Ultrastructural features of the carotid body after in vitro experiments: correlation with physiological results.

We have studied the ultrastructure and physiological properties of the rabbit carotid body superfused in vitro. After 3 h superfusion, the ultrastructural features of the carotid body cells, nerve fibres and nerve endings are similar to those observed after in vivo perfusion with fixative. After 5 h superfusion, the fluorescence of type I cells and sympathetic post-ganglionic nerve fibres appears normal, as demonstrated by the Falck method. After 6 h superfusion, some type I cells are characterized by a highly vacuolated cytoplasm whereas most of the nerve fibres and nerve endings still show a normal ultrastructure. Damaged cells are not more abundant in the centre of the organ than in the surface layer. Recordings from chemoafferent units demonstrate the possibility of superfusing the carotid body with an air-equilibrated medium without any noticeable excitation. Large and reproducible responses to hyperoxic and hypoxic superfusions are recorded. It is concluded that the in vitro superfused rabbit carotid body is a reliable and useful preparation for studying the mechanism of chemoreceptor excitation.