Rheological aspects of red blood cell aggregation

The rheological aspects of red blood cell aggregation include molecular phenomena, cell viscoelasticity, and bulk flow rheology. At the molecular level, rates at which bonds are formed and broken, the chemical energy liberation from bond formation, the elasticity of the cross-bridges and lateral mobility of cross-linking molecules must all be considered for a complete description of bond formation and distribution. Lateral migration of binding molecules occurs due to diffusion in the surface of the membrane but may also be influenced by the stresses in the membrane during separation of adhering cells. In red blood cell disaggregation, fluorescent probes have shown concentration of ligands in the region of contact close to the line of separation. The chemical potential decrement that occurs when a bond is formed provides the energy source that may deform red blood cells in the process of aggregation. The degree of aggregation and the extent of cell deformation depends on the viscoelastic properties of the cell as well as the dynamics of bond formation and repulsive potential of surface charges present, which is governed by an equation representing a balance of these energies. In flowing blood, the hydrodynamic forces applied by the plasma and surrounding cells must be added to the bond forces and elastic response of the cell. Under sufficiently strong aggregation, plug flow or large aggregates may result. At high shear rates, aggregation may be prevented due to the small contact time and high shear stresses so that no effects of aggregation may be observed. At intermediate shear stresses, transitory contact, adhesion and disaggregation may occur between neighboring cells. Such phenomena have not been analyzed in detail, but simplified models suggest that plug-like flow can occur due to hydrodynamic cell-cell interaction even when cells are not aggregated.

Connective tissue breakdown in ovulation

A meshwork of collagen over the apical region of the follicle must be breached to permit the ovum to escape. We propose that specific collagenase activity is responsible for collagen breakdown in this region. Immature rats are primed with pregnant mare serum gonadotropin (PMSG), followed at 48 h by hCG. At 8 h after hCG, collagenase activity, measured in extracts of ovarian tissue, is elevated about five-fold. Ovulation follows at 10-12 h. Ovaries from PMSG-primed rats are dissected at 48 h, placed in a perfusion apparatus, and perfused with luteinizing hormone and 3-isobutyl-1-methyl xanthine. The ovulations induced by this treatment can be blocked to the extent of 70% with a synthetic collagenase inhibitor. The activation of procollagenase is believed to involve plasminogen activator and plasmin. In support of this, we find that tranexamic acid at 1 mM inhibits ovulation about 70%. The inhibitor must be added within 3-4 h of LH to be effective. A specific plasmin inhibitor, D-Val-Phe-Lys-chloromethyl ketone, is similarly effective.

[Effect of naloxone on experimental head injury in cats]

Forty-five cats were randomly divided into four groups: (1) the control group (n = 11); (2) the head injury group (n = 17); (3) the naloxone group (n = 8); (4) the saline group (n = 9). Naloxone (10mg/kg) was directly injected into cisterna cerebello-medullaris 2 hours after injury. The results showed that naloxone had some effects in maintaining MABP, CPP, lowering of ICP and edema of brain).

Human interstitial retinoid-binding protein. Gene structure and primary structure

Interstitial retinoid-binding protein (IRBP) is synthesized and secreted by rod photoreceptor cells into the interphotoreceptor matrix and is known to bind retinoids and fatty acids. We have used cDNA clones encoding human IRBP to isolate a 15-kilobase genomic fragment that encompasses the complete human IRBP gene. The IRBP gene spans more than 11 kilobases and is interrupted by three introns, all of which are positioned near the 3'-end of the coding sequence. The 3741-base pair coding region of IRBP appears to have been generated by quadruplication of an approximately 900 base pair long ancestral gene. The deduced amino acid sequence predicts a mature protein of 1,230 residues (calculated molecular weight 133,000). The protein sequence can be aligned into four homologous segments, each consisting of about 300 residues. Sequence similarity between segments is as high as 60% when conservative substitutions are taken into account. Two putative N-linked glycosylation sites are located in highly conserved domains in the center of the first and second segment of IRBP. A domain consisting of 41 residues at the COOH-terminal end of the third segment has 15 matching residues (38%) with an intradiscal loop of rhodopsin, a retinal-binding protein in rod photoreceptors.

Beta-endorphin-like immunoreactivity in CSF of patients with acute head injury. A clinical report of 36 cases

beta-endorphin-like immunoreactivity (beta-ELI) was measured in the cerebrospinal fluid (CSF) of 36 patients with acute head injury and 12 controls. The mean values of beta-ELI in CSF of controls and patients with moderate and severe acute head injury were 51.9 +/- 5.6 pg/ml, 110.5 pg/ml, and 173.8 +/- 20.1 pg/ml respectively, with significant difference between them (p less than 0.05). The results showed that beta-ELI increased in CSF of acute head injury patients.

One-dimensional steady continuum model of retraction of pseudopod in leukocytes

A one-dimensional steady state continuum mechanics model of retraction of pseudopod in leukocytes is developed. The retracting pseudopod is assumed to move bodily toward the main cell body, the bulk motion of which can be represented by cytoplasmic flow within a typical stream tube through the leukocyte. The stream tube is approximated by a frictionless tube with prescribed geometry. The passive rheological properties of cytoplasm in the main cell body and in the pseudopod are modeled, respectively, by Maxwell fluid and Hookean solid. The two regions are assumed to be separated by a sharp interface at which actin gel solates and thereby changes its rheological properties as it flows from the pseudopod to the main cell body. The driving mechanism responsible for the active retraction motion is hypothesized to be a spontaneous deformation of the actin gel, analogous but not necessarily equal to the well known actin-myosin interaction. This results in an active contractile stress being developed in the pseudopod as well as in the cell cortex. The transverse traction pulls against the inclined wall of the stream tube and is transduced into an axial stress gradient, which in turn drives the flow. The tension on the tube wall is picked up by the prestressed cortical shell. Governing equations and boundary conditions are derived. A solution is obtained. Sample data are computed. Comparison of the theory with experiments shows that the model is compatible to the observations.

[A preliminary study on pollinating bees for Amomum compactum Soland ex Maton]

This article deals with the species of bees pollinating Amomum compactum, along with the laws governing their growth and decline, and the pollinating effect of Nomia and Ceratina in the field.

A continuum model of protrusion of pseudopod in leukocytes

The morphology of human leukocytes, the biochemistry of actin polymerization, and the theory of continuum mechanics are used to model the pseudopod protrusion process of leukocytes. In the proposed model, the pseudopod is considered as a porous solid of F-actin network, the pores of which are full of aqueous solution. G-actin is considered as a "solute" transported by convection and diffusion in the fluid phase. The pseudopod grows as actin filaments elongate at their barbed ends at the tip of the pseudopod. The driving force of extension is hypothesized as being provided by the actin polymerization. It is assumed that elongation of actin filaments, powered by chemical energy liberated from the polymerization reaction, does mechanical work against opposing pressure on the membrane. This also gives rise to a pressure drop in the fluid phase at the tip of the pseudopod, which is formulated by an equation relating the work done by actin polymerization to the local state of pressure. The pressure gradient along the pseudopod drives the fluid filtration through the porous pseudopod according to Darcy's Law, which in turn brings more actin monomers to the growing tip. The main cell body serves as a reservoir of G-actin. A modified first-order equation is used to describe the kinetics of polymerization. The rate of pseudopod growth is modulated by regulatory proteins. A one-dimensional moving boundary problem based on the proposed mechanism has been constructed and approximate solutions have been obtained. Comparison of the solutions with experimental data shows that the model is compatible with available observations. The model is also applicable to growth of other cellular systems such as elongation of acrosomal process in sperm cells.

A t(8;14)(q24;q11) translocation in a T-cell leukemia (L1-ALL) with c-myc and TcR-alpha chain locus rearrangements

Cell lines established from T-cell leukemias have recently been reported to exhibit a chromosome translocation t(8;14) involving proto-oncogene c-myc and the gene of the T-cell receptor alpha-chain(TcR-alpha). In this work, we have studied a case of T-cell leukemia presenting a t(8;14)(q24;q11) translocation that was found in fresh leukemic cells taken during relapse, but was absent in cells collected at diagnosis. Hybridization analysis showed that the breakpoint on chromosome 8 was located 3' to the c-myc exon 3. A TcR-alpha-specific original probe (D14S7, Mathieu-Mahul et al., 1985) revealed two differently rearranged patterns in DNA from leukemic cells obtained at diagnosis and during relapse. In contrast, the rearranged TcR-beta-gene DNA pattern did not change during the course of the disease, indicating that leukemic cells were clonally related. These data indicate that the chromosome breakpoint in 14q11 is situated in the TcR-alpha locus. These results suggest that translocations t(8;14) involving TcR-alpha and c-myc genes in T-cell malignancies are analogous to variant t(2;8) and t(8;22) translocations observed in Burkitt lymphoma. They also establish that the same types of molecular rearrangements due to a t(8;14)(q24;q11) translocation, at first described in T-cell lines established in culture, also exist in vivo and may play a role in the evolution of the leukemic process.