Further evidence that the classical α1A- and cloned α1c-adrenoceptors are the same subtype

Abstract

We compared the inactivation of [³H]prazosin binding sites in membrane preparations of cell-lines expressing the cloned α_1b, α_1c and α_1d-adrenoceptors after pretreatment with the alkylating agents, 10 μM chlorethylclonidine or 10 nM SZL-49 (1-(4-amino-6,7-dimethoxy-2-quinazolinyl)-4-(2-bicyclo[2.2.2]octa-2,5-diene-Z-carbonyl)-piperazine). The cloned α_1b-adrenoceptor exhibited a similar inactivation profile to that of the classical α_1B-adrenoceptor of rat liver in that chlorethylclonidine in contrast to SZL-49 produced a marked degree of inactivation. A similarity between the cloned α_1c-adrenoceptor and the classical α_1A-adrenoceptor of rat submaxillary gland was also noted in that both subtypes were highly sensitive to SZL-49 but relatively insensitive to chlorethylclonidine. The cloned α_1d-adrenoceptor displayed a unique profile in that both chlorethylclonidine and SZL-49 produced a marked inactivation of this subtype. The similarity of the alkylation-inactivation profiles between the cloned α_1c and classical α_1A-adrenoceptors support the recent proposal that these two α₁-adrenoceptors in fact correspond to the same subtype.