Evidence of a guanylyl cyclase natriuretic peptide receptor in the gills of the new zealand hagfish Eptatretus cirrhatus (Class Agnatha)

Abstract

Natriuretic peptide binding sites were examined in the gills of the hagfish Eptatretus cirrhatus (Class Agnatha, subfamily Eptatretinae) using radio-ligand binding techniques, molecular cloning and guanylyl cyclase assays. Iodinated rat atrial natriuretic peptide ((125)I-rANP) and iodinated porcine C-type natriuretic peptide ((125)I-pCNP) bound specifically to the lamellar folds and cavernous tissue of E. cirrhatus gills, and 0.3 nmol l(−1) rat ANP competed for 50 % of specific (125)I-rANP binding sites. Affinity cross-linking of (125)I-rANP to gill membranes followed by sodium dodecylsulphate-polyacrylamide gel electrophoresis revealed a single binding site of 150 kDa. In the presence of Mn(2+), 0.1 nmol l(−1) rANP inhibited cGMP production, whereas 1 micromol l(−1) rANP stimulated cGMP production rates. At 1 micromol l(−1), pCNP also stimulated cGMP production. The production of cGMP was also measured in the presence and absence of ATP with either Mn(2+) or Mg(2+). Reverse transcriptase polymerase chain reaction (RT-PCR) of hagfish gill RNA, followed by cloning and sequencing of PCR products, produced a partial cDNA sequence of a natriuretic peptide guanylyl cyclase receptor. The deduced amino acid sequence indicated 87–91 % homology with other natriuretic peptide guanylyl cyclase receptors. This study indicates the presence of a natriuretic peptide guanylyl cyclase receptor in the gills of E. cirrhatus that is similar to the natriuretic peptide guanylyl cyclase receptors in higher vertebrates. These observations demonstrate that the coupling of natriuretic peptide receptors with guanylyl cyclase has a long evolutionary history.