Expressed alpha 1-adrenoceptors in adult rat brown adipocytes are primarily of alpha 1A subtype.
The main objective of this study was to characterize the alpha 1-adrenoceptors expressed in adult rat brown adipocytes. For this purpose, membrane fractions were prepared from brown adipose tissue as well as from isolated brown adipocytes. The following are major findings: (i) BAT membranes were considerably enriched in alpha 1-adrenoceptors (specific [3H]prazosin binding, Bmax, 79.49 +/- 16.77 fmol/mg protein; KD, 0.24 +/- 0.04 nM); (ii) among the cells that comprise brown adipose tissue, brown adipocytes were enriched in alpha 1-adrenoceptors; (iii) > 95% of total alpha 1-adrenoceptors were resistant to inactivation by 20 microM chloroethylclonidine, which readily and essentially completely inactivated alpha 1B-adrenoceptors in rat liver membranes; (iv) brown adipose tissue membrane alpha 1-adrenoceptors showed high affinity towards 5-methyl urapidil (KD 7.23 +/- 2.49 nM) and WB 4101 (KD 0.66 +/- 0.30 nM) and low affinity towards BMY 7378 (KD 0.34 +/- 0.03 microM); essentially similar affinities for these drugs were seen for membranes prepared from brown adipocytes; and (v) EBDA/LIGAND analysis of 5-methyl urapidil, WB 4101, and BMY 7378 competition curves revealed the presence of a single binding site for these drugs. Recent work has documented that 5-methyl urapidil and WB 4101 interact with high affinity with alpha 1A-adrenoceptors, while BMY 7378 interacts with high affinity with alpha 1D-adrenoceptors. Taken together, these findings are consistent with the view that alpha 1-adrenoceptors expressed in adult rat BAT are mainly of the alpha 1A subtype.
Costain
W J
WJ
Department of Physiology, College of Medicine, University of Saskatchewan, Saskatoon, Canada.
Mainra
R
R
Desautels
M
M
Sulakhe
P V
PV
D017667:Adipocytes / Q000737:chemistry*; D002001:Adipose Tissue, Brown / Q000737:chemistry* / Q000166:cytology; D058668:Adrenergic alpha-1 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D002462:Cell Membrane / Q000737:chemistry; D004146:Dioxanes / Q000494:pharmacology; D005260:Female; D010879:Piperazines / Q000494:pharmacology; D051381:Rats; D018340:Receptors, Adrenergic, alpha-1 / Q000032:analysis*
D058668:Adrenergic alpha-1 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists; D004146:Dioxanes; D010879:Piperazines; D018340:Receptors, Adrenergic, alpha-1; C057446:5-methylurapidil; C010654:(2-(2',6'-dimethoxy)phenoxyethylamino)methylbenzo-1,4-dioxane; C053428:BMY 7378