AN ELECTROPHYSIOLOGICAL INVESTIGATION OF THE PROPERTIES OF A MURINE RECOMBINANT 5-HT3 RECEPTOR STABLY EXPRESSED IN HEK-293 CELLS

1 The pharmacological and biophysical properties of a recombinant 5-HT 3 receptor have been studied by use of patch-clamp techniques applied to HEK 293 cells stably transfected with the murine 5-HT3 R-A cDNA. 2 At a holding potential of -60 mV, 77% of cells investigated responded to ionophoretically applied 5-HT with an inward current. Such currents were unaffected by methysergide (1 mu M), or ketanserin (1 mu M), but were antagonized in a concentration-dependent and reversible manner b y the selective 5-HT3 receptor antagonist, ondansetron (IC50 = 440 pM) and the non-selective antagonists (+)-tubocurarine (IC50 = 1.8 nM) an d metoclopramide (IC50 50 nM). 3 The 5-HT-induced current reversed in sign (E(5-HT)) at approximately -2 mV and exhibited inward rectificati on. The influence of extra- and intracellular ion substitutions upon E (5-HT) indicates the 5-HT-evoked current to be mainly mediated by a mi xed monovalent cation conductance. 4 Calcium and magnesium (0.1-10 nM) produced a concentration-dependent, voltage-independent, inhibition o f the 5-HT-induced response. Zinc (0.3-300 mu M) exerted a biphasic ef fect with low concentrations enhancing, and high concentrations depres sing, the 5-HT-evoked current. 5 Fluctuation analysis of inward curren ts evoked by a low (1 mu M) concentration of 5-HT suggests the current to be mediated by the opening of channels with a conductance of 420 f S. 6 The pharmacological and biophysical properties of the 5-HT3 R-A a re similar to those previously described for 5-HT3 receptors native to murine neuroblastoma cell lines, with the exception that the function of the recombinant receptor was enhanced by low concentrations of zin c. This observation suggests that the properties of the native recepto r are not completely represented by the 5-HT3 R-A subunit alone.