Differential structural requirements for fibrinogen binding to platelets and to endothelial cells.

The cytoadhesins represent a group of RGD receptors that belongs to the integrin superfamily of adhesion molecules. Members of this cytoadhesin family include the platelet GPIIb-IIIa and the vitronectin receptors. These glycoproteins share the same beta-subunit, which is associated with different alpha subunits to form an alpha/beta heterodimer. In the present study, we have analyzed the fine recognition specificy of the cytoadhesins from platelets and endothelial cells for the adhesive protein, fibrinogen. Two sets of synthetic peptides, RGDX peptides and peptides corresponding to the COOH terminus of the fibrinogen gamma chain, were compared for their structure-function relationships in the two cellular systems. The results indicate that: (a) both RGDX and gamma-chain peptides inhibit the binding of fibrinogen to platelets and endothelial cells; (b) a marked influence of the residue at the COOH- and NH2-terminal positions of each peptide set can be demonstrated on the two types; and (c) RGDX and gamma peptides have differential effects on platelets and endothelial cells with respect to fine structural requirements. These results clearly indicate that while the platelet and endothelial cytoadhesins may interact with similar peptidic sequences, they express a different fine structural recognition.

[Society, medicine and caregiver stress]. / Société, médecine et souffrance des soignants.

CARING STAFF DISTRESS: Is a theme regularly discussed among those who care for patients. The current approach is in favor of the psychological interpretation of this distress. This approach is obviously pertinent, but could be widened to a more sociological vision: is the demand that society places on medicine excessive? THE SEARCH FOR AUTONOMY: The demand of the society emerges in a social universe that privileges the autonomy of the individual. Medicine serves this research for autonomy. Techniques, instrumentalization of the body, and the search for mastery engender the collective utopia of the perfect body; medicine has become a new faith, keeper of potential redemption measures. THE MEDIATOR FUNCTION OF CARING STAFF: Part of the caring staff distress is generated by the encounter between the utopia of health and the reality of suffering patients. In the present context of our society, one of the caring staff's missions is to act as mediator between the patient and the experience of the disease, the patient and the representation that he/she has of his/her body and health, and society and the expectations society projects on medicine.

An in vitro model giving access to adhesion plaques.

A new approach was investigated to study the interaction between integrins and actin via intracytoplasmic proteins. Because intracellular processes are hampered by the limiting plasma membrane, we developed an in vitro model with cells perforated by a bacterial toxin, streptolysin O. The specific conditions for the use of permeabilized cells to study the intramolecular associations occurring at adhesion plaques are described. The two cell types used, HUVEC and CHO, showed that the choice of the perforation method is of great importance. After perforation of cells in a monolayer, 75 +/- 10% of the cells remained adherent to a fibronectin substrate; after perforation of cells in suspension, only 25 +/- 10% of the cells readhered. Specific conditions were required however to maintain these adhesive properties up to 4 h: the presence of 1 mM Mg++ in the medium was crucial, and it was necessary to layer the cells on a specific coat rather than a substitute such as gelatin. Immunofluorescence investigations of actin, talin and vinculin, and Normarsky differential interference contrast microscopy showed retention of focal adhesion plaques in perforated cells. Moreover, in perforated cells antibodies directed against actin led to actin disorganization, showing that our model of perforated cells in a monolayer can give new insight to adhesion study.

Semi-intact CHO and endothelial cells: a tool to probe the control of integrin activity?

An in vitro assay has been developed using semi-intact cells, made with the bacterial toxin streptolysin O, in order to measure integrin activity in relation to the cytosol environment. In this assay, the cytosolic content can easily be modified while the receptor binding activity is measured by monitoring the interaction of specific radiolabeled substrates with the cell surface. Using two different cell types, i.e., wild-type Chinese hamster ovary cells and human endothelial cells in culture, it has been shown that the binding activities of the fibronectin and fibrinogen receptors become cytosol-dependent on perforated cells. Furthermore, this control depends on micromolar concentrations of intracellular calcium, suggesting that calcium or calcium binding protein(s) may play a key role in controlling integrin activity.