Human fetal tracheal smooth muscle produces spontaneous electromechanical oscillations that are Ca2+ dependent and cholinergically potentiated.

Although the electromechanical properties of, and the cholinergic innervation to adult airway smooth muscle has been extensively studied, the little information is available on developing human airway smooth muscle, and the role of cholinergic mechanisms in regulating bronchomotor tone. A total of 7 tracheae obtained at the time of elective abortion and between 12-16 weeks of gestational development were used in this study. For each trachea, muscle tension and transmembrane potentials were measured simultaneously using an isometric force transducer and a standard 3-M KCl-filled glass microelectrode. All preparations showed spontaneous electrical oscillations approximately 8 mV in amplitude, which could be increased using electrical field stimulation, or exogenously applied acetylcholine. This was accompanied by a corresponding increase in muscle tension. Atropine (0.1 microM) abolished this potentiation, but had no apparent effect on the oscillations. Slow-wave activity was completely suppressed in the absence of extracellular Ca2+, or in the presence of verapamil (1 microM) or quinidine (1 microM). It appears that these oscillations of membrane potential may be potentiated by cholinergic mechanisms which regulate cell membrane ion channels, thus serving to change excitability in a rhythmic manner.