Refer to the figure. The figure shows the molecular events occurring in a rod photoreceptor in the absence of light.Which of the following best describes the "dark current" that is active in these cells?

Question

Refer to the figure.  The figure shows the molecular events occurring in a rod photoreceptor in the absence of light.Which of the following best describes the "dark current" that is active in these cells?

Quizplus · Accepted Answer

In the absence of light, the rod cell membrane is depolarized due to the presence of an open channel that allows Na+ and Ca2+ to flux into the cell. This channel is permeable to Na+ and Ca2+ and is known as a non-selective cation channel. This channel is kept open by the presence of cyclic guanosine monophosphate (cGMP) in the cytoplasm, which binds to and activates the channel. GMP-gated channels prevent Na+ and Ca2+ from entering the cell but in this case, the channel is open, therefore, option B is incorrect. Transducin and PDE are not yet activated since light is absent, therefore, option D is incorrect. A change in rhodopsin leads to depolarization, not hyperpolarization, of the membrane, therefore, option E is incorrect. Since the channel is open, Na+ is able to enter the cell, therefore option C is the correct choice.

Refer to the Figure