SLO2.1 and NALCN form a functional complex to modulate myometrial cell excitability

At the end of pregnancy, the uterus transitions from a quiescent state to an excitable, contractile state. These changes are linked to depolarization of the myometrial smooth muscle cell (MSMC) resting membrane potential. The membrane potential is primarily determined by the balance between an outward potassium (K+) leak current and an inward sodium (Na+) leak current. We recently described a Na+-activated K+ channel (SLO2.1) and a non-selective Na+ leak channel (NALCN) in human MSMCs. Here, we asked whether these channels function together. We show that SLO2.1 currents are activated by an inward NALCN-dependent Na+ leak current, leading to MSMC hyperpolarization. The regulation of the membrane potential by NALCN/SLO2.1 activity modulates both Ca2+ entry through VDCCs, and myometrial contractility. Finally, NALCN and SLO2.1 are in proximity to one another in human MSMCs. We conclude that SLO2.1 and NALCN function together to regulate human MSMC membrane potential and excitability.