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The staphylococcal bi-component leukotoxins constitute a family included in the super-family of the beta-sheet-structured pore-forming toxins. They may be produced by Staphylococcus aureus and by Staphylococcus intermedius and their target cells vary according to the molecules. The mode of action proceeds by the sequential binding of the class S proteins, then by that of the class F proteins at the surface of the membranes. Then, the activation of cellular calcium-channels precedes the pore formation which seems to be sensitive to several monovalent cations. The cell response is inflammatory and includes the neosynthesis as well as the secretion of leukotriene B4, interleukin -8, histamine. The injection of leukotoxins to rabbits generates cell chemotaxis , vasodilatation, and tissue necrosis. The association of the production of leukotoxins with clinical syndromes concerns several aspects of the pathology of S. aureus, and confers to these leukotoxins an important role of virulence factors.

The reproducibility of the limulus amoebocyte lysate (LAL) test with the use of a chromogenic substrate was evaluated in the presence of 5 bacterial endotoxins (2 from Escherichia coli, 1 from Salmonella, 1 from Serratia marcescens and 1 from Vibrio cholerae) and the FDA reference endotoxin EC5. Endotoxins from E. coli 055B5, S. marcescens and V. cholerae were significantly more active than the reference endotoxin (p less than 0.01). Addition of Mg2+ activated the LAL chromogenic reaction (optimum = 160 mmol/l added), whereas Ca2+ in concentrations above 5 mmol/l inhibited the reaction. As little as 0.3 mmol/l Zn2+ strongly inhibited the reaction. Inhibition by Zn2+ was partly suppressed by addition of 160 mmol/l Mg2+. These divalent cations modified the LAL chromogenic reaction when added in the first step of the reaction (incubation with endotoxin and LAL reagent). The LAL chromogenic reaction was not modified by divalent cations when these were added in the second step of the reaction (with the chromogenic substrate).

Electrical and mechanical activities of frog skeletal muscle fibres were simultaneously investigated under conditions which allow the development of a strontium permeability. It was shown that the contraction elicited by a long lasting Sr response depends upon two mechanisms: a potential dependent one, and a mechanism which is related to the entry of Sr ions into the cell through the tubular membrane.