Characterization and localization of the rabbit ocular calcitonin gene-related peptide (CGRP)-receptor component protein (RCP)

PURPOSE. To determine whether the calcitonin gene-related peptide (CGRP) re ceptor component protein (RCP), a novel signal transduction molecule, is re quired for CGRP signaling in the rye and to determine potential ocular site s of CGRP action. METHODS. The cDNA for the rabbit ocular RCP homologue was cloned using a co mbination of reverse transcription-polymerase chain reaction (RT-PCR) and r apid amplification of cDNA ends (RACE). Function of the rabbit ocular RCP w as assessed using a sensitive oocyte-based assay, which utilizes the protei n kinase A (PKA)-sensitive cystic fibrosis transmembrane conductance regula tor (CFTR) as a sensor of cAMP formation. RCP expression in the rabbit eye was localized using immunohistochemistry. RESULTS. A 2063-bp cDNA for the rabbit ocular RCP was cloned and sequenced. Expression of the rabbit RCP cDNA confers CGRP responsiveness in a sensiti ve oocyte-based assay. Antisense oligonucleotides made to the ocular RCP ab olishes CGRP responsiveness of ciliary body and iris mRNA in the oocyte-CFT R assay. Localization of RCP protein in the rabbit eye using immunohistoche mistry demonstrated RCP immunoreactivity in the ciliary body and iris blood vessels, as well as in layers of the ciliary epithelium. CONCLUSIONS. The rabbit ocular RCP appears to be required for signal transd uction at ocular CGRP receptors and is localized to sites previously report ed to bind CGRP, which affect intraocular pressure and neurogenic inflammat ion.