Modes of Accessing Bicarbonate for the Regulation of Membrane Guanylate Cyclase (ROS-GC) in Retinal Rods and Cones

• Published in: eNeuro 2019-01, Vol.6 (1), p.ENEURO.0393-18.2019
• Main Authors: Makino, Clint L, Duda, Teresa, Pertzev, Alexandre, Isayama, Tomoki, Geva, Polina, Sandberg, Michael A, Sharma, Rameshwar K
• Format: Article
• Language: English
• Subjects: Acetazolamide - pharmacology; Ambystoma; Animals; Bicarbonates - metabolism; Carbon Dioxide - metabolism; Carbonic Anhydrase Inhibitors - pharmacology; Carbonic Anhydrases - genetics; Carbonic Anhydrases - metabolism; Cattle; Cell Membrane - drug effects; Cell Membrane - metabolism; Chlorocebus aethiops; COS Cells; Cyclic GMP - metabolism; Gene Expression; Guanylate Cyclase - genetics; Guanylate Cyclase - metabolism; Mice; New Research; Receptors, Cell Surface - metabolism; Recombinant Proteins - metabolism; Retinal Cone Photoreceptor Cells - cytology; Retinal Cone Photoreceptor Cells - drug effects; Retinal Cone Photoreceptor Cells - metabolism; Retinal Rod Photoreceptor Cells - cytology; Retinal Rod Photoreceptor Cells - drug effects; Retinal Rod Photoreceptor Cells - metabolism; Tissue Culture Techniques; Vision, Ocular - drug effects; Vision, Ocular - physiology
• ISSN: 2373-2822; 2373-2822
• DOI: 10.1523/ENEURO.0393-18.2019

The membrane guanylate cyclase, ROS-GC, that synthesizes cyclic GMP for use as a second messenger for visual transduction in retinal rods and cones, is stimulated by bicarbonate. Bicarbonate acts directly on ROS-GC1, because it enhanced the enzymatic activity of a purified, recombinant fragment of bovine ROS-GC1 consisting solely of the core catalytic domain. Moreover, recombinant ROS-GC1 proved to be a true sensor of bicarbonate, rather than a sensor for CO . Access to bicarbonate differed in rods and cones of larval salamander, , of unknown sex. In rods, bicarbonate entered at the synapse and diffused to the outer segment, where it was removed by Cl -dependent exchange. In contrast, cones generated bicarbonate internally from endogenous CO or from exogenous CO that was present in extracellular solutions of bicarbonate. Bicarbonate production from both sources of CO was blocked by the carbonic anhydrase inhibitor, acetazolamide. Carbonic anhydrase II expression was verified immunohistochemically in cones but not in rods. In addition, cones acquired bicarbonate at their outer segments as well as at their inner segments. The multiple pathways for access in cones may support greater uptake of bicarbonate than in rods and buffer changes in its intracellular concentration.