rhodopsin mediated signaling pathway

Definition

Target type: biologicalprocess

A G protein-coupled receptor signaling pathway initiated by the excitation of rhodopsin by a photon, and ending with the regulation of a downstream cellular process. [GOC:bf, GOC:dph, GOC:hb, GOC:signaling, GOC:tb]

Rhodopsin-mediated signaling is a crucial pathway in vision, triggered by light absorption in the retina. It begins with rhodopsin, a G protein-coupled receptor (GPCR) embedded in the membrane of rod photoreceptor cells.

1. **Light Absorption:** When light enters the eye, it strikes rhodopsin, specifically its retinal chromophore. This causes a conformational change in rhodopsin, converting it from its inactive cis form to the active trans form.

2. **Activation of Transducin:** The activated rhodopsin molecule interacts with a G protein called transducin (Gt). This interaction causes transducin to release GDP and bind GTP, becoming activated.

3. **Activation of Phosphodiesterase:** The activated transducin, now bound to GTP, activates a phosphodiesterase enzyme (PDE). This activation occurs through the interaction of transducin's α subunit with PDE.

4. **Hydrolysis of cGMP:** Activated PDE catalyzes the hydrolysis of cyclic guanosine monophosphate (cGMP), a second messenger molecule. cGMP levels decrease significantly in the photoreceptor cell.

5. **Closure of Ion Channels:** cGMP normally keeps sodium (Na+) channels open in the plasma membrane of rod cells, allowing Na+ influx. However, when cGMP levels drop due to PDE activity, these channels close.

6. **Hyperpolarization:** Closure of Na+ channels reduces the flow of positive ions into the cell, leading to hyperpolarization. This change in membrane potential is the signal that is transmitted to other retinal neurons.

7. **Signal Amplification:** The rhodopsin-mediated signaling pathway exhibits significant amplification. A single photon absorbed by rhodopsin can lead to the activation of hundreds of transducin molecules, which in turn can activate thousands of PDE molecules.

8. **Adaptation and Termination:** To prevent prolonged signaling and allow adaptation to changing light conditions, several mechanisms regulate the pathway:

* **Rhodopsin Deactivation:** The activated form of rhodopsin is rapidly deactivated by a protein called rhodopsin kinase, which phosphorylates rhodopsin.
* **Arrestin Binding:** Phosphorylated rhodopsin binds to arrestin, further inhibiting its activity.
* **cGMP Resynthesis:** The levels of cGMP are restored by guanylyl cyclase, an enzyme that catalyzes the synthesis of cGMP.

9. **Visual Signal Transmission:** The hyperpolarization of the rod cell leads to a series of events in the retinal circuitry, ultimately transmitting the visual signal to the brain via the optic nerve.

The rhodopsin-mediated signaling pathway is a complex and tightly regulated process that allows us to perceive light and adapt to changes in light intensity. It is essential for vision and plays a vital role in our ability to interact with the world around us.'
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Proteins (2)

Compounds (74)