Add time:08/02/2019         Source:sciencedirect.com

We sought to examine the effects of endothelin-1 on the intracellular free Ca2+ concentration ([Ca2+]i) and mitogenic response in the neuroblastoma cell line, B103 (B103 cells). The results obtained from an [125I] endothelin-1 binding assay demonstrated that B103 cells express the endothelin receptor. The Bmax and Kd values for [125I]endothelin-1 binding were 70±36 fmol/mg protein and 52±13 pM, respectively. Endothelin-1 failed to stimulate cAMP formation, but it did inhibit forskolin-induced cAMP formation. Endothelin-1 also stimulated the accumulation of [3H]inositol phosphates. These results indicate that the endothelin receptor in B103 cells couples with Gi and Gq but not with Gs. Monitoring of [Ca2+]i showed that endothelin-1 evoked a transient increase in [Ca2+]i; this remained even in the absence of extracellular Ca2+. However, no sustained, endothelin-1-induced increase in [Ca2+]i due to extracellular Ca2+ influx was detected. The endothelin B receptor-selective antagonist, 2,6-Dimethylpiperidinecarbonyl-γ-Methyl-Leu-Nin-[Methoxycarbonyl]-d-Trp-d-Nle (BQ 788), abolished the endothelin-1-induced increase in [Ca2+]i, while the endothelin ETA receptor-selective antagonist, cyclo-d-Asp-Pro-d-Val-Leu-d-Trp (BQ 123), failed to inhibit it. These results indicate that B103 cells express endothelin ETB receptor or an endothelin ETB-like receptor predominantly and have no Ca2+ channels activated by endothelin-1. Endothelin-1 activated mitogen-activated protein kinase in B103 cells. However, based on the data for 3-(4,5-dimethy-2-thiazolyl)-2,5-diphenyl tetrazolium bromide, [3H]thymidine incorporation, and apoptosis screening assays, endothelin-1 induces neither mitogenesis nor apoptosis. These results suggest that endothelin-1 has no role in the mitogenic response in B103 cells, and this is consistent with the notion that an endothelin-1-induced sustained increase in [Ca2+]i plays a role in endothelin-1-induced cell proliferation.

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