Gating of Protein Channels. Gating of protein channels
provides a means of controlling ion permeability of
the channels. This is shown in both panels of Figure 4-5
for selective gating of sodium and potassium ions. It is
believed that some of the gates are actual gatelike extensions
of the transport protein molecule, which can close
the opening of the channel or can be lifted away from the
opening by a conformational change in the shape of the
protein molecule itself.
The opening and closing of gates are controlled in two
principal ways: