Fibronectin and proteoglycans as determinants of cell-substratum adhesion.

When normal or SV40-transformed Balb/c 3T3 cells are treated with the Ca++-specific chelator EGTA, they round up and pull away from their footpad adhesion sites to the serum-coated tissue culture substrate, as shown by scanning electron microscope studies. Elastic membranous retraction fibers break upon culture agitation, leaving adhesion sites as substrate-attached material (SAM) (Cells leave "footprints" of substrate adhesion sites during movement by a very similar process.) SAM contains 1-2% of the cell's total protein and phospholipid content and 5-10% of its glucosamine-radiolabeled polysaccharide, most of which is glycosaminoglycan (GAG). By one- and two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis, there is considerable enrichment in SAM for specific GAGs; for the glycoprotein fibronectin; and for the cytoskeletal proteins actin, myosin, and the subunit protein of the 10 nm-diameter filaments. Fibrillar fibronectin of cellular origin and substratum-bound fibronectin of serum origin (cold-insoluble globulin, CIg) have been visualized by immunofluorescence microscopy. The GAG composition in SAM has been examined under different cellular growth and attachment conditions. Heparan sulfate content correlates with glycopeptide content (derived from glycoprotein). Newly attaching cells deposit SAM with principally heparan sulfate and fibronectin and little of the other GAGs. Hyaluronate and chrondroitin proteoglycans are coordinately deposited in SAM as cells begin spreading and movement over the substrate. Cells attaching to serum-coated or CIg-coated substrates deposited SAM with identical compositions. The proteoglycan nature of the GAGs in SAM has been examined, as well as the ability of proteoglycans to form two classes of reversibly dissociable "supramolecular complexes" - one class with heparan sulfate and glycopeptide-containing material and the second with hyaluronate-chondroitin complexes. Enzymatic digestion of "intact" SAM with trypsin or testicular hyaluronidase indicates that (1) only a small portion of long-term radiolabeled fibronectin and cyto-skeletal protein is bound to the substrate via hyaluronate or chondroitin classes of GAG; (2) most of the fibronectin, cytoskeletal protein and heparan sulfate coordinately resist solubilization; and (3) newly synthesized fibronectin, which is metabolically labile in SAM, is linked to SAM by hyaluronate- and/or chondroitin-dependent binding. All of our studies indicate that heparan sulfate is a direct mediator of adhesion of cells to the substrate, possibly by binding to both cell-surface fibronectin and substrate-bound CIg in the serum coating; hyaluronate-chondroitin complexes in SAM appear to be most important in motility of cells by binding and labilizing fibronectin at the periphery of footpad adhesions, with subsequent cytoskeletal disorganization.     

Solid-state laser intensity stabilization at the 10(-8) level

A high-power, low-noise photodetector, in conjunction with a current shunt actuator, is used in an ac-coupled servo to stabilize the intensity of a 10-W cw Nd:YAG laser. A relative intensity noise of 1 x 10(-8) Hz(-1/2) at 10 Hz is achieved.     

Molecular contrast in optical coherence tomography by use of a pump-probe technique

We describe a novel technique for contrast enhancement in optical coherence tomography (OCT) that makes possible molecular-specific imaging for what is believed to be the first time. A pump-probe technique is employed in which a pulsed pump laser is tuned to ground-state absorption in a molecule of interest. The location of the target molecule population is derived from the resulting transient absorption of OCT sample-arm light acting as probe light. A signal processing technique for three-dimensional localization of the transient absorption signal is described, and preliminary results exhibiting OCT contrast from methylene blue dye in multilayer and scattering phantoms are presented.     

Imaging and velocimetry of the human retinal circulation with color Doppler optical coherence tomography

Noninvasive monitoring of blood flow in retinal microcirculation may elucidate the progression and treatment of ocular disorders, including diabetic retinopathy, age-related macular degeneration, and glaucoma. Color Doppler optical coherence tomography (CDOCT) is a technique that allows simultaneous micrometer-scale resolution cross-sectional imaging of tissue microstructure and blood flow in living tissues. CDOCT is demonstrated for the first time in living human subjects for bidirectional blood-flow mapping of retinal vasculature.     

HARVESTING IN POPULATION MODELS WITH DELAYED RECRUITMENT AND AGE-DEPENDENT MORTALITY

We formulate a Volterra equation model to describe the effect of harvesting on populations with delayed recruitment and age-dependent mortality. This model is more complicated mathematically than the unharvested model, and we describe some numerical simulations which indicate the possible qualitative behaviours.     

Mixed metal PtxMyLz complexes of L = 1-methyluracil and 1-methylthymine: Preparation and spectroscopic studies

The reactions of cis-(NH₃)₂PtL₂ (L = 1-MeT or 1-MeU, the anions of 1-methylthymine or 1-methyluracil respectively) in water with various salts of Fe(II), Fe(III), Co(II), Ni(II), Cu(II) or Ag(I) have produced 14 new heteronuclear complexes of the general types: cis-[(NH₃)₂PtL₂ML₂Pt(NH₃)₂]X_n·mH₂O or cis-(NH₃)₂PtL₂MX_n·mH₂O, and also with silver(I) perchlorate a complex of stoichiometry cis-{(NH₃)₂Pt(1-MeU)₂}₂· 3AgClO₄·6H₂O. Comparisons are made with previously reported heteronuclear species derived from cis-(NH₃)₂PtL₂ and factors influencing the type of heteronuclear complex formed are discussed, particularly the versatility of binding patterns with Ag(I). A tetranuclear structure is suggested for the compound of stoichiometry cis-(NH₃)₂Pt(1-MeU)₂·FeSO₄·3H₂O involving iron(II) ions linked by sulphate bridges. The electronic spectra of the trinuclear complexes cis-[(NH₃)₂Pt(1-MeU)₂M(1-MeU)₂Pt(NH₃)₂] (NO₃)₂·mH₂O (M = Fe, Co or Ni) are reported. They show that the trans-MO₄Pt₂ geometry results in a very severely trans-elongated ligand field about the central metal ion, M. This conclusion is supported by the Mössbauer spectrum in the case of the iron(II) complex. The X- and Q-band EPR spectra of the Fe(III) analogue are also reported.     

Macrocycle complexation chemistry 30: Comparison of the crystal structures of [La(NO3)3(15-crown-5)] and [La(NO3)3(monoaza-15-crown-5)]

For part 29, see Rogerset al. (1989).     

Primary to secondary sphere coordination of 18-crown-6 to lanthanide (III) nitrates: Structural analysis of [Pr(NO3)3-(18-crown-6)] and [M(NO3)3(OH2)3]·18-crown-6 (M=Y,Eu, Tb−Lu)

The direct reaction of hydrated lanthanide nitrate salts with 18-crown-6 in 31 CH₃CNCH₃OH has resulted in the isolation and structural characterization of [Pr(NO₃)₃(18-crown-6)] and [M(NO₃)₃(OH₂)₃]·18-crown-6 (M=Y, Eu, Tb–Lu). (The Eu and Yb analogs were confirmed with preliminary cell data only.) [Pr(NO₃)₃(18-crown-6)] is 12-coordinate icosahedral and crystallizes in the orthorhombic space group Pbca with (at 20°C)a=12.230(2),b=15.598(4),c=21.777(9)Å andD _calc=1.89 g cm^–3 forZ=8. The seven isostructural [Pr(NO₃)₃(18-crown-6)] complexes all contain 9-coordinate capped square antiprismatic metal centers hydrogen bonded via the bound water molecules to D_3d 18-crown-6 within the lattice to form hydrogen bonded polymeric chains. Each complex is orthorhombic Pnma with cell parameters as follows: M=Tb (20°C):a=15.242(6),b=14.253(11),c=11.070(6)Å,D _calc=1.83 g cm^–3 forZ=4; M=Dy (20°C):a=15.248(3),b=14.239(5),c=11.058(3)Å,D _calc=1.84 g cm^–3 forZ=4; M=Y (19°C):a=15.260(2),b=14.238(2),c=11.048(3) Å,D _calc=1.64 g cm^–3 for Z=4; M=Ho (20°C):a=15.226(4),b=14.208(15),c=11.028(3)Å,D _calc=1.86 g cm^–3 forZ=4; M=Er (20°C):a=15.250(3),b=14.208(7),c=11.028(3)Å,D _calc=1.87 g cm^–3 forZ=4; M=Tm (20°C):a=15.246(6),b=14.190(16),c=11.013(6) Å,D _calc=1.88 g cm^–3 forZ=4; M=Lu (21°C):a=15.244(9),b=14.158(6),c=10.980(7)Å,D _calc=1.90 g cm^–3 forZ=4.     

Minimum SNR and acquisition for bias-free estimation of fractional anisotropy in diffusion tensor imaging - a comparison of two analytical techniques and field strengths

Although it is known that low signal-to-noise ratio (SNR) can affect tensor metrics, few studies reporting disease or treatment effects on fractional anisotropy (FA) report SNR; the implicit assumption is that SNR is adequate. However, the level at which low SNR causes bias in FA may vary with tissue FA, field strength and analytical methodology. We determined the SNR thresholds at 1.5 T vs. 3 T in regions of white matter (WM) with different FA and compared FA derived using manual region-of-interest (ROI) analysis to tract-based spatial statistics (TBSS), an operator-independent whole-brain analysis tool. Using ROI analysis, SNR thresholds on our hardware-software magnetic resonance platforms were 25 at 1.5 T and 20 at 3 T in the callosal genu (CG), 40 at 1.5 and 3 T in the anterior corona radiata (ACR), and 50 at 1.5 T and 70 at 3 T in the putamen (PUT). Using TBSS, SNR thresholds were 20 at 1.5 T and 3 T in the CG, and 35 at 1.5 T and 40 at 3 T in the ACR. Below these thresholds, the mean FA increased logarithmically, and the standard deviations widened. Achieving bias-free SNR in the PUT required at least nine acquisitions at 1.5 T and six acquisitions at 3 T. In the CG and ACR, bias-free SNR was achieved with at least three acquisitions at 1.5 T and one acquisition at 3 T. Using diffusion tensor imaging (DTI) to study regions of low FA, e.g., basal ganglia, cerebral cortex, and WM in the abnormal brain, SNR should be documented. SNR thresholds below which FA is biased varied with the analytical technique, inherent tissue FA and field strength. Studies using DTI to study WM injury should document that bias-free SNR has been achieved in the region of the brain being studied as part of quality control.