Optical Measurements of Oxygen and Electrical Measurements of Oxygen Chemoreception in the Cat Carotid Body

Abstract

Measurements of oxygen pressures within the carotid body have been of particular importance for elucidating the mechanism(s) of oxygen chemoreception. An optical technique based on the quenching of phosphorescence by oxygen that is capable of imaging oxygen within the microvasculature has been developed (Rumsey et al, 1988, Wilson et al, 1991). These optical measurements are non-invasive and in particular have the advantage of determining oxygen pressures throughout the entire tissue. We have previously applied this technology to the study of the isolated perfused/superfused cat carotid body and oxygen chemoreception (Rumsey et al, 1991), relying primarily on imaging of phosphorescence intensity. Although the latter is quite useful for following dynamic changes in oxygen pressures, calculation of oxygen pressure is only qualitative. In addition, the carotid body was perfused and superfuised with cell-free media (Iturriaga et al, 1991). In the present report, we describe measurements of oxygen pressure determined from images in phosphorescence lifetimes (Wilson et al, 1991) in the cat carotid body using an in vivo preparation (Lahiri and DeLaney, 1975). These determinations were compared to those obtained previously with the in vitro preparation, thereby permitting comparison of the oxygenation of this organ in the presence and absence of blood, respectively. In both cases, chemosensory discharge was recorded in order to provide measurements of the expression of oxygen chemoreception.