Low-temperature-induced transmembrane potential changes in mesophyll cells of Arabidopsis thaliana, Helianthus annuus and Vicia faba

Glass microelectrodes were inserted into mesophyll cells of intact leaves from higher plants: Arabidopsis thaliana, Helianthus annuus and Vicia faba var minor , and transient membrane potential changes were recorded in response to a sudden temperature drop. The cold-induced potential changes were unaffected by an anion channel inhibitor (anthracene-9-carboxylic acid) and potassium channel inhibitor (tetraethyl ammonium ion). Verapamil, a calcium channel inhibitor, caused significant suppression of the cold-induced potential changes. In the presence of calmoduline antagonists (trifluoperazine and N -6-aminohexyl-5-chloro-1-naphtalenesulphonamide), their amplitudes decreased and their durations were prolonged. Neomycin, which suppresses phospholipase C, also caused substantial inhibition of the amplitudes of the cold-induced potential changes. It is concluded that cold-evoked membrane potential changes are due to calcium influxes from both the apoplast and internal stores.     

The impact of neuraminidase on apoptosis in cultures of blood lymphocytes isolated from rats bearing morris hepatoma

Lymphocytes were obtained by heart-punction from rats bearing Morris hepatoma. In the short term, 18-hour cultures of these lymphocytes exhibited a significantly higher amount of apoptotic cells than lymphocyte cultures from the healthy, control animals. Neuraminidase, injected into the caudal vein of the rats with Morris hepatoma, caused a marked lowering in the amount of apoptotic blood-lymphocytes and an elevation of the amount of viable cells. The possible mechanism of neuraminidase preventing the apoptosis of blood-circulating lymphocytes in tumour hosts is discussed herein.     

Cellular 8-oxo-7,8-dihydro-2'-deoxyguanosine 5'-triphosphate pyrophosphohydrolase activity of human and mouse MTH1 proteins does not depend on the proliferation rate

Mammalian MTH1 proteins, homologs of Escherichia coli MutT, are enzymes decomposing 8-oxo-7,8-dihydro-2'-deoxyguanosine 5'-triphosphate (8-oxo-dGTP) to 8-oxo-7,8-dihydro-2'-deoxyguanosine 5'-monophosphate and inorganic pyrophosphate. They play an antimutagenic role by preventing the incorporation of promutagenic 8-oxo-dGTP into DNA. MTH1 gene expression is higher in some physiological types of mammalian cells and in numerous cancer cells, but the mechanism of that upregulation still remains unclear. It has been hypothesized that MTH1 expression might be associated with a proliferation rate of the cells. Therefore, we tested this hypothesis by comparing the functional levels of MTH1 gene expression measured as the 8-oxo-dGTPase activity of its protein products in normal mouse livers and hepatectomized regenerating livers. Although the proliferation rate of the hepatocytes in the regenerating livers was much higher than that in control livers, as confirmed by immunohistochemical assay of proliferating cell nuclear antigen, the 8-oxo-dGTPase activity was not different. In a second approach, we used 57 lines of human cancer cells in which 8-oxo-dGTPase activity was measured and confronted with cell population doubling time. No significant correlations between 8-oxo-dGTPase activity and proliferation rate were observed within groups of six leukemia, eight melanoma, nine lung, seven colon, six central nervous system, six ovarian, eight renal, and seven breast cancer cell lines. Thus, we conclude that the MTH1 expression manifested as the 8-oxo-dGTPase activity of its protein products in mammalian cells is not associated with proliferation rate. Our results will help in further testing of the hypothesis that MTH1 overexpression may be a specific marker of carcinogenesis and/or oxidative stress.     

Concentrations of heavy metals and PCBs in the tissues of European beavers (Castor fiber) captured in northeastern Poland

European beavers (Castor fiber) from two regions were examined to identify exposure to persistent environmental contaminants. A reference group was comprised of six animals from the Forest Division of Srokowo, and an exposed group was comprised of five animals from the vicinity of a former military airport operated in 1918–1986—both from Warmia land in Poland. ¹³⁷Cs in beavers' muscles was considered negligible for the overall condition and reproduction of the animals. Elevated levels of Cd and Pb occurred in the kidneys and liver of beavers from a former military airport area. dl-PCBs were found in the liver of all specimens, and pCB no. 118 was a dominant compound. Beavers as animals living both in water and land habitats can be good bioindicators of heavy metal environmental pollution caused by human activity. Despite the significant contamination of former military sites in northeastern Poland, the beaver population shows an upward trend, reflecting the excellent adaptation of this species to a changing environment.     

Thermotropic phase behaviour of lipid bilayers containing carotenoid pigment canthaxanthin: a differential scanning calorimetry study

In this study we address the problem of the effect of canthaxanthin on the thermotropic properties of lipid membranes formed with lipids which differ in the thickness of their hydrophobic core, size of polar heads or presence of the ester carbonyl group. For all the lipids a decrease in main transition enthalpy has been observed, indicating that canthaxanthin alters the membrane properties in its gel phase. The strongest influence of canthaxanthin on main phase transition and pretransition has been observed for the lipid having the thinnest hydrophobic region. Component analysis indicates a distinct cooperativity change, which most probably colligates with the formation of new thermotropic phases. The effect of canthaxanthin has been almost negligible in the case of phosphatidylethanolamines. The absence of the ester carbonyl group results in different thermotropic behavior, especially for low canthaxanthin concentrations. The effect of canthaxanthin is explained in terms of its organization within the membrane.     

Arsenite interactions with phospholipid bilayers as molecular models for the human erythrocyte membrane

There are scanty reports concerning the effects of arsenic compounds on the structure and functions of cell membranes. With the aim to better understand the molecular mechanisms of the interaction of arsenite with cell membranes we have utilized bilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), representative of phospholipid classes located in the outer and inner monolayers of the human erythrocyte membrane, respectively. The capacity of arsenite to perturb the bilayer structures was determined by X-ray diffraction and fluorescence spectroscopy, whilst the modification of their thermotropic behaviour was followed by differential scanning calorimetry (DSC). The experiments carried out by X-ray diffraction and calorimetry clearly indicated that NaAsO(2) interacted with DMPE and modified its thermotropic behaviour. No such information has been so far reported in the literature.     

Sperm morphology of the Eurasian beaver, Castor fiber: an example of a species of rodent with highly derived and pleiomorphic sperm populations

The structural organization of the spermatozoon from the Eurasian beaver, Castor fiber (Family: Castoridae), was determined and compared to that of other sciuromorph rodents. The beaver spermatozoon has a head, which is variable in form but usually paddle-shaped, with a small nucleus and very large acrosome, and a tail that is relatively short compared to that of most other rodents. Transmission electron microscopy indicates that in most testicular spermatozoa the acrosome projects apically, although in a few it becomes partly flexed. During the final stages of maturation, however, the acrosome becomes highly folded so that the apical segment comes to lie alongside part of the acrosome that occurs lateral to the nucleus, with, in some cases, fusion taking place between the outer acrosomal membranes. The sperm nucleus is wedge-shaped, being broader basally and narrowing apically with an occasional large nuclear vacuole occurring. This spermatozoon structure is markedly different from that found in the other species of Geomyoidea, which is the sister group of the Castoridae. The findings thus emphasize the highly divergent nature of the beaver spermatozoon and demonstrate that, within the proposed Infraorder Castorimorpha, very large differences in sperm structure have evolved.