An Energy-Barrier Model for the Permeation of Monovalent and Divalent Cations Through the Maxi Cation Channel in the Plasma Membrane of Rye Roots

1999 ◽  
Vol 168 (1) ◽  
pp. 63-75 ◽  
Author(s):  
P.J. White ◽  
M.S. Ridout
Keyword(s):  
Plasma Membrane ◽  
Energy Barrier ◽  
Divalent Cations ◽  
Cation Channel ◽  
Barrier Model

scholarly journals Studies on the mechanism of expression of secreted fibrinogen on the surface of activated human platelets

Blood ◽  
1989 ◽  
Vol 73 (5) ◽  
pp. 1226-1234 ◽  
Author(s):  
C Legrand ◽  
V Dubernard ◽  
AT Nurden
Keyword(s):  
Monoclonal Antibody ◽  
Plasma Membrane ◽  
Synthetic Peptides ◽  
Divalent Cations ◽  
Adenosine Diphosphate ◽  
Human Platelets ◽  
Plasma Fibrinogen ◽  
Fab Fragments ◽  
Polymer Formation ◽  
Activated Platelets

Abstract Affinity purified anti-fibrinogen (anti-Fg) Fab fragments were used to study the mechanism of expression of alpha-granule fibrinogen on activated platelets. Low amounts of the radiolabeled anti-Fg Fab bound to unstimulated or adenosine diphosphate (ADP)-stimulated cells. They readily bound to platelets stimulated with collagen, alpha-thrombin or gamma-thrombin in the presence of divalent cations. At 1 n mol/L alpha- thrombin or 25 nmol/L gamma-thrombin, platelet fibrinogen was expressed on the surface of the cells notwithstanding the presence of AP-2, a monoclonal antibody to the glycoprotein (GP) IIb-IIIa complex, or the synthetic peptides Arg-Gly-Asp-Ser and gamma 400–411, all substances that prevented the binding of plasma fibrinogen to platelets. These results suggest that platelet fibrinogen may interact with its receptors during its translocation from the alpha-granules to the plasma membrane and, thus, not occupy the same sites as those available for plasma fibrinogen on the surface of the cell. Furthermore, we found that platelet fibrinogen was expressed on the thrombin-stimulated platelets of a Glanzmann's thrombasthenia variant that failed to bind plasma fibrinogen. Normal platelets stimulated with 5 nmol/L alpha- thrombin bound increased amounts of the anti-fg Fab, the additional expression being inhibited by the anti-GP IIb-IIIa monoclonal antibody or by Gly-Pro-Arg-Pro, an inhibitor of fibrin polymer formation. This suggests that rebinding to externally located GP IIb-IIIa complexes becomes important once fibrin is formed.

scholarly journals Murine fetal liver macrophages bind developing erythroblasts by a divalent cation-dependent hemagglutinin.

1988 ◽  
Vol 106 (3) ◽  
pp. 649-656 ◽  
Author(s):  
L Morris ◽  
P R Crocker ◽  
S Gordon
Keyword(s):  
Plasma Membrane ◽  
Divalent Cation ◽  
Plasma Membranes ◽  
Fetal Liver ◽  
Divalent Cations ◽  
Membrane Receptors ◽  
Erythroid Cells ◽  
Mammalian Development ◽  
Trypsin Treatment ◽  
Plasma Membrane Receptors

During mammalian development the fetal liver plays an important role in hematopoiesis. Studies with the macrophage (M phi)-specific mAb F4/80 have revealed an extensive network of M phi plasma membranes interspersed between developing erythroid cells in fetal liver. To investigate the interactions between erythroid cells and stromal M phi, we isolated hematopoietic cell clusters from embryonic day-14 murine fetal liver by collagenase digestion and adherence. Clusters of erythroid cells adhered to glass mainly via M phi, 94% of which bound 19 +/- 11 erythroblasts (Eb) per cell. Bound Eb proliferated vigorously on the surface of fetal liver M phi, with little evidence of ingestion. The M phi could be stripped of their associated Eb and the clusters then reconstituted by incubation with Eb in the presence of divalent cations. The interaction required less Ca++ than Mg++, 100 vs. 250 microM for half-maximal binding, and was mediated by a trypsin-sensitive hemagglutinin on the M phi surface. After trypsin treatment fetal liver M phi recovered the ability to bind Eb and this process could be selectively inhibited by cycloheximide. Inhibition tests showed that the Eb receptor differs from known M phi plasma membrane receptors and fetal liver M phi did not bind sheep erythrocytes, a ligand for a distinct M phi hemagglutinin. We propose that fetal liver M phi interact with developing erythroid cells by a novel nonphagocytic surface hemagglutinin which is specific for a ligand found on Eb and not on mature red cells.

The Plasma Membrane ATPase of Dunaliella parva

1989 ◽  
Vol 44 (1-2) ◽  
pp. 128-138 ◽  
Author(s):  
Hartmut Gimmler ◽  
Lothar Schneider ◽  
Rosemarie Kaaden
Keyword(s):  
Plasma Membrane ◽  
Higher Plants ◽  
Divalent Cations ◽  
Gradient Centrifugation ◽  
Anion Transport ◽  
Hypersaline Environment ◽  
Plasma Membrane Atpase ◽  
Dunaliella Parva ◽  
Membrane Atpases ◽  
Membrane Atpase

Abstract Plasma membrane Mg2+, Ca2+ ATPases were isolated from Dunaliella parva by differential centrifugation and subsequent sucrose gradient centrifugation and analyzed for their properties with special emphasis on ecophysiological requirements of this extremely salt-tolerant alga. Most properties (Vmax- and KM-values, substrate specificity, vanadate and DES sensitivity, resistance against ouabain) indicate that the ATPases of the plasma membrane of D. parva are basically of the same type as that found in the plasma membrane of other algae or higher plants. However, some interesting deviations from the normal characteristics of plasma membrane ATPases of plants were observed for the Dunaliella ATPases. These modifications partially may reflect adaptations of the ATPase and/or the microenvironment of the ATPase to the highly saline environment of this alga; 1) The plasma membrane ATPase of D. parva requires unusually high concentrations of divalent cations (up to 100 mM Mg2+ or Ca2+) for maximal activity. Both cations can substitute for each other. 2) The plasma membrane ATPase of D. parva is extremely resistant against salt. It was stimulated by NaCl or KC1 at concentrations up to 800 mM , whereas at higher salt concentrations the enzyme was inhibited. However, about 2.5 M NaCl was required for halfmaximal inhibition of ATPase activity. 3) The ATPase was inhibited by inhibitors of anion transport such as SITS and D ID S . which suggests direct or indirect involvement of ATPase in anion transport. The possible functions of the plasma membrane ATPases are discussed with special emphasis on problems related to the hypersaline environment of this alga.

Sign in / Sign up

Export Citation Format

Share Document