Inhibition by steroids of [¹⁴C]-guanidinium flux through the voltage-gated sodium channel and the cation channel of the 5-HT₃ receptor of N1E-115 neuroblastoma cells

Abstract

Effects of some naturally occurring steroids and synthetic analogues on the cation flux through the cation channel of the 5-HT₃ receptor and the voltage-gated and tetrodotoxin-sensitive sodium channel were studied in N1E-115 mouse neuroblastoma cells by measuring the 2-min influx of the organic cation [¹⁴C]-guanidinium. The cation fluxes in intact cells were either induced by 2 min exposure of the cells to 5-hydroxytryptamine (5-HT, 100 µM) or to veratridine (1 mM).

Influx of [¹⁴C]-guanidinium through both channels was concentration-dependently inhibited by all compounds studied. The rank order of potency for inhibition of the 5-HT₃ receptor-induced cation flux was clomiphene ≅ cyproterone acetate > estradiol > progesterone ≅ allotetrahydrodeoxycorticosterone > alfaxalone ≅ testosterone >aldosterone > dexamethasone. With the exception of dexamethasone and testosterone, which were more potent at the voltage-dependent sodium channel, and progesterone and testosterone, which were about nearly equipotent in inhibiting both cation channels, the steroids were twofold (alfaxalone, allotetrahydrodeoxycorticosterone) to 107-fold (cyproterone acetate) more potent at the 5-HT₃ receptor channel than at the voltage-gated sodium channel. The potencies of the steroids (and the synthetic analogues) for inhibition of the 5-HT₃ receptor-induced [¹⁴C]-guanidinium influx were correlated with their lipophilicity (log P values). A similar correlation between log P values and pIC₅₀ values for the steroid-induced inhibition of the veratridine-evoked cation influx through the voltage-gated sodium channel was only found when cyproterone acetate (a compound with extremely low inhibitory potency at this channel) was not included in the regression analysis.

The results indicate that both the 5-HT₃ receptor channel and the voltage-gated sodium channel are targets for steroids. The relationship between most of the compounds in inhibiting both cation channels and lipophilicity is compatible with a common mechanistic principle in steroid-induced inhibition of the two channels, i.e. a nonspecific hydrophobic interaction with certain membrane lipids in the neighbourhood of the two channels.