Elasmobranch fishes, including sharks, rays, and skates, use specialized electrosensory organs called ampullae of Lorenzini to detect extremely small changes in environmental electric fields. Electrosensory cells within these ampullae can discriminate and respond to minute changes in environmental voltage gradients through an unknown mechanism. Here we show that the voltage-gated calcium channel CaV1.3 and the big conductance calcium-activated potassium (BK) channel are preferentially expressed by electrosensory cells in little skate (Leucoraja erinacea) and functionally couple to mediate electrosensory cell membrane voltage oscillations, which are important for the detection of specific, weak electrical signals. Both channels exhibit unique properties compared with their mammalian orthologues that support electrosensory functions: structural adaptations in CaV1.3 mediate a low-voltage threshold for activation, and alterations in BK support specifically tuned voltage oscillations. These findings reveal a molecular basis of electroreception and demonstrate how discrete evolutionary changes in ion channel structure facilitate sensory adaptation.