Journals of Gerontology Series A: Biological Sciences and Medical Sciences, Vol 54, Issue 12 M601-M606, Copyright © 1999 by The Gerontological Society of America
Effect of age on plasma membrane asymmetry and membrane fluidity in human leukocytes and platelets
JM Noble, TH Thomas and GA Ford
Department of Medicine, University of Newcastle Upon Tyne, United Kingdom.
BACKGROUND: We determined whether ageing changes in plasma membrane
phospholipid asymmetry were related to changes in membrane physical
characteristics. METHODS: Plasma membrane asymmetry was determined in
polymorphonuclear leukocytes (PMN), lymphocytes, and platelets from 45
healthy young (mean 29 years, 26 male) and 28 healthy elderly (mean 70
years, 15 male) subjects by flow cytometric measurement of annexin V
binding to cell surface phosphatidylserine. Membrane fluidity in
lymphocytes and platelets from young and elderly subjects was determined by
fluorescence polarization of 1,6-diphenyl- 1,3,5- hexatriene (DPH) and
(4-trimethylammonium)-DPH (TMA). RESULTS: In elderly subjects, a higher
proportion of lymphocytes had specific annexin V binding to
phosphatidylserine (PS) than in young subjects (young: median percentage of
cells with specific annexin V binding to PS 5.3 [second to fourth quintiles
range 3.8-8.7]; elderly: 8.5 [5.2- 17.2]; p = .028). No ageing change in
annexin V binding to PMN was observed (young: 35.0% [21.8-53.5]; elderly:
39.6% [27.4-69.8]; p = .42). Platelets had no specific annexin V binding
(young: median molecules of annexin V specific binding 3.8 [0.4-11.3];
elderly: -1.4 [- 4.8-1.7]; p = .23). Superficial membrane fluidity was
increased in lymphocytes (TMA anisotropy, young: 0.271 [0.259-0.289];
elderly: 0.262 [0.242-0.279];p = .004), but not in platelets (young: 0.273
[0.259- 0.293]; elderly: 0.269 [0.248-0.284]; p = .12). Lymphocyte annexin
V binding correlated with TMA (r = -.65, p = .022), but not DPH anisotropy
(r = -.39, p = .18). CONCLUSIONS: Plasma membrane asymmetry is decreased
with age in human lymphocytes, but not in human PMN or platelets. The
increased proportion of lymphocytes with loss of plasma membrane asymmetry
corresponds to the ageing changes in superficial membrane fluidity observed
in lymphocytes. Such alterations in lymphocyte plasma membrane structure
with age could account for changes in membrane-bound receptor function
described with ageing, and may contribute to alterations in immune
responsiveness and vascular thrombosis seen in older humans.
