Micropipette aspiration of guinea pig megakaryocytes: absence of fragmentation and dependence on maturation stage

Article Abstract:

The production of platelets, small fragments of very large bone marrow cells called megakaryocytes, is vital for blood clotting. The process of platelet production has never been clearly defined. While some hold that the process requires a megakaryocyte to differentiate into platelet 'territories' which fragment at a critical period, others hold that the platelets are released by fragmentation of cellular extensions or pseudopodia. A study was conducted to determine whether mechanical stress on the surface of megakaryocytes of guinea pigs can lead to platelet fragmentation. Even at the highest level of stress no segmentation was observed. The inability to produce segmentation mechanically suggests that the development of platelets is a late developmental feature that could not be induced in the relatively juvenile guinea pig megakaryocytes that formed the available pool of cells used in this experiment.

Research, Growth, Cell differentiation

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Demonstration of single chain urokinase-type plasminogen activator on human platelet membrane

Article Abstract:

Platelets, or small, irregular cellular fragments that are involved in blood coagulation formation, are able to enhance fibrinolysis in laboratory tests. This breaking-down, or fibrinolytic activity, is attributed to the presence of a urinary type plasminogen activator. Biochemical testing of the membrane indicates that the urinary plasminogen actively observed in the broken platelets is associated with the outer protein layer of the cell membrane. Immunofluorescent staining has also showed the presence of urinary type plasminogen activity at this site in intact platelets. It is possible that the observation of clot degradation which is occasionally seen when clots are associated with high numbers of platelets could be related to this finding. Further studies may allow researchers to determine whether blocking urinary plasminogen activity would eliminate platelet dependent clot lysis.

Membrane proteins, Plasminogen activators, Fibrinolytic agents, Fibrinolysis

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High pp60c-src level in human platelet dense bodies

Article Abstract:

This biochemical study investigates the rate of biosynthesis of phosphorylated proteins which occurs normally, following stimulation with thrombin-activated human blood platelets. Thrombin is the enzyme which is responsible for converting a soluble protein into an insoluble clot. Thrombin stimulation caused a marked increase in the manufacture of proteins containing phosphotyrosine. Further experimentation allowed the identification of a relatively small protein, pp60c-src, which is similar to the protein associated with the induction of tumors in certain animals (the normal cellular homolog of the transforming protein of Rous sarcoma virus). The protein was found to be associated with specific subcellular granules (dense bodies), and is, perhaps, related to the initiation of platelet activity.

Analysis, Proteins, Thrombin, Oncogenes, Bioavailability

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