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 31 degrees C). Results Low temperature (34 or 31 degrees C) reduced high-K+-induced (72.7 mm) muscle contraction and increased [Ca2+]i, but it enhanced carbachol-induced (1 microm) 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. Conclusions Exposure of airway smooth muscle to low temperature leads to an increase in agonist-induced muscle contractility, with a decrease in [Ca2+]i. The inhibition of voltage-dependent Ca2+ channel activity by exposure to low temperature and by volatile anesthetics cam be attributed, at least in part, to the decrease in [Ca2+]i.