Store-operated calcium entry is required for sustained contraction and Ca 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 oscillations underlie this contraction of ASMCs and the magnitude of this contraction is proportional to the Ca oscillation frequency. Sustained contraction and Ca oscillations require an influx of extracellular Ca , although the mechanisms and pathways mediating this Ca influx during agonist-induced ASMC contraction are not well defined. By inhibiting store-operated calcium entry (SOCE) or voltage-gated Ca channels (VGCCs), we show that SOCE, rather than Ca influx via VGCCs, provides the major Ca entry pathway into ASMCs to sustain ASMCs contraction and Ca 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 oscillations within airway smooth muscle cells (ASMCs). Sustained Ca oscillations require a Ca influx to replenish Ca losses across the plasma membrane. Our previous studies implied store-operated calcium entry (SOCE) as the major pathway for this Ca 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 channel inhibitors (nifedipine and nimodipine) on airway contraction and Ca oscillations and SOCE-mediated Ca 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 oscillations, in a manner similar to that observed in zero extracellular Ca ([Ca ] ). In addition, GSK7975A and GSK5498A inhibited increases in intracellular Ca ([Ca ] ) in ASMCs with depleted Ca -stores in response to increased [Ca ] , demonstrating a response consistent with the inhibition of SOCE. However, GSK7975A and GSK5498A did not reduce Ca release via IP receptors stimulated with IP released from caged-IP . By contrast, nifedipine and nimodipine only partially reduced airway contraction, Ca oscillation frequency and SOCE-mediated Ca influx. These data suggest that SOCE is the major Ca influx pathway for ASMCs with respect to sustaining agonist-induced airway contraction and the underlying Ca oscillations. The mechanisms of SOCE may therefore form novel targets for new bronchodilators.