Name: light-gated ion flow in channel rhodopsins
Uploaded: 2023-04-30T10:11:31.000Z
Duration: 1 min 11 s
Channel: JoVE

Most unicellular green algae have light-sensitive transmembrane proteins called channelrhodopsins or ChRs that serve as sensory photoreceptors in the flagellar membrane.
The ChR is a cation channel with a photon-absorbing molecule or chromophore covalently bound within its transmembrane domain.
Upon absorption of light, the chromophore triggers a conformational change in the channel, allowing the cations to pass through.
This cation influx generates an electric current in the flagellum, causing it to propel the alga towards light.
Due to their light sensitivity, channelrhodopsins are often used as a research tool in animal models.&#160;
For instance, a channelrhodopsin-expressing neuron can be triggered externally with just exposure to light and initiate transmission of a nerve impulse.
Using this technique, called optogenetics, scientists can map the activity within the neural circuit, even in the deeper areas of the brain without the use of any invasive equipment.

channel rhodopsins

Channel Rhodopsins

Most organisms use photoreceptors to sense and respond to light. Examples of photoreceptors include bacteriorhodopsins and bacteriophytochromes in some bacteria, phytochromes in plants, and rhodopsins in the photoreceptor cells of the vertebral retina. The light-sensitive property of these receptors is because of the bound chromophores, such as bilin in the phytochromes and retinal in the rhodopsins.
Rhodopsins belong to the family of cell surface proteins called G-protein coupled receptors, which are involved in signal transduction across biological membranes. The rhodopsin family of proteins acquired divergent functions during evolution, such as acting as light receptors, ion pumps, and ion channels. One such subfamily of rhodopsins is channelrhodopsins or ChR that function as light-sensitive ion channels. Naturally occurring ChRs were first discovered in green microalgae, Chlamydomonas reinhardtii. Their role in algae involves coupling light to flagellar motion, thereby allowing the organism to acquire optimum light for photosynthesis and survival.
The structure of ChR protein includes seven membrane-spanning domains and a covalently bound light-sensitive protein called an all-trans-retinal chromophore. Upon illumination with blue light, ChR undergoes a conformational change and opens to allow the diffusion of cations, such as H+, Na+, K+, and Ca+, passively down their concentration gradient. The influx of ions across the membrane produces large photocurrents that activate the cell. Due to their fast activation by light, ChR have given rise to a new research approach in neurobiology called optogenetics.

Most organisms use photoreceptors to sense and respond to light. Examples of photoreceptors include bacteriorhodopsins and bacteriophytochromes in some ...

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JoVE Core

Cell Biology

Unit 1

Channels and the Electrical Properties of Membranes

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KEY TERMS AND CONCEPTS

light-gated ion flow in channel rhodopsins

Channel rhodopsins are light-sensitive ion channels found in some organisms. They belong to the rhodopsin family, which also includes photoreceptors in bacteria, plants, and the vertebrate retina. These proteins use bound chromophores, such as retinal in rhodopsins and bilin in phytochromes, to respond to light.

Rhodopsins are a group of cell surface proteins called G-protein coupled receptors. These proteins help move signals across biological membranes. Over evolution, the rhodopsin family gained different roles, including light sensing, ion pumping, and ion channel activity.

Channel rhodopsins, or ChRs, were first found in the green microalga Chlamydomonas reinhardtii. In algae, they help link light to flagellar motion. This connection helps the organism move toward the best light conditions for photosynthesis and survival.

A channel rhodopsin protein has seven membrane-spanning domains and a covalently bound all-trans-retinal chromophore. When blue light hits the protein, it changes shape and opens. Cations such as H+, Na+, K+, and Ca+ then move down their concentration gradient through the membrane.

This ion flow creates large photocurrents that activate the cell. Because channel rhodopsins respond so quickly to light, they have become important in neurobiology. This light-controlled approach is called optogenetics.

Light-Gated Ion Flow in Channel Rhodopsins

light-gated-ion-flow-in-channel-rhodopsins

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resting potential decay

Resting Membrane Potential Maintenance

The resting membrane potential stays near -70 mV in a neuron because the membrane allows ions to move in a selective way. At rest, the membrane is slightly permeable to sodium ions (Na+) and chloride ions (Cl-) and highly permeable to potassium ions (K+). Ion channels and pumps keep the concentration differences between the inside and outside of the cell in place. Potassium leak channels let K+ move out of the cell at rest. This outward movement makes the inside of the cell more negative. A...

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Channel rhodopsins are light-sensitive ion channels found in some organisms. They belong to the rhodopsin family, which also includes photoreceptors in bacteria, plants, and the vertebrate retina. These proteins use bound chromophores, such as retinal in rhodopsins and bilin in phytochromes, to respond to light. Rhodopsins are a group of cell surface proteins called G-protein coupled receptors. These proteins help move signals across biological membranes. Over evolution, the rhodopsin family...

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excitatory-and-inhibitory-effects-of-neurotransmitters

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muscle contraction

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the-role-of-ion-channels-in-neuronal-computation

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key terms and concepts

Explore how channel rhodopsins use blue light to open ion channels, create photocurrents, and help algae move. A clear high school biology summary.

Light-Gated Ion Flow in Channel Rhodopsins | JoVE K12

cell biology

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Light-Gated Ion Flow in Channel Rhodopsins

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