Hemorheology and oxygen transport in vertebrates. A role in thermoregulation?

We studied the effect of temperature on blood rheology in three vertebrate species with different thermoregulation and erythrocyte characteristics. Higher fibrinogen proportion to total plasma protein was found in turtles (20%) than in pigeons (5.6%) and rats (4.2%). Higher plasma viscosity at room temperature than at homeotherm body temperature was observed in rats (1.69 mPa x s at 20 degrees C vs. 1.33 mPa x s at 37 degrees C), pigeons (3.40 mPa x s at 20 degrees C vs. 1.75 mPa x s at 40 degrees C), and turtles (1.74 mPa x s at 20 degrees C vs. 1.32 mPa x s at 37 degrees C). This fact allow us to hypothesize that thermal changes in protein structure may account for an adjustment of the plasma viscosity. Blood viscosity was dependent on shear rate, temperature and hematocrit in the three species. A different behaviour in apparent and relative viscosities between rat and pigeon at environmental temperature was found. Moreover, the blood oxygen transport capacity seems more affected by a reduction of temperature in rats than in pigeons. Both findings indicate a greater influence of temperature on mammalian erythrocyte than on nucleated red cells, possibly as a consequence of differences in thermal sensitivity and mechanical stability between them. A comparison between the three species revealed that apparent blood viscosity measured at homeotherm physiological temperature was linearly related to the hematocrit level of each species. However, when measured at environmental temperature, rat blood showed a higher apparent viscosity than those found in species with non-nucleated red cells, thus indicating a higher impact of temperature decrease on blood viscosity in mammals. This suggest that regional hypothermia caused by cold exposure may affect mammalian blood rheological behaviour in a higher extent than in other vertebrate species having nucleated red cells and, consequently, influencing circulatory function and oxygen transport.     

Modelling sediment transport in shallow lakes — interactions between sediment transport and sediment composition

In shallow, wind exposed lakes, the light conditions, the cycling of nutrients, heavy metals and organic micro-pollutants and changes in the local composition of the sediment top layer can be dominated by resuspension/erosion of bottom sediment and sedimentation of suspended solids. A 2 dimensional model for Sediment Transport, Resuspension and Sedimentation in Shallow lakes (STRESS-2d), based on an existing transport model, is discussed. In the model, mass balance equations for the water compartment and the bottom sediment are solved numerically. Up to 7 sediment fractions can be taken into account, each having a specific set of resuspension/erosion and sedimentation parameter values. Several options for modelling the changes in the bottom sediment composition are available.A simulation experiment for Lake Veluwe (The Netherlands), in which model options with and without the distinction of sediment fractions were used, showed that using sediment fractions to account for the variability in the sediment composition leads to an improvement of the model results, particularly the simulated phosphorus sediment-water exchange fluxes. For Lake Ketel (The Netherlands) two options for modelling changes in the bottom sediment composition are compared. It is shown that an option in which a thin water-sediment layer on top of the more consolidated bottom sediment is simulated provides an improvement in the simulation of the suspended solids concentration.     

Azole Resistance in Aspergillus fumigatus—Current Epidemiology and Future Perspectives

Azole resistance in Aspergillus fumigatus isolates is increasingly reported in different nosologic contexts with variable prevalence in different countries. Mutations in the target of triazoles are widely described in azole-resistant clinical isolates. The recovery of mutated/resistant isolates is described either in patients undergoing long-term azole treatment or after inhalation of environmentally acquired resistant isolates. Acquisition in patients during azole therapy highlights the capacity of this fungus to adapt to its environment, but it has a low impact in terms of public health, as interhuman transmission of A. fumigatus is uncommon. Environmentally acquired resistant isolates may propagate and affect populations at risk. The use of triazoles as first-line therapy or prophylaxis could lead to selection of resistant isolates in patients, because most isolates harbor azole cross-resistance. Although mold-active triazoles have provided major progress in the prophylaxis and treatment of Aspergillus infection, the increase of azole resistance could question their use in humans.     

Chymotrypsinogen · inositol phosphatide complexes and the transport of digestive enzyme across membranes

Chymotrypsinogen A was almost quantitatively extracted from aqueous solution in the presence of inositol phosphatides at relatively low concentrations of both ligands. Calcium ion facilitated the interaction at concentrations of 10^?4–10^?5 M. A water-insoluble chymotrypsinogen · Ca²⁺ · inositol phosphatide complex was formed with an apparent stochiometry of 3 mol phospholipid : 3 mol Ca²⁺ : 1 mol protein. Small changes in the structure of the protein prevented complex formation; in particular, the almost identical α-chymotrypsin, did not form complexes under the conditions studied. On the other hand, an homologous, but structurally substantially different, secretory protein, trypsinogen, did form complexes. Water-insoluble complexes were not formed with albumin, carbonic anhydrase or lactic dehydrogenase under the same circumstances. Neither phosphatidylethanolamine nor phosphatidylcholine formed complexes with chymotrypsinogen. Phosphatidylserine formed complexes, but was less effective than inositol phosphatides. Complex formation and stability was dependent upon “critical” concentrations of both Ca²⁺ and H⁺. Extraction of the protein from solution increased from neglible to complete when the calcium concentration of the medium was raised slightly from 1.0 · 10^?4 M to 1.5·10^?4 M. Conversely, dissociation was complete when H⁺ concentration was decreased slightly from pH 6.5 to 7.0. The complex is apparently formed as the result of specific electrostatic interactions between the polar head group of the inositol phosphatide and the protein, with the nonpolar alipathic fatty acid chains of the phospholipid providing a hydrophobic microenvironment for the protein. It is proposed that such complexes could account for the movement of digestive enzyme through membranes.     

Glucosylceramides of oat root plasma membranes — physicochemical behaviour in natural and in model systems

Glucosylceramides from oat root plasma membranes have been characterized using HPLC-particle beam-mass spectrometry, differential scanning calorimetry, low angle X-ray diffraction and surface balance technique. 24:1-OH was dominating fatty acid (90%) together with 24:0-OH and 22:1-OH. The sphingosine base was sphingadienine isomers and the monosaccharide α and β glucose. Differential scanning calorimetry of an aqueous dispersion of glucosylceramide revealed during heating an endothermic gel-liquid crystalline transition with double peaks at 47° and 51°C, the lowest known for naturally occurring glucosylceramides. A cooling scan after the endothermic gel-liquid transition showed one exotherm at 15°C and if this was followed by another heating scan a large exotherm appeared with a peak at 18°C. During the second heating the matrix was hydrated and the exotherm at 18°C reflects then the transition between the supercooled metastable gel phase and the corresponding hydrated form. The calorimetric data indicate a lamellar phase which during the cooling scan appeared as an supercooled liquid crystalline phase. Low angle X-ray diffraction confirmed these calorimetric data. The surface pressure-area-curves of pure oat glucosylceramides were more expanded than those of bovine origin. Mixtures of oat glucosylceramides and phosphatidylcholine species similar to those present in oat root plasma membranes showed molecular miscibility but no interaction.     

Pneumocystis Carinii Pneumonia—Problems in Diagnosis and Therapy in 24 Cases

Twenty-four instances of Pneumocystis carinii pneumonia were recognized in 23 patients at the Stanford University Hospitals between 1962 and 1970. The affected persons could be broadly characterized as “compromised” hosts. All but one were receiving immunosuppressive drug therapy for such underlying disease as hematopoietic malignant disease, collagen vascular disorder, and organ transplant rejection. The one patient not receiving immunosuppressant medication had congenital dysgammaglobulinemia and suffered two discrete bouts of pneumocystis pneumonia. Most of the patients were concomitantly infected with other “opportunistic” pathogens.Open lung biopsy remained the most reliable method of antemortem diagnosis of pneumocystis infection during this eight-year period. It resulted in little morbidity. Unfortunately, direct examination of appropriately stained sputum specimens for cysts was almost uniformly nonproductive.The majority of patients received specific antipneumocystis drug treatment (pentamidine isethionate or pyrimethamine and sulfadiazine). “Cure” was achieved when institution of therapy was prompt and duration of therapy approached the empirically recommended two-week course.The fact that pneumocystis pneumonia can be controlled if recognized early is compelling reason to pursue diagnosis of pneumocystosis in an appropriate clinical setting, namely, in patients with impaired host defenses who have pulmonary infection unresponsive to conventional therapy. There is hope that a noninvasive (serological) technique will be developed shortly to simplify identification of this not uncommon cause of diffuse interstitial pneumonitis.     

Cl− transport in basolateral renal medullary vesicles: I. Cl− transport in intact vesicles

Summary This paper provides the results of studies which characterized conductive³⁶Cl^– flux in basolaterally enriched membrane vesicles prepared from rabbit renal outer medulla. Conductive³⁶Cl^– uptake was studied under two different experimental conditions. In the first,³⁶Cl^– flux was driven by an inside positive voltage created with oppositely directed Cl^– and gluconate gradients. In the second, an inwardly direct K⁺ gradient was used to drive³⁶Cl^– uptake. By these two methods, voltage-sensitive³⁶Cl^– uptake was shown to comprise about 45 and 65%, respectively, of the initial rates of total³⁶Cl^– flux. Separate paired studies demonstrated that the conductive³⁶Cl^– uptake was inhibited by the Cl^– channel blocker diphenylamine-2-carboxylate (DPC) with an IC₅₀ for DPC of 154 m. The voltagedependent³⁶Cl^– uptake had an activation energy of 6.4 kcal/mole. This³⁶Cl^– conductance had an anion selectivity sequence of I^–>Cl^–NO ₃ ^– gluconate.     

Modes of Cl− transport across the mucosal and serosal membranes of urodele intestinal cells

Summary The characteristics of Cl^– movement across luminal and basolateral membranes ofAmphiuma intestinal absorptive cells were studied using Cl^–-sensitive microelectrodes and tracer³⁶Cl techniques. Intracellular Cl^– activity (a _Cl ⁱ ) was unchanged when serosal Cl^– was replaced; when luminal Cl^– was replaced cell Cl^– was rapidly lost. Accordingly, the steady statea _Cl ⁱ could be varied by changing the luminal [Cl]. As luminal [Cl] was raised from 1 to 86mM,a _Cl ⁱ rose in a linear manner, the mucosal membrane hyperpolarized, and the transepithelial voltage became serosa negative. In contrast, the rate of Cl^– transport from the cell into the serosal medium, measured as the SITS-inhibitable portion of the Cl^– absorptive flux, attained a maximum whena _Cl ⁱ reached an apparent value of 17mm, indicating the presence of a saturable, serosal transport step. The stilbeneinsensitive absorptive flux was linear with luminal [Cl], suggestive of a paracellular route of movement. Intracellulara _Cl was near electrochemical equilibrium at all but the lowest values of luminal [Cl] after interference produced by other anions was taken into account.a _Cl ⁱ was unaffected by Na replacement, removal of medium K, or elevation of medium HCO ₃ ^– . Mucosae labeled with³⁶Cl lost isotope into both luminal and serosal media at the same rate and from compartments of equal capacity. Lowering luminal [Cl] or addition of theophylline enhanced luminal Cl^– efflux. It is concluded that a conductive Cl leak pathway is present in the luminal membrane. Serosal transfer is by a saturable, stilbene-inhibitable pathway. Luminal Cl^– entry appears to be passive, but an electrogenic uptake cannot be discounted.     

The erythrocyte membranes in β-thalassemia. Lower sialic acid levels in glycophorin

The sialic acids content of glycophorin of thalassemic erythrocyte membranes is about 25% lower than in glycophorin of normal erythrocyte membranes. Glycophorin extracted from old thalassemic erythrocytes separated by density centrifugation, has about half the sialic acids content found in glycophorin extracted from young thalassemic erythrocytes. Possible sialidase activity was sought in the plasma and erythrocyte membranes of thalassemic erythrocytes. No increased sialidase activity was detected in the plasma of the patients as compared to that of normal donors. Thus, other sites for sialidase activity, or other possibilities have to be explored to account for the increased sialic acid hydrolysis of glycophorin of the thalassemic erythrocytes.     

Na+, Li+ and Cl− transport by brush border membranes from rabbit jejunum

Na+, Li+, K+, Rb+, Br-, Cl- and SO4(2-) transport were studied in brush border membrane vesicles isolated from rabbit jejunum. Li+ uptakes were measured by flameless atomic absorption spectroscopy, and all others were measured using isotopic flux and liquid scintillation counting. All uptakes were performed with a rapid filtration procedure. A method is presented for separating various components of ion uptake: 1) passive diffusion, 2) mediated transport and 3) binding. It was concluded that a Na+/H+ exchange mechanism exists in the jejunal brush border. The exchanger was inhibited with 300 microM amiloride or harmaline. The kinetic parameters for sodium transport by this mechanism depend on the pH of the intravesicular solution. The application of a pH gradient (pHin = 5.5, pHout = 7.5) causes an increase in Jmax (50 to 125 pmol/mg protein . sec) with no change in Kt (congruent to 4.5 nM). Competition experiments show that other monovalent cations, e.g. Li+ and NH4+, share the Na+/H+ exchanger. This was confirmed with direct measurements of Li+ uptakes. Saturable uptake mechanisms were also observed for K+, Rb+ and SO4(2-), but not for Br-. The Jmax for K+ and Rb+ are similar to the Jmax for Na+, suggesting that they may share a transporter. The SO4(2-) system appears to be a Na+/SO4(2-) cotransport system. There does not appear to be either a Cl-/OH- transport mechanism of the type observed in ileum or a specific Na+/Cl- symporter.     

Ethacrynic Acid in Blood Transfusion—its Effects on Plasma Volume and Urine Flow in Severe Anaemia in Pregnancy

Thirty grossly anaemic pregnant Nigerian women with venous haematocrit levels varying between 6 and 17%, had their plasma volumes estimated by the Evans blue dye dilution technique, both before and immediately after direct transfusion of packed blood cells. Parenteral ethacrynic acid was added to the blood for transfusion in 20 patients, seven of whom were in anaemic heart failure on admission. Ethacrynic acid used in this way was successful in the prevention of acute pulmonary oedema, and it produced acute diuresis as well as a reduction of plasma volume in the majority of cases. This technique of direct transfusion with ethacrynic acid is simple, and it may well replace exchange transfusion as a means of treating patients with anaemic heart failure.     

Phosphate transport and its relationship to cation movements in Ehrlich Lettré ascites tumor cells.

In view of the importance of P_i in the control of cell metabolism, it was of interest to study the mechanism and regulation of P_i uptake by ascites tumor cells. For this purpose, the incorporation of ³²P_i into Ehrlich Lettré cells was compared when competitive anions and inhibitors which alter cation movements were present. Anions such as sulfanilate (35 mm) and succinate (30 mm) decrease ³²P_i uptake by ca. 35%, suggesting that transport is mediated by a protein similar to the 100,000 M_r anion carrier isolated from erythrocyte membranes. Furosemide, a diuretic which bears a structural analogy to sulfanilate inhibitors of anion transport, also decreases ³²P_i incorporation at concentrations as low as 2 × 10^?5m. This inhibitor blocks cation exchange in ascites tumor cells, and from the present data, it is suggested that a possible function of the furosemidesensitive cation exchange protein is to facilitate anion transport. Ouabain, known to inhibit (Na⁺ + K⁺)-ATPase and its dephosphorylation, stimulates the rate of incorporation of ³²P_i into cells and also raises the net inorganic phosphate level. The stimulation of ³²P_i incorporation is decreased by sulfanilate or succinate. In contrast to the effects of ouabain, addition of 10 mm K⁺, which is known to stimulate (Na⁺ + K⁺)-ATPase and its dephosphorylation, decreases ³²P_i incorporation. These observations suggest that anion transport and energy-dependent Na⁺ and K⁺ movements may be closely coupled to the intact cell.