Dual effects of a 2-benzylquinuclidinium derivative on α7-containing nicotinic acetylcholine receptors in rat hippocampal interneurons

Nicotinic acetylcholine receptors (nAChRs) are widely distributed in the brain. Particularly α7-containing nAChRs, associated with several physiological roles and pathologies, are one of the most abundant. Here, we studied 2-(4-hexyloxybenzyl)-1-methylquinuclidin-1-ium iodide (designated as 8d), on ion currents elicited by choline, ICh, (Ch, a selective agonist for α7-containing nAChRs), recorded in interneurons from the stratum radiatum of the rat hippocampal CA1 region by using the whole-cell voltage-clamp technique. The 8d-concentration/Ch-response relationship exhibited high and low inhibitory affinities for α7-containing nAChRs, with IC50 values of 0.59 and 6.80 μM, respectively. Interestingly, 8d in a range of 3-10 μM exerted opposite effects: a short early potentiation and a long late inhibition of the ICh; and 8d alone elicited a non-decaying inward current. Furthermore, potentiation and inhibition of the ICh by 8d depended on the membrane potential, both being stronger at -20 than at -70 mV; indicating that 8d interacts with at least two sites into the ion channel/receptor complex: one for potentiating and another for inhibiting the α7-containing nAChRs. These results suggest that 8d may act as agonist, antagonist and positive modulator of α7-containing nAChRs in hippocampal interneurons.