Which of the following best describes the permeability to sodium and potassium in rod cells in response to the light?: (A) Decreased sodium permeability, decreased potassium permeability, (B) Decreased sodium permeability, increased potassium permeability, (C) Decreased sodium permeability, no change in potassium permeability, (D) Increased sodium permeability, decreased potassium permeability
Answer is C. Activated rhodopsin (metarhodopsin II) closes cGMP-gated sodium channels by lowering levels of cGMP; this action decreases sodium permeability. Potassium permeability is not affected.