2. Chemical (ligand) gating. Some protein channel gates
are opened by the binding of a chemical substance (a
ligand) with the protein; this causes a conformational or
chemical bonding change in the protein molecule that
opens or closes the gate. This is called chemical gating
or ligand gating. One of the most important instances of
chemical gating is the effect of acetylcholine on the socalled
acetylcholine channel. Acetylcholine opens the
gate of this channel, providing a negatively charged pore
about 0.65 nanometer in diameter that allows uncharged
molecules or positive ions smaller than this diameter to
pass through. This gate is exceedingly important for
the transmission of nerve signals from one nerve cell to
another (see Chapter 45) and from nerve cells to muscle
cells to cause muscle contraction (see Chapter 7).