Differential regulation of platelet aggregation and aminophospholipid exposure by calpain.
Aggregation, exposure of procoagulant phospholipids and shedding of microparticles are platelet responses that depend on activating conditions. To determine how these different responses are interconnected, we simultaneously measured fibrinogen (Fg) binding and aminophospholipid exposure on activated platelets by means of flow cytometry. Low calcium ionophore (A23187) concentrations induced Fg binding but not annexin V binding. In contrast, high A23187 concentrations induced annexin V binding but not Fg binding. Collagen, both alone and in the presence of thrombin, induced both Fg and annexin V binding. Dual labelling was found on 38 +/- 9% of platelets stimulated by thrombin plus collagen. The regulatory role of calpain in these platelet functions was investigated. When calpain was partially inhibited by 2 microg/ml calpeptin, Fg binding still occurred but aminophospholipid exposure was limited. By contrast, complete inhibition of calpain by 100 microg/ml calpeptin or E64d decreased Fg binding but enhanced aminophospholipid exposure. In these latter conditions, cytosolic calcium-extruding systems were inhibited. The results suggest that (i) conditions that favour aminophospholipid exposure tend to decrease the aggregation process and (ii) calpain determines the switch to either aggregation or aminophospholipid exposure by controlling intracellular calcium.
Bachelot-Loza
Christilla
C
INSERM U765, Faculté des Sciences Pharmaceutiques et biologiques, Université Paris V, Paris, France. christilla.bachelot-loza@univ-paris5.fr
Badol
Perrine
P
Brohard-Bohn
Brigitte
B
Fraiz
Nuria
N
Cano
Ernesto
E
Rendu
Francine
F
D017304:Annexin A5 / Q000378:metabolism; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D000001:Calcimycin / Q000494:pharmacology; D002154:Calpain / Q000502:physiology*; D002478:Cells, Cultured; D003094:Collagen / Q000494:pharmacology; D005340:Fibrinogen / Q000378:metabolism; D005434:Flow Cytometry; D006801:Humans; D007476:Ionophores / Q000494:pharmacology; D049294:Phospholipid Transfer Proteins / Q000097:blood*; D015539:Platelet Activation / Q000187:drug effects / Q000502:physiology*; D010974:Platelet Aggregation / Q000187:drug effects / Q000502:physiology; D013917:Thrombin / Q000494:pharmacology
D017304:Annexin A5; D007476:Ionophores; D049294:Phospholipid Transfer Proteins; D000001:Calcimycin; D005340:Fibrinogen; D003094:Collagen; D013917:Thrombin; D002154:Calpain