Mechanisms of amphipath-induced stomatocytosis in human erythrocytes
SL Schrier, A Zachowski and PF Devaux
Division of Hematology, Stanford University School of Medicine, CA.
We studied stomatocytosis induced in human red blood cells (RBC) by
vinblastine and chlorpromazine, monitoring the movements of spin- labeled
phosphatidylcholine (PC*) and sphingomyelin (SM*) by electron spin
resonance (ESR) spectroscopy. This technique allows determination of the
fraction of labeled lipids, respectively, on the external leaflet, on the
cytosol face, or trapped in endocytic vacuoles. Both vinblastine and
chlorpromazine produce a time- and concentration- dependent stomatocytic
shape change, which is paralleled by a shift of approximately 10% to 33% of
outer leaflet SM* and PC* inward. Of this amount, 8% to 12% was trapped in
endocytic vacuoles and 8% to 19% had flipped to the inner leaflet.
Vanadate, while inhibiting the stomatocytosis, did not block the flip of
either SM* or PC* to the inner leaflet. To explain the inhibiting effect of
vanadate, as well as the adenosine triphosphate (ATP) requirement for
drug-induced stomatocytosis, we propose the following model: (1) addition
of amphipath partially scrambles the bilayer; and (2) the flop of
phosphatidylserine (PS) and phosphatidylethanolamine (PE) to the outer
leaflet provides substrate for the aminophospholipid translocase (APLT),
which flips back PS and PE inward faster than PC or SM can diffuse
outward--thereby producing inner layer expansion or stomatocytosis. This
role of APLT accounts for the vanadate inhibition of amphipath
stomatocytosis. However, the vanadate effect can be overcome by increasing
the amphipath concentration, which at such levels probably passively
expands the inner leaflet.
Volume 79,
Issue 3,
pp. 782-786,
02/01/1992
Copyright © 1992 by The American Society of Hematology
