Endothelin-1 decreases [Ca2+]i via Na+/Ca2+ exchanger in CHO cells stably expressing endothelin ETA receptor

Endothelin ETA receptor couples to G(q/11) protein that transduces a variety of receptor signals to modulate diverse cellular responses including Ca2+ mobilization. Stimulation of endothelin ETA receptor with endothelin-1 is generally believed to induce an increase in intracellular Ca2+ concentration ([Ca2+](i)) via G(q/11) protein. Here we provide the first convincing evidence that endothelin-1 elicited Gq/11 protein-dependent and -independent 'decrease' in [Ca2+](i) via Na+/Ca2+ exchanger (NCX) in Chinese hamster ovary (CHO) cells stably expressing human endothelin ETA receptor. In the cells treated with 1 mu M thapsigargin, an inhibitor of endoplasmic Ca2+ pump, that induces an increase in [Ca2+](i) via capacitative Ca2+ entry, endothelin-1 induced a decrease in [Ca2+](i) which was partially inhibited by YM-254890, a specific inhibitor of G(q/11), indicating that G(q/11)-dependent and independent pathways are involved in the decrease. The endothelin-1-induced decrease in [Ca2+](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 [Ca2+](i). Molecular approach with RT-PCR demonstrated the expression of mRNA for NCX 1, NCX2 and NCX3. These results suggest that stimulation of endothelin ETA receptor with endothelin-1 activates the forward mode NCX through G(q/11)-dependent and -independent mechanisms: the NCX exports Ca2+ out of the cell depending on Na+ gradient across the cell membrane, resulting in the decrease in [Ca2+](i). (c) 2007 Elsevier B.V All rights reserved.