LOCALIZATION OF CYCLASE AND CYCLIC NUCLEOTIDE PHOSPHODIESTERASE ACTIVITIES IN RETINAL PIGMENT EPITHELIAL CELLS OF THE GUINEA PIG

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The localization of cyclic nucleotide synthesizing-(adenylate cyclase and guanylate cyclase) and degrading-(cAMP- and cGMP-phosphodiesterase) enzyme activities was studied histo- and cytochemically in the retinal pigment epithelial cells (RPE) by means of newly developed methods. Adenylate cyclase activity was localized on the apical plasmalemma and gap junctions of the RPE, but not on the outer segments of the photoreceptors held by apical plasmalemma of the RPE. Guanylate cyclase activity was observed on the apical plasmalemma and gap junctions of the RPE, and also intensely on the disc and plasma membranes of the photoreceptor outer segments. cAMP-phosphodiesterase activity was localized on the apical plasmalemma of the RPE, but no reaction products were seen on the gap junctions and on the outer segments. In contrast, intense cGMP-phospho-dieterase activity was observed both on the apical plasmalemma of the RPE and in the outer segments. There were no notable reaction precipitates on the gap junctions of the RPE. In the control experiments, cAMP- and cGMP-phosphodiesterase activity was drastically inhibited both in the RPE and outer segments by 2 mM IBMX or 5 mM theophyline, two potent inhibitors to cyclic nucleotide phosphodiesterse. No such specific potent inhibitors exist for cyclase. The results are discusscd in connection with the phagocytotic activity and other important functions of the RPE cells.
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