Effects of MK-447 on thrombin-induced aggregation, secretion of ATP, and [Ca2+]i mobilization in rabbit platelets.
OBJECTIVE
To study the effects of MK-447 on aggregation release reaction and intracellular calcium mobilization by thrombin.


METHODS
Aggregation and release reaction were assessed by light transmission and ATP content in rabbit citrate platelet-rich plasma (PRP), and cytosolic-free calcium was measured by fluorescence and imaging.


RESULTS
MK-447 (2-aminomethyl-4-t-butyl-6-iodophenol hydrochloride) induced a decrease in light transmission (DLT), so called platelet shape change, without detectable aggregation and secretion of ATP, and increased intracellular calcium concentration ([Ca2+]i) slightly in washed single platelet loaded with Fura 2, the peak value being about 160 nmol.L-1. These effects were not inhibited by egtazic acid 3 mmol.L-1 or indometacin 3 mumol.L-1. The pretreatment of PRP with MK-447 700 mumol.L-1 reduced the DLT by thrombin, potentiated and enhanced thrombin-induced aggregation and secretion of ATP in a concentration-dependent manner. Thrombin-induced [Ca2+]i mobilization (peak value: 369 +/- 45 nmol.L-1) was further enhanced by the administration of MK-447 at 2 min before the addition of thrombin, and the peak value reached 623 +/- 121 nmol.L-1 (P < 0.01).


CONCLUSIONS
MK-447-induced platelet shape change was involved in intracellular calcium release in this preparation. MK-447 enhanced thrombin-induced aggregation and release reaction and these effects of MK-447 on aggregation and release reaction by thrombin might result from the synergistic effect of intracellular calcium mobilization.
Li
B Y
BY
Department of Pharmacology, School of Medicine Kitasato University, Kanagawa, Japan.
Bai
Y
Y
Li
G Z
GZ
Li
W H
WH
Katori
M
M
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology*; D001792:Blood Platelets / Q000378:metabolism; D002084:Butylated Hydroxytoluene / Q000031:analogs & derivatives* / Q000494:pharmacology; D002118:Calcium / Q000097:blood*; D010974:Platelet Aggregation / Q000187:drug effects*; D011817:Rabbits; D013917:Thrombin / Q000494:pharmacology
D000894:Anti-Inflammatory Agents, Non-Steroidal; D002084:Butylated Hydroxytoluene; C013753:2-aminomethyl-4-t-butyl-6-iodophenol; D000255:Adenosine Triphosphate; D013917:Thrombin; D002118:Calcium