Adipose conversion of Ob17 preadipocytes : Relationships between cell division and fat cell cluster formation

Adipose conversion of Ob17 preadipocyte cells proceeds after confluence with the formation of fat cell clusters, due to the coexistence of cells susceptible or not to adipose conversion. In order to determine whether commitment to differentiation occurs after quiescence or during exponential growth, the spatial arrangement of Obl7 cells was destroyed at different times before and after confluence by trypsinization followed by cell reinoculation. The resulting distribution of lipid-filled cells, as compared to non-replated control cells, indicates that both insusceptible and susceptible cells are present during the growth phase in the absence of insulin. It is shown that the formation of fat cell clusters of large size is due to mitoses of susceptible cells during a limited period of time after confluence. Blockade of post-confluent mitoses by selective elimination of cells in the S phase abolishes the formation of clusters of large size, but single differentiated cells and clusters containing a few cells remain present. Therefore post-confluent mitoses are not necessary for the differentiation to occur, but rather they serve to amplify the proportion of adipose cells relative to non-adipose cells.     

Regulation of adipose cell differentiation. II. Kinetics of induction of the aP2 gene by fatty acids and modulation by dexamethasone.

Fatty acids behave as activators of the aP2 gene expression in committed, lipid-free, non-terminally differentiated Ob1771 cells. Like fatty acids, dexamethasone provokes a dose-dependent accumulation of aP2 mRNA. However, fatty acids and dexamethasone act through different mechanisms to activate the aP2 gene expression since i) fatty acids and dexamethasone act in a synergistic manner; ii) the effect of dexamethasone is rapid and transient (maximal effect after 8 h), whereas that of fatty acids is slower, and maintained as long as the inducer is present and is fully reversible upon fatty acid removal; iii) the induction of the aP2 gene expression by dexamethasone does not require ongoing protein synthesis, while the response to fatty acids is completely prevented by cycloheximide; and iv) the induction of the aP2 gene expression by fatty acids but not by dexamethasone is confined to preadipocyte cell lines. This suggests that the process of activation by fatty acids, rather than the expression of the aP2 gene, is unique to adipose cells. Besides their effects on the aP2 gene, fatty acids activate the expression of the acyl CoA synthetase gene which encodes another protein involved in fatty acid metabolism. Activation of both genes by fatty acids appears not to be mediated by the CCAAT enhancer binding protein, a nuclear factor reported as transactivator of the aP2 promoter activity, since the enhancer binding protein mRNA is not expressed under these conditions.     

Dihydropyridine Modulation of Voltage-Activated Calcium Channels in PC12 Cells: Effect of Pertussis Toxin Pretreatment

In this study, we report the effect of pertussis toxin pretreatment on dihydropyridine modulation of voltage-sensitive calcium channels in PC12 cells. The rise in intracellular calcium concentration caused by potassium depolarization is not affected significantly by pertussis toxin pretreatment. Nicardipine, a dihydropyridine derivative, added either before or after potassium-induced depolarization, reduces the resultant elevation in cytosolic calcium level both in control and in pertussis toxin-treated cells. The dihydropyridine agonist Bay K 8644, when added before potassium, is able to enhance the potassium-induced spike of cytosolic calcium levels, an effect significantly reduced by pertussis toxin pretreatment. Moreover, the addition of Bay K 8644 after potassium holds the intracellular calcium concentration at a cytosolic sustained level during the slow inactivating phase of depolarization. This effect of Bay K 8644 is inhibited by nicardipine. Pertussis toxin pretreatment slightly weakens the effect of Bay K 8644 when added after potassium-induced depolarization, whereas it significantly reduces the nicardipine inhibition of cytosolic calcium rise stimulated by potassium and Bay K 8644, but not by potassium alone. In conclusion, our findings suggest that a pertussis toxin-sensitive guanine nucleotide regulatory protein could be involved in the interaction between dihydropyridine derivatives and voltage-dependent calcium channels.     

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.     

Interleukin 6 modulation of second messenger systems in anterior pituitary cells.

We investigated the effect of interleukin-6 (IL-6) on second messenger systems in anterior pituitary (AP) cells. The acute exposition of membranes derived from the pituitary gland to IL-6 did not modify basal and forskolin-stimulated adenylate cyclase (AC) activity, as well as inositol phosphate (IP) production and free [Ca(++)]i. Preincubation of AP cells with IL-6 for 20 min did not affect basal second messengers levels, while completely abolished the stimulation by VIP of AC activity, partially inhibited forskolin-stimulated cAMP formation and reduced TRH-stimulated IP production. Finally, the pretreatment of AP cells for 20 min with IL-6 also reduced the TRH-induced rise in free [Ca(++)]i.     

Polymorphism of human thyroxine binding serum globulin (TBG); existence of a new form of serum protein without detectable triiodothyronine binding power

Two kinds of TBG polymorphism are described in human, one found in deglycosylated TBG from individual blood donors, the other is a genetically determined polymorphism. TBG from plasma samples from a patient with toxic goiter, not autoimmune, (p)TBG, from the patient's mother (m)TBG and from individual donors (n)TBG, were labeled with [125I]T4 or [125I]T3 and submitted to isoelectric focusing (IEF), followed by autoradiography. Three faint [125I]T4 radiolabeled bands were detectable in (p)TBG while four strong [125I]T4 radiolabeled bands were detectable in (m)TBG and (n)TBG), respectively. IEF of the [125I]T3 incubated serum samples resulted in no detectable isoelectric radiolabeled band for (p)TBG while a normal pattern was found in (m)TBG and in (n)TBG, respectively. These data suggest a new intraindividual not linked to sexual chromosome X polymorphism characterized by a loss in hormone binding.     

Correction to: Synthesis,protonation constants and biological activity determination of amino acid–salicylaldehyde‑derived Schiff bases

Amino Acids - Unfortunately in the online published article, the name of compound “L-salicylidenealanine” was published with incorrect spelling in the section “Synthesis of...     

8,000 years of climate,vegetation, fire and land-use dynamics in the thermo-mediterranean vegetation belt of northern Sardinia (Italy)

Vegetation History and Archaeobotany - Knowledge about the vegetation history of Sardinia, the second largest island of the Mediterranean, is scanty. Here, we present a new sedimentary record...     

Spatial genetic patterns of Octopus vulgaris Mediterranean populations support the hypothesis of a transitional zone across the Siculo-Tunisian Strait

Hydrobiologia - Recent research hypothesised that the Siculo-Tunisian Strait might fit, at least for some species, the picture of a genetic transitional zone instead of a sharp genetic break...