Relationship between tissue po2 and chemoreceptor activity of the carotid body in vitro

Tissue pO2 (pgO2) and sinus nerve activity were recorded in the carotid body in vitro under hypoxic conditions produced either by interrupting the superfusion flow or by lowering the pO2 of the medium (pmO2). The pgO2 gradient is the steeper the higher pmO2 is. These findings point to a pO2-dependent oxygen consumption. Under hypoxia produced by interrupting the superfusion flow, pgO2 declines slowly down to final values and, concomitantly, the chemoreceptor discharge increases. Under hypoxia produced by lowering pmO2, pgO2 decreases rapidly down to values of about 3 torr, whereas the chemoreceptor discharge at first increases and then decreases, in spite of a maintained low pgO2. The pO2 threshold where the chemoreceptor starts firing under hypoxia, varies between 9 and 90 torr.