NATRIURETIC PEPTIDE BINDING-SITES IN THE GILLS OF THE POUCHED LAMPREYGEOTRIA-AUSTRALIS

Iodinated atrial natriuretic peptide (ANP) binding sites were examined in the gills and ventral aorta of the adult upstream-migrating lampre y Geotria australis using tissue section autoradiography, in vitro com petition analysis and affinity cross-linking, while guanylate cyclase assays were performed on gill membranes of both adult and juvenile lam preys, A partial natriuretic peptide (NP) receptor sequence was amplif ied using reverse transcription/polymerase chain reaction (RT-PCR), Th e results indicated that there was specific NP binding to the aortic e ndothelium and to pillar cell regions in the axial plate and secondary lamellae, In competition studies, 50 % of NP binding was abolished by 4 nmol l(-1) rat ANP, 35 nmol l(-1) porcine C-type NP (CNP) and 45 nm ol l(-1) C-ANF (a truncated ANP), Affinity cross-linking followed by S DS-PAGE demonstrated two binding sites at 205 and 65 kDa under non-red ucing conditions and at 85 and 65 kDa under reducing conditions. Guany late cyclase assays demonstrated that, while no NP-stimulated GC activ ity occurred in adult lampreys, NP-stimulated enhancement of cyclic GM P accumulation was found in juveniles in fresh water and more particul arly in salt water. RT-PCR amplified a 471 base pair fragment with 68 % amino acid sequence homology to the eel natriuretic peptide receptor D (NPR-D), This study suggests that NP binding sites in the adult gil l and aorta are of an NPR-C/D type, whereas an additional GC-coupled s ite exists in juveniles.