What happens to the concentration of cGMP when rhodopsin activates transducin?

When rhodopsin activates transducin, the concentration of cyclic guanosine monophosphate (cGMP) decreases. This process is part of the phototransduction pathway in the photoreceptor cells of the retina.

In darkness, cGMP levels are relatively high, which keeps sodium channels in the photoreceptor membranes open, allowing a steady influx of sodium ions and resulting in a depolarized state of the cell. When rhodopsin is exposed to light, it changes conformation and activates the G protein transducin. Once transducin is activated, it in turn activates phosphodiesterase (PDE), an enzyme that hydrolyzes cGMP into GMP.

As phosphodiesterase breaks down cGMP, the levels of cGMP in the cell decrease. This reduction in cGMP leads to the closure of sodium channels, causing the cell to hyperpolarize. The hyperpolarization decreases the release of neurotransmitters, signaling the presence of light to the bipolar cells and ultimately to the brain.

Therefore, the process directly links the activation of rhodopsin to the decrease in cGMP concentration, illustrating a crucial step in the mechanism by which photoreceptors convert