Smooth muscle from the respiratory tract: Effects of altered gas tensions

STRIPS of bovine tracheal smooth muscle were subjected to changes in the gas tensions of the Krebs solution bathing them. Contractions were produced by 50 Hz sine-wave electrical field stimulation, either in single bursts, or repetitively throughout the experiment.Hypoxia (Po2 99, 55 or 22 mm Hg, pH 7.4) decreased the response to single bursts of stimuli by 22-56 per cent (P<0.01). Hypoxia also reduced the resting tension by 72 per cent (P<0.005). All changes due to altered gas tensions were, at least partially, reversible by returning the tissue to standard conditions.Hypercapnic acidosis (Pco2 140-150 mm Hg, pH 6.7-7.0) reduced the response to single bursts of stimuli by 6 per cent (P<0.01) and reduced the response to repetitive bursts of stimuli by 16 per cent (P<0.01). Acapnic alkalosis (Pco2 0 mm Hg, pH 7.9) did not significantly alter the response to repetitive stimulation.It is concluded that hypoxia, and to a lesser extent hypercapnia, can directly modify tone in the airways, and may contribute to regulation of airflow in the tracheobronchial tree.