Increased Potassium Permeability by Calcium in Hypochromic Red Blood Cells

The red blood cell (RBC) content of Na⁺ and K⁺ were measured both on fresh cells from normal, heterozygous β-thalassaemic and iron-deficiency-anaemic subjects, and on the same cells incubated for 24 h, at 37° C, either in presence or in absence of Calcium (Ca²⁺). Ca²⁺ did not increase membrane permeability to Na⁺, but increased the K⁺ loss, both from normal cells and to a greater degree much more from hypochromic cells. Glucose largely prevented the K⁺ loss from hypochromic cells incubated either in absence or in presence of Ca²⁺, probably maintaining an adequate level of ATP during the incubation. EDTA only partially decreased the permeability to K⁺ in hypochromic cells incubated for 24 h at 37° C, possibly removing Ca²⁺ bound to the cell membrane. The results suggest that Ca²⁺ does not represent the primary cause of K⁺ leak in hypochromic cells, but it is able to enhance a pre-existing peculiar abnormality of the cell membrane when the ATP level slows down.