在本篇論文中，我們探討鼠神經膠質瘤細胞 C6 內之環狀腺嘌呤單磷核苷酸濃度之增加，對於該細胞內之內皮素受體基因表現之調控。當 C6 細胞以 1mM 之雙丁烷基環狀腺嘌呤單磷核苷酸處理一天後，發現其細胞上之碘 125 標誌之內皮素特異性結合，只剩為原來未處理前之約百分之四十。以放射性配位體結合試驗與北方墨點分析方法，證明了 C6細胞上之內皮素受體屬於 A 亞型受體，不管是在有無以環狀腺嘌呤單磷核苷酸處理 C6 細胞情形下皆然。 進而以北方墨點分析方法與細縫雜交反應法進行分析 C6 細胞之 RNA 量，發現雙丁烷基環狀腺嘌呤單磷核苷酸可抑制 C6 細胞之內皮素 A 亞型受體之基因表現。當環狀腺嘌呤單磷核苷酸處理 C6 細胞後 4 小時內，便可測得其內皮素 A 亞型受體之 RNA量只剩為原先之百分之十，繼續處理一天後，其 RNA 量會緩慢回升至原先量之百分四十。本研究結果證明了雙丁烷基環狀腺嘌呤單磷核苷酸處理 C6 細胞後，對於其細胞上內皮素 A亞型受體之向下調控作用，不僅會減少其受體之結合量，亦會降低其 mRNA 量。

In this study, we have investigated the gene expression of endothelin receptors in rat astrocytoma C6 cells regulated by the increase of intracellular cAMP. Following treatment with 1 mM dibutyryl cAMP, the specific binding of [125I]-endothelin-1 to the C6 cells was down-regulated to about 40% of the original level. Radioligand binding assay and Northern blot analysis indicated that endothelin receptors on C6 cells, which were either treated or untreated with 1 mM dibutyryl cAMP, belong to subtype A. Analysis of RNA by Northern blotting and slot hybridization demonstrated that the presence of dibutyryl cAMP induced the down regulation of ETA endothelin receptor gene in C6 cells. The level of ETA mRNA was rapidly reduced to about 10% of its initial level after 4 hour treatment with dibutyryl cAMP and then was slightIy elevated to about 40% after one day treatment. All the findings suggest that the down regulation of ETA receptor in C6 cells by the treatment of dibutyryl cAMP occurs not only at the receptor binding level but also at the mRNA level.