Abstract
It is now known that the alpha sub(1)-adrenoceptors comprise a heterogenous population of receptor subtypes. Three of the alpha sub(1)-adrenoceptors have now been cloned including the alpha sub(1a/d)-adrenoceptor, the alpha sub(1b)-adrenoceptor and the alpha sub(1c)-adrenoceptor. Radioligand binding assays and functional studies in native tissues support the existence of alpha sub(1)-adrenoceptor subtypes; however, complete agreement between the pharmacological properties of the cloned receptors and receptors from native tissues has not yet been achieved. We have reported that the rat parotid gland contains the alpha sub(1A)-adrenoceptor and an alpha sub(1)-adrenoceptor that has not been identified previously. Using radioligand binding we will describe the pharmacological characteristics of this atypical alpha sub(1)-adrenoceptor subtype. We will also provide evidence using functional measurements of smooth muscle contraction that this receptor subtype is also present in other tissues from other species. Finally, the similarity between the atypical alpha sub(1)-adrenoceptor and alpha sub(1)-adrenoceptors with low affinity for prazosin will be discussed.