Endothelin-sensitive Intracellular Ca2+ Store Overlaps with Caffeine-sensitive One in Rat Aortic Smooth Muscle Cells in Primary Cultures

We made use of quin2 microfluorometry to determine the effects of endothelin (ET) on cytosolic free Ca2+ concentrations [Ca2+]i) in rat aortic smooth muscle cells in primary culture. In Ca2+-containing medium, ET induced a rapid and sustained elevation of [Ca2+]i. In the latter component, in particular, the elevation of [Ca2+]i was inhibited by diltiazem. In Ca2+-free medium, ET induced a rapid and transient [Ca2+]i elevation, which was not inhibited by diltiazem. When the caffeine-sensitive intracellular Ca2+ store was practically depleted by repeated treatment with caffeine in Ca2+-free media, ET did not elevate [Ca2+]i. Thus, it was suggested that ET induces [Ca2+]i elevation not only by extracellular Ca2+-dependent, mechanisms but also by releasing Ca2+ from the intracellular store, and that the ET-sensitive Ca2+ store may overlap with the caffeine-sensitive one, in cultured vascular smooth muscle cells.