Block of Na+ Currents and Suppression of Action Potentials in Cultured Hippocampal Neurons by Gs-458967

Abstract

Voltage-gated Na+ channels (NaChs) are common targets for anti-epileptic drugs due to their role in the initiation and propagation of action potentials in central neurons. NaCh blocking agents, such as phenytoin and lamotrigine, act by blocking peak Na+ current (INa) in voltage- and frequency- dependent manner. A recent study showed that GS-458967 (GS967) is a potent blocker of cardiac INa. However, the effects of GS967 on neuronal INa and action potentials were not examined. Thus, using isolated rat cultured hippocampal neurons, effects of GS967 on neuronal INa and excitability were determined. GS967 (10-1000 nM) caused a voltage- (−60 mV) and frequency (10 Hz)-dependent block of INa with IC50 values of 40.6±4.0 (n=4, at each concentration) and 477.0±53.0 nM (n=4, at each concentration), respectively. However, tonic block of INa was minimal (7.6±0.5 % at 1000 nM, n= 4). GS967 decreased the sustained repetitive firing (SRF) in response to a 1-sec depolarizing current injection with an IC50 value of 47.8±2.8 nM (n=3-4, at each concentration). Consistent with minimal tonic block of INa, the compound had no effect on the amplitude of the first action potential during SRF (2.2±0.8 % at 300 nM). Furthermore, GS967 reversibly reduced the epileptiform activity induced by NMDA activation (removal of extracellular Mg2+) with an IC50 value of 50.7±1.4 nM (n=3-5, at each concentration). In addition, the effects of GS967 on ligand-gated ion channels that are essential for synaptic inhibition or excitation were tested. GS967 (1000 nM) had no effect on GABA-activated currents (4.2±3.4%, n=8). At 1000 nM, GS967 inhibited NMDA-activated currents by 18.2±6.2% (n=5). Taken together, these findings provide preliminary evidence that GS967 could be effective in controlling abnormal neuronal firing.