Northern Elephant Seal Platelets are Protected From Platelet Activation Associated with Rapid Decompression
The Biostabilization Program, University of California-Davis, Davis CA,
Northern Elephant Seals (NES) are routinely subjected to high pressures
and cold temperatures, yet, unlike humans, do not suffer from the thrombotic effects of platelet
activation associated with rapid decompression.1,2,3,4 High pressures and cold
temperatures have been shown to increase membrane order,5 thus we determined the
iochemical and biophysical characteristics of NES platelets.
NES platelets undergo cold-induced shape change as they are chilled from
37°C to 4°C. Below 20°C there is a sharp increase in the number of activated
cells, as defined by the presence of multiple filopodia and/or a spherical shape. This
cold-induced shape change correlates with the main membrane phospholipid phase transition, which
was determined using Fourier Transform Infrared Spectroscopy (FTIR).
FTIR analysis demonstrates that NES platelets have a very broad phase
transition (Tm), with two transitions centered at 21°C and 8-10°C. Removal
of cholesterol, using 10mM Methyl-β-cyclodextrin, resulted in more sharply defined
transitions, with an increase in membrane fluidity above the main Tm (8-10°C),
and a decrease in fluidity below Tm. This is consistent with the proposed role of
cholesterol as a regulator of membrane phospholipid order.
Cholesterol-rich membrane microdomains, or rafts, have been demonstrated to
play a key role in human platelet intracellular signaling.6 We labeled NES platelets
with the lipophilic dye, diIC18
(1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanineperchlorate), which preferentially
inserts into ordered membrane domains, and observed that NES platelets form raft aggregates
after incubation at 4oC. Removal of cholesterol results in disruption of raft
NES platelets were pressurized to 160 atmospheres, held at high pressure for
one hour, then decompressed rapidly (within 5 minutes) and fixed immediately for morphologic
analysis. Three hundred cells were counted for each condition, and human platelets were
subjected to identical conditions for comparison. The number of activated NES platelets
increased by 45%, however, human platelet activation increased by 310% following this pressure
excursion. These results suggest that NES platelets are more resistant to decompression-induced
platelet activation than human platelets.
We thank Frances Gulland and Martin Haulena and staff of the The Marine
Mammal Center (Sausalito, CA), Dan Crocker (Sonoma State University), and Burney LeBoeuf
(University of California- Santa Cruz) for their assistance in our obtaining elephant seal
blood. This work was supported by NIH grant ROHL57810 (F. Tablin).
1. Murayama M. 1987. Compression inhibits aggregation of human
platelets under high hydraulic pressure. Thrombosis Research 45: 729-738
2. Philp RB, Inwood MJ, Ackles KN, Radonski MW. 1974. Effects of
decompression on platelets and hemostasis in men and the influence of antiplatelet drugs.
Aerospace Medicine 45(3): 231-240
3. Price RA, Ogston D, Macdonald AG. 1986. Effects of high
pressure on platelet aggregation in vitro. Undersea Biomedical Research 13(1):
4. Pickles DM, Ogston D, Macdonald AG. 1990. Effects of
hydrostatic pressure and inert gases on platelet aggregation in vitro. Journal of
Applied Physiology 69(6): 2239-2247
5. Hazel JR, Williams EE. 1991. The role of alterations in
membrane lipid composition in enabling physiological adaptation of organisms to their physical
environment. Progress in Lipid Research 29: 167-227.
6. Gousset K, Wolkers WF, Tsvetkova NM, Oliver AE, Field CL,
Walker NJ, Crowe JH, Tablin F. 2001. Evidence for a physiological role for membrane rafts in
human platelets. J. Cell. Physio. 190:117-128.