Ca2+ and Ca2+ channel antagonists in the control of human small cell lung carcinoma cell proliferation

Small cell lung carcinoma cells possess voltage-dependent calcium channels (VDCCs) of the L, omega-conotoxin-sensitive and P-like type. We hypothesized that these VDCCs might regulate the secretion of autocrine growth factors and thus influence the proliferation of these cells. We found that extracellular Ca2+ plays a stimulatory role in the proliferation of the GLC8 cell line. L-type calcium channel blockers of the dihydropyridine, phenylalkylamine and benzothiazepine classes inhibited [3H]thymidine incorporation in these cells, however at concentrations higher than those required to block L-type channel function. Moreover, the growth of murine Swiss 3T3 fibroblasts which do not possess L-type Ca2+ channels, was inhibited by the Ca2+ channel antagonists at the same effective concentrations as in small cell lung carcinoma cells. omega-conotoxin and omega-agatoxin IVA, which block the N- and P-type channel respectively, had no effect on GLC8 cell proliferation. It is concluded that the presence of extracellular Ca2+ is a positive stimulus for small cell lung carcinoma cell growth. However, under our experimental conditions, the calcium channel blockers inhibited DNA synthesis most probably by a mechanism other than VDCC antagonism.