Whole cell and
patch clamp techniques were used to investigate the properties of
5-HT3 receptors of a murine
neuroblastoma cell line (N1E-115) and adult rabbit
nodose ganglion neurones. In addition, some preliminary results from
guinea-pig nodose ganglion neurones are presented. In such cells, voltage-clamped at -60 mV,
5-HT (10 microM) induced an inward current associated with a conductance increase. The results of
ion substitution experiments suggest that the
5-HT activated
ion channel is permeable to both Na+ and K+
ions with a permeability ratio (PNa/PK) of 0.94 and 0.92 for rabbit
nodose ganglion cells and N1E-115 cells respectively. On outside out membrane patches excised from rabbit
nodose ganglion neurones,
5-HT (1 microM) activated clearly discernible single channel currents with a conductance of 16.6 +/- 0.7 pS (n = 4). In contrast, fluctuation analysis of
5-HT induced whole cell currents suggests that the single channel conductance of N1E-115 cells is only 0.3 pS, a value some 50 fold lower. The 5-HT-induced whole cell currents recorded from all three preparations were antagonised by the
selective 5-HT3 receptor antagonist ondansetron (GR38032F) and by the less
selective agents
metoclopramide,
cocaine and (+)-
tubocurarine. However, these preparations demonstrate a differential sensitivity to some antagonists. In particular, (+)-
tubocurarine was a potent antagonist in N1E-115 cells (IC50 = 0.85 nM) but was approximately 200 fold (IC50 = 156 nM) and 1200 fold (IC50 = 10 microM) less potent in rabbit and
guinea-pig nodose ganglion neurones respectively. Additionally, a novel effect of
ketamine (10 microM) to potentiate the 5-HT-induced current of rabbit
nodose ganglion neurones is described.
