Physiological oxygen concentration gives an oscillating spontaneous tone in guinea-pig tracheal preparations

The spontaneous tone in isolated six-segment preparations of guinea-pig tra chea was examined. In 12% oxygen (corresponding to normal systemic arterial oxygen pressure) the preparations developed a spontaneous tone with regula r oscillations (6.6 min(-1)), usually grouped in so-called complexes (7.5 h (-1)). The average tone during an entire complex amounted to 12% of a maxim um KCI-induced contraction. The complex tone was highly stable during obser vation periods of at least 4 h, and was reversibly transformed to the 'clas sical', smooth type when exposed to 94% oxygen. Stretch of preparations in low oxygen resulted in a fast, stable change of tone, while preparations in traditionally high oxygen reacted slower, and lost 40% of the active tensi on during the hour following stretch. Indomethacin (10 mu M) did not elimin ate the oscillating behaviour, but reduced the average size of the tone by 44%. Exposure to the C-fibre blocking agent capsaicin (50 mu M) and the loc al anaesthetic lidocaine (1 mM) completely eliminated the oscillations and complexes, although the preparations retained a smooth tone. Atropine, prop ranolol and tetrodotoxin did not affect the complex tone. This study demons trates for the first time that guinea-pig tracheal preparations that are ex posed to near-physiological oxygen concentrations develop a new type of osc illating spontaneous tone, which is largely prostaglandin-independent. but appears to require transmitter release from sensory C-fibres. We argue that the complex tone is physiological, and that traditionally high oxygen (95% ) probably results in non-physiological hyperoxic changes in this preparati on.