[Intracellular Ca2+ behavior and activation of calpain-I in activated platelets].
A relationship between intracellular Ca2+ concentration ([Ca2+]i) and calpain-I activation and change in subcellular localization of the enzyme in activated platelets were investigated. The [Ca2+]i exhibited a biphasic response after stimulation with thrombin. Activation of calpain-I was measured by determination of the appearance of active 76 and 78 kDa forms accompanying the disappearance of the 80 kDa form, the inactive form, on immunoblots. Calpain-I was activated dependent on the extent of the initial elevation of [Ca2+]i. For maximum activation (60%) 300-500 nM [Ca2+]i was required and half-maximal activation occurred at 160-220 nM [Ca2+]i. The active 76 kDa form was observed only in the fraction containing subcellular organelles and plasma membrane of activated platelets. It was demonstrated that the localization of calpain-I was changed from the cytosol to the membrane and calpain-I was activated on the membrane by Ca2+, elevated through the initial elevation after activation of platelets.
Ishii
H
H
Department of Clinical Biochemistry, Faculty of Pharmaceutical Sciences, Teikyo University.
Suzuki
Y
Y
Kuboki
M
M
Kazama
M
M
D002118:Calcium / Q000097:blood*; D002154:Calpain / Q000097:blood*; D006801:Humans; D015539:Platelet Activation / Q000187:drug effects; D013917:Thrombin / Q000494:pharmacology
D013917:Thrombin; D002154:Calpain; D002118:Calcium