title: Alpha1-adrenoceptor subtypes on rat afferent arterioles assessed by radioligand binding and RT-PCR.
abstract: We utilized [3H]prazosin saturation and competition radioligand binding studies to characterize the expression of alpha1-adrenoceptors in preglomerular vessels. mRNA for adrenoceptor subtypes was assayed using RT-PCR. The vessels were isolated using an iron oxide-sieving method. [3H]prazosin bound to a single class of binding sites (Kd 0.087 +/- 0.012 nM, Bmax 326 +/- 56 fmol/mg protein). Phentolamine displaced [3H]prazosin (0.2 nM) with a pK(i) of 8.37 +/- 0.09. Competition with the selective alpha1A-adrenoceptor antagonist 5-methylurapidil fit a two-site model (pK(i) 9.38 +/- 0.21 and 7.04 +/- 0.15); 59 +/- 3% of the sites were high-affinity, and 41 +/- 3% were low-affinity binding sites. Competition with the alpha1D-adrenoceptor antagonist 8-(2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl)-8-azaspiro[4.5]decane-7,9-dione dihydrochloride (BMY-7378) fit a one-site model with low affinity (pK(i) 6.83 +/- 0.03). The relative contents of alpha1A-, alpha1B-, and alpha1D-adrenoceptor mRNAs were 64 +/- 5, 25 +/- 5, and 11 +/- 1%, respectively. Thus there was a very good correlation between mRNA and receptor binding for the subtypes. These data indicate a predominance of the alpha1A-adrenoceptor subtype in rat renal resistance vessels, with smaller densities of alpha1B- and alpha1D-adrenoceptors.
authors.affiliation: Department of Cell and Molecular Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7545, USA.
authors.forename: M
authors.initials: M
authors.lastname: Salomonsson
authors.forename: M
authors.initials: M
authors.lastname: Oker
authors.forename: S
authors.initials: S
authors.lastname: Kim
authors.forename: H
authors.initials: H
authors.lastname: Zhang
authors.forename: J E
authors.initials: JE
authors.lastname: Faber
authors.forename: W J
authors.initials: WJ
authors.lastname: Arendshorst
mesh_terms: D000818:Animals; D001160:Arterioles / Q000378:metabolism*; D001667:Binding, Competitive; D007668:Kidney / Q000098:blood supply*; D008297:Male; D012333:RNA, Messenger / Q000032:analysis; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D018340:Receptors, Adrenergic, alpha-1 / Q000032:analysis* / Q000145:classification / Q000187:drug effects; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014655:Vascular Resistance
chemical_list: C547715:Adra1a protein, rat; C547721:Adra1d protein, rat; D012333:RNA, Messenger; D018340:Receptors, Adrenergic, alpha-1