Synthesis of optically active diols using an efficient polymer bound cinchona alkaloid derivative

A new insoluble polymer containing a Cinchona alkaloid derivative has been synthesized and used as chiral ligand in the heterogeneous enantioselective dihydroxylation of olefins. It is shown that the enantioselectivity of the optically active diols obtained from both aliphatic and aromatic substrates is always comparable to that observed in the homogeneous phase under the same reaction conditions. A method for evaluating the enantiomeric excesses of the optically active products is also described. © 1995 Wiley-Liss, Inc.     

ABA-regulated promoter activity in stomatal guard cells

CDeT6-19 is an ABA-regulated gene which has been isolated from Craterostigma plantagineum . The CDeT6-19 gene promoter has been fused to the β- glucuronidase reporter gene ( GUS ) and used to stably transform Arabidopsis thaliana and Nicotiana tabacum . This construct has been shown to be expressed in stomatal guard cells and often in the adjacent epidermal cells of both species in response to both exogenous ABA and drought stress. These results indicate that the stomatal guard cell is competent to relay an ABA signal to the nucleus. In contrast GUS expression directed by the promoter from a predominantly seed-specific, ABA-regulated gene, Em , or the promoter from the ABA-regulated CDeT27-45 gene is not detectable in the epidermal or guard cells of tobacco or Arabidopsis in response to ABA. The fact that not all ABA-regulated gene promoters are active in stomatal guard cells suggests that effective transduction of the signal is dependent upon particular regions within the gene promoter or that guard cells lack all or part of the specific transduction apparatus required to couple the ABA signal to these promoters. This suggests that there are multiple ABA stimulus response coupling pathways. The identification of a regulatory sequence from an ABA-induced gene which is expressed in stomatal guard cells creates the possibility of examining the role of Ca²⁺ and other second messengers in ABA-induced gene expression.     

Urinary excretion of PGE2 and renal function in acute myocardial infarction

In 17 hospitalized patients affected by acute myocardial infarction (AMI) PGE2 urinary excretion, renal function and, furthermore, cortisol urinary excretion were tested during a 21 days trial. In 12 patients all the parameters under consideration underwent a similar trend: PGE2 urinary excretion exactly like glomerular filtration rate, Na+ excretion and diuresis tended to be reduced during the first 5 days and they rapidly recovered the normality after this period. Cortisol urinary excretion displayed a characteristic pattern: i.e. the highest values were observed in the first days, followed by a progressive decrease towards physiological levels since the 4th day. Different findings were obtained in 5 cases treated with an antiinflammatory drug (Indoprophen i.m. 200 mg x2 die). In fact the low levels of urinary PGE2 on the first days did not display any increasing and GFR, urinary flow, and Na+ tubular balance underwent irregular and not significant variations. These data suggest that an impaired Prostaglandin synthesis may be related to a compromised renal function often occurring in AMI.     

Human leukemic K562 cells: differential effects of 5-azacytidine on DNA methylation of epsilon-, gamma-globin and 7SL RNA genes

5 Azacytidine ribonucleoside (5 Aza CR), greatly enhances erythroid differentiation of the K562(h) cell line, with a sharp increase of embryonic and fetal globin gene expression. This phenomenon is correlated with the undermethylation of gamma-globin but not of epsilon-globin, as the epsilon-globin gene is already extensively undermethylated before 5AzaCR induction. By contrast no variations in both DNA methylation and expression are observed in 7SL RNA genes.     

Modulation of Ca2+ efflux and rebounding Ca2+ transport in rat liver mitochondria

The independent pathway for Ca2+ efflux of rat liver mitochondria exhibits a sharp temperature and pH dependence. The Arrhenius plot displays a break at 18 degrees C, activation energy being about 117 kJ/mol below 18 degrees C and 59 kJ/mol above 18 degrees C. The pH profile is bell-shaped, with a broad optimum at pH 7.0. These properties of the efflux pathway, together with the membrane potential modulation recently described (Bernardi, P. and Azzone, G.F. (1983) Eur. J. Biochem. 134, 377-383), suggest an explanation for the phenomenon of rebounding Ca2+ transport. Addition of a Ca2+ pulse to respiring mitochondria causes (i) a phase of rapid Ca2+ uptake, leading to a decrease of extramitochondrial free Ca2+ to a lower level with respect to that maintained before Ca2+ addition, and (ii) a slower phase of net Ca2+ efflux, leading to restoration of the steady-state extramitochondrial free Ca2+ preceeding Ca2+ addition. Evidence is provided that the excess Ca2+ uptake is linked to transient inactivation of the efflux pathway due to membrane depolarization. Conversely, the efflux phase is linked to reactivation of the efflux pathway upon repolarization. The efflux component of the rebound cycle and the isolated efflux pathway exhibit similar dependence on temperature, pH and membrane potential.     

Effect of polyunsaturated fatty acids on experimental ulcer in the rat

The increase of gastric mucosal defensive reachons under linoleic acid loading (20 mg/kg i.m. x 2 x 10 die; 140-220 mg/kg per os x 2 x 15 die), was evaluated in hydrocortisone treated rats (10 mg/kg i.m. x 2 x 10 die) and in rats stressed by immobilisation at a low temperature (at 4 degrees for 1 hour). The incidence and extent of gastric lesions were recorded, in both samples treated differentialy, and in control groups. Although the results were not similarly significant in every case, the capacity of the linoleic acid administrations in limiting the gastric mucose injury was evident. This protective capacity is not dependent on the lesive agent.     

Enhanced Superoxide Production with on Change of the Antioxidant Activity in Gingival Fluid of Patients with Chronic Adult Periodontitis

In the gingival crevicular fluid (GCF) of control and chronic adult periodontitis (CAP) patients there is a spontaneous release of O₂^- radicals from polymorphonuclear leukocytes (PMN). The addition of the exogenous stimuli phorbol myrystate acetate (PMA) decreased the O₂^- formation in control GCF, while in CAP patients produced a marked enhancement of O₂^- generation.

The circulating PMN of control subjects did not show a spontaneous O₂^- formation, differently from CAP patients. On the contrary, a similar O₂^- production was measured when the circulating PMN were stimulated with PMA.

Moreover, the antioxidant activity measured in 10μl of cell free gingival supernatant (GS) of control and CAP patients had the same values by inhibiting 12.6% and 18.9% respectively of the O₂^- formation supported by a xanthine/xanthine oxidase system.

Probably, the protective or destructive effect of PMN in GCF of CAP patients depends on the variations of the rate of O₂^- formation in respect to the intrinsic antioxidant property of GS.     

Modulation of the mitochondrial megachannel by divalent cations and protons.

In patch-clamp experiments on rat liver mitoplasts, the 1.3 nanosiemens (in 150 mM KCl) mitochondrial megachannel was activated by Ca2+ and competitively inhibited by Mg2+, Mn2+, Ba2+, and Sr2+. Cyclosporin A, which inhibits the megachannel, also showed a competitive behavior versus Ca2+. The pore is regulated by pH in the physiological range; lower pH values cause its closure in a Ca(2+)-reversible manner. The modulating sites involved in these effects are located on the matrix side of the membrane. As illustrated in the companion paper (Bernardi, P., Vassanelli, S., Veronese, P., Colonna, R., Szabó, I., and Zoratti, M. (1992) J. Biol. Chem. 267, 2934-2939), the calcium-induced permeability transition of mitochondria is affected by these various agents in a similar manner. The results support the identification of the megachannel with the pore believed to be involved in the permeabilization process. The kinetic characteristics of the single channel events support the idea that the megachannel is composed of cooperating subunits.     

Maitotoxin-Induced Intracellular Calcium Rise in PC 12 Cells: Involvement of Dihydropyridine-Sensitive and ω-Conotoxin-Sensitive Calcium Channels and Phosphoinositide Breakdown

The biological activities of maitotoxin are strictly dependent on the extracellular calcium concentration and are always associated with an increase of the free cytosolic calcium level. We tested the effects of voltage-sensitive calcium channel blockers (nicardipine and omega-conotoxin) on maitotoxin-induced intracellular calcium increase, membrane depolarization, and inositol phosphate production in PC12 cells. Maitotoxin dose dependently increased the cytosolic calcium level, as measured by the fluorescent probe fura 2. This effect disappeared in a calcium-free medium; it was still observed in the absence of extracellular sodium and was enhanced by the dihydropyridine calcium agonist Bay K 8644. Nicardipine inhibited the effect of maitotoxin on intracellular calcium concentration in a dose-dependent manner. The maitotoxin-induced calcium rise was also reduced by pretreating cells with omega-conotoxin. Pretreatment of cells with maitotoxin did not modify 125I-omega-conotoxin and [3H]PN 200-110 binding to PC12 membranes. Nicardipine and omega-conotoxin inhibition of maitotoxin-evoked calcium increase was reduced by pertussis toxin pretreatment. Maitotoxin caused a substantial membrane depolarization of PC12 cells as assessed by the fluorescent dye bisoxonol. This effect was reduced by pretreating the cells with either nicardipine or omega-conotoxin and was almost completely abolished by the simultaneous pretreatment with both calcium antagonists. Maitotoxin stimulated inositol phosphate production in a dose-dependent manner. This effect was reduced by pretreating the cells with 1 microM nicardipine and was completely abolished in a calcium-free EGTA-containing medium. The findings on maitotoxin-induced cytosolic calcium rise and membrane depolarization suggest that maitotoxin exerts its action primarily through the activation of voltage-sensitive calcium channels, the increase of inositol phosphate production likely being an effect dependent on calcium influx. The ability of nicardipine and omega-conotoxin to inhibit the effect of maitotoxin on both calcium homeostasis and membrane potential suggests that L- and N-type calcium channel activation is responsible for the influx of calcium following exposure to maitotoxin, and not that a depolarization of unknown nature causes the opening of calcium channels.     

Are blue-green algae a suitable food for zooplankton? An overview

One of the reasons suggested to explain the dominance of blue-greens in eutrophic lakes is that they are not used as food by zooplankton; and even when ingested, they are poorly utilized.

An increase in herbivores might be the expected result of biomanipulation of the aquatic food chain. This attempt at controlling the algae population is, however, destined to fail if zooplankton do not also utilize blue-greens as food. In this respect, a series of in-lake experimental results indicates that after the food chain has been biomanipulated, there is a decrease in blue-green density in periods when there is an increase in herbivores. Is this only an accidental result or are the two facts interrelated; in other words, can the decrease in the density of blue-greens be attributed to the increased use of them by zooplankton herbivores?

The suitability of blue-greens as food for zooplankton has been widely investigated by many authors with contrasting and inconclusive results. Two main factors seem to play important role in determining their suitability as food: the biochemical properties of the different species, or even different strains of the same species; and the shape and size of the colonies.

In particular, biochemical properties can result in toxic effects on zooplankton, while size and shape may strongly interfere with filtering, thus reducing the possibility of gathering food.