Enhanced basal tension in isolated rat tracheal smooth muscle stimulated by electric field stimulation under low temperature

Abstract

Exposure to cold causes cutaneous vasoconstriction to reduce body heat loss, while the airway warms up the inspired cold air, thus suggesting that cooling might evoke a response in tracheal smooth muscle different from that in cutaneous blood vessels. The aim of this study was to evaluate the effect of temperature on isolated rat trachea, with or without electric field stimulation (EFS). Tissue bath for isolated trachea was used. An in vitro isometric contraction of trachea from healthy male Sprague-Dawley rat (body weight: ≥ 200 g) was continuously recorded. Tension in strips of rat trachea that were untreated and treated with EFS, was continuously recorded in stepwise manner at temperatures varying from 37 °C to 7 °C or from 7 °C to 37 °C. Results indicated that descent and re-ascent of temperature produced temperature-dependent tension changes. Basal tension of the trachea decreased when temperature was reduced if EFS was not applied. EFS-induced spike contraction decreased when temperature was reduced, while basal tension increased at the same time. We concluded that low temperature induced rapid and reproducible contraction in isolated rat tracheal strip only if EFS was applied. Increasing temperature reduced basal tension and enhanced EFS-induced spike contraction of the trachea at the same time.

Keywords: in vitro study; Trachea; low temperature; smooth muscle.

Figure 1

Original recording of basal tension of trachea strips at different temperatures with or without EFS. (Upper) Decrease in temperature enhanced basal tension and reduced EFS-induced spikes contraction of tracheal strip. (Middle) Without EFS, temperature decrease lessened basal tension. An initial spike under changing temperature was also noted. (Bottom) Decellularized strip showed a reaction to temperature changes similar to that of tracheal strip without EFS treatment. EFS (electrical field stimulation).

Figure 2

Average basal tension of tracheal strips at different temperatures. Comparing with the tracheal strip without EFS or decellularized tracheal strips, the basal tension of tracheal strips with EFS increased significantly between 7 °C and 37 °C. EFS (electrical field stimulation).

Figure 3

The basal tension of tracheal strips without EFS decreased significantly between 37 °C, 25 °C, 15 °C and 7 °C. The basal tension of strips at 25 ºC, 15 ºC and 7 ºC are 57.8% ± 4.3%, 42.5% ± 4.9% and 27.5% ± 5.6% of contraction respectively as compared with that at 37 ºC calculated as 100%. EFS (electrical field stimulation). Results were mean ± SD (n = 6).

Figure 4

EFS-induced spike contraction of tracheal strips at different temperatures. The EFS-evoked tension peaks of the trachea was 100% and 35.0% ± 12.8% of the control values at 37°C and 7°C, respectively; indicating significant decrease in spike tension of tracheal strips between 7°C and 37°C. EFS (electrical field stimulation). Results were mean ± SD (n = 6).