Das SK, Mukherjee S, Banerjee DK. Beta-adrenoreceptors of multiple affinities in a clonal capillary endothelial cell line and its functional implication.
Mol Cell Biochem 1994;
140:49-54. [PMID:
7877597 DOI:
10.1007/bf00928365]
[Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
beta-Adrenoreceptor has been studied in a clonal capillary endothelial cell line established from the vascular bed of the bovine adrenal medulla. [3H]Dihydroalprenolol ([3H]DHA) binding to the isolated plasma membranes from these cells has demonstrated the presence of beta-adrenoreceptors with two different affinities. The dissociation constants (Kd) have been found to be 0.27 +/- 0.09 x 10(-9) M and 2.96 +/- 0.31 x 10(-9) M, respectively with the corresponding Bmax of 5.1 +/- 0.05 and 70.0 +/- 0.2 pmol/mg protein, respectively. Inhibition of [3H]DHA binding to the beta-receptor by atenolol (a beta 1-antagonist) and ICI 118,551 (a beta 2-antagonist) has suggested that the IC50cor (= Ki) for atenolol and ICI 118,551 for high affinity site are 0.08 +/- 0.03 x 10(-12) M and 0.25 +/- 0.08 x 10(-12) M, respectively. This, therefore, indicates that both atenolol and ICI 118,551 are able to displace the bound ligand effectively but the beta 1-selective antagonist atenolol is 3 times more potent than its beta 2 counterpart, ICI 118,551. Displacement of [3H]DHA binding to the endothelial cell plasma membrane by the agonists isoproterenol, epinephrine and norepinephrine has established a relative order of Ki for these agents as isoproterenol (0.56 +/- 0.19 x 10(-9) M) < epinephrine (0.77 +/- 0.26(-9) M) > or = norepinephrine (0.71 +/- 0.24 x 10(-9) M) for the high affinity site. The corresponding values for the low affinity site, however, are 4.62 +/- 0.64 x 10(-9) M, 6.21 +/- 0.86 x 10(-9) M and 5.90 +/- 0.82 x 10(-9) M, respectively for the same agonists. Increased intracellular cAMP accompanied with cellular proliferation in the presence of isoproterenol has suggested not only the coupling of beta-adrenoreceptors to the adenylate cyclase system but also its involvement in endothelial cell proliferation.
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