Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Vision-producing cells fail ’taste-test,’ treat key light-detecting molecules identically

23.10.2003


Johns Hopkins scientists have discovered that the eye’s vision-producing rods and cones cannot tell the difference between their respective light-detecting molecules. The findings appeared in a recent issue of Nature.



At the heart of the researchers’ side-by-side comparison is the quest to solve a fundamental mystery of vision: how rods and cones have such different sensitivities to light despite using very similar processes to detect it.

Rods function in near darkness, while rarer cones function in bright light, providing vibrant color vision. In each cell type, the process of forming vision begins when light activates a cell-specific molecule, called a visual pigment, and ends when the cell emits an electrical signal.


To set up the "taste test," the Hopkins researchers created frogs whose rods contained, in addition to their usual pigment, a pigment found only in cones. The researchers expected the rods to treat the two pigments differently -- picking up signals only from its native pigment and spurning the other -- or to behave a little like cones.

"Surprisingly, the cell’s response to light was identical regardless of which pigment was activated," says King Wai Yau, Ph.D., professor of neuroscience in Johns Hopkins’ Institute for Basic Biomedical Sciences. "It’s as though the label of ’rod’ pigment and ’cone’ pigment is gone. The pigments alone do not explain the cells’ functional differences."

Some scientists had speculated that the pigment defines a cell’s role in vision, making a rod, a rod or a cone, a cone. Until now, however, no experiments have measured whether starting the process with the "wrong" pigment affects the cell’s critical characteristics -- the size and shape of the electrical signals it produces.

Studying individual rods containing both the rod pigment, called rhodopsin, and a cone pigment (called human red cone pigment), the Johns Hopkins scientists discovered for the first time that rod machinery treats both pigments the same. The findings prove that functional differences between rods and cones stem in part from the cellular environments they offer, rather than inherent differences in their pigments, says Yau, who is also a Howard Hughes Medical Institute investigator.

Both pigments detect light by absorbing it and changing their structures in specific ways (called isomerization), thereby triggering events that generate an electrical signal. The pigment molecules then relax and eventually return to their original forms, ready to start the process anew.

Cone pigment relaxes 10 times faster than rod pigment, which led many scientists to assume that this timing difference would explain rods’ and cones’ different sensitivities. However, the Hopkins team showed that both pigments were "turned off" at the same time when in the same cell, well before either pigment relaxed, says Vladimir Kefalov, Ph.D., a postdoctoral fellow in neuroscience.

The real off-switch turns out to be addition of a phosphate group to the activated pigment, and subsequent binding by a protein called arrestin, says Yingbin Fu, Ph.D., a Howard Hughes postdoctoral fellow in neuroscience. Even though rods and cones each have their own phosphate-adding enzyme, the rod version recognizes the cone pigment as an equally appropriate target, says Yau. In separate experiments using a mutant version of the cone pigment that couldn’t be phosphorylated, the rod did in fact produce a longer signal.

Only one inherent characteristic of the cone pigment -- its instability -- seemed to contribute to rods’ and cones’ sensitivity differences. Unlike rod pigment, cone pigment spontaneously changes its shape even without exposure to light, causing cones to generate false signals that reduces their sensitivity. Through a number of calculations, Kafelov determined that, in primates, this cone pigment "noise" could account for roughly half of the normal sensitivity difference between cones and rods.


The experiments were funded by the National Institutes of Health and the Howard Hughes Medical Institute. Authors on the paper are Kefalov, Fu, Yau and Nicholas Marsh-Armstrong, all of Johns Hopkins. Marsh-Armstrong is also affiliated with the Kennedy Krieger Institute.

On the Web:
Nature, Oct. 2, 2003
http://www.nature.com/nature

Joanna Downer | EurekAlert!
Further information:
http://www.hopkinsmedicine.org/
http://www.nature.com/nature

More articles from Life Sciences:

nachricht Bolstering fat cells offers potential new leukemia treatment
17.10.2017 | McMaster University

nachricht Ocean atmosphere rife with microbes
17.10.2017 | King Abdullah University of Science & Technology (KAUST)

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Ocean atmosphere rife with microbes

17.10.2017 | Life Sciences

Neutrons observe vitamin B6-dependent enzyme activity useful for drug development

17.10.2017 | Life Sciences

NASA finds newly formed tropical storm lan over open waters

17.10.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>