On the solution of mathematical models of herd immunity in human helminth infections

The general solution of the mathematical model of herd immunity to human helminth infections recently proposed by Anderson and May [3] is obtained. The numerical solution of a more accurate biological model is indistinguishable from the corresponding exact solution of a more tractable mathematical model. Computer simulations of some particular cases of this model support the notion that both ecological and immunological factors determine the observed convex patterns of age-prevalence and age-intensity curves of human helminth infections.This work was made thanks to the advise and support of Dr. Robert M. May while the author was Postdoctoral Fellow at Princeton University     

Extramacrochaetae,a trans-acting gene of the achaete-scute complex of Drosophila involved in cell communication

Summary Phenotypic analyses of genetic combinations involving the gene extramacrochaetae (emc) reveal its participation in the differentiation of both sensory elements and wing veins. The study of near-amorphic alleles of emc in mitotitc recombination clones indicates that it also affects cell proliferation. These clones show abnormal sizes, shapes and spatial distribution. They differentiate extra sensory elements as well as extra veins. A gain of function mutation in the gene causes opposite phenotypes in both differentiation systems. The effects of the mutant on proliferation and patterning are consistent with the emc gene being involved in the transfer of information between neighbouring cells, which leads to the spatial expression of the achaetescute gene complex and genes involved in vein formation.     

Calcium transport sensitive to ruthenium red in cytochrome oxidase vesicles reconstituted with mitochondrial proteins

We describe a calcium transport that is sensitive to ruthenium red in liposomes reconstituted with mitochondrial extracts. This system is able to build an internally negative membrane potential, which allows the electrogenic influx of Ca²⁺ and Sr²⁺. Proteins with molecular weights higher than 35 kDa were incorporated to the vesicles, and enhanced the accumulation of the cation in an energy-dependent fashion.     

Hidden smectic properties of a chiral side-chain co-oligomer

We recently showed that a side-chain industrial co-oligosiloxane presents a quenchable enlarged blue phase behaviour at the cholesteric-isotropic phase transition. In this paper, we present the results of a structural study based on X-ray diffraction, differential scanning calorimetry and optical measurements. In particular, the smectic A organisation is demonstrated in the lower temperature domain, which was hitherto understood as a cholesteric phase. A structural model for this phase is proposed on the basis of the analysis of the anisotropic scattering of stretched fibers. Our results also suggest that the observed glass transition is indeed a rather complex phenomenon, which seems to involve not only the freezing of the main chains, but also smectic correlations at the side-chain level. Moreover, the calorimetric study indicates that, notwithstanding the conservation of the processed film's optical properties, low kinetic reorganisations occur at room temperature.     

An ATP-dependent Na/Mg countertransport is the only mechanism for Mg extrusion in squid axons

The components of magnesium efflux in squid axons have been studied under internal dialysis and voltage clamp conditions. The present report rules out the existence of an ATP-dependent, Na₀- and Mg₀-independent Mg²⁺ efflux (ATP-dependent Mg²⁺ pump) leaving the Mg²⁺---Na⁺ exchange system as the only mechanism for Mg²⁺ extrusion. The main features of the Mg²⁺ efflux are: (1) The efflux is completely dependent on ATP. (2) The efflux can be activated either by external Na⁺ (forward Mg²⁺---Na⁺ exchange) or external Mg²⁺ (Mg²⁺---Mg²⁺ exchange). (3) The mobility of the Mg²⁺ exchanger in the Na₀⁺-loaded form is greater than that in the Mg²⁺-loaded one. (4) In variance with the Na⁺---Ca²⁺ exchange mechanism, Mg²⁺---Mg²⁺ exchange is not activated by external monovalent cations. (5) ATPγS replaces ATP in activating Mg²⁺---Na⁺ exchange suggesting that a phosphorylation/dephosphorylation process regulates this transport mechanism.     

Solubilization of the active vasoactive intestinal peptide receptor from human colonic adenocarcinoma cells

The non-ionic detergent n-octyl-beta-D-glucopyranoside was used to solubilize the VIP (vasoactive intestinal peptide) receptor from human colonic adenocarcinoma cell line HT29-D4. The binding of monoiodinated 125I-VIP to the solubilized receptor was specific, time-dependent, and reversible. Scatchard analysis of data obtained from competitive displacement of monoiodinated 125I-VIP by native VIP suggested the presence of two classes of VIP binding sites with Kd values of 0.32 and 46.7 nM. The binding capacities of these two classes were 1.7 x 10(10) and 30.2 x 10(10) sites/mg of proteins, respectively. The solubilized receptor retained the specificity of the human VIP receptor towards the peptides of the VIP/secretin/glucagon family. The order of potency in inhibiting monoiodinated 125I-VIP binding was VIP (IC50 = 1.0 x 10(-9) M) much greater than peptide histidine methionine amide (IC50 = 10(-7) M) greater than growth hormone-releasing factor (IC50 = 3 x 10(-7) M) greater than secretin (IC50 greater than 10(-6) M); glucagon had no effect on VIP binding. The reducing agent dithiothreitol inhibited in a dose-dependent manner the binding of 125I-VIP. Covalent cross-linking experiments between the solubilized receptor and 125I-VIP showed that after sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography two major and one minor polypeptides of Mr 67,000, 72,000, and 83,000 were specifically labeled. When analyzed by gel filtration, the n-octyl-beta-D-glucopyranoside-solubilized 125I-VIP-receptor complex was resolved into two major peaks with molecular mass in the range of 60-70 and 270-300 kDa. Thus, the soluble form of the VIP receptor was probably a multimeric complex in which disulfide bonds may play an important role to hold the receptor in an active configuration.     

Microhabitat utilization by two leptodactylid frogs in the Andes of central Chile

Summary Some basic parameters of the life history of Alsodes montanus and Alsodes tumultuosus (Anura-Leptodactylidae), were studied from 1977 to 1980 by periodic field observations at Farellones and La Parva (33–34° south lat.; 2,700–3,000 m above sea level). Special attention was paid to strategies of resource partitioning in relation to gross features of the environment. The latter was unstable with a relative short period favorable for activity of the animals. Physical environmental differences between the first and second season of this study, resulted in a decrease in total number of active adults, a reduction in the duration of larval activity and a shift in microhabitat preferences of larvae.During the favorable season, October to May, adults of both species showed spatial and temporal segregation, related to different physical features of the environment; larvae did not show temporal segregation. Larvae of both species were found in seven different microhabitats; only in one of these did they show significant difference in microhabitat preference, A. tumultuosus was found more often in crevices. Microhabitat dimensions were more important than time and food resources in the separation of the niches of the two species. The segregation of niche dimensions, microhabitat, diel and annual activity and food were not complementary.Coexistence was therefore observed with the species tending to use different resources. When the same resource was used, it was not limiting.     

Estimation of the mechanical parameters of the human respiratory system

A numerical algorithm has been developed for the estimation of the mechanical parameters of the human respiratory system. In order to estimate the pulmonary resistance and the dynamic pulmonary elastance, the transpulmonary pressure and the airflow at the mouth or nose are expanded in Chebyshev series. The nonlinear mathematical lung model and a set of measurements for airflow and pressure are then handled by the numerical technique. The lung model includes a component to account for turbulent flow in the larynx and trachea. This contribution presents an alternative method for lung parameter estimation and differs from most existing methods in that it does not need measurements for the tidal volume. It therefore eliminates the use of a body plethysmograph. The method may also find potential application to various other parameter identification problems.     

Desangeloylshairidin,X-ray structure determination of a sesquiterpene lactone from Guillonea scabra

The structure and absolute configuration of desangeloylshairidin, a guaianolide isolated from Guillonea scabra, have been established by X-ray diffraction analysis. No conformational change was observed in its seven-membered ring between the crystal and deuterochloroform solution states.