Bicarbonate, an important naturally occurring compound in the body, plays essential roles in buffering pH, aiding in digestion, and neutralizing lactic acid produced during physical exertion. Much of the bicarbonate in our bodies comes from carbon dioxide that is produced as waste in all cells as well as from that ingested with certain foods and beverages.
Now, a study led by HMS researchers in the Makino Laboratory at Massachusetts Eye and Ear reports that bicarbonate also alters how we see: It modifies the visual signal generated by specialized retinal cells that detect light. The study appeared online March 12 in the Journal of Biological Chemistry.
Within those specialized cells, known as rod and cone photoreceptors, a soluble molecule called cGMP links photon absorption to the electrical activity of a photoreceptor. When it is exposed to light, cGMP is destroyed and ion channels are closed. Positively charged sodium ions cease to enter the rod or cone, and the membrane potential becomes more negative or hyperpolarized. Bicarbonate helps photoreceptors recover from the loss of cGMP by stimulating guanylate cyclase, an enzyme key to the synthesis of cGMP.
“By opposing the effect of light, bicarbonate limits the size of the photon response and quickens its recovery,” says lead author Clint Makino, an HMS associate professor of ophthalmology at Mass Eye and Ear and director of the Makino Laboratory. “As a result, sensitivity to light is slightly lower, but our ability to track moving objects is improved. An intriguing implication is that vision may change with metabolic state, although further research is necessary to confirm this.”
“It is now known,” he adds, “that in some types of retinal diseases, a genetic defect causes cGMP in the rods and cones to rise to lethal levels. Once lost, rods and cones are not replaced, leading to irreversible blindness.”
Scientists in the Makino Laboratory want to investigate the possibility that controlling bicarbonate levels in the eye will slow the progress of, or even prevent, eye diseases.
Photo: Ralph C. Eagle, Jr./Science Source