Role of phosphoinositide 3-kinase in the nonselective cation channel activation by endothelin-1/endothelinB receptor

We recently demonstrated that endothelin-1 (ET-1) activates two types of Ca2+ permeable nonselective cation channel (designated NSCC-1 and NSCC-2) in Chinese hamster ovarian cells expressing endothelin(B) receptor (CHO-ETBR). These channels can be discriminated using the Ca2+ channel blockers, LOE 908 and SK&F 96365. LOE 908 is a blocker of NSCC-1 and NSCC-2, whereas SK&F 96365 is a blocker of NSCC-2. In this study, we investigated the possible role of phosphoinositide 3-kinase (PI3K) in the ET-1-induced activation of NSCCs in CHO-ETBR using wortmannin and LY-294002, inhibitors of PI3K. ET-1-induced Ca2+ influx was partially inhibited in CHO-ETBR 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-ETBR were sensitive to LOE 908 and resistant to SK&F 96365. In conclusion, NSCC-2 is stimulated by ET-1 via PI3K-dependent cascade, whereas NSCC-1 is stimulated independently of the PI3K pathway. Moreover, PI3K seems to be required for the initiation of the Ca2+ entry through NSCC-2 but not for its maintenance.