Induction of vascular smooth muscle alpha-isoactin expression in BC3H1 cells

An isoactin analysis was performed on L-[35S]cysteine labeled BC3H1 cells to determine if these smooth muscle-like cells synthesize vascular smooth muscle actin. Three different NH2-terminal peptides were identified on thin layer electrophoretograms of DNase I-purified and trypsin-digested BC3H1 cell actin. Results obtained from secondary digestion with thermolysin or Staphylococcus aureus V8 protease showed that the most acidic NH2-terminal peptide was derived from vascular smooth muscle alpha-isoactin. Treatment of cell monolayers with serum-free medium caused a 3-fold increase in the level of alpha-isoactin expression and a concomitant decrease in the level of non-muscle beta- and gamma-isoactin. Cell-cell contact was required for induction of alpha-isoactin, and the effects of serum depletion on isoactin expression and cell growth were reversible. The intensity of about 11 out of 500 polypeptide spots on two-dimensional gels of BC3H1 cell polypeptides also was influenced by the culture conditions. The finding that smooth muscle isoactin expression was coupled to cell growth conditions indicate the potential usefulness of BC3H1 cells in studies of isoactin expression and utilization during vascular smooth muscle development.     

A new experimental model for myocutaneous flaps: latissimus dorsi of the rabbit--an anatomic study

A new experimental model, the latissimus dorsi flap of the rabbit, was studied. This was found to be a relatively inexpensive research model. Its use is advocated for composite tissue transfer as transposition, island, or free myocutaneous flaps.     

Dosimetric mapping in BIORACK on IML2

Seven detector packages consisting of plastic nuclear track detectors, nuclear emulsions and thermoluminescence dosimeters were exposed in different locations inside BIORACK during the IML2 mission. The detectors supplement each other in their registration characteristics and cover well the different contributions of the space radiations to the dose. In this report, results are given on total dose measurements, cosmic ray flux and neutron dose. Total doses differ by up to a factor of 1.5 and heavy ion fluxes by more than a factor of 6 in the different locations. The results are compared with those of previous missions. The mission equivalent dose for the astronauts was calculated from the measurements to be 3.8 mSv.     

Isolation and characterization of plasma membrane-associated cortical granules from sea urchin eggs

Cortical granules, which are specialized secretory organelles found in ova of many organisms, have been isolated from the eggs of the sea urchins Arbacia punctulata and Strongylocentrtus pupuratus by a simple, rapid procedure. Electron micropscope examination of cortical granules prepared by this procedure reveals that they are tightly attached to large segments of the plasma membrane and its associated vitelline layer. Further evidence that he cortical granules were associated with these cell surface layers was obtained by (125)I-labeling techniques. The cortical granule preparations were found to be rich in proteoesterase, which was purified 32-fold over that detected in a crude homogenate. Similarly, the specific radioactivity of a (125)I-labeled, surface glycoprotein was increased 40-fold. These facts, coupled with electron microscope observations, indicate the isolation procedure yields a preparation in which both the cortical granules and the plasma membrane-vitelline layer are purified to the same extent. Gel electrophoresis of the membrane-associated cortical granule preparation reveals the presence of at least eight polypeptides. The major polypeptide, which is a glycotprotein of apparent mol wt of 100,000, contains most of the radioactivity introduced by (125)I-labeling of the intact eggs. Lysis of the cortical granules is observed under hypotonic conditions, or under isotonic conditions if Ca(2+) ion is present. When lysis is under isotonic conditions is induced by addition of Ca(2+) ion, the electron-dense contents of the granules remain insoluble. In contrast, hypotonic lysis results in release of the contents of the granule in a soluble form. However, in both cases the (125)I-labeled glycoprotein remains insoluble, presumably because it is a component of either the plasma membrane or the vitelline layer. All these findings indicate that, using this purified preparation, it should be possible to carry out in vitro studies to better define some of the initial, surface-related events observed in vivo upon fertilization.     

Substrate-associated macromolecules promote cytodifferentiation of BC3H1 myogenic cells.

Differentiated mouse BC3H1 myogenic cells secrete substrate-associated macro-molecules (SAM) which restrict the proliferation of undifferentiated cells and promote both cell shape changes and expression of predominantly the vascular smooth muscle (VSM)-specific isoform of the contractile protein alpha-actin. While we previously reported that high cell density was required for stimulating maximal expression of VSM alpha-actin in BC3H1 cells (Strauch and Reeser: Journal of Biological Chemistry 264:8345-8355, 1989), the permissive effect of SAM on myoblast cytodifferentiation was not at all dependent on the formation of cell to cell contacts. This observation suggests that biogenesis of an extracellular matrix rather than the formation of physical contacts between cells may be the rate-limiting step for induction of VSM alpha-actin expression at high cell density. The biologically active moieties in SAM that promote cytodifferentiation also are expressed by mouse embryonic fibroblast cell lines and are distinctly different from a class of adheron-like macromolecules released by differentiated BC3H1 myocytes directly into the culture medium. While SAM was cell growth restrictive, reconstituted particulate material (RPM) prepared from myocyte-conditioned medium promoted the adhesion and proliferation of growth-arrested myoblasts. SAM and RPM are composed of different polypeptide subunits which collectively may establish microenvironmental conditions that are permissive for BC3H1 myogenic cell differentiation.