No evidence for altered intracellular calcium-handling in airway smooth muscle cells from human subjects with asthma

Background Asthma is characterized by airway hyper-responsiveness and variable airflow obstruction, in part as a consequence of hyper-contractile airway smooth muscle, which persists in primary cell culture. One potential mechanism for this hyper-contractility is abnormal intracellular Ca 2+ handling. Methods We sought to compare intracellular Ca 2+ handling in airway smooth muscle cells from subjects with asthma compared to non-asthmatic controls by measuring: i) bradykinin-stimulated changes in inositol 1,4,5-trisphosphate (IP 3 ) accumulation and intracellular Ca 2+ concentration, ii) sarco/endoplasmic reticulum Ca 2+ -ATPase (SERCA) expression, iii) mechanisms of cytoplasmic Ca 2+ clearance assessed following instantaneous flash photolytic release of Ca 2+ into the cytoplasm. Results We found no differences in airway smooth muscle cell basal intracellular Ca 2+ concentrations, bradykinin-stimulated IP 3 accumulation or intracellular Ca 2+ responses. Quantification of SERCA2 mRNA or protein expression levels revealed no differences in ASM cells obtained from subjects with asthma compared to non-asthmatic controls. We did not identify differences in intracellular calcium kinetics assessed by flash photolysis and calcium uncaging independent of agonist-activation with or without SERCA inhibition. However, we did observe some correlations in subjects with asthma between lung function and the different cellular measurements of intracellular Ca 2+ handling, with poorer lung function related to increased rate of recovery following flash photolytic elevation of cytoplasmic Ca 2+ concentration. Conclusions Taken together, the experimental results reported in this study do not demonstrate major fundamental differences in Ca 2+ handling between airway smooth muscle cells from non-asthmatic and asthmatic subjects. Therefore, increased contraction of airway smooth muscle cells derived from asthmatic subjects cannot be fully explained by altered Ca 2+ homeostasis.