RT Journal Article
SR Electronic
T1 Mechanism of inositol 1,4,5-trisphosphate-induced aggregation in saponin-permeabilized platelets.
JF Journal of Pharmacology and Experimental Therapeutics
JO J Pharmacol Exp Ther
FD American Society for Pharmacology and Experimental Therapeutics
SP 947
OP 955
VO 260
IS 3
A1 I Knezevic
A1 J P Dieter
A1 G C Le Breton
YR 1992
UL http://jpet.aspetjournals.org/content/260/3/947.abstract
AB The present study investigated the relationship between inositol 1,4,5-trisphosphate (IP3), thromboxane (TX)A2 and ADP in IP3-induced activation of saponin-permeabilized platelets. The time course of the different responses indicated that IP3-induced Ca++ mobilization and TXA2 production preceded both aggregation and secretion. Furthermore, platelet aggregation occurred coincident with secretion. In contrast, U46619- [15(S)-hydroxy-11,9-epoxymethano-prosta-5Z,13E-dienoic acid] and A23187-induced aggregation was commensurate with Ca++ mobilization, and preceded the secretion response. Indomethacin and SQ29,548 ([1S-[1 alpha,2 beta(5Z),3 beta,4 alpha]]-7-[3-[[2-[(phenylamino)carbonyl]hydrazino]methyl]- 7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid) inhibited IP3-mediated aggregation by 100%, Ca++ mobilization by 80% and secretion by 90%. A23187 exhibited a different inhibition profile, in that only secretion was blocked (65%). U46619-induced responses were completely inhibited by SQ29,548 and unaffected by indomethacin. Pretreatment of the platelets with creatine phosphate/creatine phosphokinase (CP/CPK), which removes secreted ADP, produced 100% inhibition of IP3-induced aggregation, 90% inhibition of Ca++ mobilization and 72% inhibition of secretion. On the other hand, CP/CPK was ineffective in blocking any of the A23187-induced responses. Concerning U46619, CP/CPK produced a 30% attenuation of maximal aggregation and 78% inhibition of both Ca++ mobilization and secretion. These results in saponin-permeabilized platelets demonstrate that IP3-induced aggregation is a secretion-mediated process which requires both TXA2 and secreted ADP. Taken together, the findings suggest that IP3 is not capable of directly causing platelet aggregation, but may function in platelets to amplify an initial agonist response through TXA2 production and secretion.