Store-operated calcium entry is required for sustained contraction and Ca2+ oscillations of airway smooth muscle

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 Ca2+ oscillationswithin airway smoothmuscle cells (ASMCs). SustainedCa(2+) oscillations require a Ca2+ influx to replenish Ca2+ losses across the plasma membrane. Our previous studies implied store-operated calcium entry (SOCE) as the major pathway for this Ca2+ 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 Ca2+ channel inhibitors (nifedipine and nimodipine) on airway contraction and Ca2+ oscillations and SOCE-mediated Ca2+ 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 Ca2+ oscillations, in a manner similar to that observed in zero extracellular Ca2+ ([Ca2+] e). In addition, GSK7975A and GSK5498A inhibited increases in intracellular Ca2+ ([Ca2+] i) in ASMCs with depleted Ca2+-stores in response to increased [Ca2+] e, demonstrating a response consistent with the inhibition of SOCE. However, GSK7975A and GSK5498A did not reduce Ca2+ release via IP3 receptors stimulated with IP3 released from caged-IP3. By contrast, nifedipine and nimodipine only partially reduced airway contraction, Ca2+ oscillation frequency and SOCE-mediated Ca2+ influx. These data suggest that SOCE is the major Ca2+ influx pathway for ASMCs with respect to sustaining agonist-induced airway contraction and the underlying Ca2+ oscillations. The mechanisms of SOCE may therefore form novel targets for new bronchodilators.