Factors Influencing Calcium Influx in Endotoxin-Challenged Fibroblasts

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Abstract
The role of cell density and pH on Ca influx was studied in normal and endotoxin-challenged cultured [mouse] 3T6 fibroblasts. In normal fibroblasts, at low cell densities, there was no marked difference in Ca influx at pH 6.6, 7.4, and 7.8, at high cell densities, the Ca influx was markedly higher at pH 6.6 as compared to that at pH 7.8. Endotoxin treatment for 4 h at low cell density and in alkaline pH (7.4-7.8) increased Ca influx in a dose-dependent manner. In contrast, at high cell density and low pH (6.6), endotoxin treatment markedly decreased Ca influx in a dose- and time-dependent manner. These endotoxin-induced changes in Ca influx were not fully compensated by altered Ca efflux because total Ca content of the cells was altered. The efficacy of the endotoxin varied depending on the bacterial source of the endotoxin and the method of purification. There was a relationship between the effect of different endotoxins on the increase in Ca influx and the inhibition of cell proliferation. Endotoxin did not decrease, but slightly increased cell proliferation when added to high cell density cultures even at a concentrationof 200 .mu.g/ml.