Figure 3: Cumulative concentration-response curves for SP (a, c) and frequency-response curves for electrical field stimulation (EFS; b, d) in tracheal smooth muscle after 1 day (a, b) and 5 days (c, d) exposure to FA (open circles) or SS (circles). The solid triangle showed that atropine (final concentration 10−6 M) totally abolished EFS-induced airway smooth muscle contraction. Responses to SP and EFS are plotted as a percentage of the 10−5 M MCh response. Values are means SE; in each group. *Significant difference in EFS between FA and SS exposure, .