ACTIVIN-A AND ALL-TRANS-RETINOIC ACID COOPERATIVELY ENHANCED THE FUNCTIONAL-ACTIVITY OF L-TYPE CA2-LINE( CHANNELS IN THE NEUROBLASTOMA C1300 CELL)

Activin, a member of the transforming growth factor-beta superfamily, regulates various physiological functions. In the present study, we in vestigated the effect of activin on neuronal differentiation, particul arly the functional activity of voltage-dependent Ca2+ channels, in mu rine neuroblastoma C1300 cells. A slight K+-induced increase in the in tracellular free Ca2+ ([Ca2+](i)) was observed in C1300 cells untreate d and treated with either activin A or all-trans-retinoic acid, while treatment with both agents significantly enhanced the increase. The [C a2+](i) increases potentiated by activin A and all-trans-retinoic acid were nearly abolished in the presence of 1.0 mM nickel or in the abse nce of extracellular Ca2+. Nifedipine (0.1 mu M) and omega-conotoxin ( 1.0 mu M), inhibitors of L- and N-type Ca2+ channels, respectively, pa rtially inhibited these responses, however the inhibitory effects of t hese compounds were not additive. In addition, Bay K 8644, an activato r of L-type Ca2+ channels, enhanced the K+-induced [Ca2+](i) increase. These findings indicated that depolarization evoked the Ca2+ influx, at least in part, through L-type Ca2+ channels in C1300 cells treated with both activin A and all-trans-retinoic acid. (C) 1997 Academic Pre ss.