Magazine article Science News

Turnabout in Vision: Messenger Unmasked

Magazine article Science News

Turnabout in Vision: Messenger Unmasked

Article excerpt

A small molecule called cyclic GMP has now been recognized by scientists as the crucial messenger chemical in both types of cells that sense light in animals' eyes. Light striking the retina of the eye trigges in these photoreceptor cells a cascade of molecular events that eventually generates the electricla signals essential for vision. For almost 15 years, scientists had favored a hypothetical description of this cascade in which light released calcium from storage within a photoreceptor cell, and this "messenger" calcium interacted with channels in the outer membrane to produce the electrical signal.

The recent direct evidence that the internal messenger is cyclic GMP rather than calcium ions comes out of experiments with a powerful, relatively new technique called "patch clamping" (SN: 11/7/81, p. 295). Rather than dealing with all the complexities of a cell, the patchclamp technique isolates a small circular segment of outer membrane from a photoreceptor cell--a rod or a cone. Solutions containing calcium ions or cyclic GMP are applied to each side of this membrane patch, and channel activity is monitored.

Such experiments demonstrate that exposing the inner surface of the rod cell the channels to open, but calcium does not have this effect. These results were reported earlier this year by several independent research teams led by Evgeniy E. Fesenko at the USSR Academy of Sciences in Pushchino, King-Wai Yu at the University of Texas Medical Branch in Galveston, T. …

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