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.     

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.     

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.     

Watching tubules glow and branch

Branching morphogenesis is an important mechanism of animal development yet, until recently, most details about this highly dynamic process have had to be inferred from fixed tissues. Several groups have now developed transgenic animals in which branching tubules express fluorescent proteins, enabling their morphogenesis to be studied dynamically using time-lapse microscopy. The results have shown that branch emergence is highly variable, that sprouting tracheae and blood vessels guide themselves by filopodial projections, that branching morphogenesis can involve highly ordered cell rearrangements, and that branches are subject to intense remodelling. Though they are very new, these fluorescent systems have already expanded our knowledge of branching morphogenesis; future work, in which fluorescence might be used to report processes in addition to anatomy, promises an even greater advance.     

Ice sheets and nitrogen

Snow and ice play their most important role in the nitrogen cycle as a barrier to land–atmosphere and ocean–atmosphere exchanges that would otherwise occur. The inventory of nitrogen compounds in the polar ice sheets is approximately 260 Tg N, dominated by nitrate in the much larger Antarctic ice sheet. Ice cores help to inform us about the natural variability of the nitrogen cycle at global and regional scale, and about the extent of disturbance in recent decades. Nitrous oxide concentrations have risen about 20 per cent in the last 200 years and are now almost certainly higher than at any time in the last 800 000 years. Nitrate concentrations recorded in Greenland ice rose by a factor of 2–3, particularly between the 1950s and 1980s, reflecting a major change in NO_x emissions reaching the background atmosphere. Increases in ice cores drilled at lower latitudes can be used to validate or constrain regional emission inventories. Background ammonium concentrations in Greenland ice show no significant recent trend, although the record is very noisy, being dominated by spikes of input from biomass burning events. Neither nitrate nor ammonium shows significant recent trends in Antarctica, although their natural variations are of biogeochemical and atmospheric chemical interest. Finally, it has been found that photolysis of nitrate in the snowpack leads to significant re-emissions of NO_x that can strongly impact the regional atmosphere in snow-covered areas.     

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 ).     

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.     

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".     

Technical information sheets

World Federation for Culture Collections

Technical information sheets     

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.     

Fibrils in marsupial enamel tubules

Summary Serial etching of cross-sectioned prisms in undecalcified adult marsupial enamel from different species, revealed distinct cylindrical acid-resistant fibrils that were demonstrable by light microscopy and by scanning electron microscopy. No fibrils were found in the enamel of Vombatus.The fibrils and the organic matrix in the remainder of the enamel stain differently. The fibrils project from the center of prisms or the borderline between prisms and interprismatic substance.It is concluded that the fibrils are chemically different from the organic matrix in the enamel, that they constitute the compact, homogenous, and morphologically well defined organic contents of the tubules in adult marsupial enamel.Since most of the material was obtained from dry museum crania, it is concluded that the fibrils are not destroyed by prolonged drying.The scanning electron micrographs were taken at the Electron Microscopical Unit for Biological Sciences, Oslo, Norway.