Properties of the basal calcium influx in human red blood cells

摘要

The basal ~(45)Ca~(2+) influx in human red blood cells (RBC) into intact RBC was measured. ~(45)Ca~(2+) was equilibrated with cells with t_(1/2) = 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/l_(packed cells) (n = 6) at 37 ℃. The average value of the Ca~(2+) influx rate was 43.2 ± 8.9 μmol/l_(packed 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 ℃. The basal Ca~(2+) influx was saturable with Ca~(2+) up to 5 mmol/l but at higher extracellular Ca~(2+) concentrations caused further increase of basal Ca~(2+) influx. The ~(45)Ca~(2+) 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 Ca~(2+) influx. The results show that the basal Ca~(2+) influx is mediated by a carrier and is under control of intracellular regulatory circuits. The effect of uncoupler shows that the Ca~(2+) influx is in part driven by the proton-motive force and indicates that the influx and efflux of Ca~(2+) are coupled via the RBC H~+ homeostasis.