Functional Analysis of Large Conductance Ca2+-Activated K+ Channels: Ion Flux Studies by Atomic Absorption Spectrometry

Although techniques such as 86Rb+ flux provide a sensitive measure of K+ channel activity, the relatively short half-life and high-energy emission, together with the quantities of radioactive material generated, hinder the usefulness of flux-based formats in high throughput screening efforts. This study elaborates on the utilization of flame atomic absorption spectrometry (AAS) techniques for a nonradioactive rubidium efflux assay for large conductance Ca2+-activated K+ channels (BKCa) channels. Utilizing human embryonic kidney (HEK293) cells expressing the BKCa α subunit, a 96-well cell-based nonradioactive rubidium efflux screen for channel openers and inhibitors was established. Known BKCa channel openers, including NS1608, NS1619, and NS-8, activated rubidium efflux with EC50 values ranging from 1 to 4 μM in both radioactive and nonradioactive efflux formats. Compounds such as iberiotoxin, paxilline, and charybdotoxin inhibited rubidium efflux responses evoked by the BKCa channel opener NS1608 in both...