Rapid Decompression Induces Micro-vesiculation but Not Activation in Northern Elephant Seal Platelets
Decompression causes platelet activation in scuba divers, breath-hold divers, and in vitro platelet suspensions, which contributes to the effects of decompression sickness (DCS). Marine mammals do not appear to suffer from decompression-associated illness; however, the effects of pressure and decompression on blood platelets have not been previously studied in any marine mammal. We examined the effects of decompression on northern elephant seal platelets using flow cytometry and fluorescence microscopy to determine alterations in platelet activation.
Elephant seal platelets were pressurized to 160 atmospheres, held for one hour, and then decompressed rapidly over a five-minute period. Upon decompression, cells were incubated with fluorescently labeled fibrinogen, activated by the addition of a platelet agonist (ADP or thrombin), and fixed in paraformaldehyde. Platelets were evaluated immediately after decompression, at 30 minutes, one hour, two hours, and four hours post-decompression. There was no significant increase in the mean fluorescence intensity of pressurized elephant seal platelets in relation to control (unpressurized) cells at any time following decompression. In contrast, the same pressure excursion caused a significant increase in human platelet mean fluorescence in comparison to controls, indicating an increase in platelet activation with decompression. The presence of increased events in the R4 gate, previously shown to contain platelet microvesicles, occurred in both human and elephant seal platelets subjected to pressure, and was greatest at the four-hour time point. Microvesicles are associated with pro-coagulant activity in human platelets.1,2 However, elephant seal platelets did not bind increasing fibrinogen, while human platelets bound increasing amounts of fibrinogen relative to controls, suggesting that while elephant seal platelets produce microvesicles, they do so by an activation-independent mechanism. Because maintaining normal homeostasis is critical to any diving animal, these findings may help characterize the adaptive response of northern elephant seals to repeated high-pressure excursions.
Funding by NHLBI 57810 (FT).
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2. Sims PJ, T Wiedmer, CT Esmon, HJ Weiss, SJ Shattil. 1989. Assembly of the platelet prothrombinase complex is linked to vesiculation of the platelet plasma membrane. J Biological Chem 264(29):17049-17057.