Endothelin-1 decreases [Ca]i via Na/Ca exchanger in CHO cells stably expressing endothelin ETA receptor

Endothelin ETA receptor couples to Gq/11 protein that transduces a variety of receptor signals to modulate diverse cellular responses including Ca mobilization. Stimulation of endothelin ETA receptor with endothelin-1 is generally believed to induce an increase in intracellular Ca concentration ([Ca]i) via Gq/11 protein. Here we provide the first convincing evidence that endothelin-1 elicited Gq/11 protein-dependent and -independent ‘decrease’ in [Ca]i via Na/Ca exchanger (NCX) in Chinese hamster ovary (CHO) cells stably expressing human endothelin ETA receptor. In the cells treated with 1 μM thapsigargin, an inhibitor of endoplasmic Ca pump, that induces an increase in [Ca]i via capacitative Ca entry, endothelin-1 induced a decrease in [Ca]i which was partially inhibited by YM-254890, a specific inhibitor of Gq/11, indicating that Gq/11-dependent and -independent pathways are involved in the decrease. The endothelin-1-induced decrease in [Ca]i was markedly suppressed by 3’,4’-dichlorobenzamil hydrochloride, a potent NCX inhibitor, and also by a replacement of extracellular Na with Li, which was not transported by NCX, indicating a major role of NCX operating in the forward mode in the endothelin-1-induced decrease in [Ca]i. Molecular approach with RT-PCR demonstrated the expression of mRNA for NCX1, NCX2 and NCX3. These results suggest that stimulation of endothelin ETA receptor with endothelin-1 activates the forward mode NCX through Gq/11-dependent and -independent mechanisms: the NCX exports Ca out of the cell depending on Na gradient across the cell membrane, resulting in the decrease in [Ca]i.