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Ferreira JJ, Kent LN, McCarthy R, Butler A, Ma X, Peramsetty N, Amazu C, Zhang A, Whitter GC, England SK, Santi CM. SLO2.1/NALCN Functional Complex Activity in Mouse Myometrial Smooth Muscle Cells During Pregnancy. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.05.29.596465. [PMID: 38853884 PMCID: PMC11160795 DOI: 10.1101/2024.05.29.596465] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2024]
Abstract
At the end of pregnancy, the uterus transitions from a quiescent to a highly contractile state. This is partly due to depolarization of the resting membrane potential in uterine (myometrial) smooth muscle cells (MSMCs). Experiments with human MSMCs showed that the membrane potential is regulated by a functional complex between the sodium (Na+)-activated potassium (K+) channel SLO2.1 and the Na+ Leak Channel Non-Selective (NALCN). In human MSMCs, Na+ entering through NALCN activates SLO2.1, leading to K+ efflux, membrane hyperpolarization (cells become more negative inside), and reduced contractility. Decreased SLO2.1/NALCN activity results in reduced K+ efflux, leading to membrane depolarization, Ca2+ influx via voltage-dependent calcium channels, and increased MSMC contractility. However, all of these experiments were performed with MSMCs isolated from women at term, so the role of the SLO2.1/NALCN complex early in pregnancy was speculative. To address this question here, we examined the role of the SLO2.1/NALCN complex in regulating mouse MSMC membrane potential across pregnancy. We report that Slo2.1 and Nalcn expression change along pregnancy, being more highly expressed in MSMCs from non-pregnant and early pregnant mice than in those from late-pregnant mice. Functional studies revealed that SLO2.1 channels mediate a significant portion of the K+ current in mouse MSMCs, particularly in cells from non-pregnant and early pregnant mice. Activation of SLO2.1 by Na+ influx through NALCN led to membrane hyperpolarization in MSMCs from early pregnancy but not in MSMCs from later pregnancy. Moreover, we found that the NALCN/SLO2.1 complex regulates intracellular Ca2+ responses more in MSMCs from non-pregnant and early pregnancy mice than in MSMCs from late pregnancy. Together, these findings reveal that the SLO2.1/NALCN functional complex is conserved between mouse and humans and functions throughout pregnancy. This work could open avenues for targeted pharmacological interventions in pregnancy-related complications.
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Affiliation(s)
| | | | - Ronald McCarthy
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
| | - Alice Butler
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
| | - Xiaofeng Ma
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
| | - Nikita Peramsetty
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
| | - Chinwendu Amazu
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
| | - Alexander Zhang
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
| | - Grace C. Whitter
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
| | - Sarah K. England
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
| | - Celia M. Santi
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
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Yamada K, Ding WG, Omatsu-Kanbe M, Toyoda F, Tsuji S, Katsura D, Kimura F, Matsuura H, Murakami T. Expression and functional maintenance of volume-regulated anion channels in myometrial smooth muscles of pregnant mice. Exp Anim 2022; 71:123-130. [PMID: 34789619 PMCID: PMC9130036 DOI: 10.1538/expanim.21-0111] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2021] [Accepted: 10/13/2021] [Indexed: 11/15/2022] Open
Abstract
Pregnancy causes changes in the uterus, such as increased cell volume and altered water content. However, the mechanisms that protect the structure and maintain the function of uterine smooth muscle cells against these changes during pregnancy have not been clarified. This study focused on the volume-regulated anion channel (VRAC), which opens with cell swelling under low osmotic pressure and releases Cl- ions and various organic osmolytes to resist cell swelling and regulates a wide range of biological processes such as cell death. In this study, myometrial smooth muscle (MSM) tissues and cells (MSMCs) were collected from non-pregnant and pregnant mice. Using western blotting and immunocytochemistry, leucine-rich repeat containing protein 8A (LRRC8A), an essential membrane protein that constitutes part of the VRAC, was determined to be diffused throughout MSMCs including in the cell membrane. Patch-clamp experiments were performed to investigate the electrophysiology of swelling-induced Cl- currents (ICl, swell) mediated by the VRAC. No significant changes between non-pregnancy and pregnancy groups were observed in either the expression density of LRRC8A or the current density of ICl, swell, however the presence of LRRC8A on the cell membrane was significantly increased in the third trimester of pregnancy compared to the non-pregnancy. This study suggests that the VRAC may play a role, such as maintaining cellular homeostasis in the pregnant MSM.
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Affiliation(s)
- Kazutaka Yamada
- Department of Obstetrics and Gynecology, Shiga University of Medical Science, Setatsukinowa-cho, Otsu-shi, Shiga, 520-2192, Japan
| | - Wei-Guang Ding
- Department of Physiology, Shiga University of Medical Science, Setatsukinowa-cho, Otsu-shi, Shiga 520-2192, Japan
| | - Mariko Omatsu-Kanbe
- Department of Physiology, Shiga University of Medical Science, Setatsukinowa-cho, Otsu-shi, Shiga 520-2192, Japan
| | - Futoshi Toyoda
- Department of Physiology, Shiga University of Medical Science, Setatsukinowa-cho, Otsu-shi, Shiga 520-2192, Japan
| | - Shunichiro Tsuji
- Department of Obstetrics and Gynecology, Shiga University of Medical Science, Setatsukinowa-cho, Otsu-shi, Shiga, 520-2192, Japan
| | - Daisuke Katsura
- Department of Obstetrics and Gynecology, Shiga University of Medical Science, Setatsukinowa-cho, Otsu-shi, Shiga, 520-2192, Japan
| | - Fuminori Kimura
- Department of Obstetrics and Gynecology, Shiga University of Medical Science, Setatsukinowa-cho, Otsu-shi, Shiga, 520-2192, Japan
| | - Hiroshi Matsuura
- Department of Physiology, Shiga University of Medical Science, Setatsukinowa-cho, Otsu-shi, Shiga 520-2192, Japan
| | - Takashi Murakami
- Department of Obstetrics and Gynecology, Shiga University of Medical Science, Setatsukinowa-cho, Otsu-shi, Shiga, 520-2192, Japan
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Ferreira JJ, Amazu C, Puga-Molina LC, Ma X, England SK, Santi CM. SLO2.1/NALCN a sodium signaling complex that regulates uterine activity. iScience 2021; 24:103210. [PMID: 34746693 PMCID: PMC8551532 DOI: 10.1016/j.isci.2021.103210] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2021] [Revised: 07/29/2021] [Accepted: 09/29/2021] [Indexed: 01/05/2023] Open
Abstract
Depolarization of the myometrial smooth muscle cell (MSMC) resting membrane potential is necessary for the uterus to transition from a quiescent state to a contractile state. The molecular mechanisms involved in this transition are not completely understood. Here, we report that a coupled system between the Na+-activated K+ channel (SLO2.1) and the non-selective Na+ leak channel (NALCN) determines the MSMC membrane potential. Our data indicate that Na+ entering through NALCN acts as an intracellular signaling molecule that activates SLO2.1. Potassium efflux through SLO2.1 hyperpolarizes the membrane. A decrease in SLO2.1/NALCN activity induces membrane depolarization, triggering Ca2+ entry through voltage-dependent Ca2+ channels and promoting contraction. Consistent with functional coupling, our data show that NALCN and SLO2.1 are in close proximity in human MSMCs. We propose that these arrangements of SLO2.1 and NALCN permit these channels to functionally regulate MSMC membrane potential and cell excitability and modulate uterine contractility.
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Affiliation(s)
- Juan J. Ferreira
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
- Department of Neuroscience, Washington University in St. Louis, School of Medicine, St. Louis, MO 63110, USA
| | - Chinwendu Amazu
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
| | - Lis C. Puga-Molina
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
| | - Xiaofeng Ma
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
| | - Sarah K. England
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
| | - Celia M. Santi
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
- Department of Neuroscience, Washington University in St. Louis, School of Medicine, St. Louis, MO 63110, USA
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Calcium signaling cascades differentially regulate PGF 2α-induced myometrial contractions in water buffaloes (Bubalus bubalis). Naunyn Schmiedebergs Arch Pharmacol 2021; 394:1651-1664. [PMID: 33884445 DOI: 10.1007/s00210-021-02084-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2020] [Accepted: 03/30/2021] [Indexed: 10/21/2022]
Abstract
This study unravels the differential involvement of calcium signaling pathway(s) in PGF2α-induced contractions in myometrium of nonpregnant (NP) and pregnant buffaloes. Compared to the myometrium of pregnant animals, myometrium of NP buffaloes was more sensitive to PGF2α as manifested by changes in mean integral tension (MIT) and tonicity. In the presence of nifedipine, myometrial contraction to PGF2α was significantly attenuated in both NP and pregnant uteri; however, mibefradil and NNC 55-0396 produced inhibitory effects only in uterus of pregnant animals, thus suggesting the role of extracellular Ca2+ influx through nifedipine-sensitive L-type Ca2+-channels both in NP and pregnant, but T-type Ca2+ channels seem to play a role only during pregnancy. Entry of extracellular Ca2+ is triggered by enhanced functional involvement of Pyr3-sensitive TRPC3 channels and Rho-kinase pathways as evidenced by a significant rightward shift of the concentration-response curve of PGF2α in the presence of Pyr3 and Y-27632 in NP myometrium. But significant down-expressions of TRPC3 and Rho-A proteins during pregnancy apparently facilitate uterine quiescence. In the presence of Ca2+-free solution and cyclopiazonic acid (SERCA blocker), feeble contraction to PGF2α was observed in both NP and pregnant myometrium which suggests minor role of intracellular source of Ca2+ in mediating PGF2α-induced contractions in these tissues.
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Malik M, Roh M, England SK. Uterine contractions in rodent models and humans. Acta Physiol (Oxf) 2021; 231:e13607. [PMID: 33337577 PMCID: PMC8047897 DOI: 10.1111/apha.13607] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Revised: 12/07/2020] [Accepted: 12/11/2020] [Indexed: 12/18/2022]
Abstract
Aberrant uterine contractions can lead to preterm birth and other labour complications and are a significant cause of maternal morbidity and mortality. To investigate the mechanisms underlying dysfunctional uterine contractions, researchers have used experimentally tractable small animal models. However, biological differences between humans and rodents change how researchers select their animal model and interpret their results. Here, we provide a general review of studies of uterine excitation and contractions in mice, rats, guinea pigs, and humans, in an effort to introduce new researchers to the field and help in the design and interpretation of experiments in rodent models.
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Affiliation(s)
- Manasi Malik
- Center for Reproductive Health SciencesDepartment of Obstetrics and GynecologyWashington University School of MedicineSt. LouisMOUSA
| | - Michelle Roh
- Center for Reproductive Health SciencesDepartment of Obstetrics and GynecologyWashington University School of MedicineSt. LouisMOUSA
| | - Sarah K. England
- Center for Reproductive Health SciencesDepartment of Obstetrics and GynecologyWashington University School of MedicineSt. LouisMOUSA
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Hyuga S, Parry RC, Danielsson J, Vink J, Fu XW, Wu A, Dan W, Yim PD, Gallos G. Anoctamin 1 antagonism potentiates conventional tocolytic-mediated relaxation of pregnant human uterine smooth muscle. J Physiol Sci 2021; 71:7. [PMID: 33618673 PMCID: PMC9352361 DOI: 10.1186/s12576-021-00792-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2020] [Accepted: 02/07/2021] [Indexed: 12/31/2022]
Abstract
BACKGROUND Currently available tocolytic agents are not effective treatment for preterm labor beyond 48 h. A major reason is the development of maternal side effects which preclude the maintenance of an effective steady-state drug concentration. One strategy that can mitigate these side effects is utilizing synergistic drug combinations to reduce the drug concentrations necessary to elicit a clinical effect. We have previously shown that three anoctamin 1 (ANO1) antagonists mediate potent relaxation of precontracted human uterine smooth muscle (USM). In this study, we aimed to determine whether a combination of sub-relaxatory doses of tocolytic drugs in current clinical use [the L-type voltage-gated calcium channel (VGCC) blocker, nifedipine (NIF); and the β2-adrenergic (β2AR) agonist, terbutaline (TRB)] will potentiate USM relaxation with two ANO1 antagonists [benzbromarone (BB) and MONNA (MN)]. OBJECTIVE This study sought to examine the synergistic potency and mechanistic basis of two ANO1 antagonists with currently available tocolytic drugs. Functional endpoints assessed included relaxation of pre-contracting pregnant human USM tissue, inhibition of intracellular calcium release, and reduction of spontaneous transient inward current (STIC) recordings in human uterine smooth muscle cells. METHODS Human myometrial strips and primary human USM cells were used in organ bath and calcium flux experiments with different combinations of sub-threshold doses of ANO1 antagonists and terbutaline or nifedipine to determine if ANO1 antagonists potentiate tocolytic drugs. RESULTS The combination of sub-threshold doses of two ANO1 antagonists and current tocolytic drugs demonstrate a significant degree of synergy to relax human pregnant USM compared to the effects achieved when these drugs are administered individually. CONCLUSION A combination of sub-threshold doses of VGCC blocker and β2AR agonist with ANO1 antagonists potentiates relaxation of oxytocin-induced contractility and calcium flux in human USM ex vivo. Our findings may serve as a foundation for novel tocolytic drug combinations.
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Affiliation(s)
- Shunsuke Hyuga
- Department of Anesthesiology, Columbia University College of Physicians and Surgeons, 622 W. 168th St. P&S Box 46, New York, NY, 10032, USA
| | - Robert C Parry
- Department of Anesthesiology, Columbia University College of Physicians and Surgeons, 622 W. 168th St. P&S Box 46, New York, NY, 10032, USA
| | - Jennifer Danielsson
- Department of Anesthesiology, Columbia University College of Physicians and Surgeons, 622 W. 168th St. P&S Box 46, New York, NY, 10032, USA
| | - Joy Vink
- Department of Obstetrics & Gynecology, Columbia University College of Physicians and Surgeons, Columbia University Medical Center, New York, NY, USA
| | - Xiao Wen Fu
- Department of Anesthesiology, Columbia University College of Physicians and Surgeons, 622 W. 168th St. P&S Box 46, New York, NY, 10032, USA
| | - Amy Wu
- Department of Anesthesiology, Columbia University College of Physicians and Surgeons, 622 W. 168th St. P&S Box 46, New York, NY, 10032, USA
| | - William Dan
- Department of Anesthesiology, Columbia University College of Physicians and Surgeons, 622 W. 168th St. P&S Box 46, New York, NY, 10032, USA
| | - Peter D Yim
- Department of Anesthesiology, Columbia University College of Physicians and Surgeons, 622 W. 168th St. P&S Box 46, New York, NY, 10032, USA
| | - George Gallos
- Department of Anesthesiology, Columbia University College of Physicians and Surgeons, 622 W. 168th St. P&S Box 46, New York, NY, 10032, USA.
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Wray S, Arrowsmith S. Uterine Excitability and Ion Channels and Their Changes with Gestation and Hormonal Environment. Annu Rev Physiol 2020; 83:331-357. [PMID: 33158376 DOI: 10.1146/annurev-physiol-032420-035509] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We address advances in the understanding of myometrial physiology, focusing on excitation and the effects of gestation on ion channels and their relevance to labor. This review moves through pioneering studies to exciting new findings. We begin with the myometrium and its myocytes and describe how excitation might initiate and spread in this myogenic smooth muscle. We then review each of the ion channels in the myometrium: L- and T-type Ca2+ channels, KATP (Kir6) channels, voltage-dependent K channels (Kv4, Kv7, and Kv11), twin-pore domain K channels (TASK, TREK), inward rectifier Kir7.1, Ca2+-activated K+ channels with large (KCNMA1, Slo1), small (KCNN1-3), and intermediate (KCNN4) conductance, Na-activated K channels (Slo2), voltage-gated (SCN) Na+ and Na+ leak channels, nonselective (NALCN) channels, the Na K-ATPase, and hyperpolarization-activated cation channels. We finish by assessing how three key hormones- oxytocin, estrogen, and progesterone-modulate and integrate excitability throughout gestation.
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Affiliation(s)
- Susan Wray
- Department of Women's and Children's Health, University of Liverpool, Liverpool L69 3BX, United Kingdom;
| | - Sarah Arrowsmith
- Department of Women's and Children's Health, University of Liverpool, Liverpool L69 3BX, United Kingdom;
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Amazu C, Ma X, Henkes C, Ferreira JJ, Santi CM, England SK. Progesterone and estrogen regulate NALCN expression in human myometrial smooth muscle cells. Am J Physiol Endocrinol Metab 2020; 318:E441-E452. [PMID: 31935111 PMCID: PMC7191408 DOI: 10.1152/ajpendo.00320.2019] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
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 hormones and ion channels, both of which modulate myometrial smooth muscle cell (MSMC) excitability. Recently, the sodium (Na+) leak channel, nonselective (NALCN), was shown to contribute to a Na+ leak current in human MSMCs, and mice lacking NALCN in the uterus had dysfunctional labor. Microarray data suggested that the proquiescent hormone progesterone (P4) and the procontractile hormone estrogen (E2) regulated this channel. Here, we sought to determine whether P4 and E2 directly regulate NALCN. In human MSMCs, we found that NALCN mRNA expression decreased by 2.3-fold in the presence of E2 and increased by 5.6-fold in the presence of P4. Similarly, E2 treatment decreased, and P4 treatment restored NALCN protein expression. Additionally, E2 significantly inhibited, and P4 significantly enhanced an NALCN-dependent leak current in MSMCs. Finally, we identified estrogen response and progesterone response elements (EREs and PREs) in the NALCN promoter. With the use of luciferase assays, we showed that the PREs, but not the ERE, contributed to regulation of NALCN expression. Our findings reveal a new mechanism by which NALCN is regulated in the myometrium and suggest a novel role for NALCN in pregnancy.
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Affiliation(s)
- Chinwendu Amazu
- Department of Obstetrics Gynecology, Washington University in St. Louis, School of Medicine, St. Louis, Missouri
- Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, St. Louis, Missouri
| | - Xiaofeng Ma
- Department of Obstetrics Gynecology, Washington University in St. Louis, School of Medicine, St. Louis, Missouri
- Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, St. Louis, Missouri
| | - Clara Henkes
- Department of Obstetrics Gynecology, Washington University in St. Louis, School of Medicine, St. Louis, Missouri
- Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, St. Louis, Missouri
| | - Juan J Ferreira
- Department of Obstetrics Gynecology, Washington University in St. Louis, School of Medicine, St. Louis, Missouri
- Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, St. Louis, Missouri
- Department of Neuroscience, Washington University in St. Louis, School of Medicine, St. Louis, Missouri
| | - Celia M Santi
- Department of Obstetrics Gynecology, Washington University in St. Louis, School of Medicine, St. Louis, Missouri
- Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, St. Louis, Missouri
- Department of Neuroscience, Washington University in St. Louis, School of Medicine, St. Louis, Missouri
| | - Sarah K England
- Department of Obstetrics Gynecology, Washington University in St. Louis, School of Medicine, St. Louis, Missouri
- Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, St. Louis, Missouri
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Amazu C, Ferreira JJ, Santi CM, England SK. Sodium channels and transporters in the myometrium. CURRENT OPINION IN PHYSIOLOGY 2020; 13:141-144. [PMID: 39036486 PMCID: PMC11259238 DOI: 10.1016/j.cophys.2019.11.011] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
In excitable cells such as neurons and cardiomyocytes, sodium influx across the plasma membrane contributes to the resting membrane potential, and sodium is the key ion for generating action potentials. In myometrial smooth muscle cells, however, the functions of sodium influx have not been fully elucidated. This review briefly discusses the contribution of Na+ pumps to myometrial excitability but given the brevity of this article, we focus on the evidence that sodium influx through various types of channels may play numerous roles in controlling myometrial excitability.
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Affiliation(s)
- Chinwendu Amazu
- Department of Obstetrics and Gynecology, Washington University School of Medicine. St Louis. MO
| | - Juan J Ferreira
- Department of Obstetrics and Gynecology, Washington University School of Medicine. St Louis. MO
| | - Celia M Santi
- Department of Obstetrics and Gynecology, Washington University School of Medicine. St Louis. MO
| | - Sarah K England
- Department of Obstetrics and Gynecology, Washington University School of Medicine. St Louis. MO
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Electro-Mechanical Ionic Channel Modeling for Uterine Contractions and Oxytocin Effect during Pregnancy. SENSORS 2019; 19:s19224898. [PMID: 31717577 PMCID: PMC6891271 DOI: 10.3390/s19224898] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/19/2019] [Revised: 10/30/2019] [Accepted: 11/06/2019] [Indexed: 01/16/2023]
Abstract
Uterine contractions during normal pregnancy and preterm birth are an important physiological activity. Although the cause of preterm labor is usually unknown, preterm birth creates very serious health concerns in many cases. Therefore, understanding normal birth and predicting preterm birth can help both newborn babies and their families. In our previous work, we developed a multiscale dynamic electrophysiology model of uterine contractions. In this paper, we mainly focus on the cellular level and use electromyography (EMG) and cell force generation methods to construct a new ionic channel model and a corresponding mechanical force model. Specifically, the ionic channel model takes into consideration the knowledge of individual ionic channels, which include the electrochemical and bioelectrical characteristics of individual myocytes. We develop a new sodium channel and a new potassium channel based on the experimental data from the human myometrium and the average correlations are 0.9946 and 0.9945, respectively. The model is able to generate the single spike, plateau type and bursting type of action potentials. Moreover, we incorporate the effect of oxytocin on changing the properties of the L-type and T-type calcium channels and further influencing the output action potentials. In addition, we develop a mechanical force model based on the new ionic channel model that describes the detailed ionic dynamics. Our model produces cellular mechanical force that propagates to the tissue level. We illustrate the relationship between the cellular mechanical force and the intracellular ionic dynamics and discuss the relationship between the application of oxytocin and the output mechanical force. We also propose a simplified version of the model to enable large scale simulations using sensitivity analysis method. Our results show that the model is able to reproduce the bioelectrical and electromechanical characteristics of uterine contractions during pregnancy.
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Ferreira JJ, Butler A, Stewart R, Gonzalez-Cota AL, Lybaert P, Amazu C, Reinl EL, Wakle-Prabagaran M, Salkoff L, England SK, Santi CM. Oxytocin can regulate myometrial smooth muscle excitability by inhibiting the Na + -activated K + channel, Slo2.1. J Physiol 2018; 597:137-149. [PMID: 30334255 DOI: 10.1113/jp276806] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2018] [Accepted: 10/17/2018] [Indexed: 01/05/2023] Open
Abstract
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, although how this occurs is not fully understood. We identified SLO2.1, a potassium channel previously unknown 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 via 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 considered to be at least partly a result of 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 clarified. In the present study, 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. The results of the present study reveal that oxytocin may modulate MSMC electrical activity by inhibiting SLO2.1 potassium channels.
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Affiliation(s)
- Juan J Ferreira
- Washington University School of Medicine, Department of Obstetrics and Gynecology, St Louis, MO, USA
| | - Alice Butler
- Washington University School of Medicine, Department of Neuroscience, St Louis, MO, USA
| | - Richard Stewart
- Washington University School of Medicine, Department of Neuroscience, St Louis, MO, USA
| | - Ana Laura Gonzalez-Cota
- Washington University School of Medicine, Department of Obstetrics and Gynecology, St Louis, MO, USA
| | - Pascale Lybaert
- Washington University School of Medicine, Department of Obstetrics and Gynecology, St Louis, MO, USA.,Present address: Laboratoire de Physiologie et Pharmacologie (LAPP), Faculté de Médecine, Université Libre de Bruxelles, Bruxelles, Belgium
| | - Chinwendu Amazu
- Washington University School of Medicine, Department of Obstetrics and Gynecology, St Louis, MO, USA
| | - Erin L Reinl
- Washington University School of Medicine, Department of Obstetrics and Gynecology, St Louis, MO, USA.,Present address: Pharmacology Department, School of Medicine, University of Maryland, Baltimore, MD, USA
| | - Monali Wakle-Prabagaran
- Washington University School of Medicine, Department of Obstetrics and Gynecology, St Louis, MO, USA
| | - Lawrence Salkoff
- Washington University School of Medicine, Department of Neuroscience, St Louis, MO, USA
| | - Sarah K England
- Washington University School of Medicine, Department of Obstetrics and Gynecology, St Louis, MO, USA
| | - Celia M Santi
- Washington University School of Medicine, Department of Obstetrics and Gynecology, St Louis, MO, USA.,Washington University School of Medicine, Department of Neuroscience, St Louis, MO, USA
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13
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Lutton EJ, Lammers WJEP, James S, van den Berg HA, Blanks AM. Identification of uterine pacemaker regions at the myometrial-placental interface in the rat. J Physiol 2018; 596:2841-2852. [PMID: 29704394 PMCID: PMC6046083 DOI: 10.1113/jp275688] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2017] [Accepted: 04/19/2018] [Indexed: 12/16/2022] Open
Abstract
KEY POINTS Coordinated contraction of the uterine smooth muscle is essential to parturition. Histologically and physiologically defined pacemaker structures have not been identified in uterine smooth muscle. Here we report combined electrophysiological and histological evidence of zones associated with pacemaker activity in the rat myometrium. Our method relies crucially on the integration of histological and electrophysiological data in an in silico three-dimensional reconstruction of the rat myometrium at 10 μm resolution. We find that myometrial/placental pacemaking zones are closely related with placental sites and the area of disruptive myometrial remodelling surrounding such sites. If analogues of the myometrial/placental pacemaking zone are present in the human, defining their histology and physiology will be important steps towards treatment of pre-term birth, pre-eclampsia, and postpartum haemorrhage. ABSTRACT Coordinated uterine contractions are essential for delivering viable offspring in mammals. In contrast to other visceral smooth muscles, it is not known where excitation within the uterus is initiated, and no defined pacemaking region has hitherto been identified. Using multi-electrode array recordings and high-resolution computational reconstruction of the three-dimensional micro-structure of late pregnant rat uterus, we demonstrate that electrical potentials are initiated in distinct structures within the placental bed of individual implantation sites. These previously unidentified structures represent modified smooth muscle bundles that are derived from bridges between the longitudinal and circular layers. Coordinated implantation and encapsulation by invading trophoblast give rise to isolated placental/myometrial interface bundles that directly connect to the overlying longitudinal smooth muscle layer. Taken together, these observations imply that the anatomical structure of the uterus, combined with site-specific implantation, gives rise to emergent patterns of electrical activity that drive effective contractility during parturition.
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Affiliation(s)
- E Josiah Lutton
- Cell and Developmental Biology, Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, CV4 7AL, UK
| | - Wim J E P Lammers
- Bioengineering Institute, Auckland University, Auckland, New Zealand.,Department of Physiology, College of Medicine and Health Sciences, UAE University, Al Ain, United Arab Emirates
| | - Sean James
- Department of Pathology, University Hospitals Coventry and Warwickshire (UHCW), NHS Trust, Coventry, CV2 2DX, UK
| | | | - Andrew M Blanks
- Cell and Developmental Biology, Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, CV4 7AL, UK
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14
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Sharma A, Nakade UP, Jaitley P, Sharma V, Choudhury S, Garg SK. WITHDRAWN: Differential involvement of L- and T-type Ca 2+ channels, store-operated calcium channel (TRPC) and Rho-kinase signaling pathway(s) in PGF 2α-induced contractions in myometrium of non-pregnant and pregnant buffaloes (Bubalus bubalis). Prostaglandins Other Lipid Mediat 2017:S1098-8823(17)30021-7. [PMID: 28916261 DOI: 10.1016/j.prostaglandins.2017.09.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2017] [Revised: 09/05/2017] [Accepted: 09/06/2017] [Indexed: 11/30/2022]
Abstract
This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal.
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Affiliation(s)
- Abhishek Sharma
- Experimental Pharmacology Laboratory, Department of Pharmacology & Toxicology, College of Veterinary Science and Animal Husbandry, U.P. Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya, Evam Go-Anusandhan Sansthan (DUVASU), Mathura 281001, India
| | - Udayraj P Nakade
- Experimental Pharmacology Laboratory, Department of Pharmacology & Toxicology, College of Veterinary Science and Animal Husbandry, U.P. Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya, Evam Go-Anusandhan Sansthan (DUVASU), Mathura 281001, India
| | - Pooja Jaitley
- Experimental Pharmacology Laboratory, Department of Pharmacology & Toxicology, College of Veterinary Science and Animal Husbandry, U.P. Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya, Evam Go-Anusandhan Sansthan (DUVASU), Mathura 281001, India
| | - Vipin Sharma
- Experimental Pharmacology Laboratory, Department of Pharmacology & Toxicology, College of Veterinary Science and Animal Husbandry, U.P. Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya, Evam Go-Anusandhan Sansthan (DUVASU), Mathura 281001, India
| | - Soumen Choudhury
- Experimental Pharmacology Laboratory, Department of Pharmacology & Toxicology, College of Veterinary Science and Animal Husbandry, U.P. Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya, Evam Go-Anusandhan Sansthan (DUVASU), Mathura 281001, India
| | - Satish Kumar Garg
- Experimental Pharmacology Laboratory, Department of Pharmacology & Toxicology, College of Veterinary Science and Animal Husbandry, U.P. Pandit Deen Dayal Upadhyaya Pashu Chikitsa Vigyan Vishwavidyalaya, Evam Go-Anusandhan Sansthan (DUVASU), Mathura 281001, India.
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15
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McCloskey C, Rada C, Bailey E, McCavera S, van den Berg HA, Atia J, Rand DA, Shmygol A, Chan YW, Quenby S, Brosens JJ, Vatish M, Zhang J, Denton JS, Taggart MJ, Kettleborough C, Tickle D, Jerman J, Wright P, Dale T, Kanumilli S, Trezise DJ, Thornton S, Brown P, Catalano R, Lin N, England SK, Blanks AM. The inwardly rectifying K+ channel KIR7.1 controls uterine excitability throughout pregnancy. EMBO Mol Med 2015; 6:1161-74. [PMID: 25056913 PMCID: PMC4197863 DOI: 10.15252/emmm.201403944] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Abnormal uterine activity in pregnancy causes a range of important clinical disorders, including preterm birth, dysfunctional labour and post-partum haemorrhage. Uterine contractile patterns are controlled by the generation of complex electrical signals at the myometrial smooth muscle plasma membrane. To identify novel targets to treat conditions associated with uterine dysfunction, we undertook a genome-wide screen of potassium channels that are enriched in myometrial smooth muscle. Computational modelling identified Kir7.1 as potentially important in regulating uterine excitability during pregnancy. We demonstrate Kir7.1 current hyper-polarizes uterine myocytes and promotes quiescence during gestation. Labour is associated with a decline, but not loss, of Kir7.1 expression. Knockdown of Kir7.1 by lentiviral expression of miRNA was sufficient to increase uterine contractile force and duration significantly. Conversely, overexpression of Kir7.1 inhibited uterine contractility. Finally, we demonstrate that the Kir7.1 inhibitor VU590 as well as novel derivative compounds induces profound, long-lasting contractions in mouse and human myometrium; the activity of these inhibitors exceeds that of other uterotonic drugs. We conclude Kir7.1 regulates the transition from quiescence to contractions in the pregnant uterus and may be a target for therapies to control uterine contractility.
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Affiliation(s)
- Conor McCloskey
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Cara Rada
- Division of Basic Science Research, Department of Obstetrics and Gynecology, School of Medicine Washington University in St. Louis,, St. Louis, MO, USA
| | - Elizabeth Bailey
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Samantha McCavera
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Hugo A van den Berg
- Warwick Systems Biology & Mathematics Institute University of Warwick, Coventry, UK
| | - Jolene Atia
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - David A Rand
- Warwick Systems Biology & Mathematics Institute University of Warwick, Coventry, UK
| | - Anatoly Shmygol
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Yi-Wah Chan
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Siobhan Quenby
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Jan J Brosens
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Manu Vatish
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Jie Zhang
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
| | - Jerod S Denton
- Vanderbilt Institute of Chemical Biology, Vanderbilt Institute for Global Health Vanderbilt University School of Medicine Medical Center North, Nashville, TN, USA
| | - Michael J Taggart
- Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, UK
| | | | - David Tickle
- Centre for Therapeutics and Discovery, Medical Research Council Technologies, London, UK
| | - Jeff Jerman
- Centre for Therapeutics and Discovery, Medical Research Council Technologies, London, UK
| | - Paul Wright
- Centre for Therapeutics and Discovery, Medical Research Council Technologies, London, UK
| | - Timothy Dale
- BioPark, Essen BioScience Ltd, Welwyn Garden City, Hertfordshire, UK
| | | | - Derek J Trezise
- BioPark, Essen BioScience Ltd, Welwyn Garden City, Hertfordshire, UK
| | | | - Pamela Brown
- MRC Centre for Reproductive Health (CRH), Queen's Medical Research Institute University of Edinburgh, Edinburgh, UK
| | - Roberto Catalano
- MRC Centre for Reproductive Health (CRH), Queen's Medical Research Institute University of Edinburgh, Edinburgh, UK
| | - Nan Lin
- Department of Mathematics, Washington University, St. Louis, MO, USA
| | - Sarah K England
- Division of Basic Science Research, Department of Obstetrics and Gynecology, School of Medicine Washington University in St. Louis,, St. Louis, MO, USA
| | - Andrew M Blanks
- Division of Reproductive Health, Clinical Sciences Research Laboratories, Warwick Medical School University of Warwick, Coventry, UK
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17
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Abstract
Ion channels play a key role in defining myometrial contractility. Modulation of ion channel populations is proposed to underpin gestational changes in uterine contractility associated with the transition from uterine quiescence to active labour. Of the myriad ion channels present in the uterus, this article will focus upon potassium channels encoded by the KCNQ genes and ether-à-go-go-related (ERG) genes. Voltage-gated potassium channels encoded by KCNQ and ERG (termed Kv7 and Kv11, respectively) are accepted as major determinants of neuronal excitability and the duration of the cardiac action potential. However, there is now growing appreciation that these ion channels have a major functional impact in vascular and non-vascular smooth muscle. Moreover, Kv7 channels may be potential therapeutic targets for the treatment of preterm labour.
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Affiliation(s)
- Iain A Greenwood
- * St George's Medical School, Division of Biomedical Sciences, London SW17 0RE, UK.
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18
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Bülbring E, Goodford PJ, Setekleiv J. The action of adrenaline on the ionic content and on sodium and potassium movements in the smooth muscle of the guinea-pig taenia coli. BRITISH JOURNAL OF PHARMACOLOGY AND CHEMOTHERAPY 2010; 28:296-307. [PMID: 19108224 DOI: 10.1111/j.1476-5381.1966.tb01897.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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19
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Smith RC, McClure MC, Smith MA, Abel PW, Bradley ME. The role of voltage-gated potassium channels in the regulation of mouse uterine contractility. Reprod Biol Endocrinol 2007; 5:41. [PMID: 17980032 PMCID: PMC2186335 DOI: 10.1186/1477-7827-5-41] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/21/2007] [Accepted: 11/02/2007] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Uterine smooth muscle cells exhibit ionic currents that appear to be important in the control of uterine contractility, but how these currents might produce the changes in contractile activity seen in pregnant myometrium has not been established. There are conflicting reports concerning the role of voltage-gated potassium (Kv) channels and large-conductance, calcium-activated potassium (BK) channels in the regulation of uterine contractility. In this study we provide molecular and functional evidence for a role for Kv channels in the regulation of spontaneous contractile activity in mouse myometrium, and also demonstrate a change in Kv channel regulation of contractility in pregnant mouse myometrium. METHODS Functional assays which evaluated the effects of channel blockers and various contractile agonists were accomplished by quantifying contractility of isolated uterine smooth muscle obtained from nonpregnant mice as well as mice at various stages of pregnancy. Expression of Kv channel proteins in isolated uterine smooth muscle was evaluated by Western blots. RESULTS The Kv channel blocker 4-aminopyridine (4-AP) caused contractions in nonpregnant mouse myometrium (EC50 = 54 micromolar, maximal effect at 300 micromolar) but this effect disappeared in pregnant mice; similarly, the Kv4.2/Kv4.3 blocker phrixotoxin-2 caused contractions in nonpregnant, but not pregnant, myometrium. Contractile responses to 4-AP were not dependent upon nerves, as neither tetrodotoxin nor storage of tissues at room temperature significantly altered these responses, nor were responses dependent upon the presence of the endometrium. Spontaneous contractions and contractions in response to 4-AP did not appear to be mediated by BK, as the BK channel-selective blockers iberiotoxin, verruculogen, or tetraethylammonium failed to affect either spontaneous contractions or 4-AP-elicited responses. A number of different Kv channel alpha subunit proteins were found in isolated myometrium from both nonpregnant and term-pregnant mice, and one of these proteins - Kv4.3 - was found to disappear in term-pregnant tissues. CONCLUSION These findings suggest a role for Kv channels in the regulation of uterine contractility, and that changes in the expression and/or function of specific Kv channels may account for the functional changes seen in pregnant myometrium.
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Affiliation(s)
- Ryan C Smith
- Department of Pharmacology, Creighton University Medical Center, Omaha, USA, NE 68178
| | - Marisa C McClure
- Department of Pharmacology, Creighton University Medical Center, Omaha, USA, NE 68178
| | - Margaret A Smith
- Department of Pharmacology, Creighton University Medical Center, Omaha, USA, NE 68178
| | - Peter W Abel
- Department of Pharmacology, Creighton University Medical Center, Omaha, USA, NE 68178
| | - Michael E Bradley
- Department of Pharmacology, Creighton University Medical Center, Omaha, USA, NE 68178
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20
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Li Y, Je HD, Malek S, Morgan KG. ERK1/2-mediated phosphorylation of myometrial caldesmon during pregnancy and labor. Am J Physiol Regul Integr Comp Physiol 2003; 284:R192-9. [PMID: 12388473 DOI: 10.1152/ajpregu.00290.2002] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
We used a timed-pregnant rat model to track changes in myometrial contractility during pregnancy and labor and to correlate these changes with upstream signaling events. Myometrium was harvested from CO(2)-euthanized rats. Although contraction amplitudes increased at 16 and 20 days of pregnancy, contraction incidence and area under the force curve were inhibited, consistent with the myometrial quiescence of pregnancy. The Ca(2+) sensitivity of contraction was decreased at 20 days of pregnancy and this was partially reversed in labor. The protein content of h-caldesmon (h-CaD) was increased in pregnancy. A 40-fold increase in the signal from a phospho-CaD antibody specific for phosphorylation at an ERK1/2 site occurred during labor. ERK1/2 activation increased significantly at the onset of labor. Myosin light chain phosphorylation (LC20-P) increased significantly in labor compared with the nonpregnant state. Thus we conclude that the increase in CaD protein content during pregnancy may contribute to a suppression of the contractility of pregnant myometrium. Conversely, CaD phosphorylation, through an ERK1/2-mediated signaling pathway, as well as an increase in basal LC20-P, is suggested to contribute to the reversal of inhibition and promote contraction of the uterus during labor.
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Affiliation(s)
- Yunping Li
- Department of Anesthesia and Critical Care, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA.
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21
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Chipperfield AR, Harper AA. Chloride in smooth muscle. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2001; 74:175-221. [PMID: 11226512 DOI: 10.1016/s0079-6107(00)00024-9] [Citation(s) in RCA: 141] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Interest in the functions of intracellular chloride expanded about twenty years ago but mostly this referred to tissues other than smooth muscle. On the other hand, accumulation of chloride above equilibrium seems to have been recognised more readily in smooth muscle. Experimental data is used to show by calculation that the Donnan equilibrium cannot account for the chloride distribution in smooth muscle but it can in skeletal muscle. The evidence that chloride is normally above equilibrium in smooth muscle is discussed and comparisons are made with skeletal and cardiac muscle. The accent is on vascular smooth muscle and the mechanisms of accumulation and dissipation. The three mechanisms by which chloride can be accumulated are described with some emphasis on calculating the driving forces, where this is possible. The mechanisms are chloride/bicarbonate exchange, (Na+K+Cl) cotransport and a novel entity, "pump III", known only from own work. Their contributions to chloride accumulation vary and appear to be characteristic of individual smooth muscles. Thus, (Na+K+Cl) always drives chloride inwards, chloride/bicarbonate exchange is always present but does not always do it and "pump III" is not universal. Three quite different biophysical approaches to assessing chloride permeability are considered and the calculations underlying them are worked out fully. Comparisons with other tissues are made to illustrate that low chloride permeability is a feature of smooth muscle. Some of the functions of the high intracellular chloride concentrations are considered. This includes calculations to illustrate its depolarising influence on the membrane potential, a concept which, experience tells us, some people find confusing. The major topic is the role of chloride in the regulation of smooth muscle contractility. Whilst there is strong evidence that the opening of the calcium-dependent chloride channel leads to depolarisation, calcium entry and contraction in some smooth muscles, it appears that chloride serves a different function in others. Thus, although activation and inhibition of (Na+K+Cl) cotransport is associated with contraction and relaxation respectively, the converse association of inhibition and contraction has been seen. Nevertheless, inhibition of chloride/bicarbonate exchange and "pump III" and stimulation of (K+Cl) cotransport can all cause relaxation and this suggests that chloride is always involved in the contraction of smooth muscle. The evidence that (Na+K+Cl) cotransport more active in experimental hypertension is discussed. This is a common but not universal observation. The information comes almost exclusively from work on cultured cells, usually from rat aorta. Nevertheless, work on smooth muscle freshly isolated from hypertensive rats confirms that (Na+K+Cl) cotransport is activated in hypertension but there are several other differences, of which the depolarisation of the membrane potential may be the most important.Finally, a simple calculation is made which indicates as much as 40% of the energy put into the smooth muscle cell membrane by the sodium pump is necessary to drive (Na+K+Cl) cotransport. Notwithstanding the approximations in this calculation, this suggests that chloride accumulation is energetically expensive. Presumably, this is related to the apparently universal role of chloride in contraction.
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Affiliation(s)
- A R Chipperfield
- School of Life Sciences, Old Medical School, The University of Dundee, DD1 4HN, Dundee, UK.
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Bae J, Stuenkel EL, Loch-Caruso R. Stimulation of oscillatory uterine contraction by the PCB mixture Aroclor 1242 may involve increased [Ca2+]i through voltage-operated calcium channels. Toxicol Appl Pharmacol 1999; 155:261-72. [PMID: 10079212 DOI: 10.1006/taap.1998.8614] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Polychlorinated biphenyls (PCBs) are persistent environmental pollutants associated with spontaneous abortion and shortened gestation length in women and animals. In previous studies, we showed that PCB mixtures and noncoplanar ortho-substituted PCB congeners increased contractions in pregnant rat uterus. In the present study, we hypothesized that the PCB mixture Aroclor 1242 (A1242) stimulates oscillatory uterine contraction in pregnant uterus by increasing intracellular calcium concentration ([Ca2+]i). Pretreatment of uterine strips with ryanodine or thapsigargin, to deplete specific intracellular calcium stores, did not prevent the increased frequency of oscillatory contraction due to 50 microM A1242, whereas thapsigargin effectively blocked carbachol-induced stimulation of uterine contraction. However, 100 microM A1242 was unable to increase contraction in the absence of extracellular calcium or in the presence of the voltage-operated L-type calcium channel blocker nifedipine. A1242 (100 microM) was observed to partially depolarize the cell membrane of myometrial cells from pregnant rats, as measured with a potential-sensitive carbocyanine dye. Changes of [Ca2+]i were monitored in single myometrial cells loaded with the fluorescent calcium-sensitive probe fura-2. Cells exposed to 100 microM A1242 showed a delayed and sustained increase of [Ca2+]i, and this increase was completely blocked in the absence of extracellular calcium or the presence of nifedipine. Therefore, the data suggest that depolarization of the cell membrane by A1242 enabled myometrial cells to increase [Ca2+]i through activation of voltage-operated calcium channels, and the increased [Ca2+]i consequently stimulated contraction of uterine smooth muscle.
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Affiliation(s)
- J Bae
- Department of Environmental and Industrial Health, The University of Michigan, Ann Arbor, Michigan, 48109-2029, USA
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23
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Moriya T, Ishida Y, Nakamura H, Asari T, Murai A, Ohizumi Y. Vasoconstriction induced by zooxanthellatoxin-B, a polyoxygenated long-chain product from a marine alga. Eur J Pharmacol 1998; 350:59-65. [PMID: 9683015 DOI: 10.1016/s0014-2999(98)00225-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
We found that zooxanthellatoxin-B from a symbiotic marine alga, Symbiodinium sp., caused a concentration-dependent contraction of the rabbit isolated aorta at concentrations of 10(-7)-10(-5) M. Verapamil (10(-6) M) and mefenamic acid (10(-5) M) significantly attenuated the contractile response to zooxanthellatoxin-B at lower concentrations (10(-7)-10(-6) M) but not at higher concentrations (3 X 10(-6)-10(-5) M). The response to zooxanthellatoxin-B was partly inhibited by phentolamine (10(-6) M), whereas it was potentiated by ouabain (10(-5) M). Tetrodotoxin (10(-6) M), methysergide (10(-6) M), chlorpheniramine (10(-6) M) or indomethacin (3 X 10(-6) M), however, did not affect it. The zooxanthellatoxin-B-induced contraction was abolished by incubation in Ca2+-free solution. The contractile response increased in a concentration-dependent fashion with Ca2+ (0.03 and 10 mM) or Sr2 + (0.10 and 10 mM). After treatment with verapamil (10(-6) or 5 X 10(-6) M), the concentration-contractile response curves for Ca2+ and Sr2+ in the presence of zooxanthellatoxin-B were shifted to the right in parallel. MgCl2 (10 mM) shifted the concentration-response curve for Ca2+ more markedly than did verapamil. Zooxanthellatoxin-B increased tissue Na+ and reduced tissue K+ contents in the aorta, suggesting that zooxanthellatoxin-B increases Na+ and K+ permeability across the plasma membrane. These results suggest that the zooxanthellatoxin-B-induced contraction of the aorta is caused mainly by a direct action on smooth muscle, i.e., an increase in Ca2+ permeability that occurs at least partly through voltage-sensitive Ca2+ channels as well as through nonselective cation channels in the cell membrane of smooth muscle.
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Affiliation(s)
- T Moriya
- Department of Pharmaceutical Molecular Biology, Faculty of Pharmaceutical Sciences, Tohoku University, Sendai, Japan
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Hughes SJ, Hollingsworth M. The lack of a role for potassium channel opening in the action of relaxin in the rat isolated uterus; a comparison with levcromakalim and salbutamol. Br J Pharmacol 1996; 117:1435-42. [PMID: 8730736 PMCID: PMC1909433 DOI: 10.1111/j.1476-5381.1996.tb15303.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
1. The effects of relaxin in vitro in the isolated uterus from the non-pregnant rat were compared with those of levcromakalim and salbutamol in tissue bath, 42K+ -efflux and electrophysiological studies, to determine whether relaxin exhibits the characteristics of an opener of KATP-channels. 2. In uterus exposed to oxytocin (0.2 nM), tetraethylammonium (TEA, 10 mM) and glibenclamide (10 microM) produced large rightward shifts of the log10 concentration-effect curve to levcromakalim (125 fold and 118 fold, respectively). TEA (10 mM) caused only small rightward shifts of the log10 concentration-effect curves to salbutamol and relaxin (5.2 fold and 7.5 fold respectively). Glibenclamide did not antagonize salbutamol or relaxin. 3. Levromakalim (0.2 and 2 microM) suppressed the spasm evoked by low ( < or = 40 mM) but not high ( > 40 mM) concentrations of KCl. Salbutamol (1.5 nM) inhibited the spasm evoked by low concentrations of KCl ( < or = 40 mM). Salbutamol (15 nM) and relaxin (3 and 30 nM) inhibited the spasm evoked by low and high concentrations of KCl (10-80 mM). 4. Relaxin (0.12 microM) did not produce an increase in 42K+-efflux from longitudinal segments of rat myometrium. Exposure of tissues to relaxin (0.12 microM), in the presence of diltiazem (1 microM) plus KCl (20 mM), resulted in a small increase in 42K+-efflux of short duration. 5. Electrophysiological recording showed that the phasic spasms of the uterus exposed to oxytocin (0.2 nM) were accompanied by bursts of spiking activity superimposed upon a plateau potential. Inhibition of the mechanical activity of the uterus by levcromakalim (2 and 10 microM), salbutamol (30 nM) or relaxin (0.18 microM) was accompanied by a reduction in the duration of the plateau potential and the number of spikes without membrane hyperpolarization. 6. Unlike levcromakalim, relaxin did not selectively inhibit the spasm evoked by low concentrations of KCl and was not markedly antagonized by TEA or glibenclamide. Under conditions where a cromakalim-induced increase of the 42K+-efflux rate has been demonstrated, relaxin had only a very small effect. In isolated uterus from the rat, in contrast to observations in vivo, relaxin did not exhibit the characteristics of an opener of KATP-channels suggesting that another mechanism accounts for its inhibitory action.
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Affiliation(s)
- S J Hughes
- School of Biological Sciences, University of Manchester
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Izumi H, Byam-Smith M, Garfield RE. Gestational changes in oxytocin- and endothelin-1-induced contractility of pregnant rat myometrium. Eur J Pharmacol 1995; 278:187-94. [PMID: 7589154 DOI: 10.1016/0014-2999(95)00089-4] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The mechanical effects of KCl, oxytocin and endothelin-1 on pregnant rat myometrium were examined using intact strips and beta-escin-treated skinned strips. Myometrial tissues from delivering rats were more sensitive to 10.7 mM K+ compared to mid and late gestation. Maximum contractions induced by K+ were obtained at concentrations of 118 mM at mid and late gestation and during delivery. The maximum amplitude of contractions induced by oxytocin and endothelin-1 compared to the 118 mM K(+)-induced contraction increased during the progress of gestation. Maximum contractions induced by oxytocin and endothelin-1 were greater than those induced by 118 mM K+ at delivery, and maximum contractions by oxytocin were larger than those by endothelin-1 during delivery. In 10 microM nifedipine and Ca(2+)-free (containing 2 mM EGTA) solutions, 118 mM K+ contractions were completely abolished; however, both oxytocin and endothelin-1 produced contractions. In Ca(2+)-free solutions, contractions by oxytocin were larger than those by endothelin-1. In skinned myometrial strips, guanosine 5'-O-thiotriphosphate (GTP, 1 microM-1 mM), guanosine 5'-O-(gamma-thiotriphosphate) (GTP gamma S, 0.1-100 microM) and oxytocin (1 nM-0.1 microM) with 10 microM GTP, but not endothelin-1 with 10 microM GTP increased Ca2+ sensitivity of contractile force.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- H Izumi
- Department of Obstetrics and Gynecology, University of Texas Medical Branch, Galveston 77555-1062, USA
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Devedeux D, Marque C, Mansour S, Germain G, Duchêne J. Uterine electromyography: a critical review. Am J Obstet Gynecol 1993; 169:1636-53. [PMID: 8267082 DOI: 10.1016/0002-9378(93)90456-s] [Citation(s) in RCA: 243] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
On the basis of a literature review, this work summarizes uterine animal and human electromyographic information obtained at cellular, myometrial, and abdominal levels during gestation and parturition. We show that both internal and external electromyograms occur in phase with intrauterine pressure increase and exhibit similar spectra, including a slow wave (0.01 < frequency < 0.03 Hz) probably because of mechanical artifacts and a fast wave whose frequency content can be subdivided into a low-frequency band always present in every contraction and a high-frequency band related to efficient parturition contractions. Application of classic spectral techniques to electromyogram envelopes has identified group propagation but not pacemaker areas. However, no time delay or classic propagation has been demonstrated by applying the same spectral techniques to the electromyogram itself, probably because of the nonlinearity and three-dimensional nature of the propagating process.
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Affiliation(s)
- D Devedeux
- Unité de Recherche Associée, Centre National de Recherche Scientifique 858, Université de Technologie de Compiègne, France
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27
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Anwer K, Oberti C, Perez GJ, Perez-Reyes N, McDougall JK, Monga M, Sanborn BM, Stefani E, Toro L. Calcium-activated K+ channels as modulators of human myometrial contractile activity. THE AMERICAN JOURNAL OF PHYSIOLOGY 1993; 265:C976-85. [PMID: 8238323 DOI: 10.1152/ajpcell.1993.265.4.c976] [Citation(s) in RCA: 115] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The role of Ca(2+)-activated potassium (KCa) channels in the regulation of membrane potential, intracellular free calcium ([Ca2+]i) and contraction was investigated in uterine smooth muscle and myometrial cells. In an immortalized human myometrial cell line, oxytocin increased [Ca2+]i and [3H]inositol phosphate formation. Relaxin attenuated the oxytocin-induced increase in [Ca2+]i. In cell-attached patches, membrane depolarization activated a large-conductance KCa channel (179 +/- 4 pS). Iberiotoxin (IbTX), a potent blocker of "maxi" KCa channels (A. Galvez, G. Gimenez-Gallego, J. P. Reuben, L. Roy-Contanciin, P. Feigenbaum, G. J. Kaczorowski, and M. L. Garcia. J. Biol. Chem. 265: 11083-11090, 1990) produced long closed events (approximately 6 min) in these channels. In agreement with this blockage, IbTX depolarized the cells by 9.8 +/- 2.8 mV and caused a dose-dependent increase in [Ca2+]i with a half-maximal effective concentration of 0.79 nM. IbTX also caused phasic contractions in human myometrial strips and increased both the frequency and force of spontaneous contractions in estrogen-primed rat myometrial strips. Moreover, myometrial contractility was also affected by 1 mM tetraethylammonium, a concentration that blocks uterine smooth muscle KCa channels when applied to the extracellular side (G. J. Perez, L. Toro, S. D. Erulkar, and E. Stefani. Am. J. Obstet. Gynecol. 168: 652-660, 1993). These results strongly suggest that the large conductance KCa channels may actively participate in the control of human myometrial cell membrane potential and [Ca2+].
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Affiliation(s)
- K Anwer
- Department of Biochemistry, University of Texas Medical School at Houston
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Rendt JM, Toro L, Stefani E, Erulkar SD. Progesterone increases Ca2+ currents in myometrial cells from immature and nonpregnant adult rats. THE AMERICAN JOURNAL OF PHYSIOLOGY 1992; 262:C293-301. [PMID: 1539621 DOI: 10.1152/ajpcell.1992.262.2.c293] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
We examined the role of ovarian steroids in regulating Ca2+ channels in rat uterine smooth muscle. Ca2+ currents (ICa) in myometrial cells from nonpregnant adult rats and immature rats injected with either estrogen or progesterone or estrogen plus progesterone were measured with the whole cell patch-clamp method. ICa was more prominent in cells from diestrous rats than in cells from estrous rats. In cells from immature rats the ICa density was significantly greater in cells from progesterone-injected rats than in cells from estrogen-injected or noninjected rats. ICa in cells from rats injected simultaneously with progesterone and the progesterone antagonist RU-486 was not significantly greater than those from noninjected rats. These increases in ICa density are not the result of changes in ICa activation kinetics or voltage dependence, since both are unaffected by steroid injection. The kinetics and voltage dependence of the ICa current in cells from immature and nonpregnant adult rats are similar, suggesting that they represent a single population of Ca2+ channels.
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Affiliation(s)
- J M Rendt
- Department of Pharmacology, University of Pennsylvania Medical School, Philadelphia 19104
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Everts ME, Skajaa K, Hansen K. The concentration of ouabain binding sites in biopsies of uterine muscle. ACTA PHYSIOLOGICA SCANDINAVICA 1990; 139:503-10. [PMID: 2173352 DOI: 10.1111/j.1748-1716.1990.tb08952.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The concentration of Na, K-ATPase in biopsies of uterine muscle was determined by measurement of [3H]ouabain binding in the presence of vanadate. For this purpose a method previously described for skeletal muscle (Nørgaard et al. 1983) was modified. Biopsies were obtained from uterine muscle from pregnant women (during caesarian section), non-pregnant women (during hysterectomy) and from adult, non-pregnant guinea-pigs and rats. The ouabain binding site concentration in uterine muscle of the pregnant women averaged 72 +/- 2 pmol g-1 wet wt (n = 8), with an apparent dissociation constant (KD) for ouabain of 3 x 10(-9) mol l-1. The ouabain-binding capacity in uterine muscle of the non-pregnant women amounted to 83 +/- 9 pmol g-1 wet wt (n = 8). In uterine muscle of the guinea-pig, two populations of ouabain binding sites were observed: one with a maximum binding capacity of 230 pmol g-1 wet wt and an apparent KD of 1.6 x 10(-6) mol l-1, and one with a maximum capacity of 62 pmol g-1 wet wt and an apparent KD of 5 x 10(-8) mol l-1. Immediate freezing of the biopsies in liquid N2 and storage at -60 degrees C for up to 6 weeks caused no change in ouabain-binding capacity. The dry weight/wet weight ratio of the samples from different subjects showed values of around 20%. It is concluded that the concentration of Na-K pumps in human uterine muscle can be quantified by [3H]ouabain binding using samples weighing 5-10 mg.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- M E Everts
- Institute of Physiology, University of Aarhus, Denmark
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Miller SM, Garfield RE, Daniel EE. Improved propagation in myometrium associated with gap junctions during parturition. THE AMERICAN JOURNAL OF PHYSIOLOGY 1989; 256:C130-41. [PMID: 2912131 DOI: 10.1152/ajpcell.1989.256.1.c130] [Citation(s) in RCA: 95] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The hypothesis that gap junction (GJ) formation between myometrial cells at term improves electrical coupling was tested. We measured the spread of electrical excitation from six extracellular electrodes aligned on uterine strips in either the longitudinal (axial) or transverse (circumferential) direction. Spontaneous bursts propagated over the entire 15-mm recording distance in the axial direction at both preterm and parturition and showed some characteristics of a system of coupled relaxation oscillators. However, individual spikes within the bursts propagated further and with higher velocity at parturition than at preterm. In the circumferential direction, both bursts and individual spikes propagated further at parturition than before. Propagation in this axis at parturition appeared to require an intact circular muscle layer. Spikes evoked by electrical stimulation also propagated further and with higher velocity in both axes at parturition. Electron microscopy showed many GJs between uterine smooth muscle cells during parturition, but few and sometimes no GJs at preterm. Thus improved propagation was associated with increased GJ contact between myometrial cells, consistent with the hypothesis that gap junction formation at term improves electrical coupling.
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Affiliation(s)
- S M Miller
- Department of Neurosciences, McMaster University Health Sciences Centre, Hamilton, Ontario, Canada
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Hellstrand P, Lydrup ML. Spontaneous electrical and contractile activity correlated to 86Rb+ efflux in smooth muscle of guinea-pig mesotubarium. J Physiol 1988; 407:587-97. [PMID: 3256626 PMCID: PMC1191221 DOI: 10.1113/jphysiol.1988.sp017433] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
1. The spontaneous mechanical activity of guinea-pig mesotubarium consists of fused tetanic contractions lasting about 6 min, with a frequency of about four per hour. The muscle is completely relaxed between the contractions. Stretching the relaxed muscle elicits a contraction of the same appearance as the spontaneous ones. Comparison of preparations from oestrus (day 1 of the hormonal cycle), dioestrus (days 9-11) and prooestrus (days 14-15) showed no variation in the pattern of mechanical activity. 2. The resting membrane potential, measured by intracellular microelectrodes, did not differ with hormonal phase (prooestrus: -63.5 +/- 0.84 (n = 16); oestrus: -63.7 +/- 1.6 (n = 5); dioestrus: -61.6 +/- 0.77 (n = 17]. In most recordings a depolarization of a few millivolts occurred during the relaxation period (5-10 min), but in a few cells a more pronounced spontaneous depolarization of 10-15 mV was found. Ouabain (1 microM) caused depolarization by about 9 mV, both in pro- and dioestrus, leading to the initiation of maintained repetitive spiking. 3. Contraction is preceded by a depolarization lasting 10-30 s, and when a threshold is reached a train of slow waves and spikes is elicited. The frequency of slow waves and the number of spikes on each slow wave progressively decrease during the contraction, until spiking eventually ceases. 4. The spikes are resistant to tetrodotoxin (0.5 microM) and disappear in Ca2+-free medium, which also causes membrane depolarization. The duration of contractions increased with Ca2+ concentration in the range 1-5 mM. 5. The rate of 86Rb+ efflux, expressed as fractional release in 2 min intervals, showed a consistent variation during the contractile cycle in preparations with regular spontaneous activity. Relative to the value at the end of the relaxed period the efflux rate increased by about twofold during the contraction. From the beginning of the relaxed period after the contraction the efflux rate decreased by about 25% until the beginning of the next contraction. 6. It is concluded that the contractile activity in the mesotubarium, as opposed to that of the fallopian tube (Lydrup & Hellstrand, 1986a), is independent of the hormonal phase, including the period around ovulation. The mechanism for initiation of the trains of action potentials associated with spontaneous contractions may involve a gradual decrease of permeability of K+ channels or activity of the Na+-K+ pump during the relaxed period.
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Affiliation(s)
- P Hellstrand
- Department of Physiology and Biophysics, University of Lund, Sweden
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Hollingsworth M, Amédée T, Edwards D, Mironneau J, Savineau JP, Small RC, Weston AH. The relaxant action of BRL 34915 in rat uterus. Br J Pharmacol 1987; 91:803-13. [PMID: 2444298 PMCID: PMC1853592 DOI: 10.1111/j.1476-5381.1987.tb11279.x] [Citation(s) in RCA: 73] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
1 BRL 34915 (0.04-1.3 microM) caused concentration-dependent inhibition of spontaneous phasic spasms of the isolated uterus of the term pregnant rat and this effect was not antagonized by propranolol. Spasms evoked by low concentrations of KCl (less than 20 mM) were inhibited by BRL 34915 but those evoked by higher concentrations (greater than 40 mM) were unaffected. 2 In experiments using extracellular electrical recording, BRL 34915 (10 microM) selectively inhibited oxytocin-induced phasic spasms and the associated spike activity but had little effect on the tonic component of the spasms. BRL 34915, as an inhibitor of phasic spasms to oxytocin (0.2 nM), was antagonized by procaine (0.3 and 1 mM). 3 BRL 34915 (10 microM) did not inhibit Ca2+-induced spasm of saponin-skinned thin myometrial strips. 4 Intracellular microelectrode recording from myometrial strips showed that BRL 34915 (10 microM) inhibited action potentials and phasic spasms in the presence of oxytocin (0.2 nM) and produced a hyperpolarization of 5 mV. 5 In single myometrial cells under current or voltage clamp, BRL 34915 (10 microM) had no effect on action potentials and inward current in Ca2+- or Ba2+-containing media in the presence of tetraethylammonium, 4-aminopyridine and caesium chloride. In the absence of these K+-channel inhibitors, BRL 34915 had no effect on resting membrane potential, membrane resistance, action potential, inward current or outward current. 6 BRL 34915 (1 or 10 microM) had no effect on 86Rb efflux from myometrial strips. 86Rb efflux was increased by oxytocin (0.2 and 20 nM). 7 The relaxant profile of BRL 34915 in the rat uterus is similar to that described for other smooth muscles where an action to open membrane K+-channels has been proposed. BRL 34915 inhibited spike production but produced only a small hyperpolarization without a detectable increase in 86Rb efflux. Membrane resistance and transmembrane currents were unaffected. These results suggest that in the uterus the effects of BRL 34915 may be restricted to K+-channels involved in the production of pacemaker activity.
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Affiliation(s)
- M Hollingsworth
- Department of Physiological Sciences, Medical School, University of Manchester
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Markus RP, Ferreira AT, Lapa AJ. Influence of castration on the membrane reactivity of the guinea-pig vas deferens. Pflugers Arch 1987; 409:528-32. [PMID: 3627967 DOI: 10.1007/bf00583811] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The guinea-pig vas deferens is a quiescent muscle which after castration undergoes atrophy and shows spontaneous contractions preceded by membrane spike activity. The influence of castration on the spontaneous release of neurotransmitters and on the internal concentration of sodium and potassium ions was studied. Utilizing the microelectrode technique it was shown that castration induces a partial depolarization (10 mV) of the cell membrane, but did not change the frequency of spontaneous excitatory junction potentials (SEJPs) of guinea-pig vas deferens. However, the time-course and the amplitude of the SEJPs were increased after castration, probably because of changes in membrane properties related to organ atrophy. Castration probably promotes a change in the ionic permeability of the smooth muscle fibre, since the ratio pNa/pK was twice that of control muscles.
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Kirkpatrick CT, Bullock CG. Ion distribution in bovine tracheal smooth muscle and its modification by histamine. Ir J Med Sci 1986; 155:67-73. [PMID: 3710753 DOI: 10.1007/bf02940052] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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Rubiales de Barioglio S, Lacuara JL. Release of prostaglandins E and F from rat uterine strips incubated in depolarizing and hyperpolarizing solutions. PROSTAGLANDINS, LEUKOTRIENES, AND MEDICINE 1985; 20:129-38. [PMID: 3865238 DOI: 10.1016/0262-1746(85)90003-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The purpose of this study was investigate the effect of depolarizing (high K+, procaine 5 mM, high K+-Ca2+ free) or hyperpolarizing (K+ free) solutions on the generation and release of prostaglandins (PGs) E and F from the rat uterus. The output of PGs in the bathing solution was measured by bioassay. Results are expressed as ng/g dry weight/min. Under basal conditions in Krebs Ringer Bicarbonate medium, the total output of PGs (E + F) was 12.8 +/- 0.9, 20.5 +/- 2.5 and 39.1 +/- 4.3 ng/dw/min at 0-60, 60-80, 80-100 min intervals respectively, the major proportion being PGF like material in all cases. When the strips were bathed in depolarizing solution the total output increased significantly PGE being the most augmented. However, when K+ free solution was used there was a marked reduction in prostaglandins release as compared with basal conditions or depolarizing media. These results can not be attributed to osmotic effect, muscular work or neurotransmitter release from nerve endings. A close relationship between the variations in membrane potential and prostaglandins release seems to indicate that both parameters might correlate well.
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36
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Izumi H. Changes in the mechanical properties of the longitudinal and circular muscle tissues of the rat myometrium during gestation. Br J Pharmacol 1985; 86:247-57. [PMID: 4052727 PMCID: PMC1916855 DOI: 10.1111/j.1476-5381.1985.tb09456.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Changes in the mechanical properties of the longitudinal and circular muscle tissues of the rat myometrium during gestation were investigated. In isolated longitudinal and circular muscles of the rat myometrium, spontaneous contractions and contractions per unit cross-sectional area induced by 128 mM K+ and 1 X 10(-5) M acetylcholine (ACh) increased with the progress of gestation. These increases appeared in longitudinal muscles to a greater extent than in circular muscles. ACh induced the largest contraction for both intact muscle tissues, at all stages of gestation. In both muscle layers, the ACh-induced contraction reached the same amplitude as the 1 X 10(-5) M Ca-induced contraction of skinned muscles, except for the longitudinal muscle at the 22nd day of gestation. In Ca-free solution containing 2 mM EGTA, ACh produced contraction in both intact muscle tissues at all stages and the amplitude was increased during the progress of gestation, whereas the K-induced and spontaneous contractions ceased. In saponin-treated skinned muscles of both layers, the free Ca concentration required to produce contraction was lowered, the maximum amplitudes of the contraction were increased and the pCa-tension relationships shifted to the left during the progress of gestation. The results indicate that during the progress of gestation, Ca sensitivity of of the contractile proteins and mechanical responses to agonists increased and that the properties of the intracellular Ca store site were also altered in both muscle layers.
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Parkington HC. Some properties of the circular myometrium of the sheep throughout pregnancy and during labour. J Physiol 1985; 359:1-15. [PMID: 3999034 PMCID: PMC1193361 DOI: 10.1113/jphysiol.1985.sp015571] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Spontaneous electrical and mechanical activity were measured in strips of circular myometrium, stretched to in vivo length, obtained from ewes during pregnancy and parturition. The resting tension was high (280 mN/mm2) early in pregnancy and decreased gradually during the course of gestation to reach low levels (20 mN/mm2) during labour. Strips showed continuous electrical and mechanical activity up to around day 50 of pregnancy. The variability in the amplitude of the action potentials, the occurrence of many small fluctuations in membrane potential and the short space constant (0.9 mm) could be explained by impaired conduction in these tissues. During the second half of pregnancy, muscle strips showed regular bursts of spike activity and contractions with a frequency of about 4/min. The space constant (lambda) increased gradually to around 2 mm at term. The membrane time constant (tau m) remained constant at approximately 130 ms throughout gestation. Tissues from ewes in labour were not spontaneously active but action potentials could be evoked by depolarizing current pulses. The space constant increased to 4.6 +/- 0.4 mm and tau m increased to 510 +/- 50 ms at this time. Verapamil (10(-6) M) rapidly abolished electrically evoked activity in strips obtained from ewes in labour. Verapamil abolished spontaneous activity in strips from animals up to day 145 of pregnancy, though a higher concentration (2 X 10(-5) M) was required. However, action potentials could be evoked by depolarizing current pulses and these were accompanied by contractions that were 50-80% of those observed in control solution. Cobalt (2mM) had an effect on spontaneous and electrically induced activity that was similar to that of verapamil. The threshold for the initiation of an action potential was increased in all tissues in the presence of the blockers. Verapamil decreased lambda by about 50% in the later stages of pregnancy and during labour. During labour alone verapamil reduced tau m by about 50%. These results show that the onset of labour in the ewe is associated with rapid and dramatic changes in both the passive and active properties of the circular muscle of the uterus.
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Elbadawi A, Atta MA. Intrinsic neuromuscular defects in the neurogenic bladder. III. Transjunctional, short- and long-term ultrastructural changes in muscle cells of the decentralized feline bladder base following unilateral sacral ventral rhizotomy. Neurourol Urodyn 1984. [DOI: 10.1002/nau.1930030407] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Parkington HC. Intracellularly recorded electrical activity of smooth muscle of guinea pig oviduct. THE AMERICAN JOURNAL OF PHYSIOLOGY 1983; 245:C357-64. [PMID: 6638164 DOI: 10.1152/ajpcell.1983.245.5.c357] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Action potentials of the simple spike form, similar to those observed in the longitudinal myometrium, were recorded intracellularly from the strands of longitudinal muscle that are associated with the guinea pig oviduct. Action potentials recorded from the circular layer were dominated by a prolonged (1- to 10-s) plateau component that was sometimes preceded by a spike. Electrotonic potentials in response to hyperpolarizing current pulses are consistent with the view that the plateau component might be associated with an increase in membrane conductance. Action potentials of circular smooth muscle were resistant to changes in the extracellular cationic concentration. Increasing external Ca2+ prolonged the duration of the plateau component of the action potential in the region nearest the uterus on days 3 and 4 after ovulation: Ca2+ had no consistent effect at other times during the estrous cycle or on ampullary segments at any time. Reducing the concentration of external Cl- in the presence of Na+ resulted in a significant increase in the amplitude of the plateau.
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Ninomiya JG, Suzuki H. Electrical responses of smooth muscle cells of the mouse uterus to adenosine triphosphate. J Physiol 1983; 342:499-515. [PMID: 6631746 PMCID: PMC1193973 DOI: 10.1113/jphysiol.1983.sp014865] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Electrical responses of the smooth muscle cells to ATP were recorded in the longitudinal muscle of mouse myometrium, using intracellular micro-electrodes. ATP (greater than 10(-7) M) dose-dependently produced a biphasic change in the membrane potential, an initial hyperpolarization (20-30 sec) and then a depolarization. This effect of ATP was observed in all stages of gestation. The initial hyperpolarization was more quickly desensitized than the depolarization. Application of ATP for a short period (10 sec) produced only the initial hyperpolarization; the amplitude was dose-dependently increased. During the ATP-induced hyperpolarization and the depolarization, generation of spike potentials was suppressed and enhanced, respectively. Strong outward current restored the spike generation during hyperpolarization. During the ATP-induced hyperpolarization, the membrane resistance was decreased. The amplitude of the hyperpolarization was increased in low [K]0 solution and decreased in high [K]0 solutions. Pre-treatment with TEA (1 mM), procaine (1 mM), 4-aminopyridine (0.5 mM) or apamin (2 X 10(-7) M) did not, but TEA (5-10 mM) did suppress the ATP-induced hyperpolarization. Involvement of endogenous catecholamines, cyclic AMP, prostaglandins or acetylcholine in the ATP responses was ruled out. During the ATP-induced depolarization, the membrane resistance was reduced. In low [Na]0 solutions, the muscle membrane was depolarized and the amplitude of ATP-induced depolarization was reduced. In sodium-free solution, ATP produced only the initial hyperpolarization. It was concluded that the electrical responses of the smooth muscle cells of mouse myometrium to ATP consist of two components: an initial hyperpolarization with increase in the potassium conductance and a depolarization with increase in the sodium conductance.
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Martin W, Gordon JL. Spontaneous and agonist-induced 86Rb efflux from rabbit aortic smooth muscle cells in culture: a comparison with fresh tissue. J Cell Physiol 1983; 115:53-60. [PMID: 6833409 DOI: 10.1002/jcp.1041150109] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Potassium efflux was measured in rabbit aortic strips and smooth muscle cells cultured from them by monitoring the release of isotope from preparations preloaded with 86Rb. The basal rate of 86Rb efflux from rabbit subcultured aortic smooth muscle cells was eightfold higher than from freshly isolated strips, but calculations of reuptake of isotope in the tissue indicated that the measured rate constant for efflux from aortic strips underestimated the true rate by about fourfold. The rate constant for efflux from freshly dispersed cells was less than half that of subcultured cells and remained unchanged for 5 days in culture. It then rose and by around day 10 had reached the value for subcultured cells. The increase in efflux coincided with the onset of cell division. The increased rate of efflux was accompanied by an increased rate of uptake so that the internal potassium content of the cells remained constant. Heparin decreased the efflux of 86Rb from subcultured cells to that of freshly isolated cells concomitant with a reduction in the rate of proliferation. The onset of cell division and increased basal efflux of potassium was associated with a loss of responsiveness to noradrenaline and histamine as assessed by monitoring 86Rb efflux, although depolarising solutions of potassium chloride were still able to elicit a response. Responsiveness to noradrenaline and histamine could be restored by the addition of heparin. These results suggest that the lack of responsiveness of subcultured cells is not due to irreversible dedifferentiation but to a reversible loss in proliferating cells of receptors for vasoactive agents or of a coupling mechanism between receptor occupation and ion gating.
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Abstract
The spontaneous electrical and mechanical activity of the costo-uterine muscle of the guinea-pig are described. The spontaneous electrical activity, recorded intracellularly, is similar to that observed previously in longitudinal myometrium of rat (Marshall, 1959) and ionic substitution suggests that, though calcium may be the predominant ion carrying the current during the upstroke of the action potential, some influence of sodium cannot be ruled out. During dioestrus, when circulating progesterone levels are high, there is an increase in the resting membrane potential and a decrease in the frequency of electrical and mechanical activity. There is a two-fold decrease in the space constant (lambda) during dioestrus. At this time the membrane time constant (tau m) is also decreased. The diameter and length of the smooth muscle cells are smaller during dioestrus. However, the differences in cell diameter do not explain all of the differences observed in lambda at this time and it is suggested that there may be an increase in the resistance to current flow between cells. It is concluded that high circulating progesterone may bring about quiescence of target smooth muscle in two ways: by stabilizing the cell membrane and by restricting the spread of activity.
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Sims SM, Daniel EE, Garfield RE. Improved electrical coupling in uterine smooth muscle is associated with increased numbers of gap junctions at parturition. J Gen Physiol 1982; 80:353-75. [PMID: 7142952 PMCID: PMC2228686 DOI: 10.1085/jgp.80.3.353] [Citation(s) in RCA: 102] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
We have studied some passive electrical properties of uterine smooth muscle to determine whether a change in electrical parameters accompanies gap junction formation at delivery. The length constant of the longitudinal myometrium increased from 2.6 +/- 0.8 mm (X +/- SD) before term to 3.7 +/- 1 mm in tissues from delivering animals. The basis of the change was a 33% decrease in internal resistance and a 46% increase in membrane resistance. Axial current flow in an electrical syncytium such as myometrium is impeded by the cytoplasm of individual cells plus the junctions between cells. Measurement of the longitudinal impedance indicated that the specific resistance of the myoplasmic component was constant at 319 +/- 113 omega . cm before term and 340 +/- 93 omega . cm at delivery. However, a decrease in junctional resistance was apparent from 323 +/- 161 omega . cm to 134 +/- 64 omega . cm at delivery. 1.5-2 d after delivery, the junctional resistance was increased, as was the myoplasmic resistance. Thin-section electron microscopy of some of the same muscle samples showed that gap junctions were present in significantly greater numbers in the delivering tissues. Therefore, our results support the hypothesis that gap junction formation at delivery is associated with improved electrical coupling of uterine smooth muscle.
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Law RO. Techniques and applications of extracellular space determination in mammalian tissues. EXPERIENTIA 1982; 38:411-21. [PMID: 7044812 DOI: 10.1007/bf01952615] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
This review summarizes the ways in which the extracellular space (ECS) may be estimated in mammalian tissues, and briefly describes some of the uses to which the EC confinement of certain molecules (markers or tracers) may be put in the elucidation of physiological functions. The introductory section is followed by a description of the more commonly used marker molecules and their functional characteristics, and of factors likely to lead to the spurious over- or under-estimation of the ECS. Certain alternative methods are also described, in particular those based on morphological and electrical criteria which seek to demonstrate small, functionally important, changes in the size of specialized regions of the ECS (e.g. lateral cellular interspaces) without necessarily being required to provide a quantitatively precise estimate of their size. Section III describes the results of measurements of ECS in various mammalian tissues (muscle, gastro-intestinal tract, nervous tissue, crystalline lens, placenta, lung and kidney) and some applications of EC markers to investigation of cellular function (e.g. uptake of metabolic substrates and epithelial transport) and, in outline, characterization of capillary permeability. The available literature in this field is very extensive, and in the interests of brevity the reader is, where appropriate, referred to previous reviews covering specialized aspects of ECS determination and related topics.
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Germain G, Cabrol D, Visser A, Sureau C. Electrical activity of the pregnant uterus in the cynomolgus monkey. Am J Obstet Gynecol 1982; 142:513-9. [PMID: 7199259 DOI: 10.1016/0002-9378(82)90753-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Electromyographic activity in six pregnant cynomolgus monkeys was recorded in vivo by means of bipolar electrodes individually attached to the surface of the uterine corpus. These data were compared with recordings of intra-amniotic pressure obtained simultaneously by means of an open-ended, fluid-filled catheter placed in the amniotic cavity. During the last third of pregnancy, the electromyograms showed recurrent electrical complexes (trains of potentials, TOP) which lasted for about 2 minutes and whose rate of occurrence varied during the nyctohemeral period. The initiation of electrical activity in various uterine areas was always synchronous with and was related to mechanical contraction. The complex, polyphasic contractions that were observed can be explained, largely, by the variations of potentials within a train of potentials. However, a simple quantitative relationship between the mean frequency of the potentials within the TOP and the mean amplitude of the change in pressure could not be demonstrated. In contrast to data available on the woman, the increase in contractile strength at the onset of labor in the macaque appears to be due to a higher frequency of excitation of individual cells rather than the result of an improved functional coordination between the active muscular elements.
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Aickin CC, Brading AF. Measurement of intracellular chloride in guinea-pig vas deferens by ion analysis, 36chloride efflux and micro-electrodes. J Physiol 1982; 326:139-54. [PMID: 7108787 PMCID: PMC1251464 DOI: 10.1113/jphysiol.1982.sp014182] [Citation(s) in RCA: 113] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
1. Cl-sensitive micro-electrodes were used to measure the intracellular Cl activity (a(Cl) (i)) in smooth muscle cells of the guinea-pig vas deferens. The values obtained were compared with those of intracellular Cl (Cl(i)) found by both ion analysis and (36)Cl efflux.2. Various combinations of filling solution for recording membrane potential (E(m)), and type of micro-electrode were tested. The most successful, which allowed continuous recording of a(Cl) (i) for several hours, was a double-barrelled electrode using the reference liquid ion exchanger (RLIE; Thomas & Cohen, 1981). However, a(Cl) (i) measured both by simultaneous impalements of separate cells with Cl-sensitive and conventional micro-electrodes, and by double-barrelled micro-electrodes, was about 42 mM in normal Krebs solution. This is five times higher than the value from a passive distribution. E(Cl) was about -24 mV, more than 40 mV positive to E(m).3. On complete removal of extracellular Cl (Cl(o)), a(Cl) (i) fell to an apparent level of about 3 mM. If this represents interference from other anions, the maximum error in E(Cl) measured in normal Krebs solution is 2.5 mV. Replacement of Cl(o) caused a rapid increase in a(Cl) (i). This must be caused by an active transport of Cl(-) ions into the cell against their electrochemical gradient.4. The stabilized values of a(Cl) (i) measured at different levels of Cl(o) agree surprisingly well with a(Cl) (i) estimated from ion analysis and (36)Cl efflux, assuming that the intracellular activity coefficient was the same as measured in the normal Krebs solution. The relationship of a(Cl) (i) to Cl(o) was hyperbolic.5. It is concluded that Cl-sensitive micro-electrodes accurately measure a(Cl) (i) in smooth muscle cells. The remarkable agreement between the direct and indirect methods of measuring Cl(i) suggests that Cl(-) ions are not bound to a significant extent and that the compartment seen by the micro-electrodes is probably representative of the whole cell.
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Abstract
1. Ouabain (0.1 mM)-sensitive 42K influx and 24Na efflux have been measured in rabbit carotid arteries under conditions of high cellular potassium, [K]i, as well as sodium, [Na]i. About 50% of the total fluxes are ouabain-sensitive (active) under conditions of high [K]i. 2. The extracellular space, determined by 60Co-EDTA, was relatively large in comparison to cellular water. The ionic concentrations in normal solution, estimated from isotope flux components, are: [Na]i = 24; [K]i = 169; [Cl]i = 68 mmol/l cell water. 3. The ouabain=sensitive 42K influx and 24Na efflux in high-K tissues were measured at varying external concentrations of potassium, [K]o, and normal concentrations of external sodium, [Na]o. Sigmoidal kinetics were observed and fitted to a co-operative interaction model. The maximal efflux of 24Na, 0.245 muequiv/g wet weight per minute, was about 1.4 times that for 42K influx. Half-maximal stimulation was achieved at [K]0.5o of 2.4 mM for Na, and 3.4 mM for K transport. The flux ratio of Na to K approximated 1.5. 4. Increased 42K efflux was found in the presence of ouabain and the passive influx of 42K was corrected for this effect. In the absence of this correction the ouabain-sensitive 42K influx would be reduced, and the Na/K flux ratio raised to about 2. 5. The [K]o-dependence of ouabain-sensitive fluxes was measured on Na-loaded tissues. 24Na efflux exhibited saturation kinetics with a maximum of 1.18 muequiv/g wet weight per minute and [K]0.5o = 3.1 mM. The 42K influx was two thirds the active Na efflux for [K]o less than or equal to 5 mM. At high [K]o, however, the influx greatly exceeded the predicted levels. Evidence is presented for a ouabain-sensitive membrane hyperpolarization being responsible for an additional influx of 42K. 6. The ouabain-sensitive 24Na efflux showed a sigmoidal dependence on [Na]i in the presence of [K]o = 10 mM and normal [Na]o. The maximal efflux was 0.88 muequiv/g weight per minute and [Na]0.5i = 49 mmol/l cell water, which is about twice the physiological operating point. 7. It is concluded that active Na and K transport in rabbit carotid artery follow sigmoidal kinetics and the flux ratio is about 1.5. Changes in [K]o and [Na]i over the physiological range can markedly affect transport, and may regulate vascular contraction by their action on electrogenic transport.
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Lodge S, Sproat JE. Resting membrane potentials of pacemaker and non pacemaker areas in rat uterus. Life Sci 1981; 28:2251-6. [PMID: 7253820 DOI: 10.1016/0024-3205(81)90577-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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Abstract
The effects of changing bathing medium osmolality on tension generation in smooth muscle were studied on potassium-depolarized segments of rat ileum. Increasing the tonicity of the medium evokes a transient relaxation of the smooth muscle; restoration of isotonicity evokes a transient contraction of similar amplitude and time course. While immersed in hypertonic media of less than 1.3 times normal tonicity, the smooth muscle slowly increases its isometric tension; in media of nearly twice normal tonicity, the smooth muscle loses tension. All of these effects occur whether the medium is made hypertonic with added NaCl or sucrose.
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