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 Symbiotic bacteria: from hitchhiker to beetle bodyguard
28.04.2017 | Johannes Gutenberg-Universität Mainz

nachricht Nose2Brain – Better Therapy for Multiple Sclerosis
28.04.2017 | Fraunhofer-Institut für Grenzflächen- und Bioverfahrenstechnik IGB

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Fighting drug resistant tuberculosis – InfectoGnostics meets MYCO-NET² partners in Peru

28.04.2017 | Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

 
Latest News

Wireless power can drive tiny electronic devices in the GI tract

28.04.2017 | Medical Engineering

Ice cave in Transylvania yields window into region's past

28.04.2017 | Earth Sciences

Nose2Brain – Better Therapy for Multiple Sclerosis

28.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>