Light absorbance changes in the mouse carotid body during hypoxia and cyanide poisoning

The isolated carotid body (CB) of the mouse was bathed with modified Tyrode's solution (pO2, 170 Torr) and transilluminated at different wave-lengths (500-620 nm). Difference spectra (normoxia vs hypoxia--pO2, 10 Torr) showed peaks of increased light transmittance (LT) at 500 and especially at 540 and 580 nm. There were troughs of transmittance decrease at 560 and 600 nm. Similar spectra (normoxia vs NaCN 10 mM) revealed increased LT at 500 and 590 nm, whereas there was decreased LT at 550 nm. Therefore, absorbance changes induced by hypoxia and cyanide were different. As as control for residual hemoglobin (Hb) in the tissues, a segment of carotid artery was filled with blood and the same light scanning was performed. The differential signals evoked by hypoxia were much larger. There was some LT increase at 500 and 540 nm, but this effect was especially marked at 570 and 590 nm. NaCN showed the same absorbance pattern, but peaks were of lower amplitude. Thus, the CB-produced signals were not elicited by residual Hb. A stepwise decrease in the medium pO2 (from 170 to 10 Torr) surrounding the CB produced a progressive increase in LT at 540 and 580 nm starting at 120 Torr. A different pattern was evoked by 550 (cytochrome c) and 600 (cytochrome aa3) nm. With 550 nm, transmittance began to increase at about 70 Torr. LT decreased with 600 nm starting at about 120 Torr.(ABSTRACT TRUNCATED AT 250 WORDS)