Airway relaxation and inhibition of Ca²⁺ oscillations induced by cGMP analogues. (A and B) Airways contracted with 0.1 µM 5-HT were induced to relax by increasing concentrations (top bars) of (A) 8pCPT-cGMP or (B) 8Br-cGMP. Airways either recontracted slightly or remained relaxed after washout of 8pCPT-cGMP or 8Br-cGMP for 5 min. (C) Concentration–airway relaxation response induced by 8pCPT-cGMP (black line) and 8Br-cGMP (gray line). Relaxation was measured as the increase in the lumen area after 8 min of the addition of cGMP analogues and normalized to the airway contraction before the addition of the cGMP analogue (data points are mean ± SE from four slices from two mice). (D and E) The effect of either 50 µM 8pCPT-cGMP or 8-Br-cGMP on the Ca²⁺ oscillations induced by 0.1 µM 5-HT. 8pCPT-cGMP and 8Br-cGMP reduced the frequency of the Ca²⁺ oscillations induced by 5-HT. (F) Summary of the effect of cGMP analogues on the frequency of Ca²⁺ oscillations measured before (control) and after the addition of cGMP analogues (n = 5 SMCs from different slices from three mice; *, P < 0.05).