Ether-à-go-go (EAG or Kv10.1) potassium channels are strongly expressed in several mammalian brain regions. Their precise physiological roles are unclear, but increased hEAG1 channel expression has been linked to many forms of human cancer. hEAG1 channels are highly sensitive to inhibition by intracellular calcium (Ca2+i) via a poorly understood calmodulin (CaM) mediated mechanism. These channels contain large intracellular structural domains. On the N-terminus is the eag-domain (residues 1- 135) which consists of a Per-Arnt-Sim (PAS) domain joined to a smaller flexible region of 26 amino acids (1-26) known as the PAS-cap. On the C-terminus is a cyclic nucleotide binding homology domain (cNBHD), which is linked directly to the pore of the channel. Three CaM binding sites have been identified; one close to the eag-domain and two adjacent to the cNBHD. The eag-domain and cNBHD are known to be important for regulating voltage dependent gating. In this study we investigated if they are also vital for calcium dependent gating. hEAG1 currents were recorded in Xenopus oocytes using two-electrode voltage clamp. The Ca2+-ionophore ionomycin (5μM) and SERCA inhibitor thapsigargin (5μM) were applied to raise Ca2+i. Wild-type (WT) hEAG1 responded to ionomycin and thapsigargin (I & T) with an initial rapid inhibition (mean ± SEM was 72 ± 8 %, n=7) followed by a recovery phase in which the amplitude slowly increased but currents exhibited much slower time dependent kinetics and a positively shifted voltage dependence of activation. Deletion of the cNBHD abolished current inhibition by I & T (0 ± 3 %, n=5). Interestingly, whereas deleting the whole eag-domain resulted in a small increase of current in response to I & T (134 ± 11 %, n=7), deleting just the PAS-cap domain increased hEAG1 current by 950 ± 331 % (n=5). Thus, these N-terminal mutants remained sensitive to Ca2+i, but rather than being inhibited were profoundly potentiated. In the closely related hERG (Kv11.1) channel, electrostatic interactions between the PAS-cap and cNBHD have been shown to be important for regulating deactivation gating. Similar charge-charge interactions appear to be important for Ca2+i -dependent gating in hEAG1. Mutation of a negatively charged patch on the cNBHD (689EEEE693 to 689AAAA693) reduced the response to I & T so that only a 20 ± 13 % inhibition (n=8) was observed. Our results suggest that hEAG1 channels are regulated by Ca2+-CaM in a complex manner that requires an intact eag-domain and cNBHD. We propose CaM mediates at least two interactions between these domains. One that blocks conduction and requires the PAS-cap region to stabilise the closed state and another in which the channel is conducting but the voltage and time dependent gating are profoundly altered.