Effects of Phosphoinositide 3-Kinase on the Endothelin-1–Induced Activation of Voltage-Independent Ca2+ Channels and Mitogenesis in Chinese Hamster Ovary Cells Stably Expressing EndothelinA Receptor

Publisher Website
Google Scholar
Abstract
We recently demonstrated that endothelin-1 (ET-1) activates two types of Ca2+-permeable nonselective cation channel (designated NSCC-1 and NSCC-2) and a store-operated Ca2+channel (SOCC) in Chinese hamster ovary cells expressing endothelinA receptor (CHO-ETAR). In addition, these channels can be discriminated using Ca2+ channel blockers (R,S)-(3,4-dihydro-6,7-dimethoxy-isochinolin-1-yl)-2-phenyl-N,N-di[2-(2,3,4-trimethoxyphenyl)ethyl]acetamid mesylate (LOE 908) and 1-(β-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl)-1H-imidazole (SK&F 96365). LOE 908 is a blocker of NSCC-1 and NSCC-2, whereas SK&F 96365 is a blocker of SOCC and NSCC-2. In this study, we investigated the effects of phosphoinositide 3-kinase (PI3K) on the ET-1–induced activation of these channels and mitogenesis in CHO-ETAR using wortmannin and 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY 294002), inhibitors of phosphoinositide 3-kinase (PI3K). ET-1–induced Ca2+ influx was partially inhibited in CHO-ETAR pretreated with wortmannin or LY 294002. In contrast, addition of wortmannin or LY 294002 after stimulation with ET-1 did not suppress Ca2+ influx. The Ca2+channels activated by ET-1 in wortmannin or LY 294002-treated CHO-ETAR were sensitive to LOE 908 and resistant to SK&F 96365. Wortmannin also partially inhibited ET-1–induced mitogenesis. LOE 908, but not SK&F 96365, abolished the wortmannin-resistant part of mitogenesis. The IC50 values (∼30 nM) of wortmannin for the ET-1–induced Ca2+ influx and mitogenesis were similar to those for the ET-1-induced PI3K activation. In conclusion, NSCC-2 and SOCC are stimulated by ET-1 via PI3K-dependent cascade, whereas NSCC-1 is stimulated via PI3K-independent cascade. Moreover, PI3K seems to be required for the activation of the Ca2+ entry, but not for its maintenance. In addition, PI3K is involved in the ET-1–induced mitogenesis that depends on the extracellular Ca2+ influx through SOCC and NSCC-2.