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Monitoring uterine contractions during labor: current challenges and future directions. Am J Obstet Gynecol 2023; 228:S1192-S1208. [PMID: 37164493 DOI: 10.1016/j.ajog.2022.10.039] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2022] [Revised: 10/22/2022] [Accepted: 10/27/2022] [Indexed: 03/21/2023]
Abstract
Organ-level models are used to describe how cellular and tissue-level contractions coalesce into clinically observable uterine contractions. More importantly, these models provide a framework for evaluating the many different contraction patterns observed in laboring patients, ideally offering insight into the pitfalls of currently available recording modalities and suggesting new directions for improving recording and interpretation of uterine contractions. Early models proposed wave-like propagation of bioelectrical activity as the sole mechanism for recruiting the myometrium to participate in the contraction and increase contraction strength. However, as these models were tested, the results consistently revealed that sequentially propagating waves do not travel long distances and do not encompass the gravid uterus. To resolve this discrepancy, a model using 2 mechanisms, or a "dual model," for organ-level signaling has been proposed. In the dual model, the myometrium is recruited by action potentials that propagate wave-like as far as 10 cm. At longer distances, the myometrium is recruited by a mechanotransduction mechanism that is triggered by rising intrauterine pressure. In this review, we present the influential models of uterine function, highlighting their main features and inconsistencies, and detail the role of intrauterine pressure in signaling and cervical dilation. Clinical correlations demonstrate the application of organ-level models. The potential to improve the recording and clinical interpretation of uterine contractions when evaluating labor is discussed, with emphasis on uterine electromyography. Finally, 7 questions are posed to help guide future investigations on organ-level signaling mechanisms.
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Garrett AS, Means SA, Roesler MW, Miller KJW, Cheng LK, Clark AR. Modeling and experimental approaches for elucidating multi-scale uterine smooth muscle electro- and mechano-physiology: A review. Front Physiol 2022; 13:1017649. [PMID: 36277190 PMCID: PMC9585314 DOI: 10.3389/fphys.2022.1017649] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2022] [Accepted: 09/21/2022] [Indexed: 11/13/2022] Open
Abstract
The uterus provides protection and nourishment (via its blood supply) to a developing fetus, and contracts to deliver the baby at an appropriate time, thereby having a critical contribution to the life of every human. However, despite this vital role, it is an under-investigated organ, and gaps remain in our understanding of how contractions are initiated or coordinated. The uterus is a smooth muscle organ that undergoes variations in its contractile function in response to hormonal fluctuations, the extreme instance of this being during pregnancy and labor. Researchers typically use various approaches to studying this organ, such as experiments on uterine muscle cells, tissue samples, or the intact organ, or the employment of mathematical models to simulate the electrical, mechanical and ionic activity. The complexity exhibited in the coordinated contractions of the uterus remains a challenge to understand, requiring coordinated solutions from different research fields. This review investigates differences in the underlying physiology between human and common animal models utilized in experiments, and the experimental interventions and computational models used to assess uterine function. We look to a future of hybrid experimental interventions and modeling techniques that could be employed to improve the understanding of the mechanisms enabling the healthy function of the uterus.
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Qu M, Lu P, Bellve K, Lifshitz LM, ZhuGe R. Mode Switch of Ca 2 + Oscillation-Mediated Uterine Peristalsis and Associated Embryo Implantation Impairments in Mouse Adenomyosis. Front Physiol 2021; 12:744745. [PMID: 34803733 PMCID: PMC8599363 DOI: 10.3389/fphys.2021.744745] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2021] [Accepted: 10/12/2021] [Indexed: 11/13/2022] Open
Abstract
Adenomyosis is a debilitating gynecological disease of the uterus with no medicinal cure. The tissue injury and repair hypothesis for adenomyosis suggests that uterine hyperperistalsis or dysperistalsis plays a pivotal role in establishing adenomyotic lesions. However, specific impairments in uterine peristalsis and the underlying cellular signals for these changes in adenomyosis remain elusive. Here, we report a precision-cut uterine slice preparation that preserves in vivo uterine architecture and generates peristalsis similar to that seen in the whole uterus. We found that uterine peristalsis in neonatal mice at day 14 and adult mice at day 55 presents as bursts with multiple peaks induced by intracellular Ca2+ oscillations. Using a mouse model of adenomyosis induced by tamoxifen, a selective estrogen receptor modulator, we discovered that uterine peristalsis and Ca2+ oscillations from adenomyotic uteri on days 14 and 55 become spikes (single peaks) with smaller amplitudes. The peak frequency of Ca2+ oscillations or peristalsis does not show a difference between control and adenomyotic mice. However, both the estimated force generated by uterine peristalsis and the total Ca2+ raised by Ca2+ oscillations are smaller in uteri from adenomyotic mice. Uteri from adenomyotic mice on day 14, but not on day 55, exhibit hyperresponsiveness to oxytocin. Embryo implantations are decreased in adenomyotic adult mice. Our results reveal a mode switch from bursts to spikes (rather than an increased peak frequency) of uterine Ca2+ oscillations and peristalsis and concurrent hyperresponsiveness to oxytocin in the neonatal stage are two characteristics of adenomyosis. These characteristics may contribute to embryo implantation impairments and decreased fertility in adenomyosis.
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Affiliation(s)
- Mingzi Qu
- Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, MA, United States
| | - Ping Lu
- Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, MA, United States
| | - Karl Bellve
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA, United States
| | - Lawrence M Lifshitz
- Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA, United States
| | - Ronghua ZhuGe
- Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, MA, United States
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Seres-Bokor A, Kemény KK, Taherigorji H, Schaffer A, Kothencz A, Gáspár R, Ducza E. The Effect of Citral on Aquaporin 5 and Trpv4 Expressions and Uterine Contraction in Rat-An Alternative Mechanism. Life (Basel) 2021; 11:life11090897. [PMID: 34575046 PMCID: PMC8467203 DOI: 10.3390/life11090897] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2021] [Revised: 08/23/2021] [Accepted: 08/26/2021] [Indexed: 01/15/2023] Open
Abstract
Aquaporins (AQPs) are expressed in the uterus, playing a physiological role during pregnancy. An osmotic pathway—through AQP5—may modify the transient potential vanilloid 4 (TRPV4) function and uterine contraction. Our aim was to determine the role of TRPV4 antagonist citral in the regulation of pregnant uterine contraction. In vitro uterine contractions were evoked by KCl and the response was modified with citral. The expressions of TRPV4 and AQP5 were measured by RT-PCR and Western blot techniques. The lengths of gestational periods were determined in normal and LPS-induced preterm births after citral treatment, in vivo. Citral significantly decreased the uterine contraction on day 22 of pregnancy. AQP5 expression significantly increased after citral incubation; however, TRPV4 expression did not show significant changes. After citral pretreatment, the gestational period was extended both in normal and LPS-induced preterm births. Our results suppose that the downregulation of AQP5 may initiate hypertonic stress, activating TRPV4 the uterine contraction on the last day of the gestational period. The putative cooperation between AQP5 and TRPV4 may open a novel target to treat or prevent preterm birth.
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Affiliation(s)
- Adrienn Seres-Bokor
- Department of Pharmacodynamics and Biopharmacy, Faculty of Pharmacy, University of Szeged, Eötvös u. 6., 6720 Szeged, Hungary; (A.S.-B.); (K.K.K.); (H.T.)
| | - Kata Kira Kemény
- Department of Pharmacodynamics and Biopharmacy, Faculty of Pharmacy, University of Szeged, Eötvös u. 6., 6720 Szeged, Hungary; (A.S.-B.); (K.K.K.); (H.T.)
| | - Hoda Taherigorji
- Department of Pharmacodynamics and Biopharmacy, Faculty of Pharmacy, University of Szeged, Eötvös u. 6., 6720 Szeged, Hungary; (A.S.-B.); (K.K.K.); (H.T.)
| | - Annamária Schaffer
- Department of Pharmacology and Pharmacotherapy, Albert Szent-Györgyi Medical School, University of Szeged, Dóm tér 12., 6721 Szeged, Hungary; (A.S.); (A.K.); (R.G.)
| | - Anna Kothencz
- Department of Pharmacology and Pharmacotherapy, Albert Szent-Györgyi Medical School, University of Szeged, Dóm tér 12., 6721 Szeged, Hungary; (A.S.); (A.K.); (R.G.)
| | - Róbert Gáspár
- Department of Pharmacology and Pharmacotherapy, Albert Szent-Györgyi Medical School, University of Szeged, Dóm tér 12., 6721 Szeged, Hungary; (A.S.); (A.K.); (R.G.)
| | - Eszter Ducza
- Department of Pharmacodynamics and Biopharmacy, Faculty of Pharmacy, University of Szeged, Eötvös u. 6., 6720 Szeged, Hungary; (A.S.-B.); (K.K.K.); (H.T.)
- Correspondence: ; Tel.: +36-62-545-567
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Synchronized Cardiac Impulses Emerge From Heterogeneous Local Calcium Signals Within and Among Cells of Pacemaker Tissue. JACC Clin Electrophysiol 2021; 6:907-931. [PMID: 32819526 DOI: 10.1016/j.jacep.2020.06.022] [Citation(s) in RCA: 44] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2020] [Revised: 06/19/2020] [Accepted: 06/24/2020] [Indexed: 12/11/2022]
Abstract
OBJECTIVES This study sought to identify subcellular Ca2+ signals within and among cells comprising the sinoatrial node (SAN) tissue. BACKGROUND The current paradigm of SAN impulse generation: 1) is that full-scale action potentials (APs) of a common frequency are initiated at 1 site and are conducted within the SAN along smooth isochrones; and 2) does not feature fine details of Ca2+ signaling present in isolated SAN cells, in which small subcellular, subthreshold local Ca2+ releases (LCRs) self-organize to generate cell-wide APs. METHODS Immunolabeling was combined with a novel technique to detect the occurrence of LCRs and AP-induced Ca2+ transients (APCTs) in individual pixels (chronopix) across the entire mouse SAN images. RESULTS At high magnification, Ca2+ signals appeared markedly heterogeneous in space, amplitude, frequency, and phase among cells comprising an HCN4+/CX43- cell meshwork. The signaling exhibited several distinguishable patterns of LCR/APCT interactions within and among cells. Rhythmic APCTs that were apparently conducted within the meshwork were transferred to a truly conducting HCN4-/CX43+ network of striated cells via narrow functional interfaces where different cell types intertwine, that is, the SAN anatomic/functional unit. At low magnification, the earliest APCT of each cycle occurred within a small area of the HCN4 meshwork, and subsequent APCT appearance throughout SAN pixels was discontinuous and asynchronous. CONCLUSIONS The study has discovered a novel, microscopic Ca2+ signaling paradigm of SAN operation that has escaped detection using low-resolution, macroscopic tissue isochrones employed in prior studies: synchronized APs emerge from heterogeneous subcellular subthreshold Ca2+ signals, resembling multiscale complex processes of impulse generation within clusters of neurons in neuronal networks.
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Maxey AP, McCain ML. Tools, techniques, and future opportunities for characterizing the mechanobiology of uterine myometrium. Exp Biol Med (Maywood) 2021; 246:1025-1035. [PMID: 33554648 DOI: 10.1177/1535370221989259] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
The myometrium is the smooth muscle layer of the uterus that generates the contractions that drive processes such as menstruation and childbirth. Aberrant contractions of the myometrium can result in preterm birth, insufficient progression of labor, or other difficulties that can lead to maternal or fetal complications or even death. To investigate the underlying mechanisms of these conditions, the most common model systems have conventionally been animal models and human tissue strips, which have limitations mostly related to relevance and scalability, respectively. Myometrial smooth muscle cells have also been isolated from patient biopsies and cultured in vitro as a more controlled experimental system. However, in vitro approaches have focused primarily on measuring the effects of biochemical stimuli and neglected biomechanical stimuli, despite the extensive evidence indicating that remodeling of tissue rigidity or excessive strain is associated with uterine disorders. In this review, we first describe the existing approaches for modeling human myometrium with animal models and human tissue strips and compare their advantages and disadvantages. Next, we introduce existing in vitro techniques and assays for assessing contractility and summarize their applications in elucidating the role of biochemical or biomechanical stimuli on human myometrium. Finally, we conclude by proposing the translation of "organ on chip" approaches to myometrial smooth muscle cells as new paradigms for establishing their fundamental mechanobiology and to serve as next-generation platforms for drug development.
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Affiliation(s)
- Antonina P Maxey
- Laboratory for Living Systems Engineering, Department of Biomedical Engineering, USC Viterbi School of Engineering, University of Southern California, Los Angeles, CA 90089, USA
| | - Megan L McCain
- Laboratory for Living Systems Engineering, Department of Biomedical Engineering, USC Viterbi School of Engineering, University of Southern California, Los Angeles, CA 90089, USA.,Department of Stem Cell Biology and Regenerative Medicine, Keck School of Medicine of USC, University of Southern California, Los Angeles, CA 90033, USA
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Ducza E, Csányi A, Szőke É, Pohóczky K, Hajagos-Tóth J, Kothencz A, Tiszai Z, Gáspár R. Significance of transient receptor potential vanilloid 4 and aquaporin 5 co-expression in the rat uterus at term. Heliyon 2019; 5:e02697. [PMID: 31687520 PMCID: PMC6820280 DOI: 10.1016/j.heliyon.2019.e02697] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2019] [Revised: 09/13/2019] [Accepted: 10/16/2019] [Indexed: 12/15/2022] Open
Abstract
Aims Aquaporins (AQPs) are channel proteins that facilitate the rapid passive movement of water. In our studies it was proved that the decreased AQP5 expression is followed by the increase of uterine contractility. The transient receptor potential vanilloid 4 (TRPV4) is a calcium channel, which is activated in response to osmotic changes. Our aim was to determine the possible role of AQP5 in this osmotic regulation of TRPV4, thus in pregnant uterine contraction. Main methods We used RT-PCR and Western blot techniques for the detection of the TRPV4 expression during pregnancy in rat uterus. The localization of AQP5 and TRPV4 was determined by immunohistochemical studies. The role of TRPV4 in uterus contraction was investigated in an isolated organ bath system. In vitro uterus contractions were stimulated with KCl and its effect was investigated with the selective TRPV4 agonist (RN1747) and antagonist (RN1734). Key findings The TRPV4 expression continuously increased from day 18 to the last day of pregnancy. The co-expression of TRPV4 and AQP5 in the myometrium and endometrium was determined in the late pregnant uterus. The TRPV4 antagonist and agonist significantly decreased and increased uterine contraction, respectively, especially on the last day of pregnancy. Significance We presume the decreased AQP5 expression triggers hypertonic stress, which activates TRPV4 and increases uterus contraction on the day of labor. Based on these findings, we suppose the TRPV4 effect on uterus contraction is AQP5 control, which could be a new target in preterm birth therapy.
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Affiliation(s)
- Eszter Ducza
- Department of Pharmacodynamics and Biopharmacy, University of Szeged, Hungary
- Corresponding author.
| | - Adrienn Csányi
- Department of Pharmacodynamics and Biopharmacy, University of Szeged, Hungary
| | - Éva Szőke
- Department of Pharmacology and Pharmacotherapy, Medical School, University of Pécs, Pécs, Hungary
- János Szentágothai Research Center & Centre for Neuroscience, University of Pécs, Hungary
| | - Krisztina Pohóczky
- Department of Pharmacology and Pharmacotherapy, Medical School, University of Pécs, Pécs, Hungary
- János Szentágothai Research Center & Centre for Neuroscience, University of Pécs, Hungary
- Department of Pharmacology, Faculty of Pharmacy, University of Pécs, Pécs, Hungary
| | - Judit Hajagos-Tóth
- Department of Pharmacodynamics and Biopharmacy, University of Szeged, Hungary
- Department of Pharmacology and Pharmacotherapy, Interdisciplinary Excellence Centre, University of Szeged, Hungary
| | - Anna Kothencz
- Department of Pharmacodynamics and Biopharmacy, University of Szeged, Hungary
- Department of Pharmacology and Pharmacotherapy, Interdisciplinary Excellence Centre, University of Szeged, Hungary
| | - Zita Tiszai
- Department of Pharmacodynamics and Biopharmacy, University of Szeged, Hungary
| | - Róbert Gáspár
- Department of Pharmacodynamics and Biopharmacy, University of Szeged, Hungary
- Department of Pharmacology and Pharmacotherapy, Interdisciplinary Excellence Centre, University of Szeged, Hungary
- Corresponding author.
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Abstract
In the United States, the generally accepted indication for tocolytic therapy centers on suppression of preterm labor. This may be in the form of preventative therapy with progesterone in women with prior spontaneous preterm birth or as an acute intervention to suppress established uterine contractions associated with cervical change occurring at less than 37 weeks gestation. This article seeks to apply this perspective to tocolytic therapy. Here, we provide a review of current tocolytic options and what the last decade of discovery has revealed about the regulation of myometrial excitability and quiescence. Moving forward, we must incorporate the emerging molecular data that is amassing in order to develop novel and effective tocolytic therapeutic options to prevent preterm labor and spontaneous preterm birth (sPTB).
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Affiliation(s)
| | | | - George Gallos
- Department of Anesthesia, Columbia University Medical Center, New York, NY.
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9
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Carlson NS, Hernandez TL, Hurt KJ. Parturition dysfunction in obesity: time to target the pathobiology. Reprod Biol Endocrinol 2015; 13:135. [PMID: 26684329 PMCID: PMC4683915 DOI: 10.1186/s12958-015-0129-6] [Citation(s) in RCA: 72] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/07/2015] [Accepted: 11/24/2015] [Indexed: 12/23/2022] Open
Abstract
Over a third of women of childbearing age in the United States are obese, and during pregnancy they are at increased risk for delayed labor onset and slow labor progress that often results in unplanned cesarean delivery. The biology behind this dysfunctional parturition is not well understood. Studies of obesity-induced changes in parturition physiology may facilitate approaches to optimize labor in obese women. In this review, we summarize known and proposed biologic effects of obesity on labor preparation, contraction/synchronization, and endurance, drawing on both clinical observation and experimental data. We present evidence from human and animal studies of interactions between obesity and parturition signaling in all elements of the birth process, including: delayed cervical ripening, prostaglandin insensitivity, amniotic membrane strengthening, decreased myometrial oxytocin receptor expression, decreased myocyte action potential initiation and contractility, decreased myocyte gap junction formation, and impaired myocyte neutralization of reactive oxygen species. We found convincing clinical data on the effect of obesity on labor initiation and successful delivery, but few studies on the underlying pathobiology. We suggest research opportunities and therapeutic interventions based on plausible biologic mechanisms.
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Affiliation(s)
- Nicole S Carlson
- Emory University, Nell Hodgson Woodruff School of Nursing, 1520 Clifton Road NE, Atlanta, GA, 30322, USA.
| | - Teri L Hernandez
- Department of Medicine, Division of Endocrinology, Metabolism, & Diabetes, College of Nursing, University of Colorado School of Medicine, 12801 E. 17th Ave, MS 8106, Aurora, CO, 80045, USA.
| | - K Joseph Hurt
- Department of Obstetrics & Gynecology, Divisions of Maternal-Fetal Medicine & Reproductive Sciences, University of Colorado School of Medicine, 12700 East 19th Ave, MS 8613, Aurora, CO, 80045, USA.
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10
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Loftus FC, Richardson MJE, Shmygol A. Single-cell mechanics and calcium signalling in organotypic slices of human myometrium. J Biomech 2015; 48:1620-4. [PMID: 25702249 PMCID: PMC4503816 DOI: 10.1016/j.jbiomech.2015.01.046] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2015] [Accepted: 01/31/2015] [Indexed: 11/29/2022]
Abstract
Elucidation of cellular mechanisms regulating myometrial contractility is crucial for improvement in management of many obstetric abnormalities, such as premature delivery, uterine dystocia and post-partum haemorrhage. Myometrial contractions are triggered by periodic synchronous rises in intracellular calcium concentration ([Ca(2+)]i) elicited by spontaneously generated action potentials propagating throughout the entire myometrium. During labour, hormones like oxytocin and prostaglandins potentiate uterine contractions by increasing their duration, strength and frequency. The most informative approach to studying the mechanisms underlying hormonal modulation of uterine contractility is to record [Ca(2+)]i responses to hormones in intact myometrial samples that have not been subjected to enzymatic treatment for cell isolation or cell culture conditions. However, the spatio-temporal resolution of such recording is limited due to the motion artifacts occurring in contracting tissue. Here we describe the application of our newly developed motion correction algorithm to investigate the [Ca(2+)]i dynamics in control and oxytocin stimulated slices of human myometrium on a cellular level. We present evidence that oxytocin induces asynchronous [Ca(2+)]i oscillations in individual myocytes within intact myometrium which are similar to those observed in cultured cells. The oscillations occur between synchronous action potential-driven [Ca(2+)]i transients but appear to be unrelated to contractions. Furthermore, the oxytocin-triggered [Ca(2+)]i oscillations wane within 30-50min of hormone application, while the action potential induced [Ca(2+)]i transients remain augmented. We conclude that oxytocin-induced [Ca(2+)]i oscillations are not relevant to the acute regulation of myometrial contractility but may play a role in longer-term regulatory processes, for example, by triggering gene expression.
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Affiliation(s)
- Fiona C Loftus
- Warwick Systems Biology Centre, University of Warwick, Coventry, UK; Division of Translational and Systems Medicine, Warwick Medical School, University of Warwick, Coventry, UK; Warwick Systems Biology Doctoral Training Centre, University of Warwick, Coventry, UK
| | | | - Anatoly Shmygol
- Division of Translational and Systems Medicine, Warwick Medical School, University of Warwick, Coventry, UK.
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11
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Synchronization of regional contractions of human labor; direct effects of region size and tissue excitability. J Biomech 2015; 48:1614-9. [PMID: 25698238 DOI: 10.1016/j.jbiomech.2015.02.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2015] [Accepted: 02/02/2015] [Indexed: 11/23/2022]
Abstract
The mechanisms used to coordinate organ-level contractions of human labor are not universally accepted. We previously proposed a dual mechanism, where electrical activity coordinates cellular contractions into tissue-level regional contractions, and mechanotransduction synchronizes the regional contractions into organ-level contractions. The simulation of this model successfully recapitulates the phasic pressure rises typical of human labor. In this work we extend the simulation to probe the effects of three critical parameters: electrical coupling (which defines functional regions within the uterine wall), enhancement of contractile responses during action potential bursts (action potential multiplier), and the threshold for mechanical recruitment of regional myometrial contractions (threshold). We test how changing the values of these parameters modulates the ability of the uterus to generate synchronized organ-level contractions. Simulations are performed using Mathematica and a non-classical cellular automaton program we recently published. At least 15 regions are necessary to generate physiologically relevant, synchronized contractions. Organ-level synchronization was improved using higher values for the action potential multiplier. At lower values of the action potential multiplier, synchronized contractions were inhibited when the number of regions was between 32 and 44, suggesting a critical level of electrical coupling is necessary at the onset of labor. Large numbers of low threshold regions resulted in contraction patterns suggestive of hyperstimulation. This work furthers support for the electrical-mechanotransduction mechanism for organ-level synchronization of uterine contractions. The mathematical simulation provides insight regarding how cellular- and tissue-level physiology converge to express synchronized contractions of human labor.
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12
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Young RC, Barendse P. Linking myometrial physiology to intrauterine pressure; how tissue-level contractions create uterine contractions of labor. PLoS Comput Biol 2014; 10:e1003850. [PMID: 25330227 PMCID: PMC4199482 DOI: 10.1371/journal.pcbi.1003850] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2014] [Accepted: 08/09/2014] [Indexed: 11/18/2022] Open
Abstract
The mechanisms used to coordinate uterine contractions are not known. We develop a new model based on the proposal that there is a maximum distance to which action potentials can propagate in the uterine wall. This establishes "regions", where one action potential burst can rapidly recruit all the tissue. Regions are recruited into an organ-level contraction via a stretch-initiated contraction mechanism (myometrial myogenic response). Each uterine contraction begins with a regional contraction, which slightly increases intrauterine pressure. Higher pressure raises tension throughout the uterine wall, which initiates contractions of more regions and further increases pressure. The positive feedback synchronizes regional contractions into an organ-level contraction. Cellular automaton (CA) simulations are performed with Mathematica. Each "cell" is a region that is assigned an action potential threshold. An anatomy sensitivity factor converts intrauterine pressure to regional tension through the Law of Laplace. A regional contraction occurs when regional tension exceeds regional threshold. Other input variables are: starting and minimum pressure, burst and refractory period durations, enhanced contractile activity during an electrical burst, and reduced activity during the refractory period. Complex patterns of pressure development are seen that mimic the contraction patterns observed in laboring women. Emergent behavior is observed, including global synchronization, multiple pace making regions, and system memory of prior conditions. The complex effects of nifedipine and oxytocin exposure are simulated. The force produced can vary as a nonlinear function of the number of regions. The simulation directly links tissue-level physiology to human labor. The concept of a uterine pacemaker is re-evaluated because pace making activity may occur well before expression of a contraction. We propose a new classification system for biological CAs that parallels the 4-class system of Wolfram. However, instead of classifying the rules, biological CAs should classify the set of input values for the rules that describe the relevant biology.
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Affiliation(s)
- Roger C. Young
- Department of Obstetrics and Gynecology, University of Tennessee Health Science Center, Memphis, Tennessee, United States of America
- * E-mail: .
| | - Peter Barendse
- Wolfram Research, Somerville, Massachusetts, United States of America
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13
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Functional expression of T-type Ca2+ channels in spinal motoneurons of the adult turtle. PLoS One 2014; 9:e108187. [PMID: 25255145 PMCID: PMC4177857 DOI: 10.1371/journal.pone.0108187] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2014] [Accepted: 08/20/2014] [Indexed: 11/19/2022] Open
Abstract
Voltage-gated Ca2+ (CaV) channels are transmembrane proteins comprising three subfamilies named CaV1, CaV2 and CaV3. The CaV3 channel subfamily groups the low-voltage activated Ca2+ channels (LVA or T-type) a significant role in regulating neuronal excitability. CaV3 channel activity may lead to the generation of complex patterns of action potential firing such as the postinhibitory rebound (PIR). In the adult spinal cord, these channels have been found in dorsal horn interneurons where they control physiological events near the resting potential and participate in determining excitability. In motoneurons, CaV3 channels have been found during development, but their functional expression has not yet been reported in adult animals. Here, we show evidence for the presence of CaV3 channel-mediated PIR in motoneurons of the adult turtle spinal cord. Our results indicate that Ni2+ and NNC55-0396, two antagonists of CaV3 channel activity, inhibited PIR in the adult turtle spinal cord. Molecular biology and biochemical assays revealed the expression of the CaV3.1 channel isotype and its localization in motoneurons. Together, these results provide evidence for the expression of CaV3.1 channels in the spinal cord of adult animals and show also that these channels may contribute to determine the excitability of motoneurons.
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14
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Loftus FC, Shmygol A, Richardson MJE. Fine spatiotemporal activity in contracting myometrium revealed by motion-corrected calcium imaging. J Physiol 2014; 592:4447-63. [PMID: 25085893 PMCID: PMC4280886 DOI: 10.1113/jphysiol.2014.275412] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Successful childbirth depends on the occurrence of precisely coordinated uterine contractions during labour. Calcium indicator fluorescence imaging is one of the main techniques for investigating the mechanisms governing this physiological process and its pathologies. The effective spatiotemporal resolution of calcium signals is, however, limited by the motion of contracting tissue: structures of interest in the order of microns can move over a hundred times their width during a contraction. The simultaneous changes in local intensity and tissue configuration make motion tracking a non-trivial problem in image analysis and confound many of the standard techniques. This paper presents a method that tracks local motion throughout the tissue and allows for the almost complete removal of motion artefacts. This provides a stabilized calcium signal down to a pixel resolution, which, for the data examined, is in the order of a few microns. As a byproduct of image stabilization, a complete kinematic description of the contraction–relaxation cycle is also obtained. This contains novel information about the mechanical response of the tissue, such as the identification of a characteristic length scale, in the order of 40–50 μm, below which tissue motion is homogeneous. Applied to our data, we illustrate that the method allows for analyses of calcium dynamics in contracting myometrium in unprecedented spatiotemporal detail. Additionally, we use the kinematics of tissue motion to compare calcium signals at the subcellular level and local contractile motion. The computer code used is provided in a freely modifiable form and has potential applicability to in vivo calcium imaging of neural tissue, as well as other smooth muscle tissue.
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Affiliation(s)
- Fiona C Loftus
- Warwick Systems Biology Centre, University of Warwick, Coventry, UK Division of Translational and Systems Medicine, Warwick Medical School, University of Warwick, Coventry, UK Warwick Systems Biology Doctoral Training Centre, University of Warwick, Coventry, UK
| | - Anatoly Shmygol
- Division of Translational and Systems Medicine, Warwick Medical School, University of Warwick, Coventry, UK
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Lorca RA, Prabagaran M, England SK. Functional insights into modulation of BKCa channel activity to alter myometrial contractility. Front Physiol 2014; 5:289. [PMID: 25132821 PMCID: PMC4116789 DOI: 10.3389/fphys.2014.00289] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2014] [Accepted: 07/14/2014] [Indexed: 12/15/2022] Open
Abstract
The large-conductance voltage- and Ca(2+)-activated K(+) channel (BKCa) is an important regulator of membrane excitability in a wide variety of cells and tissues. In myometrial smooth muscle, activation of BKCa plays essential roles in buffering contractility to maintain uterine quiescence during pregnancy and in the transition to a more contractile state at the onset of labor. Multiple mechanisms of modulation have been described to alter BKCa channel activity, expression, and cellular localization. In the myometrium, BKCa is regulated by alternative splicing, protein targeting to the plasma membrane, compartmentation in membrane microdomains, and posttranslational modifications. In addition, interaction with auxiliary proteins (i.e., β1- and β2-subunits), association with G-protein coupled receptor signaling pathways, such as those activated by adrenergic and oxytocin receptors, and hormonal regulation provide further mechanisms of variable modulation of BKCa channel function in myometrial smooth muscle. Here, we provide an overview of these mechanisms of BKCa channel modulation and provide a context for them in relation to myometrial function.
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Affiliation(s)
- Ramón A Lorca
- Department of Obstetrics and Gynecology, Washington University in St. Louis School of Medicine St. Louis, MO, USA
| | - Monali Prabagaran
- Department of Obstetrics and Gynecology, Washington University in St. Louis School of Medicine St. Louis, MO, USA
| | - Sarah K England
- Department of Obstetrics and Gynecology, Washington University in St. Louis School of Medicine St. Louis, MO, USA
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