Transmural stimulation
Transmural stimulation, also called electrical field stimulation (EFS), was performed by placing tissues between two wire platinum electrodes (20 mm apart, Panlab Harvard Apparatus, Spain), connected to a 3165 multiplexing pulse booster stimulator (Ugo Basile, VA - Italy). Bronchial rings were contracted by EFS at increasing frequencies (EFS1-50Hz, 10V, 10s, 0.5ms, biphasic pulse) in order to simulate the vagus nerve firing (parasympathetic pathway) observed in human in vivo and thus producing frequency-response curves (FRCs) via endogenous cholinergic contractile response (Cazzola et al., 2011).