Properties of the basal calcium influx in human red blood cells

AbstractThe basal 45Ca2+ influx in human red blood cells (RBC) into intact RBC was measured. 45Ca2+ was equilibrated with cells with t1/2=15–20 s and the influx reached the steady state value in about 90–100 s and the steady state level was 1.5±0.2 μmol/lpacked cells (n=6) at 37 °C. The average value of the Ca2+ influx rate was 43.2±8.9 μmol/lpacked cells hour. The rate of the basal influx was pH-dependent with a pH optimum at pH 7.0 and on the temperature with the temperature optimum at 25 °C. The basal Ca2+ influx was saturable with Ca2+ up to 5 mmol/l but at higher extracellular Ca2+ concentrations caused further increase of basal Ca2+ influx. The 45Ca2+ influx was stimulated by addition of submicromolar concentrations of phorbol esters (phorbol 12-myristate-13-acetate (PMA) and phorbol-12,13-dibutyrate (PDBu)) and forskolin. Uncoupler (3,3′,4′,5-tetrachloro-salicylanilide (TCS) 10−6–10−5 mol/l) inhibited in part the Ca2+ influx. The results show that the basal Ca2+ influx is mediated by a carrier and is under control of intracellular regulatory circuits. The effect of uncoupler shows that the Ca2+ influx is in part driven by the proton-motive force and indicates that the influx and efflux of Ca2+ are coupled via the RBC H+ homeostasis