Characterization of agonist-induced internalization and down-regulation of beta-adrenergic receptors in isolated rat lung and heart preparations
Liao, J.F.; Change, H.T.; Chen, C.F.
Proceedings of the National Science Council Republic of China. Part B Life Sciences 17(4): 123-130
1993
ISSN/ISBN: 0255-6596 PMID: 7909616 Document Number: 408931
Using isolated lung and heart preparations from male Sprague-Dawley rats, this study characterizes whether the beta-adrenergic receptor (BAR) agonist isoproterenol (ISO) can induce internalization and downregulation of BAR in these tissues. The results showed that ISO-induced BAR internalization was time- and concentration-dependent in the lung preparations. When the lung and heart preparations were compared, however, the same ISO (10 mu-M, 30 min) treatment only induced BAR internalization in the lung but not in the heart preparations. Pretreatment of hypertonic sucrose medium (0.45-0.6 M) for 30 min inhibited about 50% of ISO-induced BAR internalization in the lung preparations. Treatment of either ISO (10 mu-M) or terbutaline (10 mu-M) for 3 hr or 12 hr did not significantly decrease the number of BAR in both tissue preparations. However, ISO (10 mu-M, 12 hr) increased the K-D value of the radioligand (125I)-iodocyanopindolol for BAR in the heart homogenates. This ISO-induced K-D change was not observed in the presence of cycloheximide (20 mu-g/ml), a protein synthesis inhibitor. In the presence of cycloheximide (20 mu-g/ml), ISO also did not decrease the BAR number in either tissue preparation.