Ion channel regulation is key to controlling neuronal excitability. However, the extent that modulators and gating factors interact to regulate channels is less clear. For Aplysia, a non-selective cation channel plays an essential role in reproduction by driving an afterdischarge in the bag cell neurons to elicit egg-laying hormone secretion. We examined the regulation of cation channel voltage- and Ca²⁺-dependence by protein kinase C (PKC) and inositol trisphosphate (IP₃) - two prominent afterdischarge signals. In excised, inside-out patches, the channel remained open longer and re-opened more often with depolarization from -90 though to +30 mV. As previously reported, PKC could closely-associate with the channel and increase activity at -60 mV. We now show that following the effects of PKC, voltage-dependence was shifted to the left (essentially enhanced), particularly at more negative voltages. Conversely, the voltage-dependence of channels lacking PKC was shifted to the right (essentially suppressed). Predictably, activity was increased at all Ca²⁺ concentrations following the effects of PKC; nevertheless, Ca²⁺-dependence was actually shifted to the right. Moreover, while IP3 did not alter activity at -60 mV, it drastically shifted Ca²⁺-dependence to the right - an outcome largely reversed by PKC. With respect to the afterdischarge, these data suggest PKC initially upregulates the channel by direct gating and shifting voltage-dependence to the left. Subsequently, PKC and IP₃ attenuate the channel by suppressing Ca²⁺-dependence. This ensures hormone delivery by allowing afterdischarge initiation and maintenance, but also prevents interminable bursting. Similar regulatory interactions may be used by other neurons to achieve diverse outputs.