Calcium diffusion in uterine smooth muscle sheets

The potassium contracture in the longitudinal muscle of estrogen- treated rat uterus was kinetically investigated. The rates of tension development after Ca addition and relaxation after Ca removal were measured under the high-potassium depolarization. Both rates decreased with an increase in preparation thickness. The relaxation rate had only a slight dependence on temperature. On the contrary, both relaxation and contraction rates in a contraction induced by an electrical stimulation strongly depended on temperature, but not on preparation size. These results suggest that the Ca diffusion process in the extracellular space is the rate-limiting step in relaxation of Ca- dependent contracture under potassium depolarization. The diffusion model, in which the effect of the unstirred layer was considered, could quantitatively explain the experimental results. The apparent diffusion coefficient in the muscle sheet was estimated to be approximately 3 x 10(-7) cm2/s. The difference from that in aqueous solution is discussed.     

Electron-microscopic study of innervation of smooth muscle cells surrounding collecting tubules of the fish kidney

Summary The fine structure of the collecting tubules of the trout and killifish kidney was studied. These tubules are surrounded by layers of smooth muscle cells which are commonly innervated. The nerve terminals contain synaptic vesicles and, occasionally, a few dense-cored granules as well. Capillaries occur in the connective tissue space between these smooth muscle cells and the collecting tubule. Epithelial cells of the collecting tubules contain abundant mitochondria and a well developed membrane system displaying parallel arrays, and were considered to be actively involved in the transport of materials. In the trout, the collecting tubules contain peculiar cells in addition to regular tubule cells. The fine structure of these peculiar cells is highly reminiscent of that of gill chloride cells. The significance of these findings may be summarized as follows: If the smooth muscles around the collecting tubule contract under neural influence, intratubular pressure may be increased and, thus affect glomerular filtration rate. The contraction of these muscles may also cause the collapse of peritubular capillaries, affecting the transport activity of tubule cells.     

Rough surfaced smooth endoplasmic reticulum in rat and mouse cerebellar Purkinje cells visualized by quick-freezing techniques

The in vivo structure of the smooth endoplasmic reticulum (ER) was visualized in rat and mouse cerebellar Purkinje cells by using quick-freezing techniques followed by freeze-substitution for ultrathin-sectioning or freeze-fracturing and deep-etching for replicas. High magnification electron microscopy of the ultrathin sections revealed a surprising finding that all the smooth ER are apparently rough surfaced, and heavily studded with a large number of small dense projections. In the soma the smooth ER appears to be similar to its rough counterpart, except that the projections are slightly smaller, less electron dense and less protrusive on the ER membranes than the ribosomes. The projections were short rectangles, 20 x 20 x 6 nm3 in size, covering the cytoplasmic surface of the smooth ER in a checker-board manner where closely packed. After freeze-etching and replication, they appeared to be composed of four subparticles, surrounding a central channel. Thus the projections are very similar to the foot structure (ryanodine receptor) of the sarcoplasmic reticulum. Furthermore, they were distributed exclusively in the ER compartment and were highly concentrated especially in the smooth ER. This localization of the projections coindides with the intracellular distribution of the inositol 1,4,5-trisphosphate (IP3) receptor determined by quantitative immunogold electron microscopy. These findings would suggest that the projections are tetramers of IP3 receptor molecules and could be used as a morphological marker for the smooth ER in Purkinje cells, which spreads from the soma to the axon and dendrite, up to the tips including the spines. In Purkinje cells tubular smooth ER runs freely in a serpentine fashion or are intertwined to make large membraneous tangles without forming cisternal stacks. It is highly probable that the ER cisternal stacks do not exist naturally in Purkinje cells but are formed artificially during the various procedures for chemical fixation.     

A nucleation--elongation mechanism for the self-assembly of side polar sheets of smooth muscle myosin.

Self-assembled filaments of smooth muscle myosin were observed by low dose electron microscopy to be flat side-polar sheets, in which the component molecules appeared straight and close-packed. Fraying experiments released small oligomers, in which molecules were staggered in parallel by about +/- 14 nm relative to two immediate neighbours, and were bound also to an antiparallel partner via a approximately 14 nm overlap at the very tip of the tail. We suggest a filament model which preserves these packing relationships. Adding stoichiometric amounts of MgATP to the filaments caused them to disassemble completely by progressive loss of material from their ends, at a limiting rate equivalent to about 2 monomers per second per end in physiological saline. The rate of the competing association reaction varied linearly with the monomer concentration, as determined in pressure-jump experiments. This suggests that myosin monomers, rather than dimers or higher oligomers, are the building blocks of these filaments. Shearing and annealing of assembled filaments appeared negligible on a time scale of a few hours. In consequence, filament number and filament length were dependent on the rate at which monomers were supplied to the assembly reaction, and on the number of filaments already present at the start of the assembly reaction.     

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Technical information sheets     

Uterine leiomyoma with tubules

We report two cases of "uterine leiomyoma with tubules" as a new pathological entity. Since these are biphasic neoplasms (composed by epithelial and mesenchimal elements), the differential diagnosis is between mixed mullerian tumors and uterine tumors resembling ovarian sex cord tumors (UTROSCTs). In the differential diagnosis, the mixed mullerian tumors are easily excluded because of histological and immunohistochemical features. UTROSCTs are similar to the lesions we reported, and the differential diagnosis requires positivity for some immunohistochemical markers as inhibin, CD99, calretinin, Melan-A. Our conclusions are that to perform a diagnosis of UTROSCT at least two immunohistochemical marker have to be expressed; in the present case they didn't, so we call the lesion "leiomyoma with tubules".     

Epiplastidial tubules inOedogonium cardiacum

Summary Rope-like structures with a diameter of about 30×50 nm occur at the cytoplasmic site of the chloroplast envelope ofOedogonium cardiacum. They seem to consist of a central tubule with surrounding electron-dense fuzzy material. The possible significance of these structures is discussed.     

Scissors for autolysosome tubules

Autophagic lysosome reformation (ALR) is a cellular process in which lysosomes are reformed through scission of proto‐lysosomes from tubular structures extruded from autolysosomes. Despite recent progress, the molecular mechanism of ALR is far from clear. A paper in this issue of The EMBO Journal has identified lysosome‐localized PI(3)P, which is generated by the VPS34–UVRAG complex in an mTOR‐dependent manner, as an important regulator of autolysosome tubule scission (Munson et al, 2015 ).     

Peroxisomes in cat and sheep mesonephric tubules

Summary Peroxisomes were identified morphologically and histochemically in the mesonephric proximal tubular cells of cat and sheep embryos at different stages of development. Close contact with smooth portions of rough endoplasmic reticulum was always observed. Marginal plates or central plates were common, cores absent. Peroxisomes could be found only in active proximal tubules. The undifferentiated mesonephric tubular cells of cat embryos younger than 20 days lacked these organelles.This study was supported by Die Deutsche Forschungsgemeinschaft.     

Rough and smooth forms of fluorescein-labelled bacterial endotoxin exhibit CD14/LBP dependent and independent binding that is influencedby endotoxin concentration.

Lipopolysaccharide (LPS, or endotoxin), is a major constituent of the outer membrane of Gram-negative bacteria. Bacteria express either smooth LPS, which is composed of O-antigen (O-Ag), complete core oligosaccharides, and the lipid A, or rough LPS which lack O-Ag but possess lipid A and progressively shorter core oligosaccharides. CD14 has been described as the receptor for complexes of LPS with LPS-binding protein (LBP). Using flow cytometry we have compared the binding of Salmonella minnesota rough LPS (ReLPS) and Escherichia coli smooth LPS labelled with fluorescein isothiocyanate (FITC-LPS) to Chinese hamster ovary (CHO) cells transfected with human CD14 gene (hCD14-CHO), to MonoMac 6 cells and to endothelial cells. Our results showed that both forms of LPS display the same binding characteristics, and that the binding of FITC-LPS to cells was both CD14- and LBP-dependent for LPS concentrations up to 100 ng.mL-1. At LPS concentrations higher than 100 ng.mL-1 we observed CD14/LBP-independent binding. CD14/LBP-dependent binding was dose dependent, saturable, and enhanced in the presence of human pooled serum (HPS), and the monoclonal anti-CD14 antibody (MY4) or unlabelled LPS could outcompete it.     

Coiling of beta-pleated sheets

To form strongly twisted β-sheets, strands have to be coiled as well as twisted (Nishikawa &; Scherga, 1976). I show that strands coil in the appropriate right-handed direction if their main-chain torsion angles fulfil the following conditions: ψ_i ? ?φ_{i + 1}, ψ_{i + 1} > ?φ_{i + 2}, ψ_{i + 2} ? ?φ_{i + 3}, ψ_{i + 3} > ?φ_{i + 4}…Lactate dehydrogenase, pancreatic trypsin inhibitor, thermolysin and concanavalin A contain strongly twisted β-sheets and in each case the strands are coiled by their φ, ψ values fulfilling these conditions.