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LAURA TEIXIDÓ Y COLS. AN. R. ACAD. NAC. FARM.

TABLE 2. Effects of the aplication of antagonists in the presence of agonists.
Results are in % of inhibition

Agonist / agonist+antagonist Amplitude (% inhib.)

FRONTAL CORTEX 42 ± 4 n = 8
nicotine/nicotine+d-tubocurarine 42 ± 4 n = 3
DMPP/DMPP+a-bungarotoxin 43 ± 1 n = 3
DMPP/DMPP+d-tubocurarine
29 n = 1
HIPPOCAMPUS 26 ± 2 n = 2
acetylcholine/acetylcholine+d-tubocurarine
Nicotine/nicotine+d-tubocurarine

d-tubocurarine was at a concentration of 10 µM and a-bungarotoxin at a concen-
tration of 10 nM

DISCUSSION

In the human brain most high affinity neuronal nicotinic
acetylcholine receptors seem to comprise an arrangement of a4ß2
subunits. Combinations with a3 subunits and homomeric a7
constitute the other major part. However various combinations of
a2, a3, a5, a6 and ß2 and ß4 subunits are also coexpressed to form
heteromeric receptors (3, 12-14).

In previous studies that have involved injecting human mRNA
to Xenopus oocytes, recombinant human neuronal nicotinic
acetylcholine receptors displayed differential sensitivity to nicotinic
agonists and antagonists and distinct kinetics, depending on the
subunit combinations and on the concentration of agonist used. The
sensitivity to the antagonists also differed depending on combination
of the subunits present in the receptor (3, 6).

We must point out that native human nicotinic acetylcholine
receptors are still active 7 hours after death, the brain extraction and
even after freezing and thawing. Here we recorded small currents
by perfusing acetylcholine over oocytes transplanted with human
brain membranes. The small amplitude of the currents may be
due to: a small number of receptors incorporated into the Xenopus
oocyte or to the poorly represented nicotinic receptors in the zones

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