Background The K+ channel KCa3.1 is expressed by several inflammatory and structural airway cells including mast cells and airway smooth muscle (ASM). We have proposed that this channel may play roles in the development of both airway inflammation and remodelling in asthma and COPD. The role of KCa3.1 channels in chemokine secretion by ASM is not known.
Aims To investigate the expression of KCa3.1 in ASM in the airways of healthy and asthmatic subjects, and its function in ex vivo cultured primary human ASM cells.
Methods Tissue was collected at bronchoscopy from subjects with asthma and healthy controls, and either processed into GMA for immunohistochemistry, or dissected for the culture of ASM. Further ASM samples were cultured from patients with COPD undergoing lung resection for carcinoma. To examine ASM chemokine production, we used our well-established cellular model of corticosteroid resistance (TNFα/IFNgamma-treated ASM cells).
Results KCa3.1 immunostaining was evident in the ASM in healthy subjects and patients with asthma. There was no difference in the level of expression between healthy subjects (n=7), and those with moderate (n=5) and severe (n=6) asthma. In cultured ASM cells exposed to TNFα/IFNgamma, both ELISA and RT-PCR demonstrated expression of CX3CL1 or CCL5 which were (1) synergistically produced at 24 h and (2) completely resistant to fluticasone pre-treatment (100 nM). We found that KCa3.1 block alone did not inhibit the secretion of CX3CL1 or CCL5. Interestingly, the failure of fluticasone to suppress CX3CL1 and CCL5 expression in response to TNFα/IFNgamma combination was reversed by TRAM-34, a selective inhibitor of KCa3.1 channels. The increased anti-inflammatory action induced by the TRAM-34-fluticasone combination was observed in cells derived from healthy (n=3), asthmatic (n=3) and COPD (n=3) patients. In addition, restoration of corticosteroid sensitivity by KCa3.1 blockers was associated with an increased GR phosphorylation on serine 211 residues.
Conclusions Together, these data suggest that targeting KCa3.1 channels could serve as a novel approach to enhancing/restoring steroid sensitivity in pulmonary disease.