ETB-mediated contraction differs between left descending coronary artery and its next branch

Pig left descending coronary artery (main artery) and its next branch (branch arteries) differ in many properties. Here we report on the receptor types and the Ca2+ pools utilized for endothelin (ET) contraction in 3 mm long de-endothelialized rings of the main (weight 7.38 ± 0.38 mg) and the branch (1.07 ± 0.03 mg) arteries. KCl (60 mM) contracted the main and the branch arteries with force of 41.8 ± 3.1 and 16.9 ± 1.0 mN (millinewton), respectively. Force of contraction for all the other agents was normalized taking the KCl value as 100%. We determined the total ET-induced responses using ET-1 and those mediated by ETB using IRL1620. In Ca2+-containing solutions, ET-1 contracted the main arteries with pECB = 8.2 ± 0.1 and a maximum force of 98 ± 5%. The branch arteries also gave similar values of pEC50 (8.4 ± 0.1) and maximum force (99 ± 14%). IRL1620 contracted the main and the branch arteries with pEC50 = 7.9 ± 0.1 but the maximum force was significantly higher in the branch arteries (44 ± 3%) than in the main (15 ± 2%). In Ca2+-free solutions, the pEC50 values for ET-1 or IRL-1620 did not change but the maximum force of contraction was diminished considerably in both main and branch arteries. Thus, the left coronary artery and its next branch differ in that the role of ETB receptors is greater in the latter.