Ca2+-dependence of endothelin-1 induced contraction of rat tail artery

1. In rat tail artery, endothelin-1(ET-1) caused an increase in the cytosolic free Ca2+ level ([Ca2+]i) followed by a relatively sustained but not steady-state contraction in Ca2+ containing solution. 2. In the early phase of the contraction, the rate of increase in [Ca2+]i, was much faster than that in muscle tension. However, after the increases in [Ca2+]i and muscle tension reached at their peaks, there was a good correlation between the changes of the two parameters. 3. ET-1 could not induce an apparent contractile response in Ca2(+)-free medium, notwithstanding it evoked a [Ca2+]i transient in this medium. 4. The results indicate that ET-1 induce a contraction of rat tail artery which is almost fully dependent on the [Ca2+]i changes, and may inhibit the Ca2(+)-sensitivity of the contractile filaments in the early phase of the contraction.