Hyperpolarizing potentials in guinea pig hippocampal CA3 neurons

There is a bewildering variety of hyperpolarizing potentials which control activity in hippocampal pyramidal cells. These include an inhibitory postsynaptic potential (IPSP) with early and late components, voltage- and calcium-dependent potassium conductances, a voltage-dependent potassium conductance modulated by muscarinic agents (the M-current), and a complex and poorly understood afterhyperpolarization following epileptiform bursts. In hippocampal CA3 pyramidal cells, mossy fiber stimulation elicits an IPSP which is made up of two readily separable components. Using the in vitro slice preparation, we investigated the underlying ionic basis of these IPSP components and compared them to other hyperpolarizing potentials characteristic of the CA3 neurons. Intracellular recordings were obtained and then tissue was exposed to bathing medium low in chloride concentration or high in potassium concentration; the ion "blockers" EGTA (intracellular); tetraethylammonium (TEA) (intra- and extracellular), and barium and cobalt (extracellular); and the gamma-aminobutyric acid (GABA)/chloride antagonists penicillin, bicuculline and picrotoxin.     

In vitro induction of lymphocyte responsiveness by a Strongylus vulgaris-derived mitogen

Proliferation in vitro of peripheral blood lymphocytes both from horses infected with Strongylus vulgaris and from helminth-free ponies was observed in the presence of extracts of the fourth and fifth stage larvae and adults of S. vulgaris. In addition, S. vulgaris extracts induced transformation in cultures of peripheral blood lymphocytes from sheep and dogs and in mouse spleen cell cultures. Nylon wool non-adherent, T cell enriched fractions of lymphocytes from both mice and horses were stimulated by the S. vulgaris larval mitogen while no proliferation was observed in cultures containing nylon wool adherent, B cell enriched fractions. Macrophage co-operation appeared not to be necessary for S. vulgaris mitogen-induced transformation of spleen cells. The S. vulgaris mitogen stimulated a subpopulation of mouse spleen cells different from those responsive to PHA, Con A and LPS. These cells might be T helper cells since B cells were stimulated to proliferate in the presence of both T cells and S. vulgaris larval mitogen. In addition, the supernatant of in vitro cultured larvae of S. vulgaris induced slight, but significant transformation of equine peripheral blood lymphocytes. Therefore, it is possible that the S. vulgaris mitogen released by both viable parasites and degenerating larvae might induce T cell dependent production of immunoglobulin in vivo and account for the beta-globulinaemia, of which IgG(T) is a major component, in S vulgaris infected horses.     

Influence of carbon dioxide concentration during growth on fluorescence induction characteristics of the Green Alga Chlamydomonas reinhardii

Carbon dioxide concentration during growth is commonly not considered to be a factor influencing the photochemical properties of plants. It was observed that fluorescence induction in Chlamydomonas reinhardii cells grown at air levels of CO₂ was both qualitatively and quantitatively different from that of cells grown at 5% CO₂. In the two cell types, measured at equivalent chlorophyll and irradiance levels, the fluorescence intensity and the ratio of the levels of peak fluorescence (F_p) to that of the initial fluorescence (F_o) were much lower in the air-adapted than in the 5% CO₂ adapted cells. The maximum fluorescence (F_max) in the presence of diuron was also lower for air-adapted cells. Roughly twice the light input was required for the air-adapted cells to give a fluorescence induction transient and intensity equivalent to that of the 5% CO₂-adapted cells. Similar properties were observed in several other unicellular green algae and in cyanobacteria. Chlamydomonas grown under variable CO₂ concentrations exhibit significant differences in photosynthetic carbon metabolism and are presumed to have altered energy requirements. The observed variation in fluorescence induction may be due to changes in the properties of the thylakoid reactions (e.g. cyclic electron flow) of Chlamydomonas cells, which may, in turn, be due to a response to the altered energy requirements.     

Leukocyte kinetics in the human lung: role of exercise and catecholamines

In six normal supine subjects epinephrine infusion produced a greater leukocytosis with smaller changes in heart rate and blood pressure than did norepinephrine or isoproterenol. Upright exercise in those subjects produced a greater leukocytosis than supine exercise at the same work load. To determine the lung's participation in these events, indium-labeled neutrophils (PMN) were given to four of the subjects. We found that 20-25% were retained in the first pass through the lung when compared with technetium-labeled erythrocytes. The number of labeled PMN in the lung gradually decreased and the number in the spleen and the liver increased. Exercise and catecholamine infusion caused an acceleration in the release of labeled cells from the lung, an increase in both labeled and unlabeled cells in the peripheral blood, and an increase in the number of labeled cells in the liver and spleen. This suggests that increased perfusion of low-flow areas in the lung may contribute to the increased leukocytosis seen in association with both exercise and catecholamine infusion.     

Photosynthetic electron transport in guard cells of diverse species

Guard cells of plants representing 18 species were assayed qualitatively for potential to conduct photosynthetic linear electron transport. These plants included C₃ pteridophytes, C₃ and C₄ monocots, and C₃, C₄, and Crassulacean acid metabolism dicots. By use of a microfluorospectrophotometer, guard cell samples in epidermal peels were isolated optically. Chlorophyll fluorescence was monitored from the onset of excitation light. For guard cells of all these species, fluorescence intensity increased during illumination. When samples were preincubated with 3-(3,4-dichlorophenyl)-1,1-dimethylurea, diuron, however, there was a more rapid increase in fluorescence. These results indicate that all tested guard cells conduct photosynthetic electron transport through the reaction center of photosystem II.     

Ontogenetic Changes in the Transport of Indol-3yl-acetic Acid into Maize Roots from the Shoot and Caryopsis

The quantities of endogenous indol-3yl-acetic acid (IAA) in endosperms and scutella of 6-day-old maize seedlings (Zea mays L. cv Giant White Horsetooth) were determined by a fluorimetric method. Endosperms were found to contain 33.4 nanograms IAA per plant, and scutella 7.5 nanograms IAA per plant. [5-³H]IAA applied to endosperms of 6-day-old seedlings moved into the roots and radioactivity accumulated at the apex of the primary root within 8 hours. Two to 7-day-old seedlings were treated simultaneously with [5-³H]IAA in the endosperm and [2-¹⁴C] IAA on the shoot apex. The patterns of transport into the root were found to change during ontogeny: in successively older plants, transport from the shoot into the roots increased relative to transport from the endosperm into the roots. The auxin required for the growth of maize roots could, therefore, partially be contributed by the shoot and endosperm. Ontogenetic changes in the relative importance of these two supplies could be of significance for the integration of growth and development between shoot and root.     

Effect ofPseudomonas aeruginosa rhamnolipid on human neutrophil migration

The effect ofPseudomonas aeruginosa heat-stable hemolysin (rhamnolipid) on human neutrophil migration has been investigated. Rhamnolipid was prepared from culture filtrate and characterized by thin-layer chromatography. The lytic activity of rhamnolipid was quantitated by titration against neutrophils. Leukocyte migration response was measured using⁵¹Cr-labeled neutrophils with a double-filter technique in modified Boyden chambers. The results suggest rhamnolipid stimulated chemotaxis as well as chemokinesis. Moreover, rhamnolipid impaired a chemotactic response toN-formyl-methionyl-leucyl-phenylalanine. These effects may be important in host-parasite interactions.     

Changes in intracellular proteolysis in Escherichia coli during prolonged growth with a low concentration of dihydrostreptomycin

Abstract Escherichia coli was cultured with a low concentration of dihydrostreptomycin (2.5 μg/ml.). Growth was similar to untreated controls for 10 h after which a slow decline in growth rate occurred; growth ceased after 20 h. Intracellular catabolism of pulse-labelled protein synthesised at various points during the antibiotic treatment increased during the first 10 h, but during the second 10 h proteolysis progressively declined to almost control values. The production of an aberrant proteolytic system is one possible explanation.     

Phenotypic changes in hydrogen evolving chemostat cultures of Rhodopseudomonas capsulata

Abstract Spontaneous nitrogenase-negative (Nif⁻ mutants of Rhodopseudomonas capsulata were observed to accumulate with time in ammonium- or glutamate-limited chemostat cultures.
Nif⁻ mutants were characterized by their inability to grow under N₂ and to reduce acetylene or produce hydrogen gas when grown on glutamate. They lacked the nitrogenase structural proteins as evidenced by immunological techniques. On the other hand, no significant differences were found in the pathways of ammonia assimilation between the Nif⁻ mutants and the wild-type strain. The Nif⁻ mutants seem to result from a mutation in a regulatory gene.