A, sample traces showing the various junction potentials associated with 20 Hz EFS for 30 s in a WT mouse IAS. In control conditions, a faster purinergic/nitrergic IJP is followed by a slower post-stimulus hyperpolarization (Aa; black trace). Following addition of MRS2500 (1 μm) and l-NNA (100 μm) the purinergic/nitrergic IJP is blocked, while the slower component remains (Ab; grey trace). Superimposing these traces shows that the NNNP hyperpolarization remains unchanged in the absence of the purinergic/nitrergic IJP (Ac). B, in the VIP−/− mouse IAS, the purinergic/nitrergic IJP is present, but post-stimulus hyperpolarization is not (Ba). Following addition of MRS2500 and l-NNA, no further hyperpolarization occurs (Bb and Bc).