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Phorbol ester stimulates calcium sequestration in saponized human platelets
1Department of Cell Biology and Anatomy, University of Pennsylvania School of Medicine, Philadelphia 19104-6058.
The Journal of Biological Chemistry
|November 25, 1987
Summary
Phorbol ester 12,13-phorbol myristate acetate (PMA) activates protein kinase C, enhancing calcium sequestration in platelets. This process, independent of cAMP or inositol trisphosphate, aids in restoring calcium levels after agonist stimulation.
Area of Science:
- Platelet biology
- Calcium signaling
- Cellular physiology
Background:
- Platelet activation by agonists releases intracellular calcium (Ca2+).
- Thrombin and ADP stimulation cause transient increases in free Ca2+.
- Previous work showed PMA accelerates Ca2+ return to baseline after thrombin.
Purpose of the Study:
- To investigate if PMA stimulates calcium sequestration in platelets.
- To determine the role of protein kinase C in this process.
Main Methods:
- Used fura-2 with intact platelets to monitor free Ca2+ levels.
- Employed saponized platelets to assess ATP-dependent 45Ca2+ uptake.
- Utilized protein kinase C inhibitor (H-7) and GTP-binding protein inhibitor (GTPγS).
Main Results:
- PMA accelerated Ca2+ restoration after both ADP and thrombin stimulation.
- H-7 slowed the return of Ca2+ to baseline levels.
- PMA pretreatment increased ATP-dependent 45Ca2+ uptake in saponized platelets.
- GTPγS reduced basal and PMA-stimulated 45Ca2+ uptake.
Conclusions:
- Activation of protein kinase C stimulates platelet calcium sequestration.
- This sequestration mechanism is independent of cAMP or inositol 1,4,5-trisphosphate.
- PMA enhances calcium restoration following agonist-induced platelet activation.