Pharmacological characterization of small‐conductance Ca²⁺‐activated K⁺ channels stably expressed in HEK 293 cells

<jats:p> <jats:list list-type="explicit-label"> <jats:list-item> <jats:p>Three genes encode the small‐conductance Ca<jats:sup>2+</jats:sup>‐activated K<jats:sup>+</jats:sup> channels (SK channels). We have stably expressed hSK1 and rSK2 in HEK 293 cells and addressed the pharmacology of these subtypes using whole‐cell patch clamp recordings.</jats:p> </jats:list-item> <jats:list-item> <jats:p>The bee venom peptide apamin blocked hSK1 as well as rSK2 with IC<jats:sub>50</jats:sub> values of 3.3 n<jats:sc>M</jats:sc> and 83 pM, respectively.</jats:p> </jats:list-item> <jats:list-item> <jats:p>The pharmacological separation between the subtypes was even more prominent when applying the scorpion peptide blocker scyllatoxin, which blocked hSK1 with an IC<jats:sub>50</jats:sub> value of 80 n<jats:sc>M</jats:sc> and rSK2 at 287 pM.</jats:p> </jats:list-item> <jats:list-item> <jats:p>The potent small molecule blockers showed little differentiation between the channel subtypes. The bis‐quinolinium cyclophane UCL 1684 blocked hSK1 with an IC<jats:sub>50</jats:sub> value of 762 pM and rSK2 at 364 pM. The antiseptic compound dequalinium chloride blocked hSK1 and rSK2 with IC<jats:sub>50</jats:sub> values of 444 n<jats:sc>M</jats:sc> and 162 n<jats:sc>M</jats:sc>, respectively.</jats:p> </jats:list-item> <jats:list-item> <jats:p>The nicotinic acetylcholine receptor antagonist d‐tubocurarine was found to block hSK1 and rSK2 with IC<jats:sub>50</jats:sub> values of 27 μ<jats:sc>M</jats:sc> and 17 μ<jats:sc>M</jats:sc> when measured at +80 mV. The inhibition by d‐tubocurarine was voltage‐dependent with increasing affinities at more hyperpolarized potentials.</jats:p> </jats:list-item> <jats:list-item> <jats:p>The GABA<jats:sub>A</jats:sub> receptor antagonist bicuculline methiodide also blocked hSK1 and rSK2 in a voltage‐dependent manner with IC<jats:sub>50</jats:sub> values of 15 and 25 μ<jats:sc>M</jats:sc> when measured at +80 mV.</jats:p> </jats:list-item> <jats:list-item> <jats:p>In conclusion, the pharmacological separation between SK channel subtypes expressed in mammalian cells is too small to support the notion that the apamin‐insensitive afterhyperpolarization of neurones is mediated by hSK1.</jats:p> </jats:list-item> </jats:list> </jats:p><jats:p><jats:italic>British Journal of Pharmacology</jats:italic> (2000) <jats:bold>129</jats:bold>, 991–999; doi:<jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" xlink:href="10.1038/sj.bjp.0703120">10.1038/sj.bjp.0703120</jats:ext-link></jats:p>