Store‐operated calcium entry is required for sustained contraction and Ca 2+ oscillations of airway smooth muscle

Key points Airway hyper‐responsiveness in asthma is driven by excessive contraction of airway smooth muscle cells (ASMCs). Agonist‐induced Ca 2+ oscillations underlie this contraction of ASMCs and the magnitude of this contraction is proportional to the Ca 2+ oscillation frequency. Sustained contraction and Ca 2+ oscillations require an influx of extracellular Ca 2+ , although the mechanisms and pathways mediating this Ca 2+ influx during agonist‐induced ASMC contraction are not well defined. By inhibiting store‐operated calcium entry (SOCE) or voltage‐gated Ca 2+ channels (VGCCs), we show that SOCE, rather than Ca 2+ influx via VGCCs, provides the major Ca 2+ entry pathway into ASMCs to sustain ASMCs contraction and Ca 2+ oscillations. SOCE may therefore serve as a potential target for new bronchodilators to reduce airway hyper‐responsiveness in asthma.Abstract Asthma is characterized by airway hyper‐responsiveness: the excessive contraction of airway smooth muscle. The extent of this airway contraction is proportional to the frequency of Ca 2+ oscillations within airway smooth muscle cells (ASMCs). Sustained Ca 2+ oscillations require a Ca 2+ influx to replenish Ca 2+ losses across the plasma membrane. Our previous studies implied store‐operated calcium entry (SOCE) as the major pathway for this Ca 2+ influx. In the present study, we explore this hypothesis, by examining the effects of SOCE inhibitors (GSK7975A and GSK5498A) as well as L‐type voltage‐gated Ca 2+ channel inhibitors (nifedipine and nimodipine) on airway contraction and Ca 2+ oscillations and SOCE‐mediated Ca 2+ influx in ASMCs within mouse precision‐cut lung slices. We found that both GSK7975A and GSK5498A were able to fully relax methacholine‐induced airway contraction by abolishing the Ca 2+ oscillations, in a manner similar to that observed in zero extracellular Ca 2+ ([Ca 2+ ] e ). In addition, GSK7975A and GSK5498A inhibited increases in intracellular Ca 2+ ([Ca 2+ ] i ) in ASMCs with depleted Ca 2+ ‐stores in response to increased [Ca 2+ ] e , demonstrating a response consistent with the inhibition of SOCE. However, GSK7975A and GSK5498A did not reduce Ca 2+ release via IP 3 receptors stimulated with IP 3 released from caged‐IP 3 . By contrast, nifedipine and nimodipine only partially reduced airway contraction, Ca 2+ oscillation frequency and SOCE‐mediated Ca 2+ influx. These data suggest that SOCE is the major Ca 2+ influx pathway for ASMCs with respect to sustaining agonist‐induced airway contraction and the underlying Ca 2+ oscillations. The mechanisms of SOCE may therefore form novel targets for new bronchodilators.