Test 2

Chinwendu Amazu, Washington University in St. Louis


During pregnancy, the uterus transitions from a quiescent state to an excitable, highly contractile state to deliver the fetus. Two important contributors essential for this transition are progesterone (P4) and estrogen (E2), which promote quiescence or contraction, respectively, by acting on the myometrial smooth muscle cells (MSMCs). While these hormones regulate uterine contractions, it is unclear how they affect electrical activity of MSMCs, which underlies uterine contractile activity. Our lab recently identified Na+ leak channel, non-selective (NALCN) as a component of the leak current in human MSMCs and showed that mice lacking NALCN in the uterus have dysfunctional labor. In this thesis, we first sought to determine whether P4 and E2 directly regulated NALCN expression and activity. We established that P4, upregulates the expression of NALCN by acting through progesterone response elements in the NALCN promoter while E2 downregulates this channel in humans MSMCs. These expression changes translated functionally as P4 significantly enhanced, and E2 significantly inhibited a NALCN-dependent leak current in human MSMCs. Our findings that NALCN is upregulated by P4, a pro-quiescent hormone: 1) contradicts the traditional concept that Na+ influx depolarizes the cell to enhance cell excitability and 2) provides a novel role for Na+ entry through NALCN. Thus, we further explored if Na+ influx through NALCN may contribute to promoting quiescence by activating other signaling pathways. We provide evidence that current through NALCN is a source of Na+ to activate SLO2.1, the Na+-activated K+ channel, which contributes to the resting membrane potential (Vm) of MSMCs. Additionally, we observed that SLO2.1 was in proximity with NALCN in human MSMCs and our data suggests these channels form a functional complex to maintain Vm and modulate intracellular Ca2+ levels. Overall, our findings identified a new form of regulation of NALCN in human MSMCs and unmasked how NALCN contributes to Vm in order to regulate myometrial excitability.