Oxytocin can regulate myometrial smooth muscle excitability by inhibiting the Na ± activated K ± channel, Slo2.1.

KEY POINTS: At the end of pregnancy, the uterus transitions from a quiescent state to a highly contractile state. This transition requires that the uterine (myometrial) smooth muscle cells increase their excitability, but how this occurs is not fully understood. We identified SLO2.1, a potassium channel heretofore unknown to be in uterine smooth muscle as a potential significant contributor to the electrical excitability of myometrial smooth muscle cells. We found that activity of the SLO2.1 channel is negatively regulated by oxytocin through Gαq-Protein-Coupled Receptor activation of protein kinase C. This results in depolarization of the uterine smooth muscle cells and calcium entry, which may contribute to uterine contraction. These findings provide novel insights into a previously unknown mechanism by which oxytocin may act to modulate myometrial smooth muscle cell excitability. Our findings also reveal a new potential pharmacological target for modulating uterine excitability.

ABSTRACT: During pregnancy the uterus transitions from a quiescent state to a more excitable contractile state. This is thought to be due, at least in part, to changes in the myometrial smooth muscle cell (MSMC) resting membrane potential. However, the ion channels controlling the myometrial resting membrane potential and the mechanism of transition to a more excitable state have not been fully elucidated. Here, we show that the sodium-activated, high-conductance, potassium leak channel, SLO2.1, is expressed and active at the resting membrane potential in MSMCs. Additionally, we report that SLO2.1 is inhibited by oxytocin binding to the oxytocin receptor. Inhibition of SLO2.1 leads to membrane depolarization and activation of voltage-dependent calcium channels, resulting in calcium influx. Our results reveal that oxytocin may modulate MSMC electrical activity by inhibiting SLO2.1 potassium channels. This article is protected by copyright. All rights reserved.