The transition from uterine quiescence to contraction is vital to the health of a newborn and mother, but timing of this event often fails to occur properly; in the U.S., 12% of babies are born preterm, and 20% are delivered following artificial induction of labor. Thus, understanding the regulation of myometrial smooth muscle cell (MSMC) electrical activity and its effect on contraction is essential for both comprehending normal labor and treating dysfunctional labor. Maintenance of uterine quiescence requires an intricate balance between excitatory depolarizing stimuli that promote contractions and inhibitory repolarizing currents that suppress uterine contraction. One predominant channel in MSMCs, the large conductance Ca2+-activated K+ channel (KCa1.1) contributes to quiescence by eliciting a potent repolarizing current in response to excitatory signals, thereby dampening MSMC contraction. In spite of strong evidence supporting the notion that the KCa1.1 channel modulates uterine excitability, the basic mechanisms involved in its physiological regulation during pregnancy remain largely uncharacterized. The long-term goal of my research is to identify the ionic mechanisms that regulate the transition from quiescence to contraction during pregnancy. The objective of this proposal is to define the mechanisms by which the KCa1.1 channel is modulated during pregnancy to control myometrial excitability. Our central hypothesis is that this channel is dynamically modulated by both intrinsic properties and by its association with modulatory proteins. In support of this idea, our preliminary studies in human MSMCs indicate that KCa1.1 is regulated by alternative translation initiation, resulting in KCa1.1 isoforms that vary in their extracellular N- termini. These N-terminal variants differ in their regulation by accessory 1-subunits. We also have generated proteomics data demonstrating that other novel modulators, including the recently described family of - subunits and the protease inhibitor 2macroglobulin (A2M), selectively associate with myometrial KCa1.1 and potentially modify channel activity. The goals of this project are to: 1) define the spatial and temporal interactions between novel proteins that interact with KCa1.1 in non-laboring and laboring human myometrium, 2) identify intrinsic properties of KCa1.1 that alter its association with interacting partners; and 3) determine the mechanism of functional regulation of KCa1.1 in both myometrial cell lines and non-laboring and laboring human myometrium. The research proposed here will establish the molecular pathways that regulate KCa1.1 activity, providing a biological basis for therapies designed to modulate uterine excitability.

Public Health Relevance

This proposal contributes to improving reproductive health by focusing on new forms of ion channel modulation that may help keep the uterus relaxed during the progression of pregnancy. The activity of this channel may contribute to understanding how normal labor proceeds. Once we ascertain this information, we envision that we can better understand certain pathophysiological conditions such as preterm labor and post-term labor occur. In the muscle layer of the uterus, expression or activity of K+ channels regulate uterine contractions and promote uterine quiescence. Knowledge gained from this proposal will help determine whether novel forms of modulation of K+ channel expression and activity impact uterine function.

National Institute of Health (NIH)
Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD)
Research Project (R01)
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Special Emphasis Panel (ZRG1-EMNR-H (02)M)
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Ilekis, John V
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Washington University
Obstetrics & Gynecology
Schools of Medicine
Saint Louis
United States
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Lorca, Ramón A; Ma, Xiaofeng; England, Sarah K (2017) The unique N-terminal sequence of the BKCa channel ?-subunit determines its modulation by ?-subunits. PLoS One 12:e0182068
Wakle-Prabagaran, Monali; Lorca, Ramón A; Ma, Xiaofeng et al. (2016) BKCa channel regulates calcium oscillations induced by alpha-2-macroglobulin in human myometrial smooth muscle cells. Proc Natl Acad Sci U S A 113:E2335-44
Reinl, Erin L; England, Sarah K (2015) Fetal-to-maternal signaling to initiate parturition. J Clin Invest 125:2569-71
Rada, Cara C; Pierce, Stephanie L; Grotegut, Chad A et al. (2015) Intrauterine telemetry to measure mouse contractile pressure in vivo. J Vis Exp :e52541
Stilley, Julie A W; Christensen, Debora E; Dahlem, Kristin B et al. (2014) FSH receptor (FSHR) expression in human extragonadal reproductive tissues and the developing placenta, and the impact of its deletion on pregnancy in mice. Biol Reprod 91:74
Lorca, Ramón A; Prabagaran, Monali; England, Sarah K (2014) Functional insights into modulation of BKCa channel activity to alter myometrial contractility. Front Physiol 5:289
Lorca, Ramón A; Stamnes, Susan J; Pillai, Meghan K et al. (2014) N-terminal isoforms of the large-conductance Ca²?-activated K? channel are differentially modulated by the auxiliary ?1-subunit. J Biol Chem 289:10095-103
Li, Youe; Lorca, Ramón A; Ma, Xiaofeng et al. (2014) BK channels regulate myometrial contraction by modulating nuclear translocation of NF-?B. Endocrinology 155:3112-22
McCloskey, Conor; Rada, Cara; Bailey, Elizabeth et al. (2014) The inwardly rectifying K+ channel KIR7.1 controls uterine excitability throughout pregnancy. EMBO Mol Med 6:1161-74
Rada, Cara C; Pierce, Stephanie L; Nuno, Daniel W et al. (2012) Overexpression of the SK3 channel alters vascular remodeling during pregnancy, leading to fetal demise. Am J Physiol Endocrinol Metab 303:E825-31

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