Low-temperature Modification of the Inhibitory Effects of Volatile Anesthetics on Airway Smooth Muscle Contraction in Dogs

Background: Because exposure to low temperature can modify the effect of volatile anesthetics on airway smooth muscle contraction, this study was conducted to investigate low-temperature modifications of the inhibitory effects of isoflurane and sevoflurane on canine tracheal smooth muscle tone by simultaneously measuring the muscle tension and intracellular concentration of Ca2+ (Ca2+]i) and by measuring voltage-dependent Ca2+ channel activity.

Methods: Ca2+]i was monitored by the 500-nm light emission ratio of preloaded fura-2, a Ca2+ indicator. Isometric tension was measured simultaneously. Whole cell patch clamp recording techniques were used to observe voltage-dependent Ca2+ channel activity in dispersed muscle cells. Isoflurane (0-3.0%) or sevoflurane (0-3%) was introduced to a bath solution at various temperatures (37, 34, or 31degrees]C).

Results: Low temperature (34 or 31degrees]C) reduced high-K+-induced (72.7 mm) muscle contraction and increased Ca2+]i, but it enhanced carbachol-induced (1 mu]m) muscle contraction with a decrease in Ca2+]i. The volatile anesthetics tested showed significant inhibition of both high-K+-induced and carbachol-induced airway smooth muscle contraction, with a concomitant decrease in Ca2+]i. The inhibition of the carbachol-induced muscle contraction by volatile anesthetics was abolished partially by exposure to low temperature. Volatile anesthetics and low-temperature exposure significantly inhibited voltage-dependent Ca2+ channel activity of the smooth muscle.