gated sodium channel function comes from the secretions found in
the skin of certain tropical frogs, such as Phyllobates terribilis from the
Amazon jungle in South America. A collection of closely related mole-
cules have been identified, called batrachotoxins (BTXs). The molecu-
lar structure of the first BTX to be identified is shown here.
Ooy° - TS NH
HO
BatrachotoxinOther BTXs are close chemical relatives.
The BTXs interact with voltage-gated sodium channels in a way
different from TTX and STX: rather than blocking the pore of the
channel and preventing sodium ions from passing through, BTXs
interact with the channel protein and prevent it from closing. If the
channels are open all the time, Na* flows through continuously, and
action potentials cannot be generated. Nerve signaling does not work,
and the same end results as with TTX and STX occur.
The muscle weakening and paralytic properties of BTX-containing
frog secretions were discovered long ago by tribal peoples of the Ama-
zonian jungle. Secretions were and still are collected from Phyllobates
frogs and applied to the tips of arrows and darts used for hunting.
Animals hit by such poison-tipped darts quickly become impaired in
their ability to move and can be more easily captured.