Influence of polyhydroxysteroids on [Ca(2+)](i)

Recently, we have shown that two biologically active, disulfated polyhydroxysteroids from the Pacific brittle star Ophiopholis aculeata stimulate Ca(2+) influx into different cell types. In the present study, 45Ca(2+) and two fluorescent calcium probes, quin-2/AM and fura-2/AM, were employed to investigate the course and amplitude of calcium signals induced in different mouse cells using an radio-isotope, spectrofluorimetry, and microcytofluorimetry techniques. The cytotoxic and hemolytic effects were not observed for both steroids at the wide range of concentrations. Steroids did not influence [3H]-uridine incorporation in a variety of cells. The investigated steroids stimulated a rapid increase in cytosolic Ca(2+) content in Ehrlich mouse carcinoma cells, mouse spleen lymphocytes, and mouse peritoneal macrophages in the concentration range 1-100 microg/ml on a dose-dependent basis. Blockers of L-type calcium channels, such as verapamil, diltiazem, nifedipine (1 x 10(-7)M), and 1mM EGTA, inhibited this process and reduced the response of cells to steroid application. The stimulatory effect of steroids on human fibroblast proliferation and mouse macrophage lysosome activity was observed also. It is suggested that the investigated compounds may act as Ca(2+)-agonists and increase Ca(2+)-transport across cell membranes.