June 2017
Volume 58, Issue 8
Open Access
ARVO Annual Meeting Abstract  |   June 2017
Bicarbonate enters a rod thru its synapse to stimulate ROS-GC in its outer segment, whereas cones generate bicarbonate intracellularly from CO2
Author Affiliations & Notes
  • Clint L Makino
    Physiology & Biophysics, Boston University School of Medicine, Boston, Massachusetts, United States
  • Alexandre Pertzev
    Research Divisions of Biochemistry and Molecular Biology, Salus University, Elkins Park, Pennsylvania, United States
  • Rameshwar K Sharma
    Research Divisions of Biochemistry and Molecular Biology, Salus University, Elkins Park, Pennsylvania, United States
  • Teresa Duda
    Research Divisions of Biochemistry and Molecular Biology, Salus University, Elkins Park, Pennsylvania, United States
  • Footnotes
    Commercial Relationships   Clint Makino, None; Alexandre Pertzev, None; Rameshwar Sharma, None; Teresa Duda, None
  • Footnotes
    Support  NIH Grant EY023980
Investigative Ophthalmology & Visual Science June 2017, Vol.58, 1027. doi:
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      Clint L Makino, Alexandre Pertzev, Rameshwar K Sharma, Teresa Duda; Bicarbonate enters a rod thru its synapse to stimulate ROS-GC in its outer segment, whereas cones generate bicarbonate intracellularly from CO2. Invest. Ophthalmol. Vis. Sci. 2017;58(8):1027.

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

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Abstract

Purpose : Bicarbonate stimulates the membrane guanylate cyclase (ROS-GC) in rods and cones, increasing the circulating current and accelerating flash response kinetics. Experimentally, this effect is elicited by bicarbonate perfusion of rods and red cones attached to a piece of retina and of isolated red cones. Isolated rods do not appear to respond to bicarbonate. Red cones are thought to express carbonic anhydrase, so the apparent difference in bicarbonate uptake between rods and cones may be due to the ability of cones to convert CO2 to bicarbonate intracellularly.

Methods : Single rods and cones were recorded with a suction electrode while being perfused with bicarbonate with or without acetazolamide, a carbonic anhydrase inhibitor. In addition, recombinant ROS-GC activity was assayed with or without carbonic anhydrase in the presence of CO2, and with or without carbonic anhydrase and acetazolamide in the presence of CO2.

Results : In vitro ROS-GC activity was increased slightly by CO2 in the absence of carbonic anhydrase, but increased several fold when carbonic anhydrase was present; the latter stimulation was inhibited by acetazolamide. Isolated rods typically failed to respond to bicarbonate, but were able to do so in electrical recordings from the outer segment, if they retained their synaptic zone. Acetazolamide did not block the effect. But acetazolamide did block stimulation of ROS-GC by bicarbonate in isolated red cones and in red cones attached to a piece of retina.

Conclusions : CO2 affects phototransduction by two modes. A rod takes in bicarbonate at its synapse. In contrast, a red cone expresses carbonic anhydrase that converts intracellular CO2 to bicarbonate.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

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