Figure 3. Agonist-induced contractions under the Ca²⁺-free, depolarized conditions in intact rabbit (A), chicken (B) and pigeon arteries (C).

High K⁺-induced contraction was abolished with removal of Ca²⁺ and addition of 2 mm EGTA. Then, 30 μm PE or 1 μm ET-1 was added. K-Ca, high-K⁺ solution containing 2 mm Ca²⁺. K-G, Ca²⁺-free, high-K⁺ solution containing 2 mm EGTA. Rabbit and pigeon arteries were pre-treated with 1 μm ryanodine in the K-G solution containing 30 mm caffeine for 30 min to deplete the SR of Ca²⁺ (Himpens et al. 1990). (n = 3–6.)