CALCIUM-CHANNEL SUBTYPES CONTROLLING SEROTONIN RELEASE FROM HUMAN SMALL-CELL LUNG-CARCINOMA CELL-LINES

Small cell lung carcinoma is an aggressive neuroendocrine tumor that s ecretes several hormones, some of which act as autocrine growth factor s. In order to obtain more information on the process of hormone secre tion from this tumor, we have studied the role of intracellular free C a2+ concentrations and voltage-operated calcium channels in the contro l of [H-3]serotonin release from in vitro growing cell lines. We found that the Ca2+ ionophore ionomycin and the Ca2+-ATPase antagonist thap sigargin induced a dose-dependent increase of intracellular Ca2+ and a parallel enhancement of [H-3]serotonin release. KCl-induced depolariz ation also stimulated a dose- and Ca2+-dependent [H-3]serotonin releas e that in the GLC8 cell line was effectively inhibited by Ca2+ channel antagonists (Cd2+, nitrendipine, verapamil, omega-conotoxin GVIA, and omega-agatoxin IVA) and potentiated by the Ca2+ channel agonist BayK8 644. Autoantibodies against Ca2+ channels present in the sera of Lambe rt-Eaton myasthenic patients antagonized KCl- but not ionomycin-induce d [H-3]serotonin release. Polymerase chain reaction analysis indicated that GLC8 cells express L-, N-, and P-type neuronal Ca2+ channel alph a1 subunits, together with two types of Ca2+ channel beta subunits. Th e presence of three functionally distinct high threshold Ca2+ channels was also revealed by patch clamp experiments; high threshold Ca2+ cha nnels were identified as dihydropyridine-sensitive (L-type), omega-con otoxin GVIA-sensitive (N-type), and omega-agatoxin IVA-sensitive (P-ty pe). Our data demonstrate that [H-3]serotonin is released by small cel l lung carcinoma cells in a Ca2+-dependent manner and that depolarizat ion-induced [H-3]serotonin release is mediated by Ca2+ influx through distinct, neuron-like, Ca2+ channel subtypes.