Orai/CRACM1 and KCa3.1 ion channels interact in the human lung mast cell plasma membrane

Abstract

Background: Orai/CRACM1 ion channels provide the major Ca2+ influx pathway for FcåRI-dependent human lung mast cell (HLMC) mediator release. The Ca2+-activated K+ channel KCa3.1 modulates Ca2+ influx and the secretory response through hyperpolarisation of the plasma membrane. We hypothesised that there is a close functional and spatiotemporal interaction between these Ca2+- and K+-selective channels. Results: Activation of FcåRI-dependent HLMC KCa3.1 currents was dependent on the presence of extracellular Ca2+, and attenuated in the presence of the selective Orai blocker GSK-7975A. Currents elicited by the KCa3.1 opener 1-EBIO were also attenuated by GSK-7975A. The Orai1 E106Q dominant-negative mutant ablated 1-EBIO and FcϵRI-dependent KCa3.1 currents in HLMCs. Orai1 but not Orai2 was shown to co-immunoprecipitate with KCa3.1 when overexpressed in HEK293 cells, and Orai1 and KCa3.1 were seen to co-localise in the HEK293 plasma membrane using confocal microscopy. Conclusion: KCa3.1 activation in HLMCs is highly dependent on Ca2+ influx through Orai1 channels, mediated via a close spatiotemporal interaction between the two channels.