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Biomedical subjects

R L Nachman

Publications and source records attributed to R L Nachman.

At least 19 recordsLinked to original sources
PubMed1979

Human complement in thrombin-mediated platelet function: uptake of the C5b-9 complex.

Thrombin-mediated platelet aggregation and release is enhanced by the presence of C3, C5, C6, C7, C8, and C9 of human complement. The interaction of thrombin with its receptor on the platelet membrane initiates activation of complement on the platelet surface. Trypsin-mediated platelet function is not enhanced by the addition of complement, probably because trypsin has no receptor on the platelet surface so activation of complement is triggered in the fluid phase and not on the platelet surface. Activation of complement by thrombin led to production of dimers of the C5b-9 complex on the platelet surface. These complexes were eluted from the platelet membrane and were identified physicochemically and morphologically. The mechanism of complement-induced enhancement of platelet function is not clear, however, it probably is mediated via the arachidonic acid transormation pathway because this activity was blocked by known inhibitors of cyclo-oxygenase, namely, aspirin and indomethacin.

Antithrombin III↗
PubMed1979

Human megakaryocytes. I. Characterization of the membrane and cytoplasmic components of isolated marrow megakaryocytes.

Human marrow megakaryocytes have been isolated with high purity and yield by processing marrow cells sequentially through density centrifugation and velocity sedimentation. Analysis of the isolated cells for various platelet-associated components by immunofluorescence demonstrated that fibrinogen, plasma factor VIII antigen (factor VIII:AGN) platelet myosin, platelet glycoproteins I and III are present on the membrane and in the cytoplasm of over 90% of marrow megakaryocytes. Parallel studies of human and mouse megakaryocytes and platelets for IgG receptor (FcR), complement receptor type one (CR1) (C3b receptor), complement receptor type two (CR2) (C3d receptor), and Ia antigen by fluorescence and (or) rosette formation methods were performed. FcR were present on most human megakaryocytes and platelets. The Ia antigen was detected on a proportion (10-15%) of human megakaryocytes but it was undetectable on human platelets. CR1 was found on 20-40% of mouse megakaryocytes and also on a proportion of mouse platelets. These differentiation markers may be of use in monitoring megakaryocyte maturation.

Animals↗
PubMed1979

Structural analysis of human platelet membrane glycoprotein I complex.

The glycoprotein I complex, consisting of two polypeptides of Mr 210,000 and 150,000, was isolated from human platelet membranes by wheat germ lectin affinity chromatography. Glycocalicin, a soluble loosely bound membrane glycoprotein of Mr 150,000 related to the glycoprotein I system, was also purified. The isolated polypeptides were radioiodinated in sodium dodecyl sulfate/polyacrylamide gels and digested with trypsin, and the labeled peptide digest was analyzed by two-dimensional high-voltage electrophoresis and thin-layer chromatography. The two polypeptides of Mr 210,000 and 150,000 in the glycoprotein I complex had essentially identical radioactive peptide maps. Glycocalicin had a completely different tryptic peptide map. These studies shed light on the molecular relationships of some of the components of the platelet membrane glycoprotein I system. The possibility is raised that the receptorlike function of the intrinsic platelet membrane glycoproteins may be related to the polymeric subunit associations of the constituent polypeptides.

Blood Platelets↗
PubMed1979

Isolation of human platelet plasma membranes with polylysine beads.

Human platelet plasma membranes were isolated with polylysine beads according to the technique developed by Jacobson and Branton (1977, Science [Wash. D. C.] 195:302--304). Lactoperoxidase-catalyzed surface iodination revealed that ninefold greater 125I specific activity was associated with the membranes isolated on beads than with whole platelets. Enrichment in the bead membrane preparation of the activities of membrane marker enzymes, bis(p-nitrophenyl)phosphate phosphodiesterase and Na,K-ATPase, was 8.0 and 4.4, respectively. Contamination with enzymes of other organelles, cytochrome oxidase and beta-glucuronidase, was relatively low as compared with membranes isolated by sucrose gradient centrifugation. Analysis by SDS polyacrylamide gel electrophoresis showed that a full complement of surface glycoproteins was present on the membranes isolated with polylysine beads. The polylysine bead technique is a rapid, reproducible and efficient method for the preparation of relatively pure platelet plasma membranes.

Blood Platelets↗
PubMed1978

Interaction of platelet membrane receptors with von Willebrand factor, ristocetin, and the Fc region of immunoglobulin G.

The agglutination of human platelets by ristocetin and von Willebrand factor was inhibited by aggregated immunoglobulin (Ig)G and by Fc fragments of IgG, but not by Fab, F(ab')(2) or pFc fragments of IgG. Because this inhibition occurred with formalin-fixed platelets as well as with normal platelets, a generalized aggregation of fluid membrane components by Fc fragments was not responsible for this inhibition of ristocetin and von Willebrand factor-induced agglutination. Reciprocal inhibition of platelet Fc receptors was produced by prior incubation of platelets with von Willebrand factor and ristocetin. Sucrose density gradient ultracentrifugation studies demonstrated that aggregated IgG did not form fluid-phase complexes with von Willebrand factor and ristocetin. Furthermore, passage of von Willebrand factor and ristocetin through a column of immobilized heat-aggregated IgG did not alter platelet agglutinating activity which indicates that aggregated IgG did not inactivate von Willebrand factor or ristocetin. Thus, it was likely that the IgG-mediated interference with platelet agglutination by ristocetin and von Willebrand factor did not occur in the fluid phase but at the platelet surface. These studies suggest that the platelet membrane Fc receptor may be either a part of, or sterically related to, the membrane glycoprotein I complex that interacts with von Willebrand factor, and that occupation of one of these surface components blocks the availability of the other.

Blood Coagulation Factors↗
PubMed1977

Myosin in cultured human endothelial cells.

Myosin was isolated from cultured human endothelial cells by extraction with 0.6 M KCl and chromatography on Sepharose 4B. The extracted endothelial cell protein was identified as myosin by the characteristic ATPase profile, that is, the ATPase was activated by Ca2 + and EDTA and inhibited by Mg2 +. On sodium dodecyl sulphate polyacrylamide gel electrophoresis, the endothelial cell myosin heavy chain migrated with a molecular weight of 200 000 as did rabbit uterine and human platelet myosin heavy chains. A crude preparation of the endothelial cell myosin reacted immunologically with an antiserum to platelet myosin, a smooth muscle type of myosin. In indirect immunofluorescence studies, antiserum to the purified endothelial cell myosin stained cultured endothelial cells in a fibrillar pattern. The fibrillar pattern was more intense when the endothelial cells were stained with antiserum to platelet myosin. The presence of myosin in the endothelial cell provides a basis for the contractility of these cells. This contractile property may plan an important role in the physiologic function of these cells.

Adenosine Triphosphatases↗
PubMed1977

Immunoinhibition of ristocetin-induced platelet aggregation.

Human platelets washed and fixed in paraformaldehyde aggregate in the presence of the antibiotic ristocetin and normal plasma. This aggregation response is abolished after digestion of the fixed platelets with chymotrypsin. Antisera to fixed washed platelets were produced in rabbits and absorbed with chymotrypsin-treated, fixed washed platelets. Monovalent Fab fragments obtained from the isolated gamma-globulin fractions of the antisera blocked ristocetin-induced aggregation of fixed washed platelets in buffer and normal platelets in platelet-rich plasma. By double-antibody immunoprecipitation, it was shown that the antibody which blocked the ristocetin reaction interacted with a platelet membrane surface protein of mol wt 155,000. The results suggest that the glycoprotein I complex on the surface of the human platelet mediates ristocetin-induced von Willebrand factor-dependent platelet aggregation.

Antibodies↗
PubMed1976

Platelet alpha2-macroglobulin and alpha1-antitrypsin.

Subcellular membrane and granule fractions derived from human platelets contain immunologically identifiable alpha2-macroglobulin and alpha1-antitrypsin. These platelet-derived inhibitors show a reaction of immunologic identity when compared to alpha2-macroglobulin and alpha1-antitrypsin purified from human plasma. Further, the platelet protease inhibitors possessed a similar subunit polypeptide chain structure to their plasma counterparts as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis. Studies of the binding of radiolabeled trypsin to the various solubilized platelet subcellular fractions suggest that the granule-associated alpha2-macroglobulin and alpha1-antitrypsin, as well as membrane-associated alpha2-macroglobulin were functionally active. Quantitatively, circulating platelets contain relatively small concentrations of these inhibitors as compared to platelet-associated fibrinogen and factor VIIIAGN. Platelet protease inhibitors may modulate the protease-mediated events involved in the formation of hemostatic plugs and thrombi.

Blood Platelets↗
PubMed1976

The platelet-endothelial cell--VIII axis.

Cultured human endothelial cells synthesize and secrete a protein(s) which has factor VIII antigen and von Willebrand factor activity. Subcellular membrane and granule fractions derived from human platelets also contain the factor VIII antigen and von Willebrand factor activity. Circulating platelets constitute a significant reservoir of VIII antigen containing approximately 15% of the amount present in platelet poor plasma. Thus normal platelets contain surface bound as well as intracellularly stored von Willebrand factor, a protein synthesized by endothelial cells which is required for normal platelet function.

Antigens↗
PubMed1976

A clinical study of the lupus anticoagulant.

Eighty-three patients with circulating anticoagulants were studied at The New York Hospital. The lupus-type anticoagulant, an inhibitor of the prothrombin activator complex, was demonstrated in 58 patients. The inhibitor was identified using the blood and tissue thromboplastin inhibition tests. Inhibition by the lupus anticoagulant was augmented in 67% of these patients by a cofactor present in normal plasma. The lupus inhibitor was detected primarily because of an unsuspected abnormal coagulation test. One-half of the patients with the lupus-type anticoagulant did not have systemic lupus erythematosus.

Anticoagulants↗
PubMed1975

Ultrastructural lesions on the surface of platelets associated with either blood coagulation or with antibody-mediated immune injury.

During blood coagulation ultrastructural lesions were produced on the platelet membrane. They were dependent on the presence of both thrombin and complement (C) and were morphologically identical to the C-dependent ultrastructural lesions (type II) seen in red cells subsequent to activation of C by the alternate mechanismmthough similar in shape they differed in size from ultrastructural lesions (type I) PRODUCED BY ACTIVATION OF C via the classic mechanismmlesions of type I were seen on the platelet surface subsequent to antibody-dependent activation of the C system.

Aluminum Hydroxide↗
PubMed1975

Subcellular platelet factor VIII antigen and von Willebrand factor.

Subcellular membrane and granule fractions derived from human platelets contain factor VIIII antigen and von Willebrand factor activity but not factor VII procoagulant activity. Circulating platelets constitute a significant reservoir of plasma factor VIII antigen, containing approximately 15% of the amount of factor VIII antigen present in platelet-poor plasma. The antibiotic ristocetin, which aggregates human platelets in the presence of von Willebrand factor, nonspecifically precipitates platelet membrane factor VIII antigen. Thus normal platelets contain surface-bound as well as internally stored von Willebrand factor, a protein synthesized by endothelial cells which is necessary for normal platelet function in vivo.

Absorption↗