Effect of calmidazolium on Ca(+2) movement and proliferation in human osteosarcoma cells

In human MG63 osteosarcoma cells, the effect of calmidazolium on Ca(2+)](i) and proliferation was explored using fura-2 and ELISA, respectively. Calmidazolium, at concentrations greater than 0.1 micromol/L, caused a rapid increase in Ca(2+)](i) in a concentration-dependent manner (EC(50) = 0.5 micromol/L). The calmidazolium-induced Ca(2+)](i) increase was reduced by 66% by removal of extracellular Ca(2+). In Ca(2+)-free medium, thapsigargin, an inhibitor of the endoplasmic reticulum Ca(2+)-ATPase, caused a monophasic increase in Ca(2+)](i), after which the effect of calmidazolium to increase Ca(2+)](i) was completely inhibited. U73122, an inhibitor of phospholipase C (PLC), abolished histamine (but not calmidazolium)-induced increases in Ca(2+)](i). Pretreatment with phorbol 12-myristate 13-acetate to activate protein kinase C inhibited the calmidazolium-induced increase in Ca(2+)](i) in Ca(2+)-containing medium by 47%. Separately, it was found that overnight treatment with 2-10 micromol/L calmidazolium inhibited cell proliferation in a concentration-dependent manner. These results suggest that calmidazolium increases Ca(2+)](i) by stimulating extracellular Ca(2+) influx and also by causing release of intracellular Ca(2+) from the endoplasmic reticulum in a PLC-independent manner. Calmidazolium may be cytotoxic to osteosarcoma cells.