Immunohistochemical localisation of alpha1B-adrenergic receptors in the rat iris

Expression of the alpha1B-adrenergic receptor was investigated immunohistochemically in the rat iris, cornea and superior cervical ganglion by using antibodies raised in chickens immunised with a peptide corresponding to a portion of the 3rd intracellular loop common to the human, hamster and rat alpha1B-adrenergic receptor. Antibodies stained COS and HEK cell membranes of cells transfected with DNA encoding and expressing the hamster alpha1B-adrenergic receptor but not membranes from cells transfected with DNA encoding and expressing the rat alpha1A-adrenergic receptor or the rat alpha1D-adrenergic receptor. Staining was abolished by preincubation of the antibodies with the peptide used for immunisation. The distribution of alpha1B-adrenergic receptor was examined immunohistochemically with this antibody (1BI3) and a previously characterised antibody (Ab506) raised in rabbits against the carboxyl-terminal decapeptide of the receptor. In the iris, alpha1B-adrenergic receptor was detected in the dilator muscle, ciliary processes and posterior epithelium but no staining was observed in the superior cervical ganglion with either antibody. By contrast, differences in tissue staining between 1BI3 and Ab506 were observed for the sphincter muscle of the iris and for the cornea. 1BI3 stained both tissues intensely, whereas Ab506 only stained the cornea weakly and the sphincter not at all. Reverse transcription/polymerase chain reaction and nucleotide sequencing confirmed the presence of mRNA encoding the epitopes recognised by 1BI3 and Ab506 in cornea and other tissues. We conclude that (1) there is a good correlation between alpha1B-adrenergic receptor mRNA and protein expression in the iris, (2) mRNA, but not protein, is detected in the superior cervical ganglion and (3) additional processes may regulate receptor expression in the cornea.