CHARACTERIZATION OF VOLTAGE-DEPENDENT CALCIUM INFLUX IN HUMAN ERYTHROCYTES BY FURA-2

Thus far, the methods used to determine erythrocyte Ca2+ influx have n ot allowed the assessment of the kinetics of ion uptake. To overcome t his drawback, we studied a new method, using the fluorescent Ca2+-chel ator fura-2, which directly quantifies intracellular Ca2+ changes in h uman erythrocytes. This method has the advantage over previous techniq ues that it monitors continuously cellular Ca2+ levels. The Ca2+ influ x is modulated by cellular membrane potential in the presence of a tra nsmembrane Ca2+ concentration gradient and exhibits a first slow incre ase of the intracellular Ca2+ concentration, followed, after the reach ment of a threshold value of 125 +/- 13 nM Ca2+, by a faster increase until a plateau is reached. The influx rate is inhibited by dihydropyr idines in the micromolar range. These findings support the hypothesis that erythrocyte Ca2+ influx is mediated by a carrier similar to the s low Ca2+ channels and is dependent on membrane depolarization. (C) 199 7 Academic Press.