M. Barann et al., 5-HT3 RECEPTORS IN OUTSIDE-OUT PATCHES OF N1E-115 NEUROBLASTOMA-CELLS- BASIC PROPERTIES AND EFFECTS OF PENTOBARBITAL, Neuropharmacology, 36(4-5), 1997, pp. 655-664
A fast solution exchange system (Dilger and Brett, 1990; Biophysics Jo
urnal 57: 723-731) with an exchange rate <1 msec was used to study 5-H
T3 (5-HT; 5-hydroxytryptamine) receptor-mediated currents in superfuse
d outside-out patches of NIE-115 mouse neuroblastoma cells. At negativ
e membrane potentials, 5-HT induced inward currents in a concentration
-dependent manner (IC50 = 3.8 mu M, Hill coefficient = 1.8). The mean
peak current at a near-maximally effective 5-HT concentration of 30 mu
M was 20.6 pA. The 5-HT3 receptor antagonist ondansetron (0.3 nM) rev
ersibly inhibited the 5-HT (30 mu M) signal by approximately 50%. The
currents induced during application of 30 mu M 5-HT for 2 sec were cha
racterized by inward rectification, a monophasic onset (tau(ON) = 37.5
msec) and, after reaching a peak, a monophasic decay (desensitization
; tau(OFF) = 391 msec). Onset and decay were slower at lower 5-HT conc
entrations. The recovery of fully desensitized patches required a wash
out period of 45 sec. Pentobarbital inhibited 5-HT-induced (30 mu M) c
urrents in a concentration-dependent manner. The maximally obtainable
inhibition with a given pentobarbital concentration was reached alread
y when it was exclusively coapplied with 5-HT (IC50 = 135 mu M, Hill c
oefficient = -0.7), since additional preexposure for at least 45 sec d
id not alter the concentration-response curve of pentobarbital. In con
clusion, outside-out patches of NIE-115 cells are suitable to study th
e kinetic properties of 5-HT3 receptor channels. The results obtained
in this model with pentobarbital are compatible with the suggestion th
at the inhibitory action of pentobarbital on 5-HT3 receptors is depend
ent on the agonist-activated (open) channel. (C) 1997 Elsevier Science
Ltd.