Cardiac ventricular beta 2-adrenoceptors in guinea-pigs and rats are localized on the coronary endothelium.
In mammalian heart tissue beta 2-adrenoceptors are known to coexist with beta 1-adrenoceptors. In the present study, evidence that beta 2-adrenoceptors in guinea-pig and rat ventricles are primarily localized on the coronary endothelium is provided by competition binding studies with the subtype-selective beta-adrenoceptor antagonists ICI 89.406 (beta 1-selective) and ICI 118.551 (beta 2-selective) on four different plasma membrane preparations. (1) Following density gradient centrifugation of cardiac ventricular microsomes from rats or guinea-pigs, endothelial plasma membranes migrated at slightly higher density than the sarcolemmal membranes, as verified by endothelial (angiotensin converting enzyme) and sarcolemmal markers (adenylate cyclase, [3H]ouabain binding). At the activity peak of angiotensin converting enzyme, the relative amount of beta 2-adrenoceptors in guinea-pigs and rats was 25% and 65%, respectively. (2) On sarcolemmal membranes corresponding to the activity peak of adenylate cyclase, beta-adrenoceptors consisted of the beta 1-type exclusively (guinea-pig), or to at least 90% (rat). (3) Cultures of coronary endothelial cells derived from guinea-pigs revealed only beta 2-adrenoceptors. (4) Isolated guinea-pig cardiomyocytes contained only beta 1-adrenoceptors, a finding recently established in rat myocytes as well.
D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D003331:Coronary Vessels / Q000378:metabolism*; D004727:Endothelium / Q000378:metabolism; D006168:Guinea Pigs; D066298:In Vitro Techniques; D020120:Iodocyanopindolol; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010869:Pindolol / Q000031:analogs & derivatives / Q000494:pharmacology; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000032:analysis*; D013045:Species Specificity
D011943:Receptors, Adrenergic, beta; D020120:Iodocyanopindolol; D010869:Pindolol