Myomodulin is a neuropeptide present in molluscs, insects, and gastropods. Within these organisms, myomodulin A specifically occurs in two identified Aplysia neurons: the ARC motor neuron [B16] and the abdominal neuron [L10].

Myomodulin modulates heart interneuron functions by decreasing the period and increasing spike frequency, alongside enhancing hyperpolarization-activated cation currents and inhibiting the electrogenic Na/K pump[1]. It also plays a role in the nervous system of the leech Hirudo medicinalis, by mediating giant glial cell response to Leydig interneuron stimulation, inducing a significant membrane outward current (EC50 approximately 2 μM) and increasing K+ conductance without desensitization or run-down[2]. Additionally, myomodulin affects ion channels across various organisms, including Aplysia, Lymnaea, and Pleurobranchaea, by differentially modulating potassium currents and decreasing Ca2+ current amplitude by 20%[3].