Electrical behavior of guinea pig tracheal smooth muscle

Department of Zoology, University of Melbourne, Parkville, Victoria 3052, Australia Intracellular recordings were taken from the smooth muscle of the guinea pig trachea, and the effects of intrinsic nerve stimulation were examined. Approximately 50% of the cells had stable resting membrane potentials of 50 ± 1 mV. The remaining cells displayed spontaneous oscillations in membrane potential, which were abolished either by blocking voltage-dependent Ca 2+ channels with nifedipine or by depleting intracellular Ca 2+ stores with ryanodine. In quiescent cells, stimulation with a single impulse evoked an excitatory junction potential (EJP). In 30% of these cells, trains of stimuli evoked an EJP that was followed by oscillations in membrane potential. Transmural nerve stimulation caused an increase in the frequency of spontaneous oscillations. All responses were abolished by the muscarinic-receptor antagonist hyoscine (1 µM). In quiescent cells, nifedipine (1 µM) reduced EJPs by 30%, whereas ryanodine (10 µM) reduced EJPs by 93%. These results suggest that both the release of Ca 2+ from intracellular stores and the influx of Ca 2+ through voltage-dependent Ca 2+ channels are important determinants of spontaneous and nerve-evoked electrical activity of guinea pig tracheal smooth muscle. excitatory junction potential