Platelets play a critical role in the mammalian cardiovascular system, particularly in thrombosis and hemostasis. Normally, platelets travel through the blood stream as thin, flat disks. Upon finding a breach in the cardiovascular system, they become activated and stick together to form clots. Activation includes a major rearrangement of cytoskeletal elements and the release of chemical messengers and proteinaceous species, important for thrombosis and hemostasis. Until recently, little was known about the biophysics of the release process. The Haynes group has pioneered the use of carbon-fiber microelectrode amperometry on platelets, allowing real-time measurement of chemical messengers as they are released from cells. Analysis of amperometric spike characteristics reveals information about the quantity and kinetics of chemical messenger release, but the driving force for activation and release remains unclear.
A popular model assumes that the granules are drawn to the center of the platelet before release occurs, indicating the importance of the cytoskeletal components that drive this centralization. To test the role that the microtubule ring and actin filaments play in activation and release, fluorescence imaging was employed herein to correlate with electrochemical measurements. Fluorescence imaging allows visualization of how the cytoskeletal components are localized during activation while amperometry tracks granular release. By correlating the data, it is clear that serotonin release occurs after centralization has been completed. To further explore the relationship between the microtubule ring and release, fluorescence imaging was performed after platelets were incubated in taxol and colchicine, drugs known to disrupt either microtubule function or block granular release, prior to activation.
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