Human bronchial epithelial cells express K_Ca3.1 mRNA and protein, and K_Ca3.1 expression is upregulated in the asthmatic bronchial epithelium.

(A) K_Ca3.1 mRNA (predicted PCR product size: 130 bp) was detected in monolayers of primary HBECs isolated from both patients with asthma (n = 10; denoted with “A”) and non-asthmatic healthy controls (n = 5; denoted with “NA”), alongside the housekeeping gene β-actin (predicted PCR product size: 146 bp). (B) qPCR revealed that K_Ca3.1 mRNA was expressed at similar levels in primary HBECs isolated from patients with asthma (n = 10) and healthy controls (n = 5). (C) An immunoreactive band of the appropriate size (K_Ca3.1: 48 kDa; β-actin: 42 kDa) was detected in lysates of primary HBECs isolated from two patients with asthma and one healthy control. (D) Quantification of K_Ca3.1 immunostaining by threshold analysis revealed that K_Ca3.1 expression was significantly elevated in asthmatic bronchial epithelium (*P = 0.007). (E) K_Ca3.1 immunostaining was significantly increased in severe asthma compared to mild asthma (**P = 0.008) and compared with healthy controls (*P = 0.002). (F) K_Ca3.1 and MUC5AC immunostaining co-localised in bronchial epithelial cells of sequential sections of biopsies from patients with asthma and healthy controls. (G) Quantification of MUC5AC immunostaining by threshold analysis revealed that MUC5AC expression was significantly increased in asthmatic bronchial epithelium (*P = 0.030), and (H) this was driven by a significant difference between the severe asthma and healthy control groups (*P = 0.034). (I) A significant correlation was found between K_Ca3.1 and MUC5AC immunostaining across the different severities of asthma and the healthy control groups (P < 0.001; r_s = 0.608). All data are plotted as median ± interquartile range; horizontal bars represent medians.