Cloning, expression, and tissue distribution of the rat homolog of the bovine alpha 1C-adrenergic receptor provide evidence for its classification as the alpha 1A subtype.
Three alpha 1-adrenergic receptors (ARs) have been cloned, i.e., the alpha 1B-, alpha 1C-, and alpha 1D-ARs. Compared with the alpha 1B subtype, the alpha 1A subtype in tissue is described as being insensitive to chloroethylclonidine and sensitive to SZL-49 and having a 10-100-fold higher affinity for a number of agonists and antagonists. The alpha 1A subtype is also expressed in a variety of rat tissues (as assessed by pharmacology), with greatest abundance in the cerebral cortex, hippocampus, vas deferens, and submaxillary gland. The cloned bovine alpha 1C-AR, though having an alpha 1A-AR pharmacology, was first reported as not being expressed in any rat tissue (as determined by Northern analysis) and was therefore designated as a new subtype. We report the cloning, expression, and characterization of the rat homolog of the bovine alpha 1C-AR. Using a human alpha 1C-AR probe obtained by polymerase chain reaction screening of a neuroblastoma cell line (SK-N-MC), both exon 1 and exon 2 of the rat alpha 1C-AR gene were cloned from a rat genomic library. These two exons were spliced together and cloned into the expression vector pMT2'. Transfection into COS-1 cells and analysis of the ligand-binding profile of the expressed protein receptor using 125I-HEAT revealed a 10-100-fold higher affinity for the alpha 1-AR antagonists 5-methylurapidil, (+)-niguldipine, WB-4101, and phentolamine and the agonists oxymetazoline and methoxamine, compared with the alpha 1B-AR. This ligand-binding profile is similar to that for endogenously expressed tissue alpha 1A-ARs. In addition, the rat alpha 1C-AR was the least sensitive of the three cloned subtypes to the alkylating effects of chloroethylclonidine but was the most sensitive to the alkylating prazosin analog SZL-49, properties also observed for the tissue alpha 1A subtype. Furthermore, by three different techniques, i.e., RNase protection assays, reverse transcription-polymerase chain reaction Northern blotting, and in situ hybridization histochemistry, the rat alpha 1C-AR mRNA was localized to alpha 1A-AR-rich tissues, such as rat vas deferens, hippocampus, aorta, and submaxillary gland. Taken together, these data suggest that this receptor may actually represent the alpha 1A subtype.
Department of Molecular Cardiology, Cleveland Clinic Research Institute, Ohio 44195.
D M
DM
Perez
M T
MT
Piascik
N
N
Malik
R
R
Gaivin
R M
RM
Graham
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D002417:Cattle; D002460:Cell Line; D003001:Cloning, Molecular; D005091:Exons; D006801:Humans; D017403:In Situ Hybridization; D007438:Introns; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D018340:Receptors, Adrenergic, alpha-1 / Q000145:classification* / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution
D012333:RNA, Messenger; D018340:Receptors, Adrenergic, alpha-1; D011994:Recombinant Proteins