Influence of flupirtine on a G-protein coupled inwardly rectifying potassium current in hippocampal neurones

Abstract

1. Previous studies have shown that flupirtine, a centrally acting, non-opioid analgesic agent, also exhibits neuroprotective activity in focal cerebral ischaemia in mice and reduces apoptosis induced by NMDA, gp 120 of HIV, prior protein fragment or lead acetate as well as necrosis induced by glutamate or NMDA in cell culture. To study the potential mechanism of the neuroprotective action of flupirtine, we investigated whether flupirtine is able to modulate potassium or NMDA-induced currents in rat cultured hippocampal neurones by use of the whole-cell configuration of the patch-clamp technique.

2. We demonstrated that 1 μM flupirtine activated an inwardly rectifying potassium current (K_ir) in hippocampal neurones (ΔI=−39±18 pA at −130 mV; n=10). This effect was dose-dependent (EC₅₀=0.6 μM). The reversal potential for K_ir was in agreement with the potassium equilibrium potential predicted from the Nernst equation showing that K_ir was predominantly carried by K⁺. Furthermore, the induced current was blocked completely by Ba²⁺ (1 mM), an effect typical for K_ir.

3. The activation of K_ir by flupirtine was largely prevented by pretreatment of the cells with pertussis toxin (PTX) indicating the involvement of a PTX-sensitive G-protein in the transduction mechanism (ΔI=−3±6 pA at −130 mV; n=8). Inclusion of cyclic AMP in the intracellular solution completely abolished the activation of K_ir (n=7).

4. The selective α₂-adrenoceptor antagonist SKF-86466 (10 μM), the selective 5-HT_1A antagonist NAN 190 as well as the selective GABA_B antagonist 2-hydroxysaclofen (10 μM) failed to block the flupirtine effect on the inward rectifier.

5. Flupirtine (1 μM) could not change the current induced by 50 μM NMDA.

6. These results show that in cultured hippocampal neurones flupirtine activates an inwardly rectifying potassium current and that a PTX-sensitive G-protein is involved in the transduction mechanism.

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