Pharmacological pleiotropism of the human recombinant alpha1A-adrenoceptor: implications for alpha1-adrenoceptor classification.
1. Three fully-defined alpha1-adrenoceptors (alpha1A, alpha1B and alpha1D) have been established in pharmacological and molecular studies. A fourth alpha1-adrenoceptor, the putative alpha1L-adrenoceptor, has been defined in functional but not molecular studies, and has been proposed to mediate contraction of human lower urinary tract tissues; its relationship to the three fully characterized alpha1-adrenoceptors is not known. 2. In the present study, binding affinities were estimated by displacement of [3H]-prazosin in membrane homogenates of Chinese hamster ovary (CHO-K1) cells stably expressing the human alpha1A-, alpha1B- and alpha1D-adrenoceptors and were compared with affinity estimates obtained functionally in identical cells by measuring inhibition of noradrenaline (NA)-stimulated accumulation of [3H]-inositol phosphates. 3. For the alpha1A-adrenoceptor, binding studies revealed a pharmacological profile typical for the classically defined alpha1A-adrenoceptor, such that prazosin, RS-17053, WB 4101, 5-methylurapidil, Rec 15/2739 and S-niguldipine all displayed subnanomolar affinity. A different profile of affinity estimates was obtained in inositol phosphates accumulation studies: prazosin, WB 4101, 5-methylurapidil, RS-17053 and S-niguldipine showed 10 to 40 fold lower affinity than in membrane binding. However, affinity estimates were not 'frameshifted', as tamsulosin, indoramin and Rec 15/2739 yielded similar, high affinity estimates in binding and functional assays. 4. In contrast, results from human alpha1B- and alpha1D-adrenoceptors expressed in CHO-K1 cells gave antagonist affinity profiles in binding and functional assays that were essentially identical. 5. A concordance of affinity estimates from the functional (inositol phosphates accumulation) studies of the alpha1A-adrenoceptor in CHO-K1 cells was found with estimates published recently from contractile studies in human lower urinary tract tissues (putative alpha1L-adrenoceptor). These data show that upon functional pharmacological analysis, the cloned alpha1A-adrenoceptor displays pharmacological recognition properties consistent with those of the putative alpha1L-adrenoceptor. Why this profile differs from that obtained in membrane binding, and whether it explains the alpha1L-adrenoceptor pharmacology observed in many native tissues, requires further investigation.
Ford
A P
AP
Institute of Pharmacology, Neurobiology Unit, Roche Bioscience, Palo Alto, CA 94304, USA.
Daniels
D V
DV
Chang
D J
DJ
Gever
J R
JR
Jasper
J R
JR
Lesnick
J D
JD
Clarke
D E
DE
D018663:Adrenergic Agents / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D016466:CHO Cells; D003001:Cloning, Molecular; D006224:Cricetinae; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D011869:Radioligand Assay; D018340:Receptors, Adrenergic, alpha-1 / Q000145:classification* / Q000187:drug effects* / Q000378:metabolism; D011994:Recombinant Proteins / Q000145:classification / Q000187:drug effects / Q000378:metabolism
C547713:ADRA1A protein, human; D018663:Adrenergic Agents; D007295:Inositol Phosphates; D018340:Receptors, Adrenergic, alpha-1; D011994:Recombinant Proteins