Submitted January 6, 2006
Accepted May 14, 2006
Reversible inhibition of the platelet procoagulant
response through manipulation of the Gardos channel
Jef L Wolfs, Simone J Wielders, Paul Comfurius, Theo Lindhout, John C Giddings, Robert F Zwaal, and Edouard M Bevers*
Dept Biochem, Cardiovascular Research Institute Maastricht, Maastricht University, the Netherlands
Department of Hematology, Welsh National School of Medicine, Heath Park, Cardiff, UK
* Corresponding author; email: em.bevers{at}bioch.unimaas.nl.
The platelet procoagulant response requires a sustained
elevation of the intracellular Ca2+
concentration, [Ca2+]i, causing
exposure of phosphatidylserine (PS) at the outer surface
of the plasma membrane. An increased [Ca2+]
i also activates Ca2+-dependent
K+ channels. Here, we investigated the
contribution of the efflux of K+ ions on the
platelet procoagulant response in collagen-thrombin
activated platelets using selective K+
channel blockers. The Gardos channel blockers
clotrimazol, charybdotoxin and quinine caused a similar
decrease in prothrombinase activity as well as in the
number of PS-exposing platelets detected by fluorescence-
conjugated annexin A5. Apamin and iberiotoxin,
inhibitors of other K+ channels, were without
effect. Only clotrimazol showed a significant inhibition
of the collagen plus thrombin-induced intracellular
calcium response. Clotrimazol and charybdotoxin did not
inhibit aggregation and release under the conditions
used. Inhibition by Gardos channel blockers was reversed
by valinomycin, a selective K+ ionophore. The
impaired procoagulant response of platelets from a
patient with Scott syndrome was partially restored by
pretreatment with valinomycin, suggesting a possible
defect of the Gardos channel in this syndrome.
Collectively, these results provide evidence for the
involvement of efflux of K+ ions through
Ca2+-activated K+ channels in the
procoagulant response of platelets, opening potential
strategies for therapeutic interventions.
