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‐HT₃ 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 μm), or ketanserin (1 μm), but were antagonized in a concentration‐dependent and reversible manner by the selective 5‐HT₃ receptor antagonist, ondansetron (IC₅₀ = 440 pm) and the non‐selective antagonists (+)‐tubocurarine (IC₅₀ = 1.8 nm) and metoclopramide (IC₅₀ 50 nm). 3 The 5‐HT‐induced current reversed in sign (E_5‐HT) at approximately – 2 mV and exhibited inward rectification. The influence of extra‐ and intracellular ion substitutions upon E_5‐HT indicates the 5‐HT‐evoked current to be mainly mediated by a mixed monovalent cation conductance. 4 Calcium and magnesium (0.1–10 nm) produced a concentration‐dependent, voltage‐independent, inhibition of the 5‐HT‐induced response. Zinc (0.3–300 μm) exerted a biphasic effect with low concentrations enhancing, and high concentrations depressing, the 5‐HT‐evoked current. 5 Fluctuation analysis of inward currents evoked by a low (1 μm) concentration of 5‐HT suggests the current to be mediated by the opening of channels with a conductance of 420 fS. 6 The pharmacological and biophysical properties of the 5‐HT₃ R‐A are 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 zinc. This observation suggests that the properties of the native receptor are not completely represented by the 5‐HT₃ R‐A subunit alone. 1995 British Pharmacological Society