Periodic fluctuations in proliferation of SV-40 transformed human skin fibroblast lines with prolonged lifespan

A human fibroblastic cell line transformed by the SV40-T antigen sequence and continuously cultured for 7 months displayed large periodic variations in cell proliferation. This contrasted with other characteristics of this cell line that remained constant: mosaic cell shape, absence of cell contact inhibition, and predominance of a hypodiploid population. Similar fluctuations in proliferative capacity were also found during the long-term growth of a transformed but nonimmortalized human fibroblastic line prior to senescence, and in the established hamster fibroblastic Nil cell line. This growth pattern suggests a recurrent stimulation of growth in these three transformed cell lines. The proliferation pattern from cultured transformed cells may thus be complex and requires further investigation. These variations presumably influence major cell functions. This observation has important implications for the analysis of data from such cell lines.Abbreviations I-SF immortalized human skin fibroblasts - T-SF transformed human skin fibroblasts - FBS fetal bovine serum     

Kinetics and stereochemistry of the microsomal epoxide hydrolase-catalyzed hydrolysis of cis-stilbene oxides

The microsomal epoxide hydrolase (mEH)-catalyzed hydrolysis of cis-4,4′–dimethylstilbene oxide ( 1a ), cis-4,4′-diethylstilbene oxide ( 1b ), cis-4,4′-diisopropylstilbene oxide ( 1c ), and cis-4,4′-dichlorostilbene oxide ( 1d ) have been investigated using rabbit liver microsomal preparations. The kinetic parameters, K_m and V_max, and the absolute stereochemistry of the reactions have been determined and compared with those of cis-stilbene oxide ( 1e ). All epoxides 1a – d are hydrolyzed by mEH with high product enantioselectivity to give (R,R)-(+)-diols with ee ≥ 90%. The presence of the substituents on the phenyl rings markedly reduces the rates of mEH catalyzed hydrolysis with respect to cis-stilbene oxide, by increasing K_m and reducing V_max in the cases of 1a , 1b , and 1d , or reducing only the V_max in the case of 1c . The very low V_max, together with a persistent ability to fit into the mEH active site, make all these epoxides, and particularly 1c , inhibitors of cis-stilbene oxide hydrolysis. The kinetic and stereochemical results are interpreted on the basis of the proposed topology of the mEH active site. © 1994 Wiley-Liss, Inc.     

Different signal transduction by epidermal growth factor may be responsible for the difference in modulation of amino acid transport between fetal and adult hepatocytes

[1-¹⁴C]-2-aminoisobutyric acid (AIB) uptake and signal transduction pattern after epidermal growth factor (EGF) stimulation were examined in freshly isolated hepatocytes from 20-day-old fetuses and 3-month-old rats. EGF induced a transient increase of AIB transport after 10 min only in adult animals; the observed unresponsiveness of fetal liver is not dependent on a lack of EGF receptors which are present though to a lesser extent on the plasma membrane in this period. As far as the production of the second messengers, inositol trisphosphate (IP₃) and calcium, is concerned, substantial differences were found: EGF increased IP₃ production in adult hepatocytes, whereas it had no effect in fetal ones. Moreover, the addition of EGF induced a calcium transient in hepatocytes from adult animals, while there was no increase in fetal cells. The lack of EGF effect on amino acid transport in fetal cells could be due to its inability to produce both IP₃ and calcium transients, suggesting that this transduction pathway is not activated during fetal life.     

Trophic exchange in Pardosa hortensis (Lycosidae, Araneae)

Young Pardosa hortensis not only need their mother's help to leave their cocoon once developed (about 20 days), as they are unable to open it by themselves, but also during the period they are carried around in the cocoon. Using radioactive markers, indirect evidence revealed that the mother periodically opens the cocoon to feed her young and reseals it with fresh silk. Water is probably the main component in trophic exchange.     

Fluorescence studies using synchrotron radiation on normal and differentiated cells labeled with parinaric acids

Changes in membrane properties during the differentiation process in K562 cells have been investigated. A decrease of lectin-induced agglutination has been detected. The agglutination assay revealed to be an early and sensitive test to monitor the induced differentiation of the K562 cells. Naturally occurring fluorescent fatty acids (cis- and trans-parinaric acids) and the recently developed multifrequency phase and modulation technique were used to study cell membrane properties. Changes in fluorescence lifetime and polarization are clearly associated with cell differentiation, suggesting the involvement of the cellular plasma membrane in the differentiation process.     

Ultrastructural changes during encystment and germination of Bdellovibrio sp.

Under proper conditions, Bdellovibrio sp. strain W cells develop into bdellocysts in appropriate prey bacteria. After attachment and penetration of the prey cell, the encysting bdellovibrio began to accumulate inclusion material and increase in size, and was surrounded by an outer layer of amorphous electrondense material. The cytoplasm of the encysting cell appeared more electron dense, and nuclear areas appeared more compact. During germination of bdellocysts, the outer wall was uniformly broken down the inclusion material changed shape and affinity for the heavy metal stain, and the nuclear areas expanded. As the outer wall was dissolved, outgrowth began with the elongation of the germinant as it emerged from the prey ghost as an actively motile cell.     

A stereochemical model for phospholipids. II: Conformational analysis and molecular packing of phosphatidylethanolamine (PE)

A partition energy method procedure was applied to select the energetically favoured conformations of phosphatidylethanolamine (PE) as polar constituents of phospholipid molecules. The result indicated a large degree of freedom for the two torsion angles of the ester bond of the phosphate and a gauche, gauche star conformation for the ethane bond.A packing process of the molecule was carried out through a potential energy calculation by considering the conformers selected above, using previously published procedure and conventions. All the arrangements which possess the best packing energy values were characterised by an orientation of the PN dipolar segment parallel to the lattice plain. Rotation of the internal torsion angles and rotation in the eulerian space of the molecule produced differences in the charged groups that interact. An additional minimum was present in the energy packing process of those conformers which have the first torsion angle of the phosphate in a trans conformation. This minimum, which corresponds to an orientation of the molecule orthogonal to the lattice plane, requires a complete neutralisation of the point charges on the system.The results of the calculation underline the importance of changes in the behaviour of the polar group of the phospholipids in the packing process.     

Mutational studies with diquat and paraquat in vitro.

Diquat and paraquat were assayed in the following tests. (1) Ames test in Salmonella typhimurium (strains TA1535, TA1537, TA1538, TA98 and TA100) with and without rat-liver microsomal fractions. (2) Resistance to 8-azaguanine in Salmonella typhimurium (strain hisG46, TA92 and TA1535. (3) Repair test in Salmonella typhimurium (strains TA1538 and TA1978). (4) Gene mutations in Aspergillus nidulans: 8-AG resistance and methionine suppression (meth A1 locus). (5) Lethal recessive damage in Aspergillus nidulans. (6) Unscheduled DNA synthesis (UDS) in human epithelial-like cells (EUE). Diquat and paraquat were positive in S. typhimurium (in the repair test and the 8-AG resistance system), in A. nidulans (for gene mutations and lethal recessive damage induction) and in EUE cells (UDS induction).