556 channel current in the presence of the other channel agonist was correlated with the amplitude of current through the other channel (Fig. 4). Furthermore, we found that IACh + ATP desensitizes faster than IATP, but more slowly than IACh, and IACh + ATP at a Vh between EACh and EATP showed a combination pattern of early outward IACh and delayed inward IATP (Fig. 6C). These results both strongly suggest that in AP neurons, IACh + ATP are carried through both nAChR and P2XR channels, and that inhibition between these channels is reciprocal. The IATP was not inhibited by co-application of ACh when the inward IACh was markedly reduced in the absence of permeant cations (Fig. 8B) or at a Vh very close to EACh (Fig. 8D), and the inhibited IATP in the presence of ACh (Fig. 5B) recovered as soon as the nAChR channel closed in the presence of dTc (Fig. 5C). 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