Modelling a tethered mammalian sperm cell undergoing hyperactivation

The beat patterns of mammalian sperm flagella can be categorised into two different types. The first involves symmetric waves propagating down the flagellum with a net linear propulsion of the sperm cell. The second, hyperactive, waveform is classified by vigorous asymmetric waves of higher amplitude, lower wavenumber and frequency propagating down the flagellum resulting in highly curved trajectories. The latter beat pattern is part of the capacitation process whereby sperm prepare for the prospective penetration of the zona pellucida and fusion with the egg. Hyperactivation is often observed to initiate as sperm escape from epithelial and ciliary bindings formed within the isthmic regions of the female oviducts, leading to a conjecture in the literature that this waveform is mechanically important for sperm escape. Hence, we explore the mechanical effects of hyperactivation on a tethered sperm, focussing on a Newtonian fluid. Using a resistive force theory model we demonstrate that hyperactivation can indeed generate forces that pull the sperm away from a tethering point and consequently a hyperactivated sperm cell bound to an epithelial surface need not always be pushed by its flagellum. More generally, directions of the forces generated by tethered flagella are insensitive to reductions in beat frequency and the detailed flagellar responses depend on the nature of the binding at the tethering point. Furthermore, waveform asymmetry and amplitude increases enhance the tendency for a tethered flagellum to start tugging on its binding. The same is generally predicted to be true for reductions in the wavenumber of the flagellum beat, but not universally so, emphasising the dynamical complexity of flagellar force generation. Finally, qualitative observations drawn from experimental data of human sperm bound to excised female reproductive tract are also presented and are found to be consistent with the theoretical predictions.

Recovery of limited-extent images aliased because of spectral undersampling

In imaging situations where observations are made in spatial-frequency space, it is often desirable to lower the number of observations to fewer than that imposed by the Nyquist criterion. It is shown that patterns of regular spectral undersampling lead to aliasing that can be partially eliminated from some regions of a limited-extent image. An algorithm is presented for determining which regions are recoverable and which are not for a given pattern. Noniterative recovery, analogous to that proposed by Walsh and Nielsen-Delaney [J. Opt. Soc. Am. A 11, 572 (1994)], is shown to be feasible in cases of regular undersampling. The work has particular relevance to magnetic resonance imaging and aperture synthesis telescopy.

Mesenchymal stem cell surface antigen SB-10 corresponds to activated leukocyte cell adhesion molecule and is involved in osteogenic differentiation

Bone marrow contains a rare population of mesenchymal stem cells (MSCs) capable of giving rise to multiple mesodermal tissues including bone, cartilage, tendon, muscle, and fat. The cell surface antigen recognized by monoclonal antibody SB-10 is expressed on human MSCs but is lost during their developmental progression into differentiated phenotypes. Here we report on the immunopurification of the SB-10 antigen and its identification as activated leukocyte-cell adhesion molecule (ALCAM). Mass spectrometry establishes that the molecular mass of ALCAM is 80,303 +/- 193 Da and that it possesses 17,763 +/- 237 Da of N-linked oligosaccharide substituents. Molecular cloning of a full-length cDNA from a MSC expression library demonstrates nucleotide sequence identity with ALCAM. We also identified ALCAM homologs in rat, rabbit, and canine MSCs, each of which is over 90% identical to human ALCAM in their peptide sequence. The addition of antibody SB-10 Fab fragments to human MSCs undergoing osteogenic differentiation in vitro accelerated the process, thereby implicating a role for ALCAM during bone morphogenesis and adding ALCAM to the group of cell adhesion molecules involved in osteogenesis. Together, these results provide evidence that ALCAM plays a critical role in the differentiation of mesenchymal tissues in multiple species across the phylogenetic tree.

Contraception in the patient with liver disease

Selection of a method of contraception in patients with liver disease can be complicated. Tubal ligation should be considered in the setting of chronic liver disease for those patients who have completed families. Multiple reversible methods of contraception are currently available but may affect hepatic disease. Estrogen-containing contraceptive methods are contraindicated in patients with acute liver disease. Progestin contraceptives appear to be safe and multiple delivery systems are available. With rare exception, barrier methods and the intrauterine device may be offered as alternative methods.

Metal hydride mediated reduction of 3-(alkylthio)oxindoles containing other potentially reducible groups

The reduction of several 3-(methylthio)oxindoles bearing ester groups on the benzene ring has been studied. The reaction is very dependent on the substitution of the oxindole, and the position of the ester group. Deprotonation of the C3 center by the metal hydride is the major initial pathway. This deprotonation plays a role in the reduction of the pendant ester group. Ester groups ortho, and presumably para, to C3 are very difficult to reduce, reaction only occurring with excess LiAlH4 at elevated temperatures. Once reduction starts, it is very difficult to stop, with reduction of the ester to a methyl group being observed. When deprotonation at this center is blocked, ester reduction becomes straightforward and can be accomplished at room temperature with LiEt3BH. Keywords: oxindole, reduction, anion.

Metal hydride mediated reduction of 1,3-dimethyl-3(methylthio)oxindole

The metal hydride mediated reduction of 4-carboethoxy-1,3-dimethyl-3-(methylthio)oxindole with lithium aluminum hydride and lithium triethylborohydride was studied. The results show that reduction of the oxindole carbonyl group is competitive with reduction of the pendant ester. The hemi-aminal that results from initial addition of hydride to the oxindole carbonyl may follow a number of reaction pathways, one of which is an unprecedented rearrangement. A mechanism is proposed that accounts for all observed products. Keywords: oxindole, reduction, rearrangement.

Exploratory study of the quenching of photosensitizers by initiators of free radical "living" polymerization

Several compounds of the type PhCR1R2-TEMPO (where TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxide) have been prepared and examined as potential photosensitized initiators for "living" free radical polymerizations. For example, these compounds are excellent quenchers of triplet xanthone (rate constants in the range (8.0–13) × 108 M−1 s−1) and result in the formation of benzylic and TEMPO radicals. The importance of excited state energy and nature of the excited triplet state have also been explored. We also tested pyrene as a possible singlet sensitizer. While pyrene fluorescence is efficiently quenched, the process does not lead to cleavage of the C—O bond. A model is proposed to account for this anomaly in the photosensitized decomposition of these TEMPO adducts. Keywords: TEMPO, laser flash photolysis, time resolved emission spectroscopy, sensitizers, quenching, photoinitiator.

A solid state NMR and X-ray crystallographic investigation of dynamic disorder in solid tetrahydronaphthalene derivatives

The solid state disorder of two tetrahydronaphthalene derivatives, N-methyl-N-methoxy-5,6,7,8-tetrahydro-1-naphthamide and 5,6,7,8-tetrahydro-1-naphthoic acid, was studied by solid state NMR and single crystal X-ray diffraction. The X-ray crystal structure of N-methyl-N-methoxy-5,6,7,8-tetrahydro-1-naphthamide was obtained at 123 K. It indicated the presence of two distinct molecular conformations. Solid state 13C CP/MAS NMR data using the dipolar dephasing technique revealed that the two conformations of the molecule are dynamically disordered, while solid state 2H NMR data, collected on a specifically deuterated analog, were used to determine the populations of each conformation as well as an apparent activation energy. Solid state NMR experiments were also used to show that 5,6,7,8-tetrahydro-1-naphthoic acid possesses the same type of dynamic disorder. Key words: deuterium NMR, solid state NMR, dynamic disorder. X-ray, tetrahydronaphthalene derivatives

A Novel Cyclopropanation

Reaction between benzaldehyde and methyl α- benzylsulfonylacetate furnishes methyl (E)-α- benzylsulfonyl-β-phenylacrylate as the exclusive Knoevenagel adduct. The related condensations between α-benzylsulfonylacetonitrile and paraformaldehyde furnish trans-1-benzylsulfonyl-2-phenylcyclopropane-1-carbonitrile in modest yields. These product structures are established by X-ray crystallographic analysis. Phenylsulfene is ruled out as an intermediate in the formation of the cyclopropane.

Assessment of argyrophilic nucleolar organizer region quantification in benign and malignant bone tumors

Quantification of argyrophilic nucleolar organizer regions has been proposed as a technique that may aid in diagnosing and predicting the biologic behavior of a variety of neoplasms. A 1-step silver staining technique was used to identify and quantify argyrophilic nuclear organizer regions in a series of 96 bone tumor specimens. Malignant bone tumors had a higher mean argyrophilic nuclear organizer region count (3.05 +/- 0.82) than giant cell tumors (1.39 +/- 0.14, p < 0.001) and benign bone tumors (1.51 +/- 0.42, p < 0.001). Despite these differences in mean counts, an overlap of argyrophilic nuclear organizer region scores was observed in some benign and malignant cases. The argyrophilic nuclear organizer region counts of the osteosarcomas were analyzed to determine whether they correlated with tumor behavior. The mean argyrophilic nuclear organizer region count of specimens from patients in whom metastatic disease developed was not significantly different than that of patients who remained disease free.

Retinoic acid stimulates interstitial collagenase messenger ribonucleic acid in osteosarcoma cells

The rat osteoblastic osteosarcoma cell line UMR 106-01 secretes interstitial collagenase in response to retinoic acid (RA). The present study demonstrates by Northern blot analysis that RA causes an increase in collagenase messenger RNA (mRNA) at 6 h, which is maximal at 24 h (20.5 times basal) and declines toward basal level by 72 h. This stimulation is dose dependent, with a maximal response at 5 x 10(-7) M RA. Nuclear run-on assays show a greater than 20-fold increase in the rate of collagenase mRNA transcription between 12-24 h after RA treatment. Cycloheximide blocks RA stimulation of collagenase mRNA, demonstrating the need for de novo protein synthesis. RA not only causes an increase in collagenase secretion, but is known to decrease collagen synthesis in UMR 106-01 cells. In this study, the increase in collagenase mRNA is accompanied by a concomitant decrease in the level of alpha 1(I) procollagen mRNA, which is maximal at 24 h (70% decrease), with a return to near-control levels by 72 h. Nuclear run-on assays demonstrated that the decrease in alpha 1 (I) procollagen expression does not have a statistically significant transcriptional component. RA did not statistically decrease the stability of alpha 1 (I) procollagen mRNA (calculated t1/2 = 8.06 +/- 0.30 and 9.01 +/- 0.62 h in the presence and absence of RA, respectively). However, transcription and stability together probably contribute to the major decrease in stable alpha 1 (I) procollagen mRNA observed. Cycloheximide treatment inhibits basal level alpha 1 (I) procollagen mRNA accumulation, demonstrating the need for on-going protein synthesis to maintain basal expression of this gene.

Prostanoid-induced expression of matrix metalloproteinase-1 messenger ribonucleic acid in rat osteosarcoma cells

Individual prostanoids have distinct potencies in activating intracellular signaling pathways and regulating gene expression in osteoblastic cells. The E-series prostaglandins (PGs) are known to stimulate matrix metalloproteinase-1 (MMP-1) synthesis and secretion in certain rodent and human osteoblastic cells, yet the intracellular events involved remain unclear. To further characterize this response and its signal transduction pathway(s), we examined prostanoid-induced expression of the MMP-1 gene in the rat osteoblastic osteosarcoma cell line UMR 106-01. Northern blot analysis demonstrated that prostaglandin E2 (PGE2) and PGE1 were very potent stimulators (40-fold) of MMP-1 transcript abundance, PGF2 alpha and prostacyclin were weak stimulators (4-fold), and thromboxane-B2 had no effect. The marked increase in MMP-1 transcript abundance after PGE2 treatment was first detected at 2 h, became maximal at 4 h, and persisted beyond 24 h. This response was dose dependent and elicited maximal and half-maximal effects with concentrations of 10(-6) and 0.6 x 10(-7) M, respectively. Cycloheximide, a protein synthesis inhibitor, completely blocked this effect of PGE2, suggesting that the expression of other genes is required. Nuclear run-on experiments demonstrated that PGE2 rapidly activates MMP-1 gene transcription, with a maximal increase at 2-4 h. The second messenger analog, 8-bromo-cAMP, mimicked the effects of PGE2 by stimulating a dose-dependent increase in MMP-1 messenger RNA (mRNA) levels, with a maximal effect quantitatively similar to that observed with PGE2. Thus, in UMR 106-01 cells, different prostanoids have distinct potencies in stimulating MMP-1 mRNA abundance. Our data suggest that PGE2 stimulation of MMP-1 synthesis is due to activation of MMP-1 gene transcription and a subsequent marked increase in MMP-1 mRNA abundance. This effect is dependent on de novo protein synthesis and is mimicked by protein kinase-A activation.

Confocal imaging of a stratified medium

The confocal imaging of stratified media (for example, thin-film structures) is investigated. A simple model is introduced for the imaging of a single layer in order to explore the axial resolution attainable. A rigorous model is also described and compared with experimental results from thin surface films. A theoretical treatment of imaging of stratified media with a continuously varying refractive index is presented, and the inverse problem of reconstructing the refractive-index profile from a confocal image is discussed.

Micellar rate enhancement studies in mixed sodium fluorocarbon/hydrocarbon surfactant solutions

Stopped-flow kinetic studies were conducted in mixed micellar solutions of fluorocarbon and hydrocarbon anionic surfactants to determine the prevalent micellar form. The probe reaction was the Niaq2+/pyridine-2-azo-p-dimethylaniline (PADA) complexation, which is many times accelerated in the presence of anionic micelles. Binding constants for Niaq2+ and PADA partitioning between bulk solution and micelles were determined through the murexide technique and solubility measurements respectively and the molar reaction volume was obtained from the Robinson equation. The three binary surfactant systems investigated had sodium perfluoroheptanoate as the fluorocarbon surfactant while the hydrocarbon surfactants were sodium decylsulfate, sodium nonanesulfonate, and sodium octanesulfonate. The kinetic results were consistent with unimicellar composition in all three systems which was not the behaviour previously found with the sodium octane sulfonate/sodium perfluoroctanoate system. The difference was attributed to closer similarity in the surfactant pair hydrophobicities as revealed through their critical micelle concentrations. Another finding was that mixed micelles synergistically can lead to a much greater solubilization of PADA than is possible through either of the pure surfactants.

Solubilization of pada in Hydrocarbon Fluorocarbon Surfactant Mixtures

Solubilities of pyridine-2-azo-p-dimethylaniline ( pada ) were determined at 25�C in four mixed fluorocarbon/hydrocarbon short-chained surfactant systems: ( i ) sodium decyl sulfate/sodium perfluoroheptanoate; (ii) sodium octanesulfonate /sodium perfluorooctanoate ; (iii) sodium octanesulfonate /sodium perfluoroheptanoate ; (iv) sodium nonanesulfonate /sodium perfluoroheptanoate. Systems ( i ), (iii) and (iv) showed micellar miscibility (one mixed micelle) and synergistic solubilization effects. System (ii) had two critical micelle concentrations pointing to two micellar forms in solution, and no synergism could be detected. From these four examples, it is deduced that single mixed micelles are formed when the critical micelle concentrations of the pure surfactants are within a factor of 3 of each other.

Is "wheelchair wrist drop" a new syndrome to watch for?

All in all, the present-day wheelchair is a poor place for nursing home patients to spend any length of time. Unfortunately, though, if you walk through a nursing home, you will find that a large number of patients spend many hours sitting in wheelchairs. We feel that the increased use of a wheelchair for daytime and evening sitting was a prominent causative factor of the radial nerve paralysis in the cases reported here, and we suspect that this syndrome is being overlooked. Since early diagnosis and prompt therapy may favorably improve the outcome, and awareness of the problem may prevent it altogether, we urge physicians to be wary of this apparently new syndrome and take precautionary measures where applicable.

A simulator-based approach to training in aeronautical decision making

The effectiveness of a simulator-based approach to training pilot skills in risk assessment and decision making was evaluated in a sample of pilots enrolled in a university aviation science program. The 16 experimental group subjects received 4 hours (h) of classroom instruction designed to enhance pilot judgment skills, followed by 4 simulated cross-country flights during which several critical inflight events occurred. Subjects in the control group received classroom instruction in basic instrument flying, followed by simulator sessions emphasizing instrument flight. Measures of pilot judgment were obtained on all subjects before and after the training, and subjects in the experimental judgment-trained group performed significantly better on the posttraining simulation than did control group subjects. The findings suggest that significant gains in pilot decision-making skill can be obtained through the use of the judgment training materials along with simulator practice.

The nuclear power industry in the United States: status and projections

One sixth of the electricity in the United States is now being generated in nuclear power plants, a remarkable achievement for a technology whose basic nuclear reaction was not even known 50 years ago. On the other hand, many of the nation's electric utilities are experiencing great difficulties completing the construction of their nuclear plants; 41 partially constructed plants have been abandoned. Those abandoned plants plus about 110 in operation and 15 still to be completed comprise the first generation of nuclear power plants in the United States. When, and even if, there will be a second generation is much in doubt. Data are presented to show that the absence of a second generation of nuclear plants will place large demands on the fossil fuels, with attendant high energy prices and high environmental costs the expected outcome. It appears that the future will bring large economic forces to start new orders for nuclear plants. On the other hand, the opposing institutional forces appear equally strong. Among the problems creating these institutional forces are the difficulty the United States is having in finding a politically acceptable approach to nuclear waste disposal and the vulnerability of power plant builders and operators to litigation and high financial risk. At present, the issue of a second generation of nuclear plants is stalemated.

Effects of bilayer cholesterol on human erythrocyte hexose transport protein activity in synthetic lecithin bilayers

In this study, we describe the effects of altered bilayer cholesterol content on reconstituted, protein-mediated sugar transport. The system used was the human erythrocyte sugar transporter (band 4.5) reconstituted into the bilayers of large unilamellar vesicles. Vesicle preparations were formed from synthetic lecithins whose bilayer cholesterol content ranged from 0 to 50 mol %. Transport was measured by microturbidimetric analysis over the temperature range of 0-65 degrees C while bilayer physical state was characterized by differential scanning calorimetry. Reconstituted transport activity was irreversibly lost between 62 and 65 degrees C. The Km for reconstituted transport was found to increase only slightly with increasing temperature and was not systematically affected by bilayer cholesterol content. The most striking observation of this study is that over certain critical cholesterol concentrations, as little as a 2.5% change in bilayer cholesterol can result in as much as a 100-fold change in Vmax per reconstituted protein. Our findings run counter to the view that increasing bilayer cholesterol content monotonically transforms a membrane into a state of "intermediate fluidity". Abrupt, cholesterol-induced bilayer reorganizations occurring at 15-20 and 30 mol % bilayer cholesterol are markedly reflected in altered sugar transport rates. Increasing the cholesterol content of crystalline distearoyllecithin bilayers inhibits the activity of the reconstituted transporter. It is apparent from these studies that bilayer "fluidity" is neither the sole nor a major determinant of the Indeed, we find the effect of cholesterol on transport activity is independent of its ability to fluidize membranes.

Effect of bilayer cholesterol content on reconstituted human erythrocyte sugar transporter activity

The influence of altered bilayer cholesterol content on the catalytic activity of the human red cell hexose transporter was examined by reconstitution of the transport protein (band 4.5) into bilayers of large unilamellar vesicles formed from dipalmitoyl lecithin and varying amounts of cholesterol. The physical state of the bilayers was characterized by differential scanning calorimetry. The major findings are as follows: changes in bilayer phase behavior occur at membrane cholesterol levels of 15 to 20 mol % and 30 to 40 mol %; and the catalytic activity of the reconstituted transporter (Vmax/transporter) correlates with bilayer phase behavior. In crystalline bilayers, this is seen as an abrupt, stimulation of activity at 15 mol % cholesterol (which is reversed at 17.5 mol %) and a gradual acceleration of activity between 30 to 40 mol % cholesterol. In fluid bilayers (where activity is high), activity is unaffected by 10, 20, and 30 mol % cholesterol. However, 12.5 and 17.5 mol % cholesterol reduce activity by 100-fold. These studies demonstrate that small changes in bilayer cholesterol content result in drastic alterations in transporter activity. Transporter sensitivity to cholesterol is a complex rather than monotonic function of bilayer cholesterol content and appears to be primarily determined by bilayer composition rather than by bilayer "fluidity."