Effect of cooling on ovalbumin-induced contraction of the tracheal muscle isolated from actively sensitized rat.

Isolated tracheal strip-chain preparations from actively sensitized rat were used to study the effect of temperature on ovalbumin-induced contraction. The preparations were suspended in an organ bath containing Krebs bicarbonate solution for isometric tension recording. A decrease of the bath temperature from 37 degrees C to 20 degrees C (cooling) had no effect on basal tone but augmented the contractile responses of the trachea caused by ovalbumin (OA, 10 micrograms/ml) and 5-hydroxytryptamine (5-HT 1-30 microM). Both responses of the trachea to OA and 5-HT were almost abolished by pretreatment of the tissue with methysergide (1 microM). The response to 5-HT was also inhibited by about 20% by atropine (1 microM) but not by tetrodotoxin (0.3 microM). On the other hand, 5-HT-induced contractile responses of the trachea which was incubated with normal and Ca2+-free Krebs bicarbonate solution containing atropine (1 microM) were both augmented by 20 degrees C. In the presence of atropine (1 microM), diltiazem in a concentration of 10 microM, which almost abolished the potassium chloride (KCl, 20-40 mM) induced contraction, caused partial depression of the contractile response to 5-HT at 20 degrees C but not at 37 degrees C. The present results demonstrate that the cooling-induced augmentation of the sensitized rat trachea to OA is due to the increase of tissue responsiveness to 5-HT which is an important chemical mediator in the anaphylactic response. The major part of the contractile response to 5-HT may be mediated by a direct action on the smooth muscle. The increased responsiveness of the tracheal smooth muscle to 5-HT with lower temperature may involve the acceleration of Ca2+ release from intracellular storage sites and Ca2+ influx through voltage-dependent Ca2+ channels.