Aim: To compare the changes of free calcium concentration in target cells killed by transmembrane tumor necrosis factor-alpha(TM-TNF-alpha) and secretory TNF-alpha(S-TNF-alpha).
Methods: The cytotoxicity of two types of TNF-alpha was tested by bioassay. The intracellular Ca(2+) concentration was determined by Frua-2.
Results: TM-TNF-alpha had cytotoxic effect on all 6 kinds of target cells, whereas S-TNF-alpha could kill only two of them. The cytotoxic activity of both types of TNF-alpha was accompanied by a dramatically increase of intracellular free Ca(2+) concentration. The intracellular Ca(2+) concentration in the target cells treated with S-TNF-alpha was obviously reduced by pretreating target cells with 10 micromol/L calcium chelator EGTA for 30 minutes (P<0.01) and the cytotoxicity of S-TNF-alpha was significantly inhibited (P<0.01), while the pretreatment with EGTA had no effect on the intracellular Ca(2+) concentration in the target cells treated with TM-TNF-alpha and the cytotoxicity of TM-TNF-alpha.
Conclusion: These results suggest that both types of TNF-alpha increase Ca(2+) concentration in target cells by promoting the redistribution of intracellular free calcium and only S-TNF-alpha seems to be able to accelerate the influx of extracellular calcium into the target cells.