Promotion and inhibition of vesicle fusion by polylysine

Polylysine induced rapid aggregation of large unilamellar vesicles composed of phosphatidylcholine-cardiolipin (1:1 molar ratio) but not their fusion. Application of the terbium-dipicolinic acid fusion assay showed that addition of polylysine at nanomolar concentrations enabled a significant lowering of the Ca2+ threshold concentration for vesicle fusion from 9 to 1 mM. Analysis of the kinetics of fusion with a mass-action kinetic model showed that polylysine enhanced significantly the rate of aggregation but affected only slightly the rate of fusion per se. Maximal enhancement of overall fusion rates occurred at a charge ratio (polylysine/cardiolipin) of about 0.5. At larger polylysine concentrations, e.g., at charge ratios greater than 3, polylysine inhibited vesicle fusion.     

The retinoblastoma gene and cell growth control

Rare diseases often provide unique and fascinating insights into the workings of biological machinery. Retinoblastoma is a good example. This hereditary disease occurs rarely (in only one out of 20,000 children), yet it opens a 'window' into the mechanisms that sit at the very center of growth control in cells throughout the body. Children who survive bilateral retinoblastoma often have offspring who are similarly affected. Indeed, transmission of the disease suggests the actions of a simple dominant Mendelian allele of high penetrance. Three years ago the wild-type allele of this gene (termed Rb) was isolated by molecular cloning. With this success has come a rich harvest of information on tumor pathogenesis and the molecular biology of cellular growth control.     

The effects of a topical PGE2 analogue on global flap ischemia in rats

The present study evaluated the ability of DHV-PGE2ME, a topically effective 16-vinyl prostaglandin E2 analogue, to improve the tolerance of skin flaps to a period of ischemia. DHV-PGE2ME and placebo were applied to bilateral island flaps on 70 anesthetized rats; then the vascular pedicle of each flap was clamped for 10 hours. Treated flaps evidenced significantly better reperfusion, as documented by quantification of fluorescein dye delivery at 90 minutes after clamp release, and they had significantly greater ultimate viability (p less than 0.05, by ANOVA). While less than 3 percent of untreated flaps survived, those treated with 1.75 and 17.5 microgram/cm2 of drug evidenced 76 and 86 percent survival, respectively. Treatment of a given flap did not affect its contralateral mate, since there was no evidence of a systemic effect. Especially since its effect can be limited to the site of application, DHV-PGE2ME should be valuable for the treatment of compromised perfusion in a variety of settings.     

Oncogenic activation of the neu-encoded receptor protein by point mutation and deletion.

The rat neu gene, which encodes a receptor-like protein homologous to the epidermal growth factor receptor, is frequently activated by a point mutation altering a valine residue to a glutamic acid residue in its predicted transmembrane domain. Additional point mutations have been constructed in a normal neu cDNA at and around amino acid position 664, the site of the naturally arising mutation. A mutation which causes a substitution of a glutamine residue for the normal valine at residue 664 leads to full oncogenic activation of the neu gene, but five other substitutions do not. Substituted glutamic acid residues at amino acid positions 663 or 665 do not activate the neu gene. Thus only a few specific residues at amino acid residue 664 can activate the oncogenic potential of the neu gene. Deletion of sequences of the transforming neu gene demonstrates that no more than 420 amino acids of the 1260 encoded by the gene are required for full transforming function. Mutagenesis of the transforming clone demonstrates a correlation between transforming activity and tyrosine kinase activity. These data indicate that the activating point mutation induces transformation through (or together with) the activities of the tyrosine kinase.     

Characterization of T helper 1 and 2 cell subsets in normal mice. Helper T cells responsible for IL-4 and IL-5 production are present as precursors that require priming before they develop into lymphokine-secreting cells

We have shown that the requirements for the production of IL-4 and IL-5 by normal L3T4+T cells from murine spleen are very different from those for the production of IL-2. Secretion of detectable quantities of IL-4 and IL-5 and induction of the mRNA for each lymphokine occurs in vitro only after cells are primed and re-stimulated. This priming can be achieved by mitogens (Con A), by antibodies to the TCR (anti-T3) or by stimulation with alloantigen. In contrast, requirements for induction of lymphokine production after priming resemble those for initial production of IL-2. Thus the majority of T cells of helper phenotype that have the potential to become IL-4- and IL-5-secreting T cells, exist in the form of precursors requiring stimulation and several days of culture as well as re-stimulation with mitogen or Ag before they become detectable as lymphokine-secreting cells. In contrast, among fresh CD4+T cells, secretion of IL-2, IL-3, granulocyte/macrophage CSF, and IFN-gamma is easily detected within 24 h of stimulation with mitogen or Ag. These observations establish that distinct phenotypes of Th cells are found at different times after stimulation and support the concept that synthesis and secretion of different lymphokines or groups of lymphokines are regulated independently. Furthermore the patterns of lymphokines secreted by fresh vs primed Th cells, which largely correspond to the patterns that have been used to define the Th1 and Th2 subsets among Th cell lines, provides evidence that different subsets of normal T cells exist that may correspond to these designations. Secretion of different lymphokines by two subsets of Th cells at different times in an immune response, and perhaps in different places, suggests a model in which the ratio of the two T cell subsets (Th1 vs Th2) and state of differentiation of each (precursor vs effector), influence or determine the direction of the response, with variations in these parameters leading to differing responses.     

Effects of a medical team coordinator on length of hospital stay.

OBJECTIVE: To determine the effect of a medical team coordinator (MTC) on the length of stay in a teaching hospital. DESIGN: Randomized controlled trial. SETTING: Two of four general medical clinical teaching units (CTUs). PATIENTS: Patients admitted to the CTUs between July and October 1990 except those who were admitted directly to an intensive care unit or whose death was expected within 48 hours. The 267 patients were randomly assigned to receive either standard medical care or standard medical care plus MTC services. INTERVENTION: The MTC was a baccalaureate nurse whose role was to facilitate administrative tasks such as discharge planning, to coordinate tests and procedures, and to collect and collate patient information. MAIN OUTCOME MEASURES: Length of hospital stay. A subgroup of 40 patients was asked to complete a brief survey on medical care information and satisfaction. RESULTS: The MTC intervention reduced the mean length of stay by 1.97 days (p less than or equal to 0.04, 95% confidence interval [CI] 1.02 to 2.92 days). Subanalysis by diagnostic group revealed that most of this effect was in an ill-defined group of disorders. In the survey more patients in the MTC group than in the other group reported being satisfied with their medical care (89% v. 62%; p less than or equal to 0.05, 95% CI 2% to 52%). CONCLUSIONS: The services of an MTC help to reduce the length of hospital stay for some groups of patients. Further research is necessary to examine which components of the MTC intervention are most effective and in what conditions.