Structure and function of window glass and Pyrex.

Window glass is a ternary mixture, while Pyrex (after window glass, the most common form of commercial glass) is a quaternary. Here, we investigate the chemical, physical, and mathematical factors that determine the compositions of these optimized glasses. Previously, we succeeded in deriving exactly the composition of window glass (sodium calcium silicate) without adjustable parameters. Borosilicates are a much more challenging problem, and Pyrex (sodium aluminum borosilicate) requires a different approach. Our analysis shows that mean-field (or global) models (networks without significant clustering) are sufficient for window glass and probably most other commercial silicate glasses. However, it appears that the most important property of pyrex, its ability to resist mechanical shocks, requires a cluster model (large medium range order). We propose such a model, and argue that it also follows from hierarchical principles. Our model is strongly supported by specific experiments, and we suggest further experiments to test the principles underlying commercial glasses.

Maternal self-administered fetal heart rate monitoring and transmission from home in high-risk pregnancies.

OBJECTIVES: To evaluate the feasibility of high-risk pregnancy surveillance by patient-directed fetal heart rate monitoring and transmission, and to assess patient satisfaction with this technology. METHODS: Thirty-six women with high-risk pregnancies performed daily non-stress tests at home and transmitted the data to our perinatal care center by telephone. At each transmission, patients were asked by a physician about perceived fetal movements and uterine contractions and given the results. If the tracing was unsatisfactory, further evaluation was performed. In addition, patients completed a questionnaire on quality of life and anxiety state before and after the study. RESULTS: All patients were able to perform the tests and transmissions. The quality of recorded data was significantly correlated with maternal body mass index, but not with gestational age at the time of monitoring or birth weight. Thirty-nine of the total 562 tracings (6.9%) were inconclusive or non-reassuring. After repeated testing, 32 of them (82%) were considered normal, and seven patients (18%) were referred for additional in-hospital evaluation. Of this group, four were discharged for further surveillance with routine home monitoring and the remaining three were hospitalized for continued evaluation. There were no significant immediate adverse maternal or neonatal outcomes as a result of the monitoring. Patient satisfaction was high. CONCLUSIONS: Daily home FHR monitoring in high-risk patients is safe and feasible at all gestational ages, based on this initial pilot evaluation. It is easily and reliably performed and accepted by patients with a high level of satisfaction.

Classical glueballs in non-Abelian Born-Infeld theory.

It is shown that the Born-Infeld-type modification of the quadratic Yang-Mills action gives rise to classical particlelike solutions prohibited in the standard Yang-Mills theory. This becomes possible due to breaking of the scale invariance by the Born-Infeld nonlinearity. New classical glueballs, which are of a sphaleronic nature, exhibit a striking similarity to the Bartnik-McKinnon solutions to the Yang-Mills theory coupled to gravity.

Extracellular calcium-sensing receptor induces cellular proliferation and activation of a nonselective cation channel in U373 human astrocytoma cells.

A receptor for extracellular calcium ions (Ca2+o), cloned from parathyroid gland, serves a critical function in Ca2+o homeostasis by regulating PTH release via "sensing" of its physiological agonist, Ca2+o. Its cloning from rat striatum revealed that the extracellular calcium-sensing receptor (CaR) could be involved in sensing ambient Ca2+o within the brain, where Ca2+ plays key roles in virtually all aspects of central nervous system (CNS) function. The CaR is expressed in neurons, oligodendrocytes, microglia and the human astrocytoma cell line, U87 where its functions include control of cellular proliferation and modulation of ion channels, such as outward K+ channels and nonselective cation channels (NCC). In this report, we have shown that the CaR is expressed in U373 cells as assessed by RT-PCR using CaR-specific primers followed by sequencing of the amplified products, by Northern blot analysis using a CaR-specific probe as well as by Western analysis utilizing a specific polyclonal anti-CaR antiserum. Furthermore, agents known to activate the cloned CaR induce increases in cellular proliferation and the open probability of an NCC. Thus our study strongly suggests that elevated levels of Ca2+o, acting via the CaR, activate an NCC that could contribute to the associated CaR-induced stimulation of proliferation.

[Fungal aspartic proteinase from Trichoderma viride. Specificity during oligopeptide hydrolysis]. / Gribnaia aspartatnaia proteinaza iz Trichoderma viride. Spetsifichnost' pri gidrolize oligopeptidov.

We isolated, purified, and characterized an aspartic protease from fungus Trichoderma viride. The pH-dependence of the enzyme functioning was determined, and its specificity in the limited proteolysis of insulin and melittin was compared to the specificities of pepsin A and gastricsin. The kinetics of melittin hydrolysis by these enzymes was studied by mass spectrometry.

Physiological regulation of epithelial tight junctions is associated with myosin light-chain phosphorylation.

Tight junctions serve as the rate-limiting barrier to passive movement of hydrophilic solutes across intestinal epithelia. After activation of Na+-glucose cotransport, the permeability of intestinal tight junctions is increased. Because previous analyses of this physiological tight junction regulation have been restricted to intact mucosae, dissection of the mechanisms underlying this process has been limited. To characterize this process, we have developed a reductionist model consisting of Caco-2 intestinal epithelial cells transfected with the intestinal Na+-glucose cotransporter, SGLT1. Monolayers of SGLT1 transfectants demonstrate physiological Na+-glucose cotransport. Activation of SGLT1 results in a 22 +/- 5% fall in transepithelial resistance (TER) (P < 0.001). Similarly, inactivation of SGLT1 by addition of phloridzin increases TER by 24 +/- 2% (P < 0.001). The increased tight junction permeability is size selective, with increased flux of small nutrient-sized molecules, e.g., mannitol, but not of larger molecules, e.g., inulin. SGLT1-dependent increases in tight junction permeability are inhibited by myosin light-chain kinase inhibitors (20 microM ML-7 or 40 microM ML-9), suggesting that myosin regulatory light-chain (MLC) phosphorylation is involved in tight junction regulation. Analysis of MLC phosphorylation showed a 2.08-fold increase after activation of SGLT1 (P < 0.01), which was inhibited by ML-9 (P < 0.01). Thus monolayers incubated with glucose and myosin light-chain kinase inhibitors are comparable to monolayers incubated with phloridzin. ML-9 also inhibits SGLT1-mediated tight junction regulation in small intestinal mucosa (P < 0.01). These data demonstrate that epithelial cells are the mediators of physiological tight junction regulation subsequent to SGLT1 activation. The intimate relationship between tight junction regulation and MLC phosphorylation suggests that a critical step in regulation of epithelial tight junction permeability may be myosin ATPase-mediated contraction of the perijunctional actomyosin ring and subsequent physical tension on the tight junction.