Subtypes of alpha-1 and alpha-2 adrenergic receptors

Abstract

The adrenergic receptors are members of the superfamily of G protein-coupled receptors. There are three major types of adrenergic receptors: alpha 1, alpha 2, and beta. Each of these three major types can be divided into three subtypes. Within the alpha 1-adrenergic receptors, alpha 1A and alpha 1B subtypes have been defined pharmacologically on the basis of reversible antagonists, such as WB4101 and phentolamine, and the irreversible antagonist chloroethylclonidine. In at least some tissues the mechanism of action of the alpha 1A subtype is related to activation of a calcium channel, whereas the alpha 1B receptor exerts its effect through the second messenger inositol trisphosphate. Both of these receptor subtypes as well as a third, the alpha 1C, have been identified by molecular cloning. Three pharmacological subtypes of the alpha 2-adrenergic receptor have also been identified. Prototypic tissues and cell lines in continuous culture have been developed for each of these subtypes, which facilitated the...