Alpha-adrenoceptors in dog mesenteric vessels--subcellular distribution and number of [3H]prazosin and [3H]rauwolscine binding sites.
Binding of the alpha-adrenergic antagonists [3H]prazosin and [3H]rauwolscine to well-characterized subcellular membrane fractions isolated from dog mesenteric arteries and veins was studied. Binding of both ligands was saturable with Kd values of 0.5 +/- 0.1 nM for [3H]prazosin and 5.85 +/- 0.85 nM for [3H]rauwolscine in arteries, and 0.87 +/- 0.4 nM for [3H]prazosin and 6.6 +/- 1.5 nM for [3H]rauwolscine in veins. In veins, the maximum number of binding sites for [3H]rauwolscine was higher than that for [3H]prazosin, whereas in arteries the maximum number of binding sites for each ligand was similar. In microsomes from dog aorta, the maximum number of bindings sites for [3H]prazosin was higher than that for [3H]rauwolscine. Neuronal membrane contamination in these studies was minimized by dissection procedures and evaluated by the comparison of [3H]saxitoxin binding in various preparations. Only mesenteric veins responded functionally to agonists acting on alpha 2 adrenoceptors. This study thus identified two distinct populations of [3H]prazosin and [3H]rauwolscine binding sites in the plasma membranes of dog mesenteric vessels and suggests that a much higher density of alpha 2-compared to alpha 1-adrenoceptor binding sites is required for a contractile response.
Shi
A G
AG
Department of Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada.
Ahmad
S
S
Kwan
C Y
CY
Daniel
E E
EE
D000818:Animals; D001665:Binding Sites; D002462:Cell Membrane / Q000201:enzymology / Q000378:metabolism; D004285:Dogs; D003576:Electron Transport Complex IV / Q000378:metabolism; D005260:Female; D007700:Kinetics; D008297:Male; D008638:Mesenteric Arteries; D008642:Mesenteric Veins; D009131:Muscle, Smooth, Vascular / Q000201:enzymology / Q000378:metabolism*; D009699:N-Glycosyl Hydrolases / Q000378:metabolism; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D011224:Prazosin / Q000378:metabolism*; D011869:Radioligand Assay; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D012530:Saxitoxin / Q000378:metabolism; D014316:Tritium; D015016:Yohimbine / Q000378:metabolism*
D011942:Receptors, Adrenergic, alpha; D014316:Tritium; D015016:Yohimbine; D012530:Saxitoxin; D009251:NADPH-Ferrihemoprotein Reductase; D003576:Electron Transport Complex IV; D009699:N-Glycosyl Hydrolases; D011224:Prazosin