Differential laminar expression of particulate and soluble guanylate cyclase genes in rat retina

Expression of both particulate and soluble forms of guanylate cyclase have been identified in adult rat retina using reverse transcriptase-PCR amplification of retinal RNA and sequencing of the cloned cDNAs. Over a 267-amino acid region, the retinal particulate guanylate cyclase was found to be identical in sequence to the GC-A form of the enzyme found in many tissues. No expression of the closely related GC-B or GC alpha forms of the enzyme was found. mRNA corresponding to both subunits of the soluble form of guanylate cyclase were detected in retinal. The sequence corresponding to the 70-kDa subunit was identical to that from rat lung over a 304-amino acid region and the sequence corresponding to the 82-kDa subunit showed only one amino acid difference over a 275-amino acid region. From Northern analyses the level of expression of the soluble guanylate cyclase in retina was higher than that in lung. In situ hybridization to sections of adult retina indicated that the particulate guanylate cyclase was expressed predominantly in rod photoreceptors. Although the soluble form of the enzyme was detected in all retinal layers, the level of expression was much higher in the inner nuclear layer. The results suggest that multiple enzymes and hence multiple regulatory pathways may control cGMP levels in rod photoreceptors and that cGMP may play an important role in neurons of the inner retina.