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Three types of cells help detect light

The internal clock shared by mammals is reset everyday by 3 types of light-sensitive cells - rods, cones and a 3rd type of cell that produces a protein, say scientists.

tech reviews Updated: Jun 26, 2003 13:13 IST
PTI

The internal clock shared by all mammals is reset each day by just three types of light-sensitive -- rods and cones, known about since the 19th century, and a third type of cell that produces a recently discovered protein, an international team of scientists reports.

The finding is as basic as it is controversial: Other scientists maintain the eyes include other types of light-sensitive cells as well.

The new study, done on mice, found that the cell trio likely accounts for the entire ability of all mammals to detect light.

Beyond seeing, the eyes also track changes in light levels to signal the body's clockwork adjustment of everything from sleep patterns to blood pressure.

"Are there other light-detection systems in the eye?" asks study co-author King-Wai Yau, of Johns Hopkins University and the Howard Hughes Medical Institute. "Essentially none. When you take these things out, that's it."

The study's details were to appear today in the electronic edition of the journal Nature.

Dr. Russell Van Gelder, of Washington University Medical School, praised the study but said it marked "the beginning of research into this field rather than its end."

Scientists have known since the 1850s that the specialised cells found in the eyes called rods and cones are sensitive to light. In 1998, scientists discovered that nerve cells in the retina that produce a protein called melanopsin also detect light, though they aren't involved in vision.