The relative contributions of store-operated and voltage-gated Ca2+ channels to the control of Ca2+ oscillations in airway smooth muscle

Airway smooth muscle contraction is typically the key mechanism underlying airway hyper-responsiveness, and the strength of muscle contraction is determined by the frequency of oscillations of intracellular calcium (Ca2+) concentration. In airway smooth muscle cells, these Ca2+ oscillations are caused by cyclic Ca2+ release from the sarcoplasmic reticulum, although Ca2+ influx via plasma membrane channels is also necessary to sustain the oscillations over longer times. To assess the relative contributions of store-operated and voltage-gated Ca2+ channels to this Ca2+ influx, we generated a comprehensive mathematical model, based on experimental Ca2+ measurements in mouse precision-cut lung slices, to simulate Ca2+ oscillations and changes in membrane potential. Agonist-induced Ca2+ oscillations are accompanied by oscillations in membrane potential, although the membrane potential oscillations are too small to generate large Ca2+ currents through voltage-gated Ca2+ channels, and thus have little effect on the Ca2+ oscillations. Ca2+ entry through voltage-gated channels only becomes important when the cell is depolarized (e. g. by a high external K+ concentration). As a result, agonist-induced Ca2+ oscillations are critically dependent on Ca2+ entry through store-operated channels but do not depend strongly on Ca2+ entry though voltage-gated channels.