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

BACKGROUND: Orai/CRACM1 ion channels provide the major Ca[superscript: 2+] influx pathway for FcεRI-dependent human lung mast cell (HLMC) mediator release. The Ca[superscript: 2+]-activated K[superscript: +] channel K[subscript: Ca]3.1 modulates Ca[superscript: 2+] influx and the secretory response through hyperpolarisation of the plasma membrane. We hypothesised that there is a close functional and spatiotemporal interaction between these Ca[superscript: 2+]- and K[superscript: +]-selective channels. RESULTS: Activation of FcεRI-dependent HLMC K[subscript: Ca]3.1 currents was dependent on the presence of extracellular Ca[superscript: 2+], and attenuated in the presence of the selective Orai blocker GSK-7975A. Currents elicited by the K[subscript: Ca]3.1 opener 1-EBIO were also attenuated by GSK-7975A. The Orai1 E106Q dominant-negative mutant ablated 1-EBIO and FcεRI-dependent K[subscript: Ca]3.1 currents in HLMCs. Orai1 but not Orai2 was shown to co-immunoprecipitate with K[subscript: Ca]3.1 when overexpressed in HEK293 cells, and Orai1 and K[subscript: Ca]3.1 were seen to co-localise in the HEK293 plasma membrane using confocal microscopy. CONCLUSION: K[subscript: Ca]3.1 activation in HLMCs is highly dependent on Ca[superscript: 2+] influx through Orai1 channels, mediated via a close spatiotemporal interaction between the two channels.