Figure 1. Selectivity, calibration and placement of biosensors.

A, responses of ATP and null biosensors to ATP, 5-hydroxytryptamine (5-HT, a representative highly electroactive interferent) and the CO₂ stimulus. The small responses to 5-HT and CO₂ are very similar in the ATP and null biosensors and subtraction of the null sensor current from the ATP biosensor current gives the net ATP signal (netATP). B, inset shows the locations of the rostral and caudal recording areas relative to landmarks such as the pyramids (py) and XIIth nerve rootlets (XII). Responses of the ATP and null biosensors to the hypercapnic stimulus when placed at the caudal location on the ventral medullary surface.