Collecting duct-derived endothelin-1 (ET-1) reduces blood pressure and inhibits Na and water reabsorption. Collecting duct ET-1 production is increased by volume expansion, however the mechanism by which this occurs is unknown. We hypothesized that intracellular calcium, which is likely to be increased by volume expansion, regulates collecting duct ET-1 synthesis. Rat inner medullary collecting ducts (IMCD) were studied in primary culture. ET-1 release was decreased by 50-70% after chelation of intracellular calcium (BAPTA), or inhibition of CaM (W7) or CaMK (KN-93). These agents reduced ET-1 mRNA to a similar degree. CaM inhibition did not affect ET-1 mRNA stability. Transfection of IMCD with rat ET-1 promoter-luciferase constructs revealed maximal activity within 1.7 kb proximal to the transcription start site; 5, 20, 35 and 90% of this activity were in the 0.08, 0.37 kb, 1 .0 and 3.0 kb promoter regions, respectively. W7 markedly inhibited activity of the 3.0 kb, but not 0.37 kb or 1.0 kb promoter regions. In contrast, W7 did not affect ET-1 release by rat aortic endothelial cells. Further, transfected endothelial cells had maximal activity in the 0.37 kb region (as compared to the 1.7 and 3.0 kb regions), while W-7 had no effect on the activity of any of these promoter regions. In summary, IMCD ET-1 synthesis is regulated by calcium/CaM/CaMK-dependent pathways. The calcium/CaM-sensitive pathway is active in IMCD, but not endothelial cells. This suggests that IMCD-specific enhancer elements exist within the ET-1 promoter that confers unique calcium responsiveness.