|
|
 Previous Article | Table of Contents | Next Article 
Affinity modulation of the platelet integrin alpha IIb beta 3 by alpha-
chymotrypsin: a possible role for Na+/Ca2+ exchanger
M Shiraga, Y Tomiyama, S Honda, H Kashiwagi, S Kosugi, M Handa, Y Ikeda, Y Kanakura, Y Kurata and Y Matsuzawa
Second Department of Internal Medicine, Osaka University Medical School,
Japan.
In the present study, we have investigated the mechanism of affinity
modulation of alpha IIb beta 3 by chymotrypsin. We first confirmed that
alpha-chymotrypsin could activate alpha IIb beta 3 (approximately 7,000
molecules per platelet) without major intracellular signaling. However, we
unexpectedly found that high concentrations of amiloride dose- dependently
inhibited 125I-fibrinogen binding to the chymotrypsin- treated platelets,
as well as the platelet aggregation (IC50 [50% inhibitory concentration]
for fibrinogen binding, 530 mumol/L). In contrast, amiloride did not
inhibit alpha IIb beta 3 activation induced by anti-alpha IIb beta 3
monoclonal antibody PT25-2 or AP5. To identify the pathway involved, the
effects of alteration of Na+ gradient in platelets were examined. Lowering
Na+ gradient by replacing extracellular Na+ with tetramethylammonium (TMA)
increased the number of activated alpha IIb beta 3 by twofold, as assessed
by fibrinogen- binding assay. The incubation of platelets with ouabain, a
Na+/K(+)- adenosine triphosphatase (ATPase) inhibitor, further augmented
alpha IIb beta 3 activation. These data suggested that a likely candidate
for the pathway was Na+/Ca2+ exchanger. At 140 mmol/L [Na+]o, 45Ca2+ influx
to the chymotrypsin-treated platelets was twofold greater than that to
non-treated platelets. Replacement of Na+ with TMA further increased the
Ca2+ influx, and the increase was inhibited by amiloride dose- dependently.
3',4'-Dichlorobenzamil (DCB) and bepridil, relatively specific inhibitors
of Na+/Ca2+ exchanger, also inhibited the chymotrypsin-induced alpha IIb
beta 3 activation, and the IC50 values of these inhibitors for fibrinogen
binding were 25 mumol/L and 52 mumol/L, respectively. Moreover, platelet
aggregation induced by various physiologic agonists was inhibited by DCB or
bepridil, while platelet agglutination by ristocetin was not. Our data
newly suggest that Na+/Ca2+ exchanger operating in reverse mode may be
directly involved in inside-out signaling that activates alpha IIb beta 3.
Volume 88,
Issue 7,
pp. 2594-2602,
10/01/1996
Copyright © 1996 by The American Society of Hematology
 CiteULike  Connotea  Del.icio.us  Digg  Reddit  Technorati What's this?
This article has been cited by other articles:
|
|
|
|
 
H. Yoshida, Y. Tomiyama, J. Ishikawa, K. Oritani, I. Matsumura, M. Shiraga, T. Yokota, Y. Okajima, M. Ogawa, J.-i. Miyagawa, et al.
Integrin-associated protein/CD47 regulates motile activity in human B-cell lines through CDC42
Blood,
July 1, 2000;
96(1):
234 - 241.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
P. Calabresi, G. A. Marfia, S. Amoroso, A. Pisani, G. Bernardi, and P. D. Hurn
Pharmacological Inhibition of the Na+/Ca2+ Exchanger Enhances Depolarizations Induced by Oxygen/Glucose Deprivation but Not Responses to Excitatory Amino Acids in Rat Striatal Neurons • Editorial Comment
Stroke,
August 1, 1999;
30(8):
1687 - 1694.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Honda, Y. Tomiyama, T. Aoki, M. Shiraga, Y. Kurata, J. Seki, and Y. Matsuzawa
Association Between Ligand-Induced Conformational Changes of Integrin alpha IIbbeta 3 and alpha IIbbeta 3-Mediated Intracellular Ca2+ Signaling
Blood,
November 15, 1998;
92(10):
3675 - 3683.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Shiraga, Y. Tomiyama, S. Honda, H. Suzuki, S. Kosugi, S. Tadokoro, Y. Kanakura, K. Tanoue, Y. Kurata, and Y. Matsuzawa
Involvement of Na+/Ca2+ Exchanger in Inside-Out Signaling Through the Platelet Integrin alpha IIbbeta 3
Blood,
November 15, 1998;
92(10):
3710 - 3720.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. J. Shattil, H. Kashiwagi, and N. Pampori
Integrin Signaling: The Platelet Paradigm
Blood,
April 15, 1998;
91(8):
2645 - 2657.
[Full Text]
[PDF]
|
|
|
|
|
