Calcium transport and ultrastructure of red cells in beta-thalassemia
intermedia
RM Bookchin, OE Ortiz, O Shalev, S Tsurel, EA Rachmilewitz, A Hockaday and VL Lew
Albert Einstein College of Medicine, Department of Medicine, Bronx, NY
10461.
Reported findings of elevated total calcium (Ca) contents in erythrocytes
(RBCs) from patients with beta-thalassemia intermedia (beta-TI) prompted
the question of whether the state and transport of Ca in these RBCs are
similar to those in sickle cell anemia (SS) RBCs where the increased Ca is
compartmentalized in endocytic inside-out vesicles and extracted by
exposure of the cells to the Ca ionophore A23187 and a Ca chelator
(ethylene glycol tetraacetic acid) and the levels of cytoplasmic free
ionized Ca [( Ca2+]i) are normal. We confirmed a high total Ca content of
51 +/- 13 mumol/L RBCs in splenectomized (SPX) beta-TI and 24 +/- 1 mumol/L
RBCs in non-SPX beta- TI. Unlike SS RBCs, however, most of the increased Ca
was in the lighter, presumably younger beta-TI RBCs, and about half the Ca
was not ionophore mobilizable but apparently firmly bound, possibly to
remnants of organelles in nucleated and other young RBCs. In the denser
RBCs from non-SPX beta-TI, total and extractable Ca amounts were normal.
beta-TI RBCs loaded with the Ca chelator Benz 2 showed an initial influx of
45Ca in the normal range, which indicated normal Ca permeability, and
near-steady-state levels of [Ca2+]i that were normal (22 +/- 7 nmol/L RBCs
in non-SPX beta-TI) or minimally increased (40 +/- 19 nmol/L RBCs in SPX
beta-TI). Serial-section electron microscopy of beta-TI ghosts from the
denser cell fractions showed more fully enclosed vesicles in non-SPX ghosts
than were seen in normal ghosts and many large vesicles and structured,
electron-dense material in SPX ghosts. A delayed extrusion of
ionophore-preloaded 45Ca only by the SPX beta-TI RBCs together with normal
[Ca2+]i suggested compartmentalization of the loaded Ca in these RBCs,
perhaps in endocytic inside-out vesicles, and normal Ca pumps. Since
beta-TI RBCs show essentially normal levels of [Ca2+]i and normal Ca
influx, their high total Ca content should not be associated with any of
the deleterious effects observed in vitro with increased levels of [Ca2+]i.
Volume 72,
Issue 5,
pp. 1602-1607,
11/01/1988
Copyright © 1988 by The American Society of Hematology
