Egg laying behavior in Aplysia is controlled by the bag cell neurons. In response to stimulation, these neurons afterdischarge and release egg laying hormone. A nonselective cation channel provides the depolarizing drive for the afterdischarge. Using cultured bag cell neurons and inside-out patches, we now show that the effect of ATP on these cation channels differs depending on whether on not PKC is associated with the channel. Previously, we demonstrated that when PKC is associated with the channel, applying ATP enhances Po (PNAS 95:10938; SFN Astr 25:503.9). In the present study, for 50% of patches (n=71) application of ATP to the cytoplasmic face increased cation channel Po, while for the other 50% of patches (n=71) ATP either had no effect or decreased Po slightly. The nature of the response was determined by the animal from which the neurons were isolated, i.e., all channels in neurons cultured from a single animal responded to ATP in the same way (increased Po in 29 animals or no effect on Po in 33 ...