Differences between the third cardiac β‐adrenoceptor and the colonic β3‐adrenoceptor in the rat

摘要: 1. The heart of several species including man contains atypical beta-adrenoceptors, in addition to coexisting beta 1- and 2-adrenoceptors. We now asked the question whether or not third cardiac beta-adrenoceptor is identical putative 3-adrenoceptor. compared properties with those 3-adrenoceptors isolated tissues rat. To study we used spontaneously beating right atria, paced left atria ventricular papillary muscles. As a likely model for studied beta-adrenoceptors colonic longitudinal muscle precontracted 30 mM KCl. 3-adrenoceptor-selective agonists, antagonists non-conventional partial agonists (ie high-affinity blockers both 2-adrenoceptors know exert also stimulant effects through 3-adrenoceptors). 2. agonist (-)-CGP 12177 caused positive chronotropic (pD2 = 7.3) inotropic 7.5). were resistant blockade by 200 nM-2 microM (-)-propranolol 3 ICI 118551 (a 2-selective antagonist) but antagonized 1 (-)-bupranolol (pKB 6.4-6.8), CGP 20712A 1-selective 6.3-6.4) 6.6 SR 59230A 3-selective antagonist, pKB 5.1-5.4). 3. cyanopindolol 7.7) 7.1). nM 6.8-7.1). 4. Neither nor muscles at concentrations between 0.2 20 microM. 5. In presence BRL 37344 (6 microM), 58611A ZD 2079 (60 microM) CL 316243 did cause modify potency efficacy atria. combination 2 (-)-noradrenaline alone. 6. relaxed colon pD2 6.9 maximum effect 55% (-)-isoprenaline. relaxant (-)-propranolol, 20712A, blocked 6.0), 6.4) 6.3). (20 surmountably (pKP 7.0); 7.0). 7. Cyanopindolol 7.0 40% expected from agonist, pKP 7.6 7.4. 8. following potent relaxants values parentheses): (9.1), (7.0), (9.0) (8.2). these only marginally affected 118551, 6.9-7.5), 6.2-6.4) 6.3-6.5). 9...