Low Dextran Research Articles

Crossbridge kinetics in chemically skinned rabbit psoas fibres when th actin-myosin lattice spacing is altered by dextran T-500

The actin-myosin lattice spacing of chemically skinned rabbit psoas fibres was osmotically altered by dextran T500, and the transient kinetic response of tension arising from maximally cycling cross-bridges was measured by sinusoidal length perturbations. The lattice spacing was estimated from the width of the fibres measured under a light microscope. As the dextran concentration was increased, the widths during both relaxation and Ca-activation decreased monotonically. The tension increased to a maximum at 7% dextran, and decreased again at further increases in dextran. Dynamic modulus (stiffness) increased monotonically with compression by dextran; this increase is primarily due to the elastic modulus. The rate constants slightly decreased between 0% and 4% dextran, then decreased rapidly at higher concentrations. The rate of oscillatory work output stayed approximately constant between 0% and 4% dextran, and sharply decreased at higher concentrations. Apparently, two independent effects occur as the lattice is compressed by dextran: (1) a compensation for the spacing change through an increase in tension and a decrease in the rate constants (this takes place at low dextran concentrations); and (2) an alteration of the crossbridge kinetics by grossly decreasing both the tension and the rate constants (at high dextran concentrations). The first effect is interpreted as a decrease in the detachment rate, while the second effect is interpreted as a decrease in the rate of the 'power stroke' reaction.

Cryoprotection of spinach chloroplast membranes by dextrans.

The cryoprotective properties of dextrans have been investigated in freezing experiments with isolated spinach thylakoids (Spinacia oleracea L.). The activity of cyclic photophosphorylation was used as an assay for membrane integrity. Dextrans of average molecular weights between 10,000 and 70,000 daltons proved to be fairly nontoxic to chloroplast membranes. On a molar basis, cryoprotective action increased with increasing molecular weight; on a unit weight basis, the cryoprotective effectiveness of different dextrans was comparable. In the presence of low dextran concentrations which are not sufficient for complete membrane preservation, the effectiveness of the polymers could be considerably increased by the addition of electrolytes. This is in contrast to cryoprotection exerted by sugars. At a given dextran concentration, membrane activity is a function of the electrolyte concentration and follows an optimum curve. If membrane-toxic action of the electrolytes and salt crystallization during freezing which complicate the situation, are not taken into consideration, the increase in membrane protection during freezing by salts was dependent on the concentration of the salts and was not much influenced by the nature of the cations and anions. At 0 °C, dextrans delayed the inactivation of thylakoids suspended in NaCl solutions. From the results it is concluded that cryoprotection produced by dextrans is caused in part by specific membrane stabilization.

Phasenzustand, Struktur und mechanische Eigenschaften des gelartigen Systems Wasser ‐ Gelatine ‐ Dextran

AbstractState of Phase, Structure and Mechanical Properties of the Gelatinous System Water‐Gelatin‐Dextran. Increasing use of water‐protein‐polysaccharide systems as plasma replacing liquids and synthetical food has led to an examination of the thermodynamic compatibility of polymers in an aqueous medium. In the examination of the state of phase of the system water‐gelatin‐dextran self‐association of gelatin was shown to be the main reason for its incompatibility with dextran. At low dextran concentrations the gelatinous system is monophasic but it proceeds to a two‐phase state at higher concentration of dextran. The monophasic system shows lower, the two‐phase system a higher flexibility than the gelatin‐gel of the same concentration.

Red cell charge as affected by low viscosity dextran.

SummaryThe effects of trauma and LVD on red cell charge were studied electrometri-cally using normal subjects, post-surgical and shock patients. The highest levels of negative colloidal charge were found in a group of 11 shock patients, all characterized by cellular aggregation and microcirculatory derangements. The administration of LVD resulted in increases of negative colloidal charge in all patients. The greatest increases (30%) were found in normal patients. LVD infusion produced a marked improvement in the circulatory status of shock patients, but the negative colloidal charge was increased only by about 5%. The results show that the effect of LVD on agglutination of erythro-cytes depends not only on the magnitude of the surface charge, but also on the physico-chemical nature of the surface which is formed.