Mitchell, Arthur; Benton, David; Moss, Guy; Dua, Vivek; (2023) BK channel modulation as a theraputic target for Cystic Fibrosis. Presented at: 18th ECFS Basic Science Conference, Dubrovnik, Croatia.

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Abstract

Background. Cystic fibrosis and is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR), an anion channel present on the apical membrane of airway epithelia. Loss of CFTR function reduces anion secretion into the airway surface liquid (ASL), causing ASL dehydration and an impairment of the innate immune response. CFTR modulator drugs seek to increase the number of functional channels at the cell membrane and the CFTR open probability. However, the apical membrane potential sits close to the reversal potential for chloride. Thus, physiologically, it seems that the co-activation of potassium channels is necessary to provide the driving force for anion secretion. Therefore, another way to increase anion secretion is to increase activation of these channels. One such target is the large conductance calcium-activated potassium channel (BK channel) [1] that also resides on the apical membrane of human bronchial epithelium. / Aim. To investigate the role of BK channels both theoretically and experimentally. / Theory. We first examined BK channel modulation by extending a model of ion transport in epithelial cells first developed by O’Donoghue et al. [2]. The extended model included an ASL compartment where depth and ion concentrations could be predicted. / Experiment. We next tested BK channel activation experimentally using CF-donor cells carrying R334W/ΔF508 CFTR mutation. Cells were grown in PneumaCultTM-Ex Plus and PneumaCult™-ALI Medium to create air-liquid interface (ALI) cultures in the absence of antibiotics and antimycotic agents. We used BK channel activator GoSlo-SR-5-6 [4] (GoSlo) to modulate the BK channel. GoSlo lowers the voltage required for half maximal activation for all BK channels, independent of their subunit composition, by about 50 mV, allowing them to stay open at relatively hyperpolarised potentials. To measure ASL depth we used the method of Ivanova et al. [3]. We investigated the effect on ASL depth on HBE cultures by measuring a control with DMSO (vehicle) applied to the basolateral side of the culture vs GoSlo (10 uM), also applied basolaterally or GoSlo applied first vs DMSO only 24 hrs later. / Results and conclusion. A simple theoretical model of ion transport in airway epithelia predicts that activation of basolateral BK channels will increase airway hydration, in agreement with data published by Manzanares and colleagues [1]. This prediction is well-matched by experiment which shows a ~77% increase in ASL depth from the DMSO baseline. BK channel activation may thus be therapeutically useful in cystic fibrosis

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