Simultaneous convective and diffusive mass transfers in a hemodialyser

The mass transfer in a hemodialyser in the presence of combined dialysis and ultrafiltration has been calculated by integration of mass fluxes across the boundary layers in blood and dialysate phase taking into account the partial rejection of solute as well as changes in local blood flow and ultrafiltration flux along the membrane. Clearances of creatinin, vitamin B12, and myoglobin have been calculated as a function of blood and ultrafiltrate flow rate and were found to be in good agreement with in vitro measurements. The data suggest the following empirical correlation for the hemodiafiltration clearance.     

Accumulation of cadmium by immobilizedZoogloea ramigera 115

Summary Zoogloea ramigera 115 was immobilized into beads of calcium-alginate and placed into batch air-bubbled column reactors. In the absence of any added nutrients the immobilized bacterium adsorbed Cd from solutions containing levels of 2 and 20 g ml^–1 per day, over a period of 21 and 20 days, respectively. Adsorption of Cd from solutions containing 20 g ml^–1 Cd was better than 90% for 16 days. Beads treated with Cd at 2 g ml^–1 never adsorbed less than 95% of the metal. Alginate adsorbed Cd as well, but inclusion of cells changed the effectiveness of adsorption. Of a 250 g ml^–1 Cd solution, alginate adsorbed 70.4% Cd in 60 min whereas alginate plus cells adsorbed 90.5% in the same time span. Temperature had no effect on adsorption by immobilized cells at levels of 2 and 10 g ml^–1 Cd. However at higher concentrations, binding was enhanced as temperature increased.Z. ramigera beads were stable during all treatments and for prolonged periods of time (21 days).     

SIMPLE GENETIC BASIS FOR IMPORTANT SOCIAL TRAITS IN THE FIRE ANT SOLENOPSIS INVICTA

Variation in queen phenotype and reproductive role in the fire ant Solenopsis invicta has been shown to have a simple genetic basis in a single introduced population in the United States. The evidence consists of an association between this variation and queen genotype at Pgm-3, a phosphoglucomutase-encoding gene. In the present study, we surveyed Pgm-3 allele and genotype frequencies in diverse populations from the native and introduced ranges of this ant to learn whether this simple genetic basis for reproductive traits is a general feature of the species or a genetic anomaly in introduced ants stemming from a recent bottleneck or the invasion of novel habitats. No egg-laying queens living in polygyne (multiple-queen) nests possessed the homozygous genotype Pgm-3^a/a in any of the study populations, yet nonreproductive females from such nests (workers as well as queens that had not yet initiated oogenesis) possessed this genotype at moderate frequencies. Remarkably, Pgm-3^a/a was the most common genotype among all classes of females, including egg-laying queens, in monogyne (single-queen) nests from all populations studied. Genotype proportions at Pgm-3 in polygyne populations typically departed strongly from the proportions expected under Hardy-Weinberg equilibrium, whereas those in monogyne populations did not. These patterns establish that a single mendelian gene influences queen reproductive role in S. invicta and that this gene uniformly is under strong directional selection in the polygyne social form only. Moreover, the perfect association of Pgm-3 genotype and reproductive role in all populations, combined with the known function of phosphoglucomutase in insect metabolism, suggest that this gene may directly influence queen phenotypes rather than merely serving as a marker for a linked gene that causes the effects.     

A micromethod for serotyping Bacillus thuringiensis

P. LAURENT, H. RIPOUTEAU, V. COSMAO DUMANOIR, E. FRACHON AND M.-M. LECADET. 1996. Serotyping of Bacillus thuringiensis is possible using 96-well microplates instead of tubes. The advantages are a reduction on the incubation time from 120 to 75 min and the amounts of antisera and bacterial suspensions needed 10-fold.     

HSP25 in isolated perfused rat hearts: Localization and response to hyperthermia

Recent investigations concentrate on the correlation between the myocardial expression of the inducible 70-kDa heat shock protein (HSP70i) by different stress conditions and its possible protective effects. Only few studies have focused on the involvement of small heat shock proteins in this process. We analyzed the location of the small heat shock protein HSP25 in isolated cardiomyocytes as well as its location and induction in isolated perfused hearts of rats. By immunofluorescence microscopy HSP25 was found to colocalize with actin in the I-band of myofibrils in cardiomyocytes of isolated perfused hearts as well as in isolated neonatal and adult cardiomyocytes. Hyperthermic perfusion of isolated hearts for 45 min resulted in modulation of different parameters of heart function and in induction of HSP25 and HSP70i. Temperatures higher than 43°C (44–46°C) were lethal with respect to the contractile function of the hearts. Compared to control hearts perfused at 37°C, significant increases during hyperthermic perfusion at 42°C and 43°C were obtained for heart rate, contraction velocity and relaxation velocity. In response to hyperthermia at 43°C and after subsequent normothermic perfusion for 135 min at 37°C, left ventricular pressure, contraction velocity and relaxation velocity remained significantly elevated. However, heart rate returned to control values immediately after the period of heat treatment. HSP25 is constitutively expressed even in normothermic perfused hearts as shown by Western blotting. Hyperthermia increased the content of HSP25 only in the left ventricular tissue. In contrast, HSP70i was strongly induced in all analyzed parts of the myocardium (left ventricle, right ventricle, septum). Our findings suggest a differential regulation of HSP25 and HSP70i expression in response to hyperthermia in isolated perfused hearts. The constitutively expressed HSP25 seems to be located adjacent to the myofibrils which implies a specific role of this protein even under unstressed conditions for the contractile function of the myocardium.     

β2-Adrenoceptor activation by zinterol causes protein phosphorylation,contractile effects and relaxant effects through a cAMP pathway in human atrium

Evidence from ventricular preparations of cat, sheep, rat and dog suggests that both ₁-adrenoceptors (₁AR) and ₂-adrenoceptors (₂AR) mediate positive inotropic effects but that only ₁AR do it through activation of a cAMP pathway. On the other hand, our evidence has shown that both ₁ AR and ₂ AR hasten relaxation of isolated human myocardium consistent with a common cAMP pathway. We have now investigated in the isolated human right atrial appendage, a tissue whose -AR comprise around 2/3 of ₁AR and 1/3 of ₂AR, whether or not ₂AR-mediated effects occur via activation of a cAMP pathway. We carried out experiments on atria obtained from patients without advanced heart failure undergoing open heart surgery. To activate ₂AR, we used the ₂AR-selective ligand zinterol. Experiments were carried out on paced atrial strips (1 Hz) and tissue homogenates and membrane particles. Zinterol caused positive inotropic and lusitropic (i.e. reduction of t_1:2 of relaxation) effects with EC₅₀ values of 3 and 2 nM, respectively. The zinterol-evoked effects were unaffected by the AR-selective antagonist CGP 20712A (300 nM) but blocked surmountably by the ₂AR-selective antagonist ICI 118551 (50 nM) which reduced both EC₅₀ values to 1 M. Zinterol stimulated adenylyl cyclase activity with an EC₅₀ of 30 nM and intrinsic activity of 0.75 with respect to (–)-isoprenaline (600 M); the effects were resistant to blockade by CGP 20712A (300 nM) but antagonised surmountably by ICI 118551 (50 nM). Zinterol bound to membrane PAR labelled with (–)-[¹²⁵I] cyanopindolol with higher affinity for ₂AR than for - 1 AR; the binding to ₂AR but not to - BAR was reduced by GTPyS (10 M). In the presence of CGP 20712A (300 nM) (–)-isoprenaline (400 M); (to activate both ₁AR and ₂AR maximally) and zinterol (10 M); increased contractile force 3.4-fold and 2.5-fold respectively and reduced relaxation tut by 32% and 18% respectively. These effects of (–)-isoprenaline and zinterol were associated (5 min incubation) with phosphorylation (pmol P/mg supernatant protein) of troponin I and C-protein to values of 8.4 ± 2.0 vs 12.4 ± 2.3 and 10.1 ± 2.5 vs 8.6 ± 1.6 respectively. (–)-Isoprenaline and zinterol also caused phosphorylation of phospholamban (1.8 ± 0.3 vs 0.4 ± 0.1 pmol P/mg respectively) specifically at serine residues. We conclude that in human atrial myocardium activation of both ₁AR and ₂AR leads to cAMP-dependent phosphorylation of proteins involved in augmenting both contractility and relaxation.     

Subcellular distribution of carbonic anhydrase in Solanum tuberosum L. leaves

The intracellular compartmentation of carbonic anhydrase (CA; EC 4.2.1.1), an enzyme that catalyses the reversible hydration of CO₂ to bicarbonate, has been investigated in potato (Solanum tuberosum L.) leaves. Although enzyme activity was mainly located in chloroplasts (87% of total cellular activity), significant activity (13%) was also found in the cytosol. The corresponding CA isoforms were purified either from chloroplasts or crude leaf extracts, respectively. The cytosolic isoenzyme has a molecular mass of 255 000 and is composed of eight identical subunits with an estimated M _r of 30000. The chloroplastic isoenzyme (M _r 220000) is also an octamer composed of two different subunits with M _r estimated at 27 000 and 27 500, respectively. The N-terminal amino acid sequences of both chloroplastic CA subunits demonstrated that they were identical except that the M _r-27 000 subunit was three amino acids shorter than that of the M _r-27 500 subunit. Cytosolic and chloroplastic CA isoenzymes were found to be similarly inhibited by monovalent anions (Cl^–, I^–, N ₃ ^- and NO ₃ ^- ) and by sulfonamides (ethoxyzolamide and acetozolamide). Both CA isoforms were found to be dependent on a reducing agent such as cysteine or dithiothreitol in order to retain the catalytic activity, but 2-mercaptoethanol was found to be a potent inhibitor. A polyclonal antibody directed against a synthetic peptide corresponding to the N-terminal amino acid sequence of the chloroplastic CA monomers also recognized the cytosolic CA isoform. This antibody was used for immunocytolocalization experiments which confirmed the intracellular compartmentation of CA: within chloroplasts, CA is restricted to the stroma and appears randomly distributed in the cytosol.Abbreviations BSA bovine serum albumin - CA carbonic anhydrase - PMSF phenylmethylsulphonyl fluoride - BAM benzamidine - DTT dithiothreitol - 2-ME 2-mercaptoethanol - PVDF polyvinylidene difluoride The authors thanks P. Carrier and Dr. B. Dimon for technical assistance with the mass-spectrometry measurements.