Enhancement of ADP-induced aggregation by 5-HT in rabbit platelets.
OBJECTIVE
To study the enhanced effects of 5-hydroxytryptamine (5-HT) on ADP-induced aggregation.


METHODS
Platelet aggregation was quantified by the light transmission, the cytosolic-free calcium ([Ca2+]i) was measured by digital fluorescent microscopy, and inositol 1,4,5-triphosphate (IP3) was determined by receptor binding assay.


RESULTS
In rabbit platelet-rich plasma (PRP), 5-HT 0.03-3 mumol.L-1 induced a decrease in light transmission (DLT) in a concentration-dependent manner with centralization of granules, as revealed by electron microscopy. The DLT was accompanied with neither platelet aggregation nor a release reaction. In single washed platelets loaded with Fura-2, 5-HT caused a concentration-dependent elevation of [Ca2+]i, and IP3 level was also transiently increased in washed platelets at 15 s after stimulation by 5-HT. Adenosine diphosphate (ADP) also caused DLT transiently in PRP before its own aggregation without a release reaction. Pretreatment of PRP or washed platelets with 5-HT, the DLT by ADP was reduced concentration-dependently and ADP-induced aggregation and [Ca2+]i mobilization were enhanced.


CONCLUSIONS
The enhancement of ADP-induced aggregation was attributed to the superimposition of the calcium release from the storage sites and calcium influx induced by ADP over the calcium release from the storage sites by 5-HT.
Li
B Y
BY
Department of Neurology, First City Hospital, Harbin, China. baiyanli@ihy.co.cn
Bai
Y
Y
Li
W H
WH
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D001792:Blood Platelets / Q000378:metabolism / Q000648:ultrastructure; D002118:Calcium / Q000097:blood*; D015544:Inositol 1,4,5-Trisphosphate / Q000097:blood; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D011817:Rabbits; D012701:Serotonin / Q000494:pharmacology*
D010975:Platelet Aggregation Inhibitors; D012701:Serotonin; D000244:Adenosine Diphosphate; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium