Relationship between cAMP and Ca2+ fluxes in human platelet membranes.
The effect of cAMP (which involved a 23 kDa protein phosphorylation) has been studied on the Ca2+ uptake and Ca2+ release from a human platelet membrane vesicle fraction. It was tested in the presence of the catalytic subunit of the cAMP-dependent protein kinase (C Sub). The addition of C Sub increased the steady state level of the Ca2+ uptake into the membrane vesicles. The effect was enhanced when tested in the absence of Ca2+ precipitating agent. The response was proportional to the dose of C Sub. Moreover, the effect varied with the Ca2+ concentration. The effect of C Sub has been tested on the inositol 1,4,5-trisphosphate (IP3)-induced Ca2+ release. A phosphorylated state of the 23 kDa protein appeared to be necessary. Indeed, a phosphorylation inhibition prevented the IP3 effect and the addition of C Sub increased the percentage of released Ca2+ (without modification of the time course). However, the C Sub dose-dependent response was not linear. The effect of cAMP on the two functions (Ca2+ uptake and Ca2+ release) appears to be different. Therefore, these results led us to suggest a more complex role of cAMP in the regulation of platelet Ca2+ concentration.
Enouf
J
J
Unité de Recherches sur la Thrombose expérimentale et l'Hémostase, INSERM U150, CNRS UA334, Hôpital Lariboisière, Paris, France.
Bredoux
R
R
Bourdeau
N
N
Giraud
F
F
Le Peuch
C
C
Lebret
M
M
Levy-Toledano
S
S
D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000097:blood*; D002384:Catalysis; D002462:Cell Membrane / Q000378:metabolism; D000242:Cyclic AMP / Q000097:blood* / Q000502:physiology; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000494:pharmacology; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism
D007295:Inositol Phosphates; D015544:Inositol 1,4,5-Trisphosphate; D000242:Cyclic AMP; D011494:Protein Kinases; D002118:Calcium