Pharmacological modulation of SK3 channels

Small-conductance, calcium-activated K⁺ channels (SK channels) are voltage-insensitive channels that have been identified molecularly within the last few years. As SK channels play a fundamental role in most excitable cells and participate in afterhyperpolarization (AHP) and spike-frequency adaptation, pharmacological modulation of SK channels may be of significant clinical importance. Here we report the functional expression of SK3 in HEK293 and demonstrate a broad pharmacological profile for these channels. Brain slice studies commonly employ 4-aminopyridine (4-AP) to block voltage-dependent K⁺ channels or a methyl derivative of bicuculline, a blocker of gamma-aminobutyric acid (GABA)-gated Cl^- channels, in order to investigate the role of various synapses in specialized neural networks. However, in this study both 4-AP and bicuculline are shown to inhibit SK3 channels (IC₅₀ values of 512 μM and 6 μM, respectively) at concentrations lower than those used for brain slice recordings. Riluzole, a potent neuroprotective drug with anti-ischemic, anticonvulsant and sedative effects currently used in the treatment of amyotrophic lateral sclerosis, activates SK3 channels at concentrations of 3 μM and above. Amitriptyline, a tricyclic antidepressive widely used clinically, inhibits SK3 channels with an IC₅₀ of 39.1±10 μM (n=6).