Endothelin-1 decreases [Ca 2+] i via Na +/Ca 2+ exchanger in CHO cells stably expressing endothelin ET A receptor

Abstract

Endothelin ET A receptor couples to G q/11 protein that transduces a variety of receptor signals to modulate diverse cellular responses including Ca 2+ mobilization. Stimulation of endothelin ET A receptor with endothelin-1 is generally believed to induce an increase in intracellular Ca 2+ concentration ([Ca 2+] i ) via G q/11 protein. Here we provide the first convincing evidence that endothelin-1 elicited G q/11 protein-dependent and -independent ‘decrease’ in [Ca 2+] i via Na +/Ca 2+ exchanger (NCX) in Chinese hamster ovary (CHO) cells stably expressing human endothelin ET A receptor. In the cells treated with 1 μM thapsigargin, an inhibitor of endoplasmic Ca 2+ pump, that induces an increase in [Ca 2+] i via capacitative Ca 2+ entry, endothelin-1 induced a decrease in [Ca 2+] 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 [Ca 2+] 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 2+] i . Molecular approach with RT-PCR demonstrated the expression of mRNA for NCX1, NCX2 and NCX3. These results suggest that stimulation of endothelin ET A receptor with endothelin-1 activates the forward mode NCX through G q/11-dependent and -independent mechanisms: the NCX exports Ca 2+ out of the cell depending on Na + gradient across the cell membrane, resulting in the decrease in [Ca 2+] i .