Intracellular calcium fluxes in human platelets.
Fluorescence changes and secretory responses have been measured on addition of various excitatory agonists to platelets loaded with the cytosolic Ca2+ probe, Quin 2 or with chlortetracycline as a probe for membrane-associated Ca2+. When extracellular [Ca2+] is decreased to less than 0.1 microM by addition of EGTA a linear correlation is observed between the extent of increase in cytosolic [Ca2+] and the extent of mobilisation of membrane-associated Ca2+ on stimulation by maximal doses of five excitatory agonists. A similar linear correlation between the increase in cytosolic [Ca2+] and the extent of ATP secretion is observed over the thrombin dose/response curve. Similar EC50 values are observed for ATP secretion, the increase in cytosolic [Ca2+] and the decrease in chlortetracycline fluorescence induced by thrombin. However, the decrease in chlortetracycline fluorescence shows a sigmoidal relationship with the increase in cytosolic [Ca2+] and a hyperbolic relationship with ATP secretion over this dose/response curve. Addition of prostaglandin D2 prior to thrombin causes parallel inhibition of the increase in cytosolic [Ca2+] and the decrease in chlortetracycline fluorescence induced by this agonist. However, addition of prostaglandin D2 after thrombin reverses the increase in cytosolic [Ca2+] induced by this agonist but fails to cause a similar reversal of the decrease in chlortetracycline fluorescence. The data provide further evidence supporting the proposal that chlortatracycline can be used as a probe to monitor mobilisation of membrane-associated Ca2+ but suggest that, in platelets stimulated in the effective absence of extracellular Ca2+, both Ca2+ mobilisation and Ca2+ removal can under some conditions involve sites which are not monitored by this probe.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000634:Aminoquinolines; D001692:Biological Transport; D001792:Blood Platelets / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000097:blood*; D002614:Chelating Agents; D002751:Chlortetracycline; D005456:Fluorescent Dyes; D006801:Humans; D066298:In Vitro Techniques; D009930:Organic Chemicals; D010974:Platelet Aggregation; D015230:Prostaglandin D2; D011457:Prostaglandins D / Q000494:pharmacology; D013050:Spectrometry, Fluorescence; D013917:Thrombin / Q000494:pharmacology
D000634:Aminoquinolines; C041685:Benz2; D002614:Chelating Agents; D005456:Fluorescent Dyes; D009930:Organic Chemicals; D011457:Prostaglandins D; D000001:Calcimycin; D000255:Adenosine Triphosphate; D013917:Thrombin; C035739:Quin2; D015230:Prostaglandin D2; D002118:Calcium; D002751:Chlortetracycline