The Journal of General Physiology, Vol 68, 29-41, Copyright © 1976 by The Rockefeller University Press
Calcium transport in intact human erthrocytes
G Plishker and HJ Gitelman
Intact human erythrocytes can be readily loaded with calcium by incubation
in hypersomotic media at alkaline pH. Erythrocyte calcium content increases
from 15-20 to 120-150 nmol/g hemoglobin after incubation for 2 h at 20
degree C in a 400 mosmol/kg, pH 7.8 solution containing 100 mM sodium
chloride, 90 mM tetramethylammonium chloride, 1 mM potassium chloride, and
10 mM calcium chloride. Calcium uptake is a time-dependent process that is
associated with an augmented efflux of potassium. The ATP content in these
cells remains at more than 60% of normal and is not affected by calcium.
Calcium uptake is influenced by the cationic composition of the external
media. The response to potassium is diphasic. With increasing potassium
concentrations, the net accumulation of calcium initially increases,
becoming maximal at 1 mM potassium, then diminishes, falling below basal
levels at concentrations above 3 mM potassium. Ouabain inhibits the
stimulatory effect of low concentrations of potassium. The inhibitory
effects of higher concentrations of potassium are ouabain insensitive and
independent of the external calcium concentration. Sodium also inhibits
calcium uptake but this inhibition can be modified by altering the external
concentration of calcium. The effux of calcium from loaded erythrocytes is
not significantly altered by changes in osmolality, medium ion composition,
or ouabain. It is concluded that hypertonicity increases the net uptake of
calcium by increasing the influx of calcium and that some part of the
sodium potassium transport system is involved in this influx process.
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