Transmembrane Calcium Movements in Resealed Human Red Cells
There is little doubt that in fresh human red cells there is a low concentration of intracellular calcium. In a careful study, Harrison & Long (1968) and Harrison, Long & Sidle (1968), using a dry ashing technique and absorption flame photometry, found only 0·0158 µmole Ca/ml. of whole cells and were able to show that calcium located in the membrane accounts completely for this figure. This means that the cell interior has a calcium concentration below 0·003 µmole/ml., assuming that, between cells and membranes, a difference of two standard errors could have been detected. In our experiments cells from defibrinated blood were washed in a solution of 145 mm NaC1 and 20 mm Tris-Cl at 4°C and were haemolysed in a five-fold volume of water. The haemolysate was extracted with an equal volume of 10% trichloroacetic acid after removal of the stromata, and we found a concentration of 0·03 µmole Ca/ml. cells after corrections were made for possible contamination of the water and reagents with calcium (Schatzmann & Vincenzi, 1969). The two figures differ by a factor of 10. The possibility exists that the temperature of the washing solution might be responsible for the discrepancy. In any event, the value is far below the free ionic calcium concentration in the plasma which surrounds the cells. Because 1 ml. plasma contains 1·5 µmole Ca2+, the ratio [Ca2+] plasma/[Ca2+] cell might be larger than 50.
KeywordsCalcium Concentration Influx Rate Ethacrynic Acid Passive Permeability High Calcium Concentration
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