| 17435380 |
Matsushita M, Tanaka Y, Koike K: Studies on the mechanisms underlying beta-adrenoceptor-mediated relaxation of rat abdominal aorta. J Smooth Muscle Res. 2006 Dec;42(6):217-25.
Mechanisms underlying beta-adrenoceptor (beta-AR)-mediated vascular relaxation were studied in the isolated rat abdominal aorta. In the endothelium-denuded helical preparations, a non-selective beta-AR agonist isoprenaline elicited a concentration-dependent relaxation. In the absence of beta-AR antagonists, isoprenaline-induced relaxation was not practically affected by an adenylyl cyclase inhibitor SQ 22,536 (300 microM), but was strongly diminished by high-KCl (80 mM). Isoprenaline-induced relaxation in the presence of SQ 22,536 was significantly diminished by iberiotoxin (IbTx, 0.1 microM), but was not affected by 4-aminopyridine (4-AP, 3 mM). Isoprenaline-induced relaxation was not also affected by SQ 22,536 (300 microM) even in the presence of CGP20712A (a beta (1)-selective antagonist) and ICI-118,551 (a beta (2)-selective antagonist) (0.1 microM for each), but was strongly diminished by high-KCl. By contrast, SQ 22,536-resistant, isoprenaline-induced relaxation in the presence of CGP20712A plus ICI-118,551 was not affected by IbTx (0.1 microM), but was inhibited significantly by 4-AP (3 mM). These results suggest that in rat abdominal aortic smooth muscle: 1) both beta (1)-/beta (2)-AR- and beta (3)-AR-mediated relaxations substantially involve cAMP-independent mechanisms; 2) beta (1)-/beta (2)-AR-mediated, cAMP-independent relaxant mechanisms are partly attributed to the large-conductance, Ca (2+)-sensitive K (+) (MaxiK, BK) channel whereas beta (3)-AR-mediated relaxant mechanisms are attributed to K (v) channel. |
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