Infectivity of the Santa Lucia (El Salvador) strain of Plasmodium falciparum to different anophelines.

Anopheles freeborni mosquitoes were much more heavily infected with the Santa Lucia strain of Plasmodium falciparum from coastal El Salvador than were any of the other species tested. Of 5 strains of A. albimanus examined, the most heavily infected was the CA-109A and the least was the Melara, both of which come from coastal El Salvador. Of the exotic anophelines, the A. maculatus was infected at a slightly higher level than was the A. balabacensis. The incidence of highly infected individual mosquitoes was greatest in the Panama-Escobal strain of A. albimanus from the Republic of Panama; the incidence was lowest in the Melara strain from El Salvador. All strains of A. albimanus developed infected salivary glands, but the A. freeborni and A. maculatus mosquitoes appeared to develop infected glands more effeciently. Infection rates in A. freeborni mosquitoes were highest if mosquitoes were fed on Aotus trivirgatus monkeys between the 19th and 25th days of patent gametocytemia.     

Developing preferences for live female models of the same or other species in white peking ducklings

The preferences of white Peking ducklings (Anas platyrhynchos) for live models was evaluated for the first 7 days of life. The models were all females: a rouen duck (Anas platyrhynchos), a white Peking duck, and a blue Andalusian chicken (Gallus gallus). In three different experiments the orientation of the models was toward the subjects, away from the subjects, and toward the subjects but with fences around the models (to control for model aggressiveness). In all cases the subjects preferred the rouen duck and not the white Peking model or the chicken. In addition, when the models were facing away from the subjects there was a significant peak of preference that appeared on day 4. The latter effect was replicated three times and is therefore considered a reliable phenomenon.     

Exchange of partners in glucagon receptor-adenylate cyclase complexes. Physical evidence for the independent,mobile receptor model

The apparent target sizes of the glucagon receptor and the catalytic unit of adenylate cyclase in rat liver plasma membranes have been measured by the technique of radiation inactivation in an electron beam. When irradiated in the uncoupled state, the apparent target size for the catalytic unit assayed by fluoride-stimulated activity was 160 000, and for the receptor assayed by specific ¹²⁵I-labelled glucagon binding was 217 000. The corresponding target size estimated from glucagon-stimulated activity after irradiation in the uncoupled state was 389 000. When the complexes were irradiated in the coupled state in the presence of glucagon, the apparent target sizes from ¹²⁵I-labelled glucagon binding, and fluoride- or glucagon-stimulated activities had similar values of 310 000, 380 000 and 421 000, respectively. However, if the complexes were allowed to uncouple by removing glucagon after irradiation and activity was then assayed after readdition of glucagon, the apparent target size from the glucagon-stimulated activity increases from 421 000 to 811 000.The pattern of apparent target sizes obtained under these different conditions has been tested against the pattern predicted for simple models of the coupling mechanism. The only simple model that is consistent with the pattern of target sizes requires the receptors and catalytic units to be present in approximately equal numbers. On binding glucagon, the receptor forms a locking interaction with the catalytic units, so that the complex and its components are inactivated as a single target with an apparent size of about 380 000 ($\text{± 15\%}$). After the removal and readdition of glucagon to complexes that were irradiated in the coupled state, the new population of complexes must contain hybrids of active and inactive partners obtained by exchange between active and inactivated complexes, to account for the doubling in apparent target size to 811 000 for glucagon-stimulated activity. This hybridization of catalytic units and receptors is the essential feature of the model that distinguishes it from others in which permanently associated complexes of the two components are activated by lateral dimersation on binding glucagon. Simple models of this type are shown to be physically improbable. It is emphasized that the models described are based only on the relationships between the apparent target sizes of components that are defined by their functions, and the apparent target sizes do not necessarily relate solely to the components that can be defined structurally as the receptor or catalytic unit.     

Transference of the high molecular weight carbohydrate sequences of fetuin to the surface of carrot embryo protoplasts

A method is described for the removal of the carbohydrate sequences of glycoproteins, and their covalent attachment to hydrocarbon chains. These synthetic membrane components may then be incorporated into liposome and cell membranes. Pronase-liberated glycopeptides derived from fetuin were linked by a reduced Schiff's base linkage to tetradecyl aldehyde. The resulting glycolipid was incorporated by external addition, into phosphatidylcholine liposomes. Glycolipid transfer to these liposomes rendered them suseptible to agglutination by wheat germ lectin, which binds N-acetylneuraminic acid, the terminal carbohydrate of the high molecular weight fetuin sugar sequence. Sequential removal of the terminal sugars, and subsequent agglutination behaviour towards various lectins, suggests that the carbohydrate sequence had been transfered intact. The glycolipid was incorporated into plant protoplast membranes by incubation with glycolipid-containing liposomes for 2 h at 37°C. These synthetic glycolipids may find a use in the study of carbohydrate-based recognition systems in animal and plant membranes. In addition they may prove useful in the development of cell and membrane tagging and handling techniques, by the insertion of sugar groups not normally present in these membranes.     

Lack of tropomyosin correlates with the absence of stress fibers in transformed rat kidney cells

We have utilized epithelial rat kidney cells and their Kirsten viral transformant (442) to examine the role of actin-binding proteins in cellular morphogenesis. Normal rat kidney cells are well spread while the transformed cells are more spherical, poorly adherent, and lack actin stress fibers (Rubin, R.W., Warren, R.H., Lukeman, D.S. and Clements, E. (1978) J. Cell Biol. 78, 28-35). By immunofluorescence, antitropomyosin prominently stains normal rat kidney cell stress fibers while only a weak, nonspecific fluorescence is observed in 442 cells. Using two-dimensional gel electrophoresis, tropomyosin can be detected in normal rat kidney cells homogenates. The tropomyosin subunits are enriched in Triton-extracted filamentous normal rat kidney cell models, and in extracts of normal rat kidney cell homogenate produced by using a rapid myosin affinity technique to isolate actin and actin-associated proteins. The identity of the tropomyosin subunits has been confirmed by electrophoretic mobility, lack of proline, and the peptide map generated by limited proteolysis. None of these techniques have detected tropomyosin in the corresponding 442 preparations. Our results suggest that the transformation of normal rat kidney cells has led to an overall reduction in tropomyosin content. This may be related to the inability of 442 cells to organize filamentous actin stress fibers.     

Dexamethasone selectively modulates basal and lipopolysaccharide-induced metalloproteinase and tissue inhibitor of metalloproteinase production by human alveolar macrophages.

To define the capacity of glucocorticoids to regulate tissue damage associated with inflammation more clearly, we have studied the effects of dexamethasone on human alveolar macrophage secretion of both a variety of metalloproteinases and also the counter-regulatory tissue inhibitor of metalloproteinases (TIMP). We found that dexamethasone selectively and coordinately inhibited expression of the following human metalloproteinases: interstitial collagenase, stromelysin, and the 92-kDa type IV collagenase, as well as TIMP. Both basal and LPS-stimulated cells exhibited similar degrees of inhibition, with greater than 50% decrease in secretion of all enzymes and TIMP observed at dexamethasone concentrations of greater than or equal to 10(-8) M in serum-containing medium. The effects of dexamethasone were mediated at a pretranslational level. In summary, our results indicate that glucocorticoids suppress the matrix-degrading phenotype that is characteristic of mature human mononuclear phagocytes, and block the effects of the most potent known signal for upregulation of metalloproteinase secretion. Similar actions in vivo would serve to limit tissue damage associated with the inflammatory response.