Guanylate cyclase (GC) in the retina catalyzes the formation of cGMP which plays a major role in the visual transduction. Although the retinal GC has not been sequenced, three membrane bound forms of GC in rat have been characterized by cDNA cloning. However, the human GC has not been cloned from human retina or liver but has been cloned from human placenta. In this study we have investigated the presence in human retina and liver of mRNA expressing a form of guanylate cyclase which has an atrial naturetic factor receptor (ANF). For this we have utilized the RNA-polymerase chain reaction (PCR); mRNA from human retina and liver, obtained from commercial source; and a cDNA library. The cDNA obtained from the library as well as the cDNA obtained from liver or retinal mRNA was used as a template for PCR reaction. The primers were designed from the reported cDNA sequence of human placental guanylate cyclase containing the ANF receptor. A product consisting of about 700 base pairs was obtained when 5'GGG-GAA- TTC-CAT-CCT-GGA-CAA-CCT-CC-3' and 5'GGG-GAA-TTC-TAG-GTC-CGA-ACC-TTG-CC-3' were used as upstream and downstream primers respectively. A product of identical size was also obtained when using cDNA that hybridized with human brain mRNA. Sequencing of the PCR product from liver and retina, using the dideoxy sequencing method of Sanger, showed that sequences of PCR product obtained from human liver and retina mRNA were identical, and were also identical to that of the human placenta ANF receptor, which has guanylate cyclase activity. Moreover, the PCR product showed 100% sequence homology with ANF receptor. Northern blot analysis of mRNA from human retina, liver and brain showed the presence of a prominent band which hybridized with [32P] cDNA probes made from the PCR products. It appears that mRNA for the GC containing ANF receptor or closely related form is expressed in human liver, retina and possibly in brain.
