ENDOTHELIN INCREASES [CA-2+]I IN M-1 MOUSE CORTICAL COLLECTING DUCT CELLS BY A DUAL MECHANISM

We tested the effects of endothelin-1 (ET-1) on intracellular calcium concentration ([Ca2+]i) of cultured M-1 mouse cortical collecting duct cells. [Ca2+]i was measured using fura 2 and a fluorescent imaging system. At a concentration of extracellular calcium ([Ca2+]o) of 1 mM, ET-1 (10(-12) to 10(-7) M) increased [Ca2+]i. A second application of ET-I had no effect on Ca2+. In contrast, application of arginine vasopressin after an initial exposure to ET-1 induced a second Ca2+ response. In the absence of extracellular Ca2+ (1 mM EGTA) ET-1 also elicited a Ca2+ peak, indicating participation of Ca2+ release from intracellular stores in the initial Ca2+ peak. At [Ca2+]o of 10 mM, ET-1 also induced an intracellular Ca2+ peak but [Ca2+]i remained significantly elevated. The Ca2+ plateau phase was abolished by nickel (10 or 100 muM) and nifedipine (0. 1 or 1 muM). We conclude that ET-1 mediates an increase in [Ca2+]i by Ca2+ release from intracellular stores and activation of a nickel- and nifedipine-sensitive Ca2+ entry mechanism.