Modulation by external Ca2+ and nicardipine of Ca2+ influx and cytosolic concentration in human erythrocytes

Summary Variations of Ca 2+ influx (evaluated by the initial rate of 45 Ca 2+ uptake) and cytosolic free Ca 2+ concentration ([Ca 2+ ] i , measured with fura-2) were investigated in human erythrocytes. When external Ca 2+ concentration ([Ca 2+ ] o) rose from 1 to 2 mM, the initial rate of Ca 2+ influx nearly doubled whereas [Ca 2+ ] i increased only by 15%. Nicardipine dose-dependently decreased both initial rate of Ca 2+ influx and [Ca 2+ ] i (up to 53 and 18%, respectively at 10 −6 M). The less marked changes in [Ca 2+ ] i than in Ca 2+ influx indicate a partial adjustment of the Ca 2+ extruding-pump activity to of Ca 2+ influx. In vivo administration of nicardipine reduced [Ca 2+ ] i only when its initial value exceeded 80nM and prevented the rise in [Ca 2+ ] i induced by the increase in [Ca 2+ ] o . Our results indicate that nicardipine may reduce Ca 2+ influx in human erythrocytes and participate in the control of [Ca 2+ ] i when elevated.