Unique Pathway of Thrombin-induced Platelet Aggregation Mediated by Glycoprotein Ib

Thrombin plays a central role in normal and abnormal hemostatic processes. It is assumed that alpha-thrombin activates platelets by hydrolyzing the protease-activated receptor (PAR)-1, thereby exposing a new N-terminal sequence, a tethered ligand, which initiates a cascade of molecular reactions leading to thrombus formation. This process involves cross-linking of adjacent platelets mediated by the interaction of activated glycoprotein (GP) IIb/IIIa with distinct amino acid sequences, LGGAKQAGDV and/or RGD, at each end of dimeric fibrinogen molecules. We demonstrate here the existence of a second alpha-thrombin-induced platelet-activating pathway, dependent on GP Ib, which does not require hydrolysis of a substrate receptor, utilizes polymerizing fibrin instead of fibrinogen, and can be inhibited by the Fab fragment of the monoclonal antibody LJIb-10 bound to the GP Ib thrombin-binding site or by the cobra venom metalloproteinase, mocarhagin, that hydrolyzes the extracellular portion of GP Ib. This alternative alpha-thrombin pathway is observed when PAR-1 or GP IIb/IIIa is inhibited. The recognition sites involved in the cross-linking of polymerizing fibrin and surface integrins via the GP Ib pathway are different from those associated with fibrinogen. This pathway is insensitive to RGDS and anti-GP IIb/IIIa antibodies but reactive with a mutant fibrinogen, gamma407, with a deletion of the gamma-chain sequence, AGDV. The reaction is not due to simple trapping of platelets by the fibrin clot, since ligand binding, signal transduction, and second messenger formation are required. The GP Ib pathway is accompanied by mobilization of internal calcium and the platelet release reaction. This latter aspect is not observed with ristocetin-induced GP Ib-von Willebrand factor agglutination nor with GP Ib-von Willebrand factor-polymerizing fibrin trapping of platelets. Human platelets also respond to gamma-thrombin, an autoproteolytic product of alpha-thrombin, through PAR-4. Co-activation of the GP Ib, PAR-1, and PAR-4 pathways elicit synergistic responses. The presence of the GP Ib pathway may explain why anti-alpha-thrombin/anti-platelet regimens fail to completely abrogate thrombosis/restenosis in the cardiac patient

Surface wax in <I>Dinckleria, Lejeunea</I> and <I>Mytilopsis</I> (Jungermanniidae)

A scanning electron microscope study of leafy liverworts revealed the presence of surface wax in Lejeunea flava (Lejeuneaceae), Mytilopsis albifrons (Lepidoziaceae), Dinckleria pleurata and D. fruticella (Plagiochilaceae).</p

Studies on Neotropical Lejeuneaceae (Jungermanniopsida). New synonyms and Ceratolejeunea temnantha (Spruce) comb. nov.

Based on the study of type material of Neotropical Lejeuneaceae, the following new combination and synonyms are proposed: Ceratolejeunea temnantha (Spruce) comb. nov. (basionym: Lejeunea temnantha), Lejeunea huctumalcensis Lindenb. et Gottsche (= Hygrolejeunea grossereticulata Gottsche ex Steph., = H. sacculata Steph., = H. wrightii Steph.), Lepidolejeunea involuta (Gottsche) Grolle (= Hygrolejeunea glaziovii Steph.), Mastigolejeunea plicatiflora (Spruce) Steph. (= Lejeunea plicata Spruce). Ceratolejeunea temnantha is described and illustrated.</p

Some additions to the Bryophyte Flora of Guadeloupe, West Indies, and new synonyms in the genera &lt;I&gt;Diplasiolejeunea&lt;/I&gt; and &lt;I&gt;Lejeunea&lt;/I&gt; (Lejeuneaceae)

31 Moose, 29 Leber- und zwei Laubmoose, werden erstmals für Guadeloupe nachgewiesen, darunter fünf neue Lebermoosgattungen: Fossombronia, Heteroscyphus, Kymatocalyx, Monodactylopsis und Zoopsidella. Folgende neue Synonyme werden in den Gattungen Diplasiolejeunea und Lejeunea vorgeschlagen: Diplasiolejeunea matoubae und D. zacatepecensis sind Synonyme von D. cavifolia; D. malleiformis subsp. balnearia, subsp. bernardii, sowie subsp. elongata werden als synonym mit D. pellucida var. malleiformis betrachtet, und D. cubensis, D. lanciloba als auch D. rudolphiana var. inflata gehören zu D. brunnea. Des weiteren werden Lejeunea filipes als Synonym von L. aphanes und L. elliottii als solches von L. sporadica erachtet.31 bryophytes, 29 hepatics and two mosses, are newly reported for Guadeloupe, among these five new generic records of hepatics: Fossombronia, Heteroscyphus, Kymatocalyx, Monodactylopsis, and Zoopsidella. The following new synonyms in the genera Diplasiolejeunea and Lejeunea are proposed: Diplasiolejeunea matoubae and D. zacatepe-censis are synonymous with D. cavifolia; D. malleiformis subsp. balnearia, subsp. bernardii, and subsp. elongata are synonymized with D. pellucida var. malleiformis, and D. cubensis, D. lanciloba as well as D. rudolphiana var. inflata are considered to belong to D. brunnea. Furtheron, Lejeunea filipes is a synonym of L. aphanes, and L. elliottii is synonymous with L. sporadica.</p

About the first record of the genus &lt;I&gt;Chonecolea&lt;/I&gt; Chonecoleaceae, Marchantiophyta) in Paraguay and its differences to related species

Chonecolea doellingeri (Nees) Grolle, whose South American record is restricted to Argentina and Brazil, is reported for the first time for Paraguay. Additionally, its differences to related species are discussed and SEM microphotographs are provided.</p

&lt;I&gt;Lejeunea adpressa&lt;/I&gt; Nees (Lejeuneaceae), a widely distributed species of tropical America

Lejeunea adpressa Nees has ovate and entire-margined leaves, bifid underleaves and 5-keeled perianths, among other typical Lejeunea features. The high variability of the species is demonstrated by the numerous synonyms proposed here, including Lejeunea magnoliae Lindenb. &amp; Gottsche, seven species and one var. of "Lejeunea subg. Eulejeunea" described by Spruce, Eulejeunea setistipa Steph., Lejeunea longifissa Steph. and "L. caespitosa sensu Schuster 1980". Four names are lectotypified. The species is described, illustrated and its geographical distribution in tropical America is documented.</p

&lt;I&gt;Taxilejeunea pulverulenta&lt;/I&gt; (Lejeuneaceae, Jungermanniopsida), a poorly known species from the Neotropics, is transferred to &lt;I&gt;Lejeunea&lt;/I&gt;

Lejeunea pulverulenta comb. nov. (basionym Taxilejeunea pulverulenta), a species known from Guadeloupe, Ecuador and Mount Roraima, Guyana is described and illustrated. The species is characterized by its yellowish-green and dull colour in the herbarium, cells with trigones, intermediate thickenings and strongly papillose and waterrepellent surface, small inflated lobules, imbricate and large underleaves with auriculate bases, gynoecia terminal on short branches with again fertile innovations, up to three gynoecia in a row.A comparison of Lejeunea pulverulenta with the morphologically closely related L. cerina and L. controversa is provided. Characteristics of the genus Taxilejeunea are briefly discussed. A lectotype for Taxilejeunea pulverulenta is designated.Lejeunea pulverulenta comb. nov. (basionym Taxilejeunea pulverulenta), a species known from Guadeloupe, Ecuador and Mount Roraima, Guyana is described and illustrated. The species is characterized by its yellowish-green and dull colour in the herbarium, cells with trigones, intermediate thickenings and strongly papillose and waterrepellent surface, small inflated lobules, imbricate and large underleaves with auriculate bases, gynoecia terminal on short branches with again fertile innovations, up to three gynoecia in a row.A comparison of Lejeunea pulverulenta with the morphologically closely related L. cerina and L. controversa is provided. Characteristics of the genus Taxilejeunea are briefly discussed. A lectotype for Taxilejeunea pulverulenta is designated.</p