Calcium-Modulated Chloride Pathways Contribute to Chloride Flux in Murine Cystic Fibrosis-Affected Macrophages

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Abstract
Cystic fibrosis (CF), a common lethal inherited disorder defined by ion transport abnormalities, chronic infection, and robust inflammation, is the result of mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein, a cAMP-activated chloride (Cl−) channel. Macrophages are reported to have impaired activity in CF. Previous studies suggest that Cl− transport is important for macrophage function; therefore, impaired Cl− secretion may underlie CF macrophage dysfunction. To determine whether alterations in Cl− transport exist in CF macrophages, Cl− efflux was measured using N-[ethoxycarbonylmethyl]-6-methoxy-quinolinium bromide (MQAE), a fluorescent indicator dye. The contribution of CFTR was assessed by calculating Cl− flux in the presence and absence of cftrinh-172. The contribution of calcium (Ca2+)-modulated Cl− pathways was assessed by examining Cl− flux with varied extracellular Ca2+ concentrations or after treatment with carbachol or thapsigargin, agents that increase intracellular Ca2+ levels. Our data demonstrate that CFTR contributed to Cl− efflux only in WT macrophages, while Ca2+-mediated pathways contributed to Cl− transport in CF and WT macrophages. Furthermore, CF macrophages demonstrated augmented Cl− efflux with increases in extracellular Ca2+. Taken together, this suggests that Ca2+-mediated Cl− pathways are enhanced in CF macrophages compared with WT macrophages.

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