Verapamil Inhibits TRESK (K(2P)18.1) Current in Trigeminal Ganglion Neurons Independently of the Blockade of Ca(2+) Influx

Tandem pore domain weak inward rectifier potassium channel (TWIK)-related spinal cord K(+) (TRESK; K(2P)18.1) channel is the only member of the two-pore domain K(+) (K(2P)) channel family that is activated by an increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) and linked to migraines. This study was performed to identify the effect of verapamil, which is an L-type Ca(2+) channel blocker and a prophylaxis for migraines, on the TRESK channel in trigeminal ganglion (TG) neurons, as well as in a heterologous system. Single-channel and whole-cell currents were recorded in TG neurons and HEK-293 cells transfected with mTRESK using patch-clamping techniques. In TG neurons, changes in [Ca(2+)](i) were measured using the fluo-3-AM Ca(2+) indicator. Verapamil, nifedipine, and NiCl(2) inhibited the whole-cell currents in HEK-293 cells overexpressing mTRESK with IC(50) values of 5.2, 54.3, and >100 μM, respectively. The inhibitory effect of verapamil on TRESK channel was also observed in excised patches. In TG neurons, verapamil (10 μM) inhibited TRESK channel activity by approximately 76%. The TRESK channel activity was not dependent on the presence of extracellular Ca(2+). In addition, the inhibitory effect of verapamil on the TRESK channel remained despite the absence of extracellular Ca(2+). These findings show that verapamil inhibits the TRESK current independently of the blockade of Ca(2+) influx in TG neurons. Verapamil will be able to exert its pharmacological effects by modulating TRESK, as well as Ca(2+) influx, in TG neurons in vitro. We suggest that verapamil could be used as an inhibitor for identifying TRESK channel in TG neurons.