Cell fragility — The key problem of microalgae mass production in closed photobioreactors

The gap between the theoretical biological potential of microalgae and the biomass productivity obtained with algal culture in tubular biophotoreactors is due to a reduced growth rate related to hydrodynamic stress of pumping. High levels of mixing are necessary to reach a turbulent flow of the culture, in order to optimize the light regime. The optimal conditions of pumping to produce this significant liquid mixing may produce some cell damage. Factors affecting this hydrodynamic stress (geometry of the bioreactor involved, type of pump utilized, morphology of algal cells, physiological conditions of microalgae, etc.) are discussed.     

Activation and inhibition of ATP-sensitive K+ channels by fluorescein derivatives.

Fluorescein derivatives are known to bind to nucleotide-binding sites on transport ATPases. In this study, they have been used as ligands to nucleotide-binding sites on ATP-sensitive K+ channels in insulinoma cells. Their effect on channel activity has been studied using 86Rb+ efflux and patch-clamp techniques. Fluorescein derivatives have two opposite effects. First, like ATP, they can inhibit active ATP-sensitive K+ channels. Second, they are able to reactivate ATP-sensitive K+ channels subjected to inactivation or "run-down" in the absence of cytoplasmic ATP. Therefore reactivation of the inactivated ATP-sensitive K+ channel clearly does not require channel phosphorylation as is commonly believed. The results indicate the existence of two binding sites for nucleotides, one activator site and one inhibitor site. Irreversible binding at either the inhibitor or the activator site on the channel was obtained with eosin-5-maleimide, resulting in irreversible inhibition or activation of the ATP-sensitive K+ channel respectively. The irreversibly activated channel could still be inhibited by 2 mM ATP. After activation by fluorescein derivatives, ATP-sensitive K+ channels become resistant to the classical blocker of this channel, the sulfonylurea glibenclamide. Negative allosteric interactions between fluorescein/nucleotide receptors and sulfonylurea-binding sites were suggested by results obtained in [3H]glibenclamide-binding experiments.     

Iodine intakes assessed by urinary iodine concentrations in healthy children aged ten months,two years,and four years

Urinary iodine excretion was assessed in 642 healthy children aged 10 mo (n=243), 2 yr (n=183), and 4 yr (n=216) living in the Paris area and originating from continental France (60.3%), North Africa (13.8%), the West Indies (9.1%), West Africa (8.3%), Southeast Asia (4.8%), and southern Europe (3.8%). Mild impairment of neurological (reflexes, tone, audiometry) and intellectual development (Brunet-Lézine scale) was assessed in relation to iodine status. Iodine excretions (median values) were 18.4, 11.9, and 10.9 μg/100 mL at 10 mo, 2 yr, and 4 yr, respectively, and risk of mild iodine deficiency (5–10 μg/100 mL) was 18.1%, 34.8%, and 38.3% for the same age groups. No relationship was found between anthropometry, global development quotient, and iodine status. High hearing thresholds were more commonly associated with lower iodine excretion, suggesting mild hearing defects. In spite of iodine prophylaxis, the risk of mild to moderate iodine deficiency still exists in France and in a number of European countries. Evaluation of neurological sequels of borderline iodine status is a major public health problem in European communities.     

Decreased heme content and cessation of cell growth in cultured chick embryo fibroblasts in the presence of horse serum: Stimulation of heme synthesis and cell growth by iron

A new spectrofluorometric method for heme quantitation in cultured fibroblasts is described. The method includes: (1) heme extraction by methanol/sulfuric acid, (2) partial purification of heme by a microchromatographic method, and (3) treatment of the purified heme by oxalic acid followed by fluorometric quantitation. Using this method, heme concentration was determined in chick embryo fibroblasts cultured in a medium supplemented with either 7% fetal bovine serum (FBS) or 10% horse serum (HS). In the presence of FBS, cultured cells actively divided and cells contained 34–55 pmol heme/mg protein. In contrast, cultures maintained in HS proliferated at a slower rate and contained 23–25 pmol heme/mg protein. The addition of 40 μM FeSO₄ to cultures maintained in the presence of HS stimulated cell proliferation, and the cellular heme concentration increased to 37–51 pmol/ mg protein. These findings suggest that the cessation of growth in the presence of HS may be due to decreased heme content in the cells and that the stimulation of cell growth by iron is mediated by its stimulation of heme synthesis.     

Correlation between cell density,membrane fluidity,and the availability of transferrin receptors in friend erythroleukemic cells

Undifferentiated Friend erythroleukemic cells (FL cells) acquire membrane microviscosity ( ), in accord with the culture cell density. At low cell density poise, whereas at confluency it increases to poise. Concomitantly, the total number of available transferrin receptors per cell decreases by about 80% upon increase in cell density. Modulation of membrane microviscosity, by artificial alteration of the membrane cholesterol level, mediates similar modulations of the availability of the transferrin receptors. The correlation between the availability of the transferrin receptors and the membrane lipid fluidity may take part in the overt decrease in iron uptake by erythroid cells along the erythropoiesis pathway.     

Stereospecific activity of 1-O-alkyl-2-O-acetyl-sn-glycero-3-phosphocholine and comparison of analogs in the degranulation of platelets and neutrophils

1-O-Hexadecyl-2-O-acetyl-$\text{sn}$-glycero-3-phosphocholine (platelet activating factor) stimulated the degranulation of rabbit platelets and human neutrophils, whereas the enantiomer, 3-O-hexadecyl-2-O-acetyl-$\text{sn}$-glycero-1-phosphocholine, was inactive. The analogs compared had the following relative potencies in degranulating platelets and neutrophils: 1-O-hexadecyl-2-O-acetyl-$\text{sn}$-glycero-3-phosphocholine > 1-O-hexadecyl-2-O-ethyl-$\text{sn}$-glycero-3-phosphocholine >$\text{rac}$-1-O-octadecyl-2-O-ethylglycero-3-phosphocholine = 1-O-hexadecyl-2-O-methyl-$\text{sn}$-glycero-3-phosphocholine >$\text{rac}$-1-O-dodecyl-2-O-ethyl-glycero-3-phosphocholine. The deacetylated compound, 1-O-hexadecyl-2-lyso-$\text{sn}$-glycero-3-phosphocholine, and 1-O-hexadecyl-2,2-dimethylpropanediol-3-phosphocholine were inactive. The active analogs selectively desensitized the response to each other in the neutrophils. It is suggested that these compounds may activate cells through interaction with a stereospecific receptor.     

Effects of ion-pairing on calculations of ionic activities of major ions in freshwater

Ion-pairing has little effect on ionic activity calculations for weakly mineralized natural water (ionic strength < 2 mM). However, for more strongly mineralized freshwaters, corrections for ion-pairing are necessary if highly accurate ionic activities are required.