[The regulatory mechanism of free Ca2+ concentration in activated platelets].
The change in intracellular Ca2+ concentration ([Ca2+]i) following platelet stimulation results from mobilization, influx and restoration of Ca2+. To determine whether inositol 1,4,5 trisphosphate (IP3) is involved in Ca2+ influx, the relationship between IP3 formation (IP3) and Ca2+ influx ( delta [Ca2+]i) was investigated in platelets stimulated wtih various agonists (thrombin, ADP, PAF, STA2, etc). The ratio of IP3 to delta [Ca2+]i varied among the agonists, although delta [Ca2+]i was increased, depending on the amount of agonist. Furthermore, in spite of the similar delta [Ca2+]i, IP3 was smaller at 20 degrees C compared with that at 37 degrees C in thrombin-stimulated platelets. These results indicate that Ca2+ influx in platelets might be regulated by receptor-operated Ca2+ channel rather than by an IP3 mediated mechanism. As for Ca2+ restoration, calpain was demonstrated to play a role through Ca(2+)-ATPase activation by limited proteolysis.
Sakon
M
M
Dept. of Surgery II, Osaka University Medical School.
Kambayashi
J
J
D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000097:blood*; D015220:Calcium Channels / Q000378:metabolism / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002154:Calpain / Q000502:physiology*; D006801:Humans
D015220:Calcium Channels; D002154:Calpain; D000252:Calcium-Transporting ATPases; D002118:Calcium