a1-Adrenoceptor subtypes on rat afferent arterioles assessed by radioligand binding and RT-PCR

Salomonsson, Max, Melinda Oker, Susan Kim, Hua Zhang, James E. Faber, and William J. Arendshorst. a1-Adrenoceptor subtypes on rat afferent arterioles assessed by radioligand binding and RT-PCR. Am J Physiol Renal Physiol 281: F172–F178, 2001.—We utilized [3H]prazosin saturation and competition radioligand binding studies to characterize the expression of a1-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 6 0.012 nM, Bmax 326 6 56 fmol/mg protein). Phentolamine displaced [3H]prazosin (0.2 nM) with a pKi of 8.37 6 0.09. Competition with the selective a1Aadrenoceptor antagonist 5-methylurapidil fit a two-site model (pKi 9.38 6 0.21 and 7.04 6 0.15); 59 6 3% of the sites were high-affinity, and 41 6 3% were low-affinity binding sites. Competition with the a1D-adrenoceptor antagonist 8-(2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl)-8-azaspiro[4.5]decane-7,9-dione dihydrochloride (BMY-7378) fit a onesite model with low affinity (pKi 6.83 6 0.03). The relative contents of a1A-, a1B-, and a1D-adrenoceptor mRNAs were 64 6 5, 25 6 5, and 11 6 1%, respectively. Thus there was a very good correlation between mRNA and receptor binding for the subtypes. These data indicate a predominance of the a1A-adrenoceptor subtype in rat renal resistance vessels, with smaller densities of a1Band a1D-adrenoceptors.