1
|
Characterization of a Family of Scorpion Toxins Modulating Ca 2+-Activated Cl - Current in Vascular Myocytes. Toxins (Basel) 2022; 14:toxins14110780. [PMID: 36356031 PMCID: PMC9699600 DOI: 10.3390/toxins14110780] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2022] [Revised: 11/02/2022] [Accepted: 11/03/2022] [Indexed: 11/12/2022] Open
Abstract
The pharmacology of calcium-activated chloride current is not well developed. Peptides from scorpion venom present potent pharmacological actions on ionic conductance used to characterize the function of channels but can also be helpful to develop organic pharmacological tools. Using electrophysiological recording coupled with calcium measurement, we tested the potent effect of peptides extracted from Leuirus quinquestratus quinquestratus venom on the calcium-activated chloride current expressed in smooth muscle cells freshly dissociated from rat portal veins. We identified one peptide which selectively inhibited the chloride conductance without effects on either calcium signaling or calcium and potassium currents expressed in this cell type. The synthetic peptide had the same affinity, but the chemical modification of the amino acid sequence altered the efficiency to inhibit the calcium-activated chloride conductance.
Collapse
|
2
|
Wray S, Prendergast C, Arrowsmith S. Calcium-Activated Chloride Channels in Myometrial and Vascular Smooth Muscle. Front Physiol 2021; 12:751008. [PMID: 34867456 PMCID: PMC8637852 DOI: 10.3389/fphys.2021.751008] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2021] [Accepted: 09/24/2021] [Indexed: 11/24/2022] Open
Abstract
In smooth muscle tissues, calcium-activated chloride channels (CaCC) provide the major anionic channel. Opening of these channels leads to chloride efflux and depolarization of the myocyte membrane. In this way, activation of the channels by a rise of intracellular [Ca2+], from a variety of sources, produces increased excitability and can initiate action potentials and contraction or increased tone. We now have a good mechanistic understanding of how the channels are activated and regulated, due to identification of TMEM16A (ANO1) as the molecular entity of the channel, but key questions remain. In reviewing these channels and comparing two distinct smooth muscles, myometrial and vascular, we expose the differences that occur in their activation mechanisms, properties, and control. We find that the myometrium only expresses “classical,” Ca2+-activated, and voltage sensitive channels, whereas both tonic and phasic blood vessels express classical, and non-classical, cGMP-regulated CaCC, which are voltage insensitive. This translates to more complex activation and regulation in vascular smooth muscles, irrespective of whether they are tonic or phasic. We therefore tentatively conclude that although these channels are expressed and functionally important in all smooth muscles, they are probably not part of the mechanisms governing phasic activity. Recent knockdown studies have produced unexpected functional results, e.g. no effects on labour and delivery, and tone increasing in some but decreasing in other vascular beds, strongly suggesting that there is still much to be explored concerning CaCC in smooth muscle.
Collapse
Affiliation(s)
- Susan Wray
- Department of Women and Children's Health, Institute of Life Course and Medical Sciences, University of Liverpool, Liverpool, United Kingdom
| | - Clodagh Prendergast
- Department of Women and Children's Health, Institute of Life Course and Medical Sciences, University of Liverpool, Liverpool, United Kingdom
| | - Sarah Arrowsmith
- Department of Life Sciences, Manchester Metropolitan University, Manchester, United Kingdom
| |
Collapse
|
3
|
Hyuga S, Danielsson J, Vink J, Fu XW, Wapner R, Gallos G. Functional comparison of anoctamin 1 antagonists on human uterine smooth muscle contractility and excitability. J Smooth Muscle Res 2019; 54:28-42. [PMID: 29937453 PMCID: PMC6013749 DOI: 10.1540/jsmr.54.28] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Background: Pre-term birth is a major health care challenge
throughout the world, and preterm labor represents a potentially reversible
component of this problem. Current tocolytics do not improve preterm labor
beyond 48 h. We have previously shown that anoctamin 1 (ANO1) channel blockade
results in relaxation of pre-contracted human uterine smooth muscle (USM). Three
drug classes with reported medicinal effects in humans also have members with
ANO1 antagonism. In this study, we compared the ability of representatives from
these 3 classes to reduce human USM contractility and excitability.
Objective: This study sought to examine the comparative potency
of 3 ANO1 antagonists on pregnant human USM relaxation, contraction frequency
reduction, inhibition of intracellular calcium release and membrane
hyperpolarization. Methods: Experiments were performed using: 1)
Ex vivo organ bath (human pregnant tissue), 2)
Oxytocin-induced calcium flux (in vitro human USM cells) and 3)
Membrane potential assay (in vitro human USM cells).
Results: Benzbromarone (BB) demonstrated the greatest potency
among the compounds tested with respect to force, frequency inhibition, reducing
calcium elevation and depolarizing membrane potential. Conclusion:
While all 3 ANO1 antagonists attenuate pregnant human uterine tissue
contractility and excitability, BB is the most potent tocolytic drug. Our
findings may serve as a foundation for future structure-function analyses for
novel tocolytic drug development.
Collapse
Affiliation(s)
- Shunsuke Hyuga
- Department of Anesthesiology, Columbia University College of Physicians and Surgeons, Columbia University Medical Center, New York, NY
| | - Jennifer Danielsson
- Department of Anesthesiology, Columbia University College of Physicians and Surgeons, Columbia University Medical Center, New York, NY
| | - Joy Vink
- Department of Obstetrics & Gynecology, Columbia University College of Physicians and Surgeons, Columbia University Medical Center, New York, NY
| | - Xiao Wen Fu
- Department of Anesthesiology, Columbia University College of Physicians and Surgeons, Columbia University Medical Center, New York, NY
| | - Ronald Wapner
- Department of Obstetrics & Gynecology, Columbia University College of Physicians and Surgeons, Columbia University Medical Center, New York, NY
| | - George Gallos
- Department of Anesthesiology, Columbia University College of Physicians and Surgeons, Columbia University Medical Center, New York, NY
| |
Collapse
|
4
|
The steroid hormone dydrogesterone inhibits myometrial contraction independently of the progesterone/progesterone receptor pathway. Life Sci 2018; 207:508-515. [PMID: 29981319 DOI: 10.1016/j.lfs.2018.07.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Revised: 06/25/2018] [Accepted: 07/03/2018] [Indexed: 12/30/2022]
Abstract
AIMS In this study, we aimed to investigate the direct effects of steroid hormones on pregnant myometrial contraction. MAIN METHODS The effect of steroids on oxytocin-induced contraction was examined in vitro using pregnant rat or human myometrium. Subsequently, we evaluated whether RU486, a potent progesterone antagonist, influenced the effects of progestin on myometrial contraction. Additionally, we evaluated the effects of progestin on high-concentration KCl-induced contraction caused by voltage-dependent calcium channels in order to investigate the mechanisms involved in this process. KEY FINDINGS Of the natural steroids examined, 17β-estradiol, progesterone, testosterone, cortisol, and aldosterone did not influence oxytocin-induced contraction at concentrations <10-6 M. Of the tested progestins, medroxyprogesterone acetate, norethisterone, chlormadinone acetate, levonorgesterol, 17α-hydroxyprogesterone capronate, and dienogest had no effect on contraction at <10-6 M. However, dydrogesterone showed rapid and direct inhibition of contraction at 10-6 M, and this inhibitory effect was dependent on dose and time. RU486 did not block the inhibitory effects of dydrogesterone on contraction. High-concentration KCl-induced contraction was also inhibited by dydrogesterone, and the inhibitory effects of dydrogesterone were observed at concentrations as low as 10-7 M. Additionally, oxytocin-induced contraction in pregnant human myometrium was inhibited by 10-6 M dydrogesterone. SIGNIFICANCE These results suggested that the rapid and direct effects of dydrogesterone on myometrial contraction were caused by a nongenomic pathway and that the progesterone receptor was not required for dydrogesterone action. Additionally, the mechanism of dydrogesterone action may involve voltage-dependent calcium channels.
Collapse
|
5
|
Abstract
In the United States, the generally accepted indication for tocolytic therapy centers on suppression of preterm labor. This may be in the form of preventative therapy with progesterone in women with prior spontaneous preterm birth or as an acute intervention to suppress established uterine contractions associated with cervical change occurring at less than 37 weeks gestation. This article seeks to apply this perspective to tocolytic therapy. Here, we provide a review of current tocolytic options and what the last decade of discovery has revealed about the regulation of myometrial excitability and quiescence. Moving forward, we must incorporate the emerging molecular data that is amassing in order to develop novel and effective tocolytic therapeutic options to prevent preterm labor and spontaneous preterm birth (sPTB).
Collapse
Affiliation(s)
| | | | - George Gallos
- Department of Anesthesia, Columbia University Medical Center, New York, NY.
| |
Collapse
|
6
|
Affiliation(s)
- Barbara M. Sanborn
- Department of Biochemistry and Molecular Biology, University of Texas Houston Medical School, PO Box 20708, Houston, TX 77225
| |
Collapse
|
7
|
Wellmann S, Bührer C. Who plays the strings in newborn analgesia at birth, vasopressin or oxytocin? Front Neurosci 2012; 6:78. [PMID: 22661926 PMCID: PMC3362806 DOI: 10.3389/fnins.2012.00078] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2012] [Accepted: 05/10/2012] [Indexed: 01/19/2023] Open
Affiliation(s)
- Sven Wellmann
- Division of Neonatology, University Children's Hospital Basel (UKBB) Basel, Switzerland
| | | |
Collapse
|
8
|
Abstract
The sarcoplasmic reticulum (SR) of smooth muscles presents many intriguing facets and questions concerning its roles, especially as these change with development, disease, and modulation of physiological activity. The SR's function was originally perceived to be synthetic and then that of a Ca store for the contractile proteins, acting as a Ca amplification mechanism as it does in striated muscles. Gradually, as investigators have struggled to find a convincing role for Ca-induced Ca release in many smooth muscles, a role in controlling excitability has emerged. This is the Ca spark/spontaneous transient outward current coupling mechanism which reduces excitability and limits contraction. Release of SR Ca occurs in response to inositol 1,4,5-trisphosphate, Ca, and nicotinic acid adenine dinucleotide phosphate, and depletion of SR Ca can initiate Ca entry, the mechanism of which is being investigated but seems to involve Stim and Orai as found in nonexcitable cells. The contribution of the elemental Ca signals from the SR, sparks and puffs, to global Ca signals, i.e., Ca waves and oscillations, is becoming clearer but is far from established. The dynamics of SR Ca release and uptake mechanisms are reviewed along with the control of luminal Ca. We review the growing list of the SR's functions that still includes Ca storage, contraction, and relaxation but has been expanded to encompass Ca homeostasis, generating local and global Ca signals, and contributing to cellular microdomains and signaling in other organelles, including mitochondria, lysosomes, and the nucleus. For an integrated approach, a review of aspects of the SR in health and disease and during development and aging are also included. While the sheer versatility of smooth muscle makes it foolish to have a "one model fits all" approach to this subject, we have tried to synthesize conclusions wherever possible.
Collapse
Affiliation(s)
- Susan Wray
- Department of Physiology, School of Biomedical Sciences, University of Liverpool, Liverpool, Merseyside L69 3BX, United Kingdom.
| | | |
Collapse
|
9
|
Rihana S, Terrien J, Germain G, Marque C. Mathematical modeling of electrical activity of uterine muscle cells. Med Biol Eng Comput 2009; 47:665-75. [DOI: 10.1007/s11517-009-0433-4] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2008] [Accepted: 12/16/2008] [Indexed: 10/21/2022]
|
10
|
Calsteren MRV, Jankowski CK, Reyes-Chilpa R, Jiménez-Estrada M, Campos MG, Zarazua-Lozada A, Oropeza M, Lesage D. X-ray and high-resolution 1H and 13C NMR of smooth muscle relaxant sesquiterpene lactones. CAN J CHEM 2008. [DOI: 10.1139/v08-158] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The structure and stereochemistry of four sesquiterpene lactones, budlein A (1), zaluzanin A (2), and glaucolides D (3a) and E (3b), isolated from Mexican Asteraceae species, for which only partial NMR data could be found in the literature, were determined. A combination of 1D and 2D high-resolution NMR experiments, such as DEPT, COSY, NOESY, ROESY, HMQC, HSQC, and HMBC, were used to completely assign the 1H and 13C spectra. The crystal structures of zaluzanin A (2) and glaucolide E (3b) were also determined. Glaucolides D and E have been previously reported to relax KCl-induced contraction in rat uterine smooth muscle; therefore, the effects of zaluzanin A and budlein A were examined in the same model. It was found that both compounds can relax contraction induced by KCl, but only zaluzanin A induced relaxation when contraction was induced with oxytocin. The preliminary biological test results according to these profiles are reported in this paper.Key words: NMR data, X-ray data, sesquiterpene lactones, Mexican Asteraceae, smooth muscle relaxant.
Collapse
|
11
|
Wray S, Noble K. Sex hormones and excitation-contraction coupling in the uterus: the effects of oestrous and hormones. J Neuroendocrinol 2008; 20:451-61. [PMID: 18266942 DOI: 10.1111/j.1365-2826.2008.01665.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In this review, we examine how far the increased understanding that we have of the events in excitation contraction can explain the effects of the oestrous cycle and sex hormones on uterine function. Observational studies of electrical and mechanical activity in the rat myometrium have shown a relative quiescence during pro-oestrous, with little propagation of any electrical events. Thus, uterine activity can be said to approximately inversely reflect plasma 17beta-oestradiol concentrations. We show that Ca(2+) signalling and mechanical activity are greatest in metoestrous and dioestrous compared to pro-oestrous and oestrous. These data are discussed in terms of hormonal effects on Ca(2+) and K(+) channels. Finally, the influence of sex hormones on lipid rafts and caveolae are considered and discussed in relation to recent findings on their role in uterine signalling and contractility, and cholesterol levels and obesity.
Collapse
Affiliation(s)
- S Wray
- The Physiological Department, School of Biomedical Sciences, University of Liverpool, Liverpool, UK.
| | | |
Collapse
|
12
|
Blanks AM, Shmygol A, Thornton S. Preterm labour. Myometrial function in prematurity. Best Pract Res Clin Obstet Gynaecol 2007; 21:807-19. [PMID: 17446138 DOI: 10.1016/j.bpobgyn.2007.03.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The primary function of the uterus during gestation is to harbour the growing conceptus in a largely quiescent environment. Upon maturation of the fetus to a point sufficient for extrauterine survival, the uterus must remodel itself sufficiently to generate forceful contractions during labour. During preterm delivery, the process of remodelling of the myometrium occurs early due to a number of different causes, although the underlying basis for myometrial contraction remains the same. This review summarises the anatomical, physiological and molecular basis for contraction. We describe the fibre structure of the human uterus and how this relates to the spread of electrical excitation during a contraction. The process of excitation within a single myometrial cell is described, as well as how this relates to contraction. We then focus on how excitation-contraction coupling is modulated by intercellular communication, pharmacomechanical-coupling and hormonal milieu. Lastly, we consider the actions of the commonly accepted uterine agonists oxytocin, prostaglandin F(2alpha), and prostaglandin E(2), and the tocolytic ritodrine.
Collapse
Affiliation(s)
- Andrew M Blanks
- Clinical Sciences Research Institute, University of Warwick, University Hospitals of Coventry and Warwickshire, Clifford Bridge Road, Coventry CV2 2DX, UK.
| | | | | |
Collapse
|
13
|
Shmygol A, Blanks AM, Bru-Mercier G, Gullam JE, Thornton S. Control of uterine Ca2+ by membrane voltage: toward understanding the excitation-contraction coupling in human myometrium. Ann N Y Acad Sci 2007; 1101:97-109. [PMID: 17332087 DOI: 10.1196/annals.1389.031] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Myometrial contractility is a complex and dynamic physiological process that changes substantially during pregnancy and culminates in childbirth. Uterine contractions are initiated by transient rises in cytoplasmic Ca(2+) concentration ([Ca(2+)](i)), which in turn are triggered and controlled by myometrial action potentials. The sequence of events between the action potential generation and the contraction initiation is referred to as excitation-contraction coupling. Hormones and other physiologically active substances affect myometrial contractility by modulating different steps in the excitation-contraction coupling process. It is therefore imperative that we understand that process to understand the regulation of myometrial contractility. The complex action potentials generated by human myometrium result from the activity of many ion channels, transporters, and pumps. Two types of myometrial action potential waveform have been described in the literature: a plateau type and a spike type. Parameters of the myometrial [Ca(2+)](i) transients and contractions differ depending on the type of action potential that triggers them. Some aspects of the excitation-contraction coupling are unique to human myometrium and cannot be found in animal models; some others are common between many species. This article reviews the current state and discusses future directions of physiological research on human myometrial excitation-contraction coupling.
Collapse
Affiliation(s)
- Anatoly Shmygol
- Clinical Sciences Research Institute, The University of Warwick Medical School, Coventry, CV2 2DX, UK.
| | | | | | | | | |
Collapse
|
14
|
Shmygol A, Gullam J, Blanks A, Thornton S. Multiple mechanisms involved in oxytocin-induced modulation of myometrial contractility. Acta Pharmacol Sin 2006; 27:827-32. [PMID: 16787565 DOI: 10.1111/j.1745-7254.2006.00393.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Oxytocin is a small peptide hormone with multiple sites of action in human body. It regulates a large number of reproduction-related processes in all species. Particularly important is its ability to stimulate uterine contractility. This is achieved by multiple mechanisms involving sarcoplasmic reticulum Ca2+ release and sensitization of the contractile apparatus to Ca2+. In this paper, we review the data published by us and other groups on oxytocin-induced modulation of uterine contractility. We conclude that sensitization of contractile apparatus to Ca2+ is the most relevant physiological effect of oxytocin on human myometrium.
Collapse
Affiliation(s)
- Anatoly Shmygol
- Clinical Sciences Research Institute, Warwick Medical School, University of Warwick, Coventry, UK.
| | | | | | | |
Collapse
|
15
|
Abstract
CONTEXT Little is known about the crosstalk between the decidua and myometrium in relation to human labor. The hormone oxytocin (OT) is considered to be a key mediator of uterine contractility during parturition, exerting some of its effects through calcium channels. OBJECTIVE The objective was to characterize the effect of OT on the T-type calcium channel in human decidual stromal cells before and after the onset of labor. DESIGN The nystatin-perforated patch-clamp technique was used to record inward T-type calcium current (I(Ca(T))) from acutely dispersed decidual stromal cells obtained from women at either elective cesarean section [CS (nonlabor)] or after normal spontaneous vaginal delivery [SVD (labor)]. SETTING These studies took place at the University of Nottingham Medical School. RESULTS I(Ca(T)) of both SVD and CS cells were blocked by nickel (IC(50) of 5.6 microm) and cobalt chloride (1 mm) but unaffected by nifedipine (10 microm). OT (1 nm to 3.5 microm) inhibited I(Ca(T)) of SVD cells in a concentration-dependent manner, with a maximal inhibition of 79.0% compared with 26.2% in decidual cells of the CS group. OT-evoked reduction of I(Ca(T)) was prevented by preincubation with the OT antagonist L371,257 in the SVD but not CS group. OT, in a concentration-dependent manner, displaced the steady-state inactivation curve for I(Ca(T)) to the left in the SVD group with no significant effect on curves of the CS group. CONCLUSION Inhibition of I(Ca(T)) by OT in decidual cells obtained during labor may signify important functional remodeling of uterine signaling during this period.
Collapse
Affiliation(s)
- Bo Liu
- Institute of Cell Signalling, University of Nottingham, Queens Medical Centre, Nottingham, United Kingdom
| | | | | |
Collapse
|
16
|
Jones K, Shmygol A, Kupittayanant S, Wray S. Electrophysiological characterization and functional importance of calcium-activated chloride channel in rat uterine myocytes. Pflugers Arch 2004; 448:36-43. [PMID: 14740218 DOI: 10.1007/s00424-003-1224-7] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2003] [Accepted: 12/01/2003] [Indexed: 10/26/2022]
Abstract
In order to better understand the mechanisms underlying excitation of the uterus, we have elucidated the characteristics and functional importance of Ca(2+)-activated Cl(-) currents ( I(Cl-Ca)) in pregnant rat myometrium. In 101/320 freshly isolated myocytes, there was a slowly inactivating tail current (162+/-48 pA) upon repolarization following depolarising steps. This current has a reversal potential close to that for chloride, and was shifted when [Cl(-)] was altered. It was activated by Ca(2+) (but not Ba(2+)) entry through L-type Ca(2+) channels, enhanced by the Ca(2+) channel agonist Bay K8644 (2 microM), and inhibited by the Cl(-) channel blockers, niflumic acid (10 microM) and anthracene-9-carboxylic acid (9-AC, 100 microM). We therefore conclude that the pregnant rat myometrium contains Ca(2+)-activated Cl(-) channels producing inward current in ~30% of its cells. When these channels were inhibited by niflumic acid or 9-AC in intact tissues, the frequency of spontaneous contractions, was significantly reduced. Niflumic acid was also shown to inhibit oxytocin-induced contractions and Ca(2+) transients. Neither 9-AC nor niflumic acid had any effect on high-K-invoked contractions. Taken together these data suggest that Ca(2+)-activated Cl(-) channels are activated by Ca(2+) entry and play a functionally important role in myometrium, probably by contributing to membrane potential and firing frequency (pacemakers) in these cells.
Collapse
Affiliation(s)
- K Jones
- Department of Physiology, The University of Liverpool, Liverpool, L69 3BX, UK
| | | | | | | |
Collapse
|
17
|
Wellman GC, Nelson MT. Signaling between SR and plasmalemma in smooth muscle: sparks and the activation of Ca2+-sensitive ion channels. Cell Calcium 2003; 34:211-29. [PMID: 12887969 DOI: 10.1016/s0143-4160(03)00124-6] [Citation(s) in RCA: 167] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Intracellular calcium ions are involved in the regulation of nearly every aspect of cell function. In smooth muscle, Ca2+ can be delivered to Ca2+-sensitive effector molecules either by influx through plasma membrane ion channels or by intracellular Ca2+ release events. Ca2+ sparks are transient local increases in intracellular Ca2+ that arise from the opening of ryanodine-sensitive Ca2+ release channels (ryanodine receptors) located in the sarcoplasmic reticulum. In arterial myocytes, Ca2+ sparks occur near the plasma membrane and act to deliver high (microM) local Ca2+ to plasmalemmal Ca2+-sensitive ion channels, without directly altering global cytosolic Ca2+ concentrations. The two major ion channel targets of Ca2+ sparks are Ca2+-activated chloride (Cl(Ca)) channels and large-conductance Ca2+-activated potassium (BK) channels. The activation of BK channels by Ca2+ sparks play an important role in the regulation of arterial diameter and appear to be involved in the action of a variety of vasodilators. The coupling of Ca2+ sparks to BK channels can be influenced by a number of factors including membrane potential and modulatory beta subunits of BK channels. Cl(Ca) channels, while not present in all smooth muscle, can also be activated by Ca2+ sparks in some types of smooth muscle. Ca2+ sparks can also influence the activity of Ca2+-dependent transcription factors and expression of immediate early response genes such as c-fos. In summary, Ca2+ sparks are local Ca2+ signaling events that in smooth muscle can act on plasma membrane ion channels to influence excitation-contraction coupling as well as gene expression.
Collapse
Affiliation(s)
- George C Wellman
- Department of Pharmacology, The University of Vermont College of Medicine, Given Building, Room B-321, 89 Beaumont Avenue, Burlington, VT 05405, USA.
| | | |
Collapse
|
18
|
Scarparo HC, Santos GCM, Leal-Cardoso JH, Criddle DN. Selective inhibitory effects of niflumic acid on 5-HT-induced contraction of the rat isolated stomach fundus. Br J Pharmacol 2000; 130:678-84. [PMID: 10821798 PMCID: PMC1572096 DOI: 10.1038/sj.bjp.0703331] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
The effects of niflumic acid (NFA), an inhibitor of calcium-activated chloride currents I(Cl(Ca)), were compared with the actions of the voltage-dependent calcium channel (VDCC) blocker nifedipine on 5-hydroxtryptamine (5-HT)- and acetylcholine (ACh)-induced contractions of the rat isolated fundus. NFA (1 - 30 microM) elicited a concentration-dependent inhibition of contractions induced by 5-HT (10 microM) with a reduction to 15. 5+/-6.0% of the control value at 30 microM. 1 microM nifedipine reduced 5-HT-induced contraction to 15.2+/-4.9% of the control, an effect not greater in the additional presence of 30 microM NFA. In contrast, the contractile response to ACh (10 microM) was not inhibited by NFA in concentrations </=100 microM, although this response was partly inhibited by nifedipine (1 microM) to 67.6+/-11. 8% of the control value. NFA (1 - 30 microM) did not affect contraction induced by either 20 mM or 60 mM KCl, suggesting that this drug was not acting via blockade of VDCCs or activation of potassium channels. In contrast, 3, 5-dichlorophenylamine-2-carboxylic acid and 4, 4'-diisothiocyanatostilbene-2,2'-disulphonic acid were less selective in their inhibitory effects, inducing reductions of 60 mM KCl-induced contraction at concentrations >/=10 microM. Our results show that NFA can exert selective inhibitory effects on the chloride-dependent 5-HT-induced contractions of the rat fundus. The data support the hypothesis that activation of Cl((Ca)) channels leading to calcium entry via VDCCs is a mechanism utilized by 5-HT, but not by ACh, to elicit contraction of the rat fundus.
Collapse
Affiliation(s)
- H C Scarparo
- Departamento de Farmacologia e Fisiologia, Faculdade de Medicina, Universidade Federal do Ceará, Cel. Nunes de Melo 1127, Porangabussu, Fortaleza, CE, Brazil
| | - G C M Santos
- Laboratório de Eletrofisiologia, Departamento de Ciências Fisiológicas, CCS, Universidade Estadual do Ceará, Av. Paranjana 1700, Fortaleza CE 60740-000, Brazil
| | - J H Leal-Cardoso
- Laboratório de Eletrofisiologia, Departamento de Ciências Fisiológicas, CCS, Universidade Estadual do Ceará, Av. Paranjana 1700, Fortaleza CE 60740-000, Brazil
| | - D N Criddle
- Laboratório de Eletrofisiologia, Departamento de Ciências Fisiológicas, CCS, Universidade Estadual do Ceará, Av. Paranjana 1700, Fortaleza CE 60740-000, Brazil
- Author for correspondence:
| |
Collapse
|
19
|
Coleman HA, Hart JD, Tonta MA, Parkington HC. Changes in the mechanisms involved in uterine contractions during pregnancy in guinea-pigs. J Physiol 2000; 523 Pt 3:785-98. [PMID: 10718755 PMCID: PMC2269841 DOI: 10.1111/j.1469-7793.2000.00785.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
1. The mechanisms involved in contraction in guinea-pig myometrium were compared at mid- and late pregnancy. Tension was recorded simultaneously with either membrane potential or cytoplasmic calcium ([Ca2+]i) in strips exposed briefly to prostaglandin F2alpha (PGF). 2. PGF-induced increases in tension were underpinned by action potentials followed by sustained depolarization and biphasic increases in [Ca2+]i at mid- (peak, 879 +/- 199 nM; sustained, 298 +/- 35 nM, n = 11) and late pregnancy (peak, 989 +/- 302 nM; sustained 178 +/- 33 nM, n = 8). 3. At mid- and late pregnancy, nifedipine (10-6 M) reduced (a) the PGF-induced increase in tension to 84 and 35 %, (b) the level attained during the depolarization by 2 and 12 mV and (c) the peak rise in [Ca2+]i to 42 and 17 %. The sustained rises in [Ca2+]i were resistant to nifedipine. 4. In Ca2+-free solution (containing 1 mM EGTA), PGF elicited an increase in tension that was 26 % of that in 2.5 mM Ca2+ and an increase in [Ca2+]i (24 % of the sustained level) at mid-pregnancy but no increase in tension or [Ca2+]i at term. 5. At both stages of pregnancy, PGF decreased the level of [Ca2+]i required to elicit increases in tension comparable to those evoked by high K+o. The slope of the tension-[Ca2+]i curves were steeper in mid- than in late pregnancy. 6. In conclusion, at mid-pregnancy, the contractile response of the guinea-pig myometrium to PGF involves Ca2+ influx through L-type voltage-operated Ca2+ channels (VOCCs) and by receptor-operated mechanisms, release of Ca2+ from intracellular stores, and an increase in the sensitivity of the contractile apparatus to Ca2+. At term the situation is different: a modest increase in the sensitivity of the contractile apparatus to Ca2+ persists and there is a major reliance on Ca2+ influx through VOCCs.
Collapse
Affiliation(s)
- H A Coleman
- Department of Physiology, Monash University, Clayton, Victoria 3800, Australia
| | | | | | | |
Collapse
|
20
|
Abstract
Local intracellular Ca(2+) transients, termed Ca(2+) sparks, are caused by the coordinated opening of a cluster of ryanodine-sensitive Ca(2+) release channels in the sarcoplasmic reticulum of smooth muscle cells. Ca(2+) sparks are activated by Ca(2+) entry through dihydropyridine-sensitive voltage-dependent Ca(2+) channels, although the precise mechanisms of communication of Ca(2+) entry to Ca(2+) spark activation are not clear in smooth muscle. Ca(2+) sparks act as a positive-feedback element to increase smooth muscle contractility, directly by contributing to the global cytoplasmic Ca(2+) concentration ([Ca(2+)]) and indirectly by increasing Ca(2+) entry through membrane potential depolarization, caused by activation of Ca(2+) spark-activated Cl(-) channels. Ca(2+) sparks also have a profound negative-feedback effect on contractility by decreasing Ca(2+) entry through membrane potential hyperpolarization, caused by activation of large-conductance, Ca(2+)-sensitive K(+) channels. In this review, the roles of Ca(2+) sparks in positive- and negative-feedback regulation of smooth muscle function are explored. We also propose that frequency and amplitude modulation of Ca(2+) sparks by contractile and relaxant agents is an important mechanism to regulate smooth muscle function.
Collapse
Affiliation(s)
- J H Jaggar
- Department of Pharmacology, College of Medicine, The University of Vermont, Burlington, Vermont 05405, USA
| | | | | | | |
Collapse
|
21
|
Taggart MJ, Wray S. Contribution of sarcoplasmic reticular calcium to smooth muscle contractile activation: gestational dependence in isolated rat uterus. J Physiol 1998; 511 ( Pt 1):133-44. [PMID: 9679169 PMCID: PMC2231104 DOI: 10.1111/j.1469-7793.1998.133bi.x] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/1998] [Accepted: 04/17/1998] [Indexed: 11/27/2022] Open
Abstract
1. The contribution of Ca2+ released from the sarcoplasmic reticulum (SR) to smooth muscle contractile activation remains poorly understood. By simultaneously monitoring cytosolic [Ca2+] ([Ca2+]i) and force in isolated rat uterine smooth muscle, we report the influence of SR Ca2+ release on contractility during conditions (a) of altered SR Ca2+ homeostasis and (b) where the only source of activating Ca2+ was derived from the SR. 2. In myometria of non-pregnant rats, ryanodine (1-50 microM), a modulator of calcium-induced calcium release (CICR), had no effect on the spontaneous [Ca2+]i or force transients. However, depletion of SR Ca2+ by inhibiting the SR Ca2+-ATPase (with cyclopiazonic acid (CPA), 20 microM) resulted in an enhancement of spontaneous [Ca2+]i and force transients. 3. In myometria of pregnant rats, although ryanodine had no effect in 40% of tissues studied it produced a small but significant enhancement of the integrated spontaneous [Ca2+]i and force transient in 60% of cases. The potentiating effects of CPA were enhanced in myometria of pregnant rats compared with non-pregnant rats, often resulting in maintained [Ca2+]i increases and contraction. 4. In zero external Ca2+, agonist-induced SR Ca2+ release resulted in transient increases in [Ca2+]i and force. The magnitude of these agonist-induced [Ca2+]i and force changes were significantly enhanced in myometria of pregnant rats. No evidence for agonist-induced Ca2+-independent force production was observed. 5. These results indicate that CICR plays little role in SR Ca2+ release from the myometrium, and that there are gestational-dependent alterations in the ability of SR Ca2+ mobilization to contribute to contractile activation. The implications of these findings for the co-ordination of myometrial [Ca2+]i signalling and contractility are discussed.
Collapse
Affiliation(s)
- M J Taggart
- The Physiological Laboratory, University of Liverpool, Liverpool L69 3BX, UK
| | | |
Collapse
|
22
|
Nakao K, Inoue Y, Okabe K, Kawarabayashi T, Kitamura K. Oxytocin enhances action potentials in pregnant human myometrium--a study with microelectrodes. Am J Obstet Gynecol 1997; 177:222-8. [PMID: 9240610 DOI: 10.1016/s0002-9378(97)70465-4] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
OBJECTIVE Our purpose was to quantitatively assess the effects of oxytocin on membrane properties in the pregnant human myometrium. STUDY DESIGN Specimens were obtained from the lower uterine segment during cesarean section at term. Electrical activity was recorded from individual cells by a conventional microelectrode method and the membrane functions were analyzed. RESULTS Two types of spontaneous action potentials were seen: a long plateau potential and a spike-like action potential. With no change in the resting membrane potential, low concentrations of oxytocin either evoked an action potential with a plateau phase, increased the amplitude and duration of the plateau potential, or increased the frequency of generation of action potentials. Oxytocin also lowered the threshold for evoking an action potential. Higher concentrations depolarized the membrane with an associated reduction in membrane resistance. CONCLUSION Oxytocin augments the excitability of pregnant human myometrial cells by multiple actions on the membrane, affecting both frequency and amplitude of action potentials.
Collapse
Affiliation(s)
- K Nakao
- Department of Pharmacology, Faculty of Medicine, Kyushu University, Japan
| | | | | | | | | |
Collapse
|
23
|
Cassoni P, Sapino A, Papotti M, Bussolati G. Oxytocin and oxytocin-analogue F314 inhibit cell proliferation and tumor growth of rat and mouse mammary carcinomas. Int J Cancer 1996; 66:817-20. [PMID: 8647655 DOI: 10.1002/(sici)1097-0215(19960611)66:6<817::aid-ijc18>3.0.co;2-#] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The effects of oxytocin (OT) and the OT-analogue F314 were investigated an xenografts of mouse mammary and colon carcinomas (TS/A and C26 tumors) and of rat mammary carcinoma (D-R3230AC). In all cases, proliferation was previously assessed by cell counting in cultured cell lines, whereas tumor growth was checked by serial measures of tumor volume and by evaluation of tumor weight at the end of the experiment. Both cell proliferation and tumor growth were inhibited by OT and F314. These data support previous observations on the inhibitory effect of OT and F314 on the growth of MCF7, T47D and MDA-MB231 human breast cancer cell lines and open new prospects for testing the effect of this hypothalamic hormone and its analogues on the control of breast carcinoma growth.
Collapse
Affiliation(s)
- P Cassoni
- Department of Biomedical Sciences and Oncology, University of Turin, 10126 Turin, Italy
| | | | | | | |
Collapse
|
24
|
Mironneau J, Macrez-Leprêtre N. Modulation of Ca2+ channels by alpha 1A- and alpha 2A-adrenoceptors in vascular myocytes: involvement of different transduction pathways. Cell Signal 1995; 7:471-9. [PMID: 8562308 DOI: 10.1016/0898-6568(95)00014-g] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Using subtype-selective agonists and antagonists, and antibodies directed against phosphatidylinositol and G-proteins, it has been shown in single myocytes of rat portal vein that both alpha 1A- and alpha 2A-adrenoceptors modulate Ca2+ channels through two distinct transduction pathways. alpha 1A-adrenoceptors couple with a Gq/G11 protein to activate a phospholipase C (PLC) which hydrolyses phosphatidylinositol to generate inositol 1,4,5-trisphosphate (InsP3) and diacylglycerol (DAG). InsP3 releases intracellular stored Ca2+ as evidenced by microspectrofluorimetry with Fura-2. The large and transient increase in [Ca2+]i activates chloride channels leading to a membrane depolarization that opens voltage-gated Ca2+ channels. In addition, DAG activates transiently protein kinase C (PKC) which increases the opening probability of Ca2+ channels through a phosphorylation-dependent process. alpha 2A-adrenoceptors do not induce Ca2+ release from intracellular stores but promote sustained Ca2+ influx through voltage-gated Ca2+ channels. The coupling involves a Gi-protein and activation of PKC by DAG. These two transduction pathways may be involved in the physiological action of noradrenaline in vascular smooth muscles.
Collapse
Affiliation(s)
- J Mironneau
- Laboratoire de Physiologie Cellulaire et Pharmacologie Moléculaire, URA CNRS 1489, Université de Bordeaux II, France
| | | |
Collapse
|