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

Pig left descending coronary artery (main artery) and its next branch (bran ch arteries) differ in many properties. Here we report on the receptor type s 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 bran ch (1.07 +/- 0.03 mg) arteries. KCl (60 mM) contracted the main and the bra nch 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 solu tions, ET-1 contracted the main arteries with pEC(50) = 8.2 +/- 0.1 and a m aximum force of 98 +/- 5%. The branch arteries also gave similar values of pEC(50) (8.4 +/- 0.1) and maximum force (99 +/- 14%). IRL1620 contracted th e main and the branch arteries with pEC(50) = 7.9 +/- 0.1 but the maximum f orce was significantly higher in the branch arteries (44 +/- 3%) than in th e main (15 +/- 2%). In Ca2+-free solutions, the pEC(50) 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 art ery and its next branch differ in that the role of ETB receptors is greater in the latter.