Verapamil Inhibits TRESK (K(2P)18.1) Current in Trigeminal Ganglion Neurons Independently of the Blockade of Ca2+ Influx

Abstract

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 Ca2+ concentration ([Ca2+](i)) and linked to migraines. This study was performed to identify the effect of verapamil, which is an L-type Ca2+ 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 [Ca2+](i) were measured using the fluo-3-AM Ca2+ indicator. Verapamil, nifedipine, and NiCl2 inhibited the whole-cell currents in HEK-293 cells overexpressing mTRESK with IC50 values of 5.2, 54.3, and > 100 mu M, respectively. The inhibitory effect of verapamil on TRESK channel was also observed in excised patches. In TG neurons, verapamil (10 mu M) inhibited TRESK channel activity by approximately 76%. The TRESK channel activity was not dependent on the presence of extracellular Ca2+. In addition, the inhibitory effect of verapamil on the TRESK channel remained despite the absence of extracellular Ca2+. These findings show that verapamil inhibits the TRESK current independently of the blockade of Ca2+ influx in TG neurons. Verapamil will be able to exert its pharmacological effects by modulating TRESK, as well as Ca2+ influx, in TG neurons in vitro. We suggest that verapamil could be used as an inhibitor for identifying TRESK channel in TG neurons.