S N
\
N Zo
®
Nicotine N
OCH; H CHa
TubocurarineThe AChR that binds nicotine is blocked (antagonized) by the mole-
cule tubocurarine, identified from a South American curare prepara-
tion, a plant extract used as an arrow-tip poison by native hunters in
the Amazonian jungle. A variety of plants are used to make curare; the
plant source of tubocurarine is a woody vine named Chondrodendron
tomentosum. This type of AChR is named the nicotinic AChR (nAChR).
It is the neurotransmitter receptor at the neuromuscular junction.
It is also present in the brain. The nAChR is now recognized as an
ionotropic receptor.
Curares are used as arrow-tip poisons because they kill by paralysis,
including stopping respiration. Blocking nAChRs at the neuromuscu-
lar junction produces muscle paralysis. Because it is a large charged
molecule (it has two quaternary-amine nitrogens), tubocurarine is
not absorbed through the digestive system. To be effective as a poison,
it must enter the blood directly, via a puncture wound. How the native
peoples of the Amazon jungle, centuries or millennia ago, discovered
such a property of an extract of one among the countless species of
plants in the jungle is an enduring mystery to contemporary science.
The shamans of the jungle have their answer—direct communication