How rapidly are adenine nucleotides converted to adenosine?
The comparisons between nucleotides summarized in Figure 4E were all made on different cells, and because of the intrinsic variability in such responses, it was difficult to determine whether the minor differences in latency, amplitude, and duration that were observed were differences between the nucleotides and adenosine or reflected cell-to-cell variation in the response. For that reason, parallel experiments were conducted using two-barrel drug application pipettes, so that direct comparisons might be made of the responses to various nucleotides and adenosine on the same cell. Figure 7 illustrates this type of comparison between AMP and adenosine and between cAMP and AMP. In cells recorded with AMP and adenosine, responses to both purines were quite similar (Fig. 7A), confirming the similarity of the responses observed in the experiments on different cells (Fig. 4). On the other hand, cAMP produced little if any effect, even when ejected using identical conditions onto the same cell
