Human cloned alpha1A-adrenoceptor isoforms display alpha1L-adrenoceptor pharmacology in functional studies.
The recombinant alpha1A-adrenoceptor displays a distinct pharmacological profile ('classical alpha1A-adrenoceptor') in homogenate binding assays, but displays the properties of the so-called alpha1L-adrenoceptor in functional studies in whole cells at 37 degrees C. As three splice variants of the human alpha1A-adrenoceptor have been described previously (alpha1A-1, alpha1A-2 and alpha1A-3), we have compared their functional pharmacological profiles, when expressed stably in Chinese hamster ovary (CHO-K1) cells (antagonist inhibition of noradrenaline-stimulated [3H]inositol phosphates accumulation). A fourth, novel isoform (alpha1A-4) has also been studied: alpha1A-4 mRNA predominates in several human tissues including prostate, liver, heart and bladder. In homogenate binding studies, all four isoforms displayed essentially identical affinity profiles, with prazosin (1-(4-amino-6,7-dimethoxy-2-quinazolinyl)-4-(2-furoyl)piperazine), tamsulosin (5-[2-[[2-(2-ethoxyphenoxy)ethyl]-amino]propyl]-2-methoxybenzen esulfonamide), RS-17053 (N-[2-(2-cyclopropylmethoxyphenoxy)ethyl]-5-chloro-alpha,alphad imethyl-1H-indole-3-ethanamine hydrochloride), WB 4101 ((2,6-dimethoxyphenoxyethyl)aminomethyl-1,4-benzodioxane hydrochloride) and 5-Me-urapidil (5-methyl-6[[3-[4-(2-methoxyphenyl)-1-piperazinyl]propyl]amino]-1,3-d imethyuracil) all displaying subnanomolar affinities. In functional studies, noradrenaline accelerated [3H]inositol phosphates production with potencies (p[A]50) of between 5.8 and 6.6. The affinities of prazosin, RS-17053, WB 4101 and 5-Me-urapidil, at antagonizing responses to noradrenaline, were reduced by approximately 10-fold (cf. binding data), while those for tamsulosin and indoramin (N-[1-[2-(1H-indol-3-yl)ethyl]-4-piperidinyl]benzamide) remained constant or increased, consistent with the previously described alpha1L-adrenoceptor. Thus, all four human recombinant alpha1A-adrenoceptor isoforms display the pharmacology of the alpha1L-adrenoceptor when studied in functional assays, consistent with the hypothesis that the putative alpha1L-adrenoceptor represents a functional phenotype of the alpha1A-adrenoceptor.
Daniels
D V
DV
Center for Biological Research, Urogenital Pharmacology, Roche Bioscience, Palo Alto, CA 94304, USA.
Gever
J R
JR
Jasper
J R
JR
Kava
M S
MS
Lesnick
J D
JD
Meloy
T D
TD
Stepan
G
G
Williams
T J
TJ
Clarke
D E
DE
Chang
D J
DJ
Ford
A P
AP
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D016466:CHO Cells / Q000187:drug effects; D019976:Cloning, Organism; D006224:Cricetinae; D006801:Humans; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000032:analysis; D020033:Protein Isoforms / Q000235:genetics / Q000494:pharmacology; D018340:Receptors, Adrenergic, alpha-1 / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D007295:Inositol Phosphates; D020033:Protein Isoforms; D018340:Receptors, Adrenergic, alpha-1; D011994:Recombinant Proteins