1. The
biophysical and
pharmacological properties of
5-hydroxytryptamine (
5-HT)-evoked currents in rabbit
nodose ganglion neurones in culture have been determined by use of the whole-cell and outside-out membrane patch recording modes of the
patch-clamp technique. 2. In 49% of cells investigated the bath application of 10(-5) M
5-HT at negative holding potentials elicited an inward current. The whole-cell response to
5-HT reversed in sign (E5-HT) at approximately -2 mV and exhibited inward rectification. 3. The influence of various
ion substitutions upon E5-HT established that the 5-HT-evoked current is mainly mediated by a mixed Na+, K+
cation conductance with little or no contribution from
Cl- ions. The omission of
Ca2+ and Mg2+ from the
extracellular solution enhanced the amplitude of the 5-HT-induced current. 4. On isolated outside-out membrane patches, the bath application of 10(-6) M
5-HT induced single channel currents with a chord conductance of approximately 17 pS at -70 mV and an
average slope conductance of 19 pS over the range -100 to -40 mV. The 5-HT-induced single channels exhibited modest inward rectification and were reduced in
frequency, but not amplitude, by the
5-HT3 receptor antagonist metoclopramide (10(-6) M). 5. The bath application of
5-HT (3 x 10(-7)-3 x 10(-5) M) to whole cells voltage clamped at -60 mV produced dose-dependent inward currents which were mimicked by 2-methyl-5-HT and 1-phenylbiguanide with equipotent
molar ratios, relative to
5-HT, of 2.5 and 32 respectively. 6. Whole-cell inward currents produced by the local pressure application of
5-HT (10(-5) M) were unaffected by 10(-6) M
methysergide, 10(-6) M
ketanserin or 10(-6) M
citalopram, but were concentration-dependently antagonized by the
selective 5-HT3 receptor antagonists tropisetron (IC50 = 4.6 x 10(-11) M)
ondansetron (IC50 = 5.7 x 10(-11) M), and
bemesetron (IC50 = 3.3 x 10(-10) M). The response to
5-HT was also blocked by the
non-selective antagonists
metoclopramide (IC50 = 1.2 x 10(-8) M),
cocaine (IC50 = 8.3 x 10(-8) M) and (+)-
tubocurarine (IC50 = 1.6 x 10(-7) M).
