Ca2+ ionophores and the activation of human blood platelets. The effects of ionomycin, beauvericin, lysocellin, virginiamycin S, lasalocid-derivatives and McN 4308.

Platelet activation is linked to an increase in the cytoplasmic Ca2+ concentration and consequently can also be induced by ionophores which mobilize Ca2+ from intracellular storage sites or transport it through the plasma membrane. The ionophores mostly used in studies on platelet activation are A 23187 and lasalocid (X-537A). The effects of eight compounds with known Ca2+-ionophoric activity in synthetic or natural membrane systems were studied in order to investigate the relationship between transport Ca2+ and activation of platelets. Inomycin acts as a true Ca2+ ionophore: it elicits rapid shape change, aggregation, the release reaction (secretion) and clot retraction (contraction). Beauvericin activates platelets too, but probably not by increasing the cytoplasmic Ca2+ concentration. Lysocellin does not activate platelets but induces a passive loss of serotonin.