12 Ion Channels!
Carrier Ionophore: Carry ions through lipid bilayer via diffusion
Channel-forming Ionophore: Channel spans entire bilayer through which ions can
Valinomycin:ionophore for K+. Its shape makes it highly selective to K+. L and D
KcsA: Bacterial K+ channel tetramer. Contains a selectivity ﬁlter for K+. Can manage
10 ions per second, 10 times a greater rate than that of valinomycin. Functional
groups at openings geometrically favour only K+ ions.
Ligand-Gated Ion Channels, such as nicotinic Ach receptors, have 4 transmembrane
helices and 5 pseudo-symmetric subunits. Antagonized by bungarotoxin, tubocuraine
(arrow poison curare) and