Fresh or ATP-depleted human red cells were loaded with calcium by a short treatment of the erythrocytes with the Ca-ionophore A23187 in isotonic NaCl medium. The ionophore was eliminated by thorough washing in isotonic KCl solution containing 0.5% albumin. Passive K-transport increased up to 60fold in fresh erythrocytes loaded with 0.5-5 mM calcium. In ATP-depleted red cells much lower (0.1 mM) intracellular calcium levels had a maximum effect on K-permeability. In both Ca-loaded fresh and ATP-depleted red cells the addition of 0.5-1 mM propranolol further enhanced K-permeability. Active Na-transport was completely inhibited by 1 mM internal calcium concentration, whereas passive Na-transport increased to about 1.5 fold. The calcium pump (efflux) was greatly activated by intracellular calcium levels between 10 and 1000 μM. Then the Ca-pumping rate reached its maximum (85 μM/l cell/min) and levelled off. Passive Ca-permeability of Ca-loaded fresh cells corresponded to the physiological low value up to intracellular Ca-concentrations of 3.0 mM; above this level it increased rapidly (up to 25 fold and 5 mM internal calcium). Passive calcium permeability of ATP-depleted cells definitely enhanced even at low intracellular calcium levels. In energized erythrocytes the morphology of the cells during Ca-loading and Ca-pumping changed according to the intracellular Ca-level. The morphological changes showed no correlation with the altered K- and Na-transport processes.
|Number of pages||7|
|Journal||Acta biologica et medica Germanica|
|Publication status||Published - Dec 1 1977|
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