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

Lead (Pb(2+)) tends to accumulate in bone from where it is released during bone resorption, thus leading to high local concentrations of Pb(2+) with the risk of cellular toxicity. We investigated the interference of Pb(2+) with the calcium release activated calcium influx (CRAC) of osteoblast-like (OBL) cells. CRAC was elicited by depletion of intracellular Ca(2+) stores with thapsigargin and/or A23187 under Ca(2+)-free conditions and re-addition of extracellular Ca(2+). The fura-2 excitation ratio (R) was used to monitor changes of the free intracellular concentration of Ca(2+) and Pb(2+), the latter being reversible by the heavy metal chelator TPEN. Five or 12. 5 microM Pb(2+) applied simultaneously with re-added Ca(2+) reduced the immediate CRAC of OBL cells to 70% or 37% of control value, respectively. An enlarged influx of Pb(2+) occurred during CRAC, which led to a 2.7-fold faster increase of R. When 1 microM Pb(2+) was added during ongoing CRAC, the Pb(2+)-mediated increase of R correlated with the degree of CRAC (r = 0.83). Inhibitory effects of Pb(2+) on Ca(2+) ATPase activity did not contribute to the aforementioned findings. Our results demonstrated that CRAC channels of OBL cells are blocked as well as permeated by Pb(2+).