Interference of lead with the calcium release activated calcium flux of osteoblast-like cells

Lead (Pb2+) tends to accumulate in bone from where it is released during bo ne resorption, thus leading to high local concentrations of Pb2+ with the r isk of cellular toxicity. We investigated the interference of Pb2+ with the calcium release activated calcium influx (CRAC) of osteoblast-like (OBL) c ells. CRAC was elicited by depletion of intracellular Ca2+ stores with thap sigargin and/or A23187 under Ca2+-free conditions and re-addition of extrac ellular Ca2+. The fura-2 excitation ratio (R) was used to monitor changes o f the free intracellular concentration of Ca2+ and Pb2+, the latter being r eversible by the heavy metal chelator TPEN. Five or 12.5 mu M Pb2+ applied simultaneously with re-added Ca2+ reduced the immediate CRAC: of OBL cells to 70% or 37% of control value, respectively. An enlarged influx of Pb2+ oc curred during CRAC, which led to a 2.7-fold faster increase of R. When 1 mu M Pb2+ was added during ongoing CRAC, the Pb2+-mediated increase of R corr elated with the degree of CRAC (r = 0.83). Inhibitory effects of Pb2+ on Ca 2+ ATPase activity did not contribute to the aforementioned findings. Our r esults demonstrated that CRAC channels of OBL cells are blocked as well as permeated by Pb2+.