Potentiation and inhibition of glycine receptors by tutin

In the present study we characterized the effects of the South American neurotoxin tutin on recombinant glycine receptors (GlyR) expressed in HEK 293 cells using whole-cell patch-clamp techniques. Tutin induced a concentration-dependent inhibition of alpha(1) and alpha(2) homomeric GlyRs, with IC(50)s of 35 +/- 1 and 15 +/- 3 mu M, respectively. The co-expression of alpha beta subunits reduced the potency of tutin, thus increasing the IC50 to 51 +/- 4 and 41 +/- 8 mu M for alpha(1)beta and alpha(2)beta GlyRs, respectively. The inhibitory effect of tutin was competitive, independent of membrane potential and reversible suggesting a pore independent site. On the other hand, low tutin concentrations enhanced the current, which was not synergic with Zn2+ or ethanol. A mutation in Lys385 altered ethanol but not tutin sensitivity, suggesting different sites for modulation of alpha 1-containing GlyRs. Our results suggest that tutin affects the GlyR by a mechanism distinct to that of picrotoxin and ethanol, and that the pharmacological profile of tutin exhibits a Zn-like behaviour. In conclusion, these results provide information on molecular mechanisms important for understanding the toxic effects of a recently discovered South American neurotoxin. (C) 2010 Elsevier Ltd. All rights reserved.