AN ELECTROPHYSIOLOGICAL INVESTIGATION OF THE PROPERTIES OF 5-HT3 RECEPTORS OF RABBIT NODOSE GANGLION NEURONS IN CULTURE

1 The biophysical and pharmacological properties of 5-hydroxytryptamin e (5-HT)-evoked currents in rabbit nodose ganglion neurones in culture have been determined by use of the whole-cell and outside-out membran e patch recording modes of the patch-clamp technique. 2 In 49% of cell s investigated the bath application of 10(-5) M 5-HT at negative holdi ng potentials elicited an inward current. The whole-cell response to 5 -HT reversed in sign (E5-HT) at approximately -2 mV and exhibited inwa rd rectification. 3 The influence of various ion substitutions upon E5 -HT established that the 5-HT-evoked current is mainly mediated by a m ixed 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 outs ide-out membrane patches, the bath application of 10(-6) M 5-HT induce d 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 inw ard rectification and were reduced in frequency, but not amplitude, by the 5-HT3 receptor antagonist metoclopromide (10(-6)M). 5 The bath ap plication of 5-HT (3 x 10(-7) - 3 x 10(-5)M) to whole cells voltage cl amped at -60 mV produced dose-dependent inward currents which were mim icked by 2-methyl-5-HT and 1-phenylbiguanide with equipotent molar rat ios, 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 th e selective 5-HT3 receptor antagonists tropisetron (IC50 = 4.6 x 10(-1 1) 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-select ive 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).