AJP - Cell Physiology, Vol 273, Issue 3 C868-C873, Copyright © 1997 by American Physiological Society
Muscarinic receptor stimulation modulates the effect of halothane on Mn2+ influx in airway smooth muscle
D. O. Warner, K. A. Jones, R. R. Lorenz and C. M. Pabelick
Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota, USA.
Prior studies suggest that the mechanism of action by which halothane
relaxes airway smooth muscle depends on the contractile state of the cell.
We hypothesized that halothane would inhibit the influx of Ca2+ into canine
airway smooth muscle cells during submaximal, but not maximal, muscarinic
stimulation. This hypothesis was tested by using the rate of quenching of
fura 2 fluorescence by Mn2+ in strips of canine tracheal smooth muscle as
an index of Ca2+ influx. Acetylcholine (ACh) produced a dose-dependent
increase in Mn2+ influx. Halothane (0.64 +/- 0.05 microM) significantly
decreased Mn2+ influx and intracellular Ca2+ concentration when added to
strips stimulated with a submaximal concentration of ACh (0.3 microM) but
had no effect on Mn2+ influx or intracellular Ca2+ concentration during
maximal stimulation with ACh (100 microM). Similar results were observed
when the strips were treated with verapamil. These results demonstrate that
anesthetic effects on Ca2+ homeostasis in intact canine tracheal smooth
muscle cells may be critically modulated by receptor-linked mechanisms.
