videnskabens Fremme and Konsul Johannes Fogh-Nielsen og fru Ella Fogh-Nielsens Légat. Part of the study was performed at the Zoological Station at Naples, Italy. The assistance of Mrs. Britt-Marie Karlsson is gratefully acknowledged.     

Myosatellite cells associated with different muscle fibre types in the Atlantic hagfish (Myxine glutinosa,L.)

Summary The incidence of myosatellite cells associated with white and red muscle fibres of the parietal muscle and red fibres of the craniovelar muscle was estimated by quantitative electron microscopy in the Atlantic hagfish (Myxine glutinosa, L.). Myosatellite cell nuclei constitute 3, 11 and 23 % of the total number of nuclei inside the basal lamina of the three types of muscle fibres, respectively. However, the total number of nuclei is highest in white fibres, most of the nuclei belonging to striated muscle cells. Myosatellite cell profiles in transverse sections constitute 23, 41 and 61 % of the number of muscle fibre profiles of the three types, respectively. The intervals between adjacent myosatellite cells are 135 m in white fibres, 55 m in red parietal fibres, and only 25 m in craniovelar fibres. Since craniovelar fibres are also comparatively thin, myosatellite cells constitute a significant fraction of the volume inside the basal lamina in these fibres. The myosatellite cells are 30–50 m long and up to 5 m thick. Some myosatellite cells possess few organelles, whereas others appear to contain many free ribosomes, granular endoplasmic reticulum, prominent Golgi apparatus and lysosome-like bodies.This investigation was supported by the Norwegian Research Council for Science and the Humanities (NAVF grant No. C20.30–37). The authors are indebted to Jorunn Line Vaaland and Berit Branil for technical assistance, and to Dr. Finn Walvig, Biological Station, University of Oslo, Drøbak, for supplying the hagfish