Coexistence of C-type natriuretic peptide and atrial natriuretic peptide systems in the bovine cornea

PURPOSE. To determine whether the cornea synthesizes natriuretic peptides a nd contains their receptors. METHODS. The synthesis of the natriuretic peptides, C-type natriuretic pept ide (CNP) and atrial natriuretic peptide (ANP), in the bovine cornea was de termined by high-performance liquid chromatography (HPLC) with radioimmunoa ssay and Southern blot analysis. The presence of natriuretic peptide recept or (NPR)-A and -B and their localizations were measured by reverse transcri ption-polymerase chain reaction (RT-PCR), in vitro autoradiography, and the activation of particulate guanylyl cyclase by natriuretic peptides in the corneal membrane. RESULTS. The serial dilution curves of corneal extracts were parallel to th e standard curves of CNP and ANP, With reversed-phase HPLC, a major immunor eactive peak of CNP or ANP was observed at the elution time corresponding w ith synthetic CNP(1-53) or atriopeptin III (APIII), respectively. The prese nce of mRNAs of CNP and ANP was also detected in the cornea by RT-PCR and/o r Southern blot analysis. Production of 3',5'-cyclic guanosine monophosphat e (cGMP) by the activation of particulate guanylyl cyclase in the corneal m embrane was stimulated by ANP, BNP, and CNP. More cGMP was produced by CNP than by the other natriuretic peptides. Specific I-125-Tyr(0)]-CNP(1-22) bi nding sites were localized in the endothelial cell layer of cornea. The app arent dissociation constant (K-d) value of the cornea was 3.06 +/- 0.73 nM and the maximum binding capacity was 3.40 +/- 0.63 femtomoles/mm(2). Both N PR-A and NPR-B mRNAs were detected by RT-PCR. CONCLUSIONS. The cornea synthesizes CNP and ANP and contains their receptor s. These results suggest that the CNP and ANP systems coexist in the bovine cornea.