Figure 6.

The effect of the photolytic release of IP₃ in SMCs exposed to (R,R)-formoterol. (A) Fluorescence image indicating the location of SMCs and ECs from the airway observed. (B) Line scan analysis (for 180 s from the white line indicated in [A]) showing that the rhythmic Ca²⁺ oscillations in two SMCs induced by 400 nM MCh were inhibited by 500 nM (R,R)-formoterol, and that this allowed the airway to relax. The subsequent flash photolysis (500 ms, jagged arrow) of caged–iso-Ins(1,4,5)P₃/PMIP₃ (caged-IP₃) in presence of MCh and (R,R)-formoterol induced a short period of Ca²⁺ oscillations. The upward shift of the fluorescence trace indicates the transient contraction of the airway induced by IP₃ release from caged-IP₃. As the Ca²⁺ oscillations slowed again, the airway relaxed. (C) Representative experiment showing that Ca²⁺ oscillations induced in an airway SMC by 400 nM MCh were initially abolished by (R)-albuterol (1 μM), but, after 2 minutes, the Ca²⁺ oscillations resumed at a lower frequency. (D) Representative experiment showing that the Ca²⁺ oscillations induced by 400 nM MCh were not affected by 5 nM (R,R)-formoterol.