Question

What alteration to an HCN channel will reduce the transport of K+ in favor of Na+ transport? HCN channels are permeable to both K+ and Na+ ions.

Answer 1

Decreasing the diameter of the channel by removing aa's. Since Na+ is chemically similar to K+, one can assume the difference must be due to the size of the atom. The K+ ion is larger than the Na+ ion, so reducing the diameter of the channel can allow Na+ to enter while preventing K+ entry. This explains clearly and perfectly how reducing the diameter reduces the

transport of K+ in favor of Na+ transport.