Fig. 1. (  A ) A schematic presentation of the experimental protocol testing propofol and carotid body chemosensitivity using three degrees of step reduction in Po²: mild, moderate, and severe. The three degrees of Po²reduction were tested in different sequence between different animals.  Black line represents perfusion with modified Tyrode’s buffer.  Black arrows indicate reduction in Po².  Shaded bars show 30-min perfusion with 100 μm propofol. (  B ) A schematic presentation of the experimental protocol testing nicotine-induced carotid body chemoreceptor responses to 500 μg nicotine.  Black line represents perfusion with modified Tyrode’s buffer.  Black arrows indicate administration of 500 μg of nicotine.  Shaded bars show perfusion with 1) propofol in one of the concentrations 10, 30, or 100 μm, 2) propofol 100 μm (Prop), propofol 100 μm + bicuculline 100 μm (Prop+Bic), propofol 100 μm + picrotoxin 100 μm (Prop+Pic). The order of the concentrations/drugs was rotated between different preparations.