The effect of cyclosporine on calcium, protein kinase C, and sodium-proton exchange in platelets.
Cyclosporine increases platelet aggregation as well as the risk of thromboembolism. To test the hypothesis that CsA stimulates platelets by activating cytosolic calcium [Ca2+]i and related mechanisms, we measured the effects of CsA on [Ca2+]i, protein kinase C (PKC), and sodium/proton (Na+/H+) exchange. [Ca2+]i was measured in human platelets with fura 2, PKC was determined by the phosphorylation of the endogenous 47 kDa protein, and Na+/H+ exchange was measured with BCECF after acidification of the platelets with propionic acid. CsA alone did not influence basal PKC activity in platelets. However, CsA augmented the thrombin-induced phosphorylation of the specific PKC substrate p47 in platelets in a dose-dependent fashion. CsA did not affect basal [Ca2+]i--however, it increased thrombin-induced calcium influx. The effect of CsA on PKC was not dependent on the CsA-induced calcium influx. CsA increased Na+/H+ exchange, which was blocked completely by a PKC inhibitor. Our results demonstrate that CsA directly augments PKC-dependent cellular mechanisms in platelets.
Haller
H
H
Department of Internal Medicine, University Hospital Steglitz, Free University of Berlin, Germany.
Spies
K
K
Lindschau
C
C
Quass
P
P
Distler
A
A
D001692:Biological Transport / Q000187:drug effects; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D016572:Cyclosporine / Q000008:administration & dosage*; D006801:Humans; D066298:In Vitro Techniques; D010750:Phosphoproteins / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D013917:Thrombin / Q000494:pharmacology
D010750:Phosphoproteins; D017923:Sodium-Hydrogen Exchangers; D016572:Cyclosporine; D011493:Protein Kinase C; D013917:Thrombin; D002118:Calcium