The rat homologue of the bovine alpha 1c-adrenergic receptor shows the pharmacological properties of the classical alpha 1A subtype.

The cDNA for the rat alpha 1c-adrenergic receptor (AR) has been cloned using a probe derived from the bovine alpha 1c-AR sequence. Clone rB7a has a 2.6-kilobase insert with a 1390-base pair open reading frame and encodes a receptor of 466 amino acids. The cloned receptor has 91% amino acid identity with the bovine alpha 1c-AR. The rat alpha 1c-AR mRNA was detected in tissues known to be enriched for the alpha 1A-AR subtype, including vas deferens, heart, kidney, and hippocampus. Rat alpha 1c-AR mRNA was absent from liver and spleen when assayed by Northern blot analyses and RNase protection assays. In COS-7 cells transfected with cDNAs encoding the three rat alpha 1-ARs, WB-4101 and benoxathian had similar binding affinities for the alpha 1a/d-AR and the alpha 1c-AR and 10-fold lower affinities for the alpha 1b-AR. The affinity of 5-methylurapidil was found to be 10- and 30-fold higher at the alpha 1c-AR than at the alpha 1a/d- and alpha 1b-ARs, respectively. (S)-(+)-Niguldipine was found to have high affinity for the rat alpha 1c-AR, with 42- and 22-fold lower affinity at the alpha 1a/d- and alpha 1b-ARs, respectively. Treatment of intact transfected COS-7 cells with chlorethylclonidine resulted in the inactivation of 19% of the alpha 1c-ARs, in contrast to 72% and 85% inactivation of the alpha 1a/d- and alpha 1b-ARs, respectively. Similarly to the other two alpha 1-ARs, the rat alpha 1c-AR is coupled to the activation of phospholipase C. Our data suggest that the rat alpha 1c-AR cDNA encodes an alpha 1-AR with the pharmacological properties previously defined for the alpha 1A subtype found in tissues.