Attachment and multiplication,morphology and protein production of human fetal primary liver cells cultured in hormonally defined media

In Vitro Cellular &; Developmental Biology - Plant -     

Succession in the southern part of the Canadian boreal forest

Forest succession following fire in a forest mosaic of northwestern Quebec has been studied in order to: (1) describe the successional pathways using communities of different ages and (2) evaluate convergence of successional pathways and possible effect of fire suppression on the establishment of steady-state communities. As a first step, ordination and classification techniques were used in order to remove changes in forest composition which are related to abiotic conditions. Then, ordinations based on tree diameter distributions were used to study shifts in species composition in relation to time since the last fire.Even under similar abiotic conditions, successional pathways are numerous. However, regardless of forest composition after fire, most stands show convergence toward dominance of Thuja occidentalis and Picea mariana on xeric sites and dominance of Abies balsamea and Thuja occidentalis on more mesic sites. Stable communities of >300 yr occur on xeric sites while on mesic sites directional succession still occurs after 224 yr. Nearly all species involved in succession are present in the first 50 yr following fire. Only Abies balsamea and Thuja occidentalis increase significantly in frequency during succession. Following initial establishment, successional processes can generally be explained by species longevity and shade tolerance. Early successional species may be abundant in the canopy for more than 200 yr while the rapid decrease of Picea glauca, a late successional species could be related to spruce budworm outbreaks. Considering the short fire rotation observed (about 150 yr), a steady-state forest is unlikely to occur under natural conditions, though it may be possible if fire is controlled.     

In vitro study of newborn rat brain maturation: implication for sudden infant death syndrome.

We have used slice preparation from newborn rats to study the development of the nucleus tractus solitarius neuronal network and brain intracellular phosphorus metabolites. As shown previously on adults, the newborn preparation retains local excitatory and inhibitory synaptic connections and enables study of intrinsic electrical properties in the nucleus tractus solitarius. Electrophysiological investigation of inhibitory synaptic transmission demonstrated a maturational step at days 4-6 after birth. Nuclear magnetic resonance spectroscopy of brain slices revealed a metabolic maturation between postnatal days 11 and 17. Results emphasize the differential maturation steps during the postnatal development of rat central nervous system. Possibly, Sudden Infant Death Syndrome may result from the abnormal timing in the occurrence of these steps.     

On the compatibility of carbon uptake rates calculated from stable and radioactive isotope data: implications for the design of experimental protocols in aquatic primary productivity

Basic differences between the ¹³C and the ¹⁴C techniques ofmeasuring carbon uptake by phytoplankton exist at the levelof the isotopic analysis. With the first method, a ratio ofisotopic abundances is measured on the sample, whereas an absoluteamount of isotope is estimated with the second method. If acarbon source other than the labeled one is utilized by thephytoplankton during incubation, the stable isotope method maybe biased. Specific uptake values will be underestimated bythis effect. It is, however, possible to obtain unbiased estimatesof the ¹³C-labeled carbon uptake by using an equation containinga term describing the final particulate carbon concentration.Only under this condition will carbon uptake rates derived from¹³C isotope data be always compatible with the ¹³C method ofmeasuring primary production ^*This paper is the result of a study made at the Group for AquaticPrimary Productivity (GAP), Second International Workshop heldat the National Oceanographic Institute, Haifa, Israel in April–May1984.     

Divergent pharmacological responses to two calmodulin inhibitors, chlorpromazine and W-7, in rat pancreatic acinar cells

The possible role of calmodulin in exocytotic secretion is supported by the presence of this calcium-binding protein in secretory cells, and by the antisecretory effects in intact secretory cells of substances which can antagonize calmodulin-stimulated enzymes in broken cell preparations. In this study, two in vitro calmodulin antagonists, W-7 and chlorpromazine, were found to produce both similar and different pharmacological effects on the secretory process in rat exocrine pancreas. Both substances blocked amylase secretion in response to carbachol or cholecystokinin octapeptide, but only chlorpromazine inhibited the ability of carbachol to stimulate 45Ca efflux from isotope-preloaded cells. Only W-7 could inhibit the secretory response to vasoactive intestinal peptide (VIP); but both W-7 and chlorpromazine were equipotent partial antagonists of VIP-stimulated cyclic AMP synthesis. Chlorpromazine increased the secretory response to melittin but W-7 did not. The divergence in biological responsiveness to W-7 and chlorpromazine makes it difficult to extrapolate the in vitro effects of these agents to similar actions in intact cell systems.     

A proton-deuterium exchange study of three types ofDesulfovibrio hydrogenases

Summary Hydrogenases are among the main enzymes involved in bacterial anaerobic corrosion of metals. The study of their mode of action is important for a full comprehension of this phenomenon. The three types ofDesulfovibrio hydrogenases [(Fe), (NiFe), (NiFeSe)] present different patterns in the pH dependence of their activity. The periplasmic enzyme fromDesulfovibrio salexigens and the cytoplasmic enzyme fromDesulfovibrio baculatus both have pH optima at 7.5 for H₂ uptake and 4.0 for H₂ evolution and H⁺–D₂ exchange reaction (measured by membrane-inlet mass-spectrometry). The H₂ to HD ratio at pH above 5.0 is higher than 1.0. The periplasmic hydrogenase fromD. gigas presents the same pH optimum (8.0) for the H⁺–D₂ exchange as for H₂ consumption. In contrast, the enzyme fromD. vulgaris has the highest activity in H₂ production and in the exchange at pH 5.0. Both hydrogenases have a H₂-to-HD ratio below 1.0.     

The relationship between hydrogen metabolism,sulfate reduction and nitrogen fixation in sulfate reducers

Summary Hydrogenase and nitrogenase activities of sulfate-reducing bacteria allow their adaptation to different nutritional habits even under adverse conditions. These exceptional capabilities of adaptation are important factors in the understanding of their predominant role in problems related to anaerobic metal corrosion. Although the D₂–H⁺ exchange reaction indicated thatDesulfovibrio desulfuricans strain Berre-Sol andDesulfovibrio gigas hydrogenases were reversible, the predominant activity in vivo was hydrogen uptake. Hydrogen production was restricted to some particular conditions such as sulfate or nitrogen starvation. Under diazotrophic conditions, a transient hydrogen evolution was followed by uptake when dinitrogen was effectively fixed. In contrast, hydrogen evolution proceeded when acetylene was substituted as the nitrogenase substrate. Hydrogen can thus serve as an electron donor in sulfate reduction and nitrogen metabolism.