Related Experiment Videos
Influence of calcium antagonists on thrombin-induced calcium mobilization and platelet-vessel wall interactions
G H Rao1, C M Smith, J G White
1Department of Laboratory Medicine and Pathology, University of Minnesota Medical School, Minneapolis 55455.
Insights
Calcium antagonists like verapamil, diltiazem, and nifedipine do not inhibit thrombin-induced calcium changes in platelets. However, diltiazem and nifedipine partially reduced platelet-vessel wall interactions.
Area of Science:
- Cardiovascular Research
- Pharmacology
- Hematology
Background:
- Cytosolic ionized calcium elevation is crucial for human platelet activation.
- Calcium antagonists are known to affect platelet function and vascular interactions.
Purpose of the Study:
- To evaluate the efficacy of verapamil, diltiazem, and nifedipine in preventing thrombin-induced calcium mobilization in platelets.
- To assess the ability of these calcium antagonists to inhibit platelet-vessel wall interactions.
Main Methods:
- Fura 2 AM-loaded human platelets were used to measure cytosolic calcium levels after thrombin stimulation.
- Platelet-vessel wall interactions were studied using a Baumgartner chamber with a rabbit aorta preparation.
- The percentage of surface area covered by platelet thrombi was quantified.
Main Results:
- Thrombin (0.2 U/ml) significantly increased cytosolic calcium levels (basal 84 +/- 18 nM to 546 +/- 76 nM).
- Verapamil, diltiazem, and nifedipine (100 microM) did not inhibit thrombin-mediated calcium elevation.
- Diltiazem and nifedipine significantly reduced platelet thrombi formation on subendothelium (39.6 +/- 3.4% for control) but were less effective than aspirin.
- The studied calcium antagonists did not inhibit thrombin-stimulated cytosolic calcium elevation in platelets.
Conclusions:
- The evaluated calcium antagonists do not inhibit thrombin-induced calcium signaling in human platelets.
- While diltiazem and nifedipine showed some effect on platelet-vessel wall interactions, they were not as effective as aspirin.
- These findings suggest that the mechanisms by which calcium antagonists affect platelet aggregation in vitro may differ from their effects on platelet-vessel wall interactions in vivo.
Abstract:
Elevation of cytosolic ionized calcium plays a critical role in human platelet activation. We have evaluated three well-characterized calcium antagonists for their ability to prevent thrombin-induced calcium mobilization in Fura 2 AM-loaded platelets and also their ability to inhibit platelet-vessel wall interactions. Thrombin (0.2 U/ml) caused significant elevation of cytosolic calcium (basal 84 +/- 18, activated 546 +/- 76 nM; n = 3). Verapamil, diltiazem, and nifedipine (100 microM) did not exert any inhibitory effect on thrombin-mediated calcium elevation. Untreated platelets perfused through a Baumgartner chamber containing a rabbit aorta preparation reacted with exposed and denuded subendothelium. The percentage of the total area covered by control platelet thrombi was 39.6 +/- 3.4. Diltiazem and Nifedipine significantly reduced the percentage of area covered by platelet thrombi, but the drugs were not as effective as aspirin (8.2 +/- 1.4). Calcium antagonists studied did not inhibit thrombin-stimulated elevation of cytosolic calcium in blood platelets. Although these drugs have been shown to prevent in vitro platelet aggregation and offer some protection against risks for atherosclerosis and thrombosis, they failed to significantly inhibit platelet-vessel wall interactions leading to formation of spread platelets and aggregates.