Page 152 - 71_04

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

RESULTS

Transplant of human brain membranes, either from cortex or
hippocampus, into Xenopus oocytes significantly decreased the
oocyte resistance (p < 0.05); (0.3 ± 0.05 MO) (n = 16) vs (0.8 ±
0.2 MO) (n = 12) in oocytes injected with H2O. Usually, after 20-
48 h of membrane injection, we recorded an inward current in
response to cholinergic agonists in 30-40% of the injected oocytes.
When acetylcholine was used some of the responses (between
40-50% of the oocytes tested) were from the muscarinic receptor
(Fig. 1a) because the response was of the oscillatory type and
remained active for several minutes and was sensitive to atropine
(Fig. 1b). In other oocytes we found a non-oscillatory response after
perfusing with the nicotinic agonists acetylcholine, or nicotine or
DMPP.

We found four kinds of nicotinic currents depending on
the agonist applied, Figs. 1 C, D, E, F. In the first kind of response
(Fig. 1 C) the current opened fast (t = 6.9 ± 2.2 s) and was maintained
while perfused with the agonist. This kind of current, which was
not so usual (8/83 responses) was observed using acetylcholine
(7/8 responses) and nicotine (1/8 responses) but not with DMPP.
The second kind of current (Fig. 1 D), the most common (53/83
responses) opened slowly (t = 19.7 ± 4.7 s) and increased until the
agonist was washed out (in some cases, we exposed the oocyte to
the agonist for 90 s and the inward current increased at a constant
rate throughout exposure. A third kind of response (Fig. 1 E, 17/83
responses) exhibited dual kinetics: it started as a fast opening
(t = 8.12 ± 1.4) but then slowed down until the agonist was washed
out (t = 16.2 ± 1.7). Finally, we identified a fourth kind of current
(Fig. 1 F) that opened with a t = 6.4 ± 0.8 s and closed spontaneously
before the agonist was washed out. This kind of current was not
usual (5/83 responses) and was observed only using DMPP (4/5) and
nicotine (1/5).

The total recording time in one oocyte varied from 40 to 90 s.
Table 1 summarizes the amplitude of responses obtained at a range
of holding potentials, –80, –90, –100 mV. In each holding potential
group, the amplitude of the currents was independent of the agonist
used, except in the case of DMPP when was measured at –90 mV.

826