April 2014
Volume 55, Issue 13
Free
ARVO Annual Meeting Abstract  |   April 2014
Bicarbonate Regulates Cyclic GMP Synthesis in Retinal Rods and Cones
Author Affiliations & Notes
  • Xiao-Hong Wen
    Department of Ophthalmology, Massachusetts Eye and Ear Infirmary & Harvard Medical School, Boston, MA
  • Tomoki Isayama
    Department of Ophthalmology, Massachusetts Eye and Ear Infirmary & Harvard Medical School, Boston, MA
  • Alexandre Pertzev
    Research Divisions of Biochemistry and Molecular Biology, The Unit of Regulatory and Molecular Biology, Salus University, Elkins Park, PA
  • Rameshwar K Sharma
    Research Divisions of Biochemistry and Molecular Biology, The Unit of Regulatory and Molecular Biology, Salus University, Elkins Park, PA
  • Clint L Makino
    Department of Ophthalmology, Massachusetts Eye and Ear Infirmary & Harvard Medical School, Boston, MA
  • Teresa Duda
    Research Divisions of Biochemistry and Molecular Biology, The Unit of Regulatory and Molecular Biology, Salus University, Elkins Park, PA
  • Footnotes
    Commercial Relationships Xiao-Hong Wen, None; Tomoki Isayama, None; Alexandre Pertzev, None; Rameshwar Sharma, None; Clint Makino, None; Teresa Duda, None
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science April 2014, Vol.55, 3032. doi:
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      Xiao-Hong Wen, Tomoki Isayama, Alexandre Pertzev, Rameshwar K Sharma, Clint L Makino, Teresa Duda; Bicarbonate Regulates Cyclic GMP Synthesis in Retinal Rods and Cones. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3032.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose: Bicarbonate, which plays a crucial role in physiological pH buffering, also regulates the catalytic activities of some membrane guanylate cyclases. To test for such a role in photoreceptors, we determined the effect of bicarbonate on ROS-GC1 and ROS-GC2 guanylate cyclase activities in biochemical assays and in single cell recordings of salamander rods and cones.

Methods: Bovine ROS-GC1, ROS-GC2, or a variety of truncated mutants of ROS-GC1 were transiently expressed in COS cells and catalytic activities were evaluated in the presence of bicarbonate. In some experiments GCAP1 or 2 was added at low calcium. The suction electrode method was used to record flash responses of single salamander rods and cones while exposing them to bicarbonate or to Ringer’s equilibrated with a high concentration of carbon dioxide.

Results: Bicarbonate increased the activities of ROS-GC1 and 2 by three to four-fold with an EC50 of ~30 to 40 mM. Furthermore, bicarbonate and GCAPs stimulated ROS-GC activity synergistically at low calcium. In single cell recordings, the addition of bicarbonate increased circulating current by as much as two-fold in rods and red cones attached to large pieces of retina. Ringer’s with a high concentration of carbon dioxide also increased the circulating current in red cones but the effect was not as readily reversible as that of bicarbonate.

Conclusions: By stimulating the basal rate of cyclic GMP synthesis, bicarbonate increases the circulating current and the size of the photon response. Since bicarbonate and GCAPs regulate guanylate cyclase activity synergistically, bicarbonate could also affect photon response kinetics. These results suggest that bicarbonate provides an additional mechanism of phototransduction modulation.

Keywords: 648 photoreceptors • 508 electrophysiology: non-clinical • 442 carbon dioxide  
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