Vanadate induces the recruitment of glut-4 glucose transporter to the plasma membrane of rat adipocytes

Summary In rat adipocytes, the insulin stimulation of the rate of glucose uptake is due, at least partially, to the recruitment of glucose transporter proteins from an intracellular compartment to the plasma membrane.Vanadate is a known insulin mimetic agent and causes an increase in the rate of glucose transport in rat adipocytes similar to that seen with insulin. The objective of the present study was to determine whether vanadate exerts its effect through the recruitment of glucose transporters to the plasma membrane.We report that under conditions where vanadate stimulates the rate of 2-deoxyglucose uptake to the same extent as insulin, the concentration of GLUT-4 in the plasma membrane was increased similarly by both insulin and vanadate, and its concentration was decreased in the low density microsomal fraction. These results suggest that vanadate induces the recruitment of GLUT-4 to the plasma membrane. The effects of vanadate and insulin on the stimulation of 2-deoxyglucose uptake and recruitment of GLUT-4 were not additive.This is the first report of an effect of vanadate on the intracellular distribution of the glucose transporter.     

Respiratory oxidation of reduced sulfur compounds by intact cells of Thiobacillus tepidarius (type strain)

Thiobacillus tepidarius (type strain) was grown in microaerophilic conditions, on tetrathionate, thiosulfate or crystalline S^o. The rates of tetrathionate, thiosulfate, elemental sulfur (S^o) and sulfite oxidation of the different cultures were measured respirometrically, using exponentially growing cells, with an oxygen electrode. Cells growing on the three different sulfur compounds retain thiosulfate-, tetrathionate, and S^o-oxidizing activities (SOA), but lack respiratory sulfite-oxidizing activity. The SOA for all the cultures was almost totally inhibited by 50 M myxothiazol, an inhibitor of the quinone-cytochrome b region, and by 10 M of the uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP). Tetrathionate- and thiosulfate-oxidizing activities were moderately and weakly inhibited by 50 M totally inhibited (>95%) all respiratory activities. This study suggests that electrons released by S^o oxidation enter the respiratory chain in the quinone-cytochrome b region.Abbreviation SOA sulfur-oxidizing activity     

Alport syndrome: a genetic study of 31 families

Thirty one families with Alport syndrome including 3 families with associated syndromes were studied. The location of the COL4A5 gene, responsible for the Alport syndrome, was determined by linkage analysis with eight probes of the Xq arm and by a radiation hybrid panel. Concordant data indicated the localization of the Alport gene between DXS17 and DXS11. Four deletions and one single base mutation of the COL4A5 gene were detected. Homogeneity tests failed to show any evidence of genetic heterogeneity superimposed on clinical heterogeneity for ophthalmic signs and end-stage renal disease age.     

Cadmium-2-acetylaminofluorene interaction in isolated rat hepatocytes

Cadmium (Cd) is a non-essential, highly toxic heavy metal and a ubiquitous environmental contaminant. Evidence exists that Cd can affect parameters which are of great importance in the response towards xenobiotics. However, there is a lack of information about the mechanisms that take place at the cellular and molecular levels upon dual exposure to Cd and other toxins. The purpose of the present work was therefore to examine the biochemical interactions between Cd and a well-known genotoxic hepatocarcinogen, 2-acetylaminofluorene (AAF) in isolated rat hepatocytes. The cells were incubated for 10 hr with a sub-cytotoxic concentration (0.22 M) of ¹⁰⁹Cd. This was followed by a 10 hr exposure to 1 M [³H]AAF. Cellular distribution of Cd and ³H was determined. Sephadex G-75 elution profiles of the cytosol showed that Cd was almost entirely associated with the intermediate molecular weight (IMW) fractions containing metallothionein (MT) (>80%), and with high molecular weight proteins. In parallel, the highest proportion of ³H was found in the low molecular weight components. Further analysis of IMW fractions by DEAE A-25 anion-exchange chromatography revealed that, in addition to Cd, there was some ³H which coeluted along with MT-I and MT-II isoforms, but preferentially with MT-I. Moreover, Cd pretreatment caused a 1.6-fold increase in MT level, as measured by the silver-saturation assay. Under these conditions, there was a 17% lower binding of ³H to the DNA. This reduced binding was neither accompanied by diminished AAF uptake nor by inhibition of cytochrome P-450 activity. Taken together, these results suggest that Cd exposure has a protective effect against the genotoxicity of AAF. MT, whose synthesis is induced, could play a role in the Cd-AAF interaction through scavenging of reactive metabolites.Abbreviations AAF 2-acetylaminofluorene - Cd cadmium - DMSO dimethyl sulfoxide - HBSS Hank's balanced salt solution - LDH lactate dehydrogenase - MT metallothionein - UDS unscheduled DNA synthesis     

Testicular expression of PC4 in the rat: molecular diversity of a novel germ cell-specific Kex2/subtilisin-like proprotein convertase.

The rat cDNA sequence of PC4 (rPC4), representing a new member of the Kex2/subtilisin-like proprotein convertases, demonstrated the presence of at least three rPC4 mRNAs resulting in the production of rPC4-A (654 amino acids), rPC4-B (619 amino acids), and rPC4-C (609 amino acids) with different C-terminal sequences. Analogous to rat PC4, three cDNAs were also found for the mouse PC4. The observed molecular diversity of PC4 mRNA possibly results from the differential splicing and/or exon skipping of the parent gene. PC4 mRNA, with a major form at 2.8 kilobases, was highly abundant in the rat testis but could not be detected by Northern analysis in any other tissues including the central nervous system and peripheral tissues. Testicular cell separation studies combined with Northern analysis indicate the high expression levels of PC4 in germ cells but not in Leydig, Sertoli, or peritubular cells. In situ hybridization histochemistry confirms the site of PC4 gene expression as the pachytene spermatocytes and the round spermatids but not in the elongating spermatids. We also demonstrate the colocalization of PC4 with proenkephalin in testicular germ cells by in situ hybridization. A study of the ontogeny of PC4 indicated that PC4 mRNA was first expressed postnatally between days 19 and 22, coinciding with the first stages of spermiogenesis. The stage-specific expression of PC4 in testis indicates its potential role in the developmental maturation of germ cells and that this convertase may play a specific physiological function in reproduction.     

The changing sensitivity to auxin of the plasma-membrane H+-ATPase: Relationship between plant development and ATPase content of membranes

The auxin sensitivity of the plasma-membrane H⁺-ATPase from tobacco leaves (Nicotiana tabacum L. cv. Xanthi) depends on the physiological state of the plant (Santoni et al., 1990, Plant Sci. 68, 33–38). Results based on the study of auxin sensitivity according to culture conditions which accelerate or delay tobacco development demonstrate that the highest auxin sensitivity is always associated with the end of the period of induction to flowering. Auxin stimulation of H⁺-translocation activity corresponds to an increase of the apparent ATPase affinity for ATP. The plasma-membrane H⁺-ATPase content, measured with an enzyme-linked immunosorbent assay using a specific anti-H⁺-ATPase antibody, varies according to plant development, and was found to increase by 100% during floral induction. The specific molecular ATPase activity also changes according to plant development; more particularly, the decrease in molecular ATPase activity upto and during the floral-induction period parallels the increase of sensitivity to indole-3-acetic acid.Abbreviations ELISA enzyme-linked immunosorbent assay - PAGE polyacrylamide gel electrophoresis - SDS sodium dodecyl sulfate Authors are grateful to Mrs. Grosclaude (Lab. Virologie, INRA, Jouy-en-Josas, France) and Mrs. Boudon (Lab. Mycoplasmes, INRA, Dijon, France) for support and advice in the preparation of antibodies. This work was supported by grants No. 89/512/6 from the E.P.R of Bourgogne and No. 89 C 0662 from M.R.T.     

Sustained primary culture of lobster (Panulirus argus) olfactory receptor neurons

Appropriate conditions were developed for primary sustained culture of olfactory neurons of the spiny lobster Panulirus argus. Neurons were cultured in a modified Liebowitz L15 media supplemented with Panulirus salts, basic minimal essential (BME) vitamins, L-glutamine, low dextrose, and either fetal calf serum (FCS) or lobster haemolymph. Neurite outgrowth and cell viability was strongly affected by choice of adherent substratum, presence of serum, and length of animal captivity. Neither nerve growth factor 7s (NGF-7s), HEPES, nor preconditioned media from the target organ, the olfactory lobe, had any gross effect on either longevity or neurite outgrowth. Five morphologically distinct neuronal cell types (8-16 mum soma diameter) could be defined based on their number and type of processes. All of these cells were electrically excitable (N = 50), and many (56%) produced either inward or outward currents in response to stimulation with single odors. The proportion of cells responding to odors increased (80%) when 10 cells were sequentially presented with a series of 3-5 odors. The finding that cultured cells maintain responsiveness to odors yet are morphologically more compact than their counterparts in situ, argues for the prospect of using these dissociated cultured olfactory receptor neurons to study signal transduction in olfaction.     

A theoretical and experimental analysis of the qP and qN coefficients of chlorophyll fluorescence quenching and their relation to photochemical and nonphotochemical events

The initial (F₀), maximal (F_M) and steady-state (F_S) levels of chlorophyll fluorescence emitted by intact pea leaves exposed to various light intensities and environmental conditions, were measured with a modulated fluorescence technique and were analysed in the context of a theory for the energy fluxes within the photochemical apparatus of photosynthesis. The theoretically derived expressions of the fluorescence signals contain only three terms, X=J₂p_2F/(1–G), Y=T/(1–G) and V, where V is the relative variable fluorescence, J₂ is the light absorption flux in PS II, p_2F is the probability of fluorescence from PS II, G and T are, respectively, the probabilities for energy transfer between PS II units and for energy cycling between the reaction center and the chlorophyll pool: F₀=X, F_M=X/(1–Y) and F_S=X(1+(YV/(1–Y))). It is demonstrated that the amplitudes of the previously defined coefficients of chlorophyll fluorescence quenching, q_P and q_N, reflect, not just photochemical (q_P) or nonphotochemical (q_N) events as implied in the definitions, but both photochemical and nonphotochemical processes of PS II deactivation. The coefficient q_P is a measure of the ratio between the actual macroscopic quantum yield of photochemistry in PS II (41-1) in a given light state and its maximal value measured when all PS II traps are open (41-2) in that state, with 41-3 and 41-4. When the partial connection between PS II units is taken into consideration, 1-q_P is nonlinearily related to the fraction of closed reaction centers and is dependent on the rate constants of all (photochemical as well as nonphotochemical) exciton-consuming processes in PS II. On the other hand, 1-q_N equals the (normalized) ratio of the rate constant of photochemistry (k_2b) to the combined rate constant (k_N) of all the nonphotochemical deactivation processes excluding the rate constant k₂₂ of energy transfer between PS II units. It is demonstrated that additional (qualitative) information on the individual rate constants, k_N-k₂₂ and k_2b, is provided by the fluorescence ratios 1/F_M and (1/F₀)–(1/F_M), respectively. Although, in theory, 41-5 is determined by the value of both k_2b and k_N-k₂₂, experimental results presented in this paper show that, under various environmental conditions, 41-6 is modulated largely through changes in k _N, confirming the idea that PS II quantum efficiency is dynamically regulated in vivo by nonphotochemical energy dissipation.Abbreviations Chl chlorophyll - F₀, F_M and F_S initial, maximal and steady-state levels of modulated Chl fluorescence emitted by light-adapted leaves - PS I and II photosystem I and II - q_P and q_N (previously defined) photochemical and nonphotochemical components of Chl fluorescence quenching     

Novel DNA structures resulting from dTam3 excision in tobacco

A Tam3 two-element system has been designed by combining an immobilized Tam3 element with a non-autonomous dTam3 element inserted into the HPT gene. The phenotypic assay employed, restored hygromycin resistance, indicated thattrans-activation of the non-autonomous dTam3 element occurred. Molecular analyses of the excision sites revealed that the ends of the dTam3 element remain in the empty donor sites. The predominant consequence of this type of excision appears to be that excised fragments fail to re-integrate into the tobacco genome. Only one case of dTam3 re-integration could be detected. The ends of this element had been degraded upon integration into the tobacco genome. Either the altered structure of the Tam3 derivatives or tobacco host factors are influencing thetrans-activation of a dTam3 element, resulting in aberrant excision.