Ca2+ channels activated by endothelin-1 in CHO cells expressing endothelin-A or endothelin-B receptors

We compared the Ca2+ channels activated by endothelin-1 (ET-1) in Chinese hamster ovary (CHO) cells stably expressing endothelin type A (ETA) or endothelin type B (ETB) receptors using the Ca2+ channel blockers LOE-908 and SK&F-96365. In both CHO-ETA and CHO-ETB, ET-1 at 0.1 nM activated the Ca2+ permeable nonselective cation channel-1 (NSCC-1), which was sensitive to LOE-908 and resistant to SK&F-96365. ET-1 at 1 nM activated NSCC-2 in addition to NSCC-1; NSCC-2 was sensitive to both LOE-908 and SK&F-96365. ET-1 at 10 nM activated the same channels as 1 nM ET-1 in both cell types, but in CHO-ETA, it additionally activated the store-operated Ca2+ channel (SOCC), which was resistant to LOE-908 and sensitive to SK&F-96365. Up to 1 nM ET-1, the level of the formation of inositol phosphates (IPs) was low and similar in both cell types, but, at 10 nM ET-1, it was far greater in CHO-ETA than in CHO-ETB. These results show that, in CHO-ETA and CHO-ETB, ET-1 up to 10 nM activated the same Ca2+ entry channels: 0.1 nM ET-1 activated NSCC-1, and ET-1 greater than or equal to 1 nM activated NSCC-1 and NSCC-2. Notably, in CHO-ETA, 10 nM ET-1 activated SOCCs because of the higher formation of IPs.