A review of recent insights into the role of the sarcoplasmic reticulum and Ca entry in uterine smooth muscle

Multiple pregnancies, the myometrium and the role of mechanical factors in the timing of labour

Multiple pregnancy remains a relatively common occurrence, but it is associated with increased risks of adverse outcomes for the mother and her babies and presents unique challenges to healthcare providers. This review will briefly discuss multiple pregnancies, their aetiology and their problems, including preterm birth, before reviewing the processes leading to normal labour onset and how they may be different in a multiple pregnancy. The mechanisms by which mechanical factors i.e., uterine distension or 'stretch' contribute to uterine excitability and the timing of labour onset will be the major focus, and how over distention may pre-dispose multiple pregnancies to preterm birth. This includes current thinking around the role of mechano (stretch) sensitive ion channels in the myometrium and changes to other important regulators of excitability and contraction which have been identified from studies using in vitro and in vivo models of uterine stretch. Physiological stimuli arising from the fetus(es) and placenta(s) will also be discussed. In reviewing what we know about the myometrium in multiple pregnancy in humans, the focus will be on twin pregnancy as it is the most common type of multiple pregnancy and has been the most studied.

The Pathophysiology of Labor Dystocia: Theme with Variations

Abnormally prolonged labor, or labor dystocia, is a common complication of parturition. It is the indication for about half of unplanned cesarean deliveries in low-risk nulliparous women. Reducing the rate of unplanned cesarean birth in the USA has been a public health priority over the last two decades with limited success. Labor dystocia is a complex disorder due to multiple causes with a common clinical outcome of slow cervical dilation and fetal descent. A better understanding of the pathophysiologic mechanisms of labor dystocia could lead to new clinical opportunities to increase the rate of normal vaginal delivery, reduce cesarean birth rates, and improve maternal and neonatal health. We conducted a literature review of the causes and pathophysiologic mechanisms of labor dystocia. We summarize known mechanisms supported by clinical and experimental data and newer hypotheses with less supporting evidence. We review recent data on uterine preparation for labor, uterine contractility, cervical preparation for labor, maternal obesity, cephalopelvic disproportion, fetal malposition, intrauterine infection, and maternal stress. We also describe current clinical approaches to preventing and managing labor dystocia. The variation in pathophysiologic causes of labor dystocia probably limits the utility of current general treatment options. However, treatments targeting specific underlying etiologies could be more effective. We found that the pathophysiologic basis of labor dystocia is under-researched, offering wide opportunities for translational investigation of individualized labor management, particularly regarding uterine metabolism and fetal position. More precise diagnostic tools and individualized therapies for labor dystocia might lead to better outcomes. We conclude that additional knowledge of parturition physiology coupled with rigorous clinical evaluation of novel biologically directed treatments could improve obstetric quality of care.

Inhibitory effect of Pyr6 (an Orai channel blocker) on agonist-induced contractions in rat uterus

AIM

Both human and rat myometrium express stromal interaction molecule (STIM) and Orai/ transient receptor potential canonical (TRPC) proteins, which are components of plasma membrane Ca²⁺ store-operated channels. There are reports that these proteins mediate agonist-induced Ca²⁺ influx in cultured myometrial cells. In this study, we aimed to determine the effects of Pyr6, an Orai channel blocker, on different agonist-induced contractions in isolated segments of rat uterus.

MAIN FINDINGS

In Ca²⁺ -free Tyrode's solution, Pyr6 (3 μM) promoted a reduction in both the magnitude and frequency of Ca²⁺ (1 mM)-induced uterine contractions after the addition of carbachol (CCh, 100 μM), but not after the addition of oxytocin (OT, 150 nM). In Ca²⁺ (0.18 mM)-Tyrode's solution, Pyr6 completely relaxed uterine contractions induced by both CCh and cloprostenol (300 nM), but not those induced by either KCI (40-80 mM) or OT. The addition of Pyr6 abolished the oscillatory uterine contractions induced by Ca²⁺ after the addition of cyclopiazonic acid (CPA, 10 μM). When pre-incubated (5 min), Pyr6 reduced the magnitude of both CCh-induced phasic and tonic contractions. The addition of Pyr2 (3 μM), an Orai and TRPC channel blocker, abolished uterine contractions induced by CCh or OT.

CONCLUSION

Considering Pyr6 as an Orai channel blocker and its inhibitory effect on uterine contractions induced by CCh, CPA, and cloprostenol, we suggest that Orai channels are required for the maintenance of contractions induced by these agonists in rat uterus.

Trophoblasts Modulate the Ca2+ Oscillation and Contraction of Myometrial Smooth Muscle Cells by Small Extracellular Vesicle- (sEV-) Mediated Exporting of miR-25-3p during Premature Labor

The placenta could transmit information to the maternal circulation via the secretion of small extracellular vesicles (sEVs), but little is known about whether and how these sEVs participate in premature labor (PTL). We speculate that miRNA plays an important role in sEV-mediated fetal-maternal information transmission. The present study was aimed at investigating whether the placenta can regulate the contraction of the maternal myometrium via sEV-mediated transmit of miR-25-3p during PTL. The expression of miR-25-3p and its targets Cav3.2 and SERCA2a in clinical samples, cells, and animal specimens was detected. The role of miR-25-3p was observed in the LPS-induced preterm labor mouse model. The sEVs from HTR-8/SVneo cells were characterized by transmission electron microscopy and nanoparticle tracking analysis. The Ca²⁺ oscillation in HMSMs was analyzed by an intracellular Ca²⁺ change tracking assay on a confocal microscope. The contraction of HMSMs was detected by a collagen matrix contraction assay. We found that miR-25-3p can directly bind to the 3′UTR of Cav3.2 and SERCA2a. The miR-25-3p level was decreased, and the expression of its targets Cav3.2 and SERCA2a was increased in the placenta and myometrium tissues of PTL patients. Forced upregulation of miR-25-3p reduced the oxidative stress and inflammation responses and the incidence of PTL in LPS-treated mice. The expression of miR-25-3p was not changed in LPS-stimulated human myometrial smooth muscle cells (HMSMs) but was strongly reduced in the trophoblast cell and its sEVs. Additionally, the trophoblast cell line HTR-8/SVneo could transmit miR-25-3p into HMSMs via sEVs. The sEVs derived from LPS-stimulated trophoblasts upregulated the expression of Cav3.2 and SERCA2a and triggered Ca²⁺ oscillation as well as the contraction of HMSMs; these effects were partially reversed by the overexpression of miR-25-3p in the trophoblasts. Further, the upregulation of miR-25-3p induced changes of Ca²⁺ oscillation and contraction of HMSMs mediated by sEVs which were also abrogated by the knockdown of miR-25-3p in HMSMs. The results demonstrated that miR-25-3p plays a crucial role in PTL via Cav3.2- and SERCA2a-mediated Ca²⁺ oscillation and contraction of HMSMs. PTL seems to be related to the decreased exosomal miR-25-3p content transmitted by the trophoblasts under inflammatory conditions.

Markers of vitamin D metabolism and premenstrual symptoms in healthy women with regular cycles

STUDY QUESTION

Are insufficient 25-hydroxyvitamin D (25(OH)D) concentrations, and other markers of vitamin D metabolism, associated with premenstrual symptoms in healthy women with regular menstrual cycles?

SUMMARY ANSWER

25(OH)D insufficiency was associated with specific physical premenstrual symptoms, while no associations were observed with psychological symptoms or with other markers of vitamin D metabolism.

WHAT IS KNOWN ALREADY

Prior studies evaluating vitamin D and premenstrual symptoms have yielded mixed results, and it is unknown whether 25(OH)D insufficiency and other markers of vitamin D metabolism are associated with premenstrual symptoms.

STUDY DESIGN, SIZE, DURATION

We used two cohorts of women with regular menstrual cycles; 1191 women aged 18-40 years in EAGeR (cross-sectional analysis of a prospective cohort within a randomized trial) and 76 women aged 18-44 years in BioCycle (prospective cohort). In EAGeR, premenstrual symptoms over the previous year were assessed at baseline, whereas in BioCycle, symptoms were assessed prospectively at multiple points over two menstrual cycles with symptoms queried over the previous week. In both cohorts, symptomatology was assessed via questionnaire regarding presence and severity of 14 physical and psychological symptoms the week before and after menses. Both studies measured 25(OH)D in serum. We also evaluated the association of additional markers of vitamin D metabolism and calcium homeostasis, including intact parathyroid hormone (iPTH), calcium (Ca), fibroblast growth factor 23 (FGF23), and 1,25 dihydroxyvitamin D (1,25(OH)2D) with premenstrual symptoms in the BioCycle cohort.

PARTICIPANTS/MATERIALS, SETTING, METHODS

One cohort of women actively seeking pregnancy (Effects of Aspirin in Gestation and Reproduction (EAGeR)) and one cohort not seeking pregnancy (BioCycle) were evaluated. Log-binomial regression was used to estimate risk ratios (RR) and 95% CIs for associations between insufficient 25(OH)D (<30 ng/ml) and individual premenstrual symptoms, adjusting for age, BMI, race, smoking, income, physical activity, and season of blood draw.

MAIN RESULTS AND THE ROLE OF CHANCE

25(OH)D insufficiency was associated with increased risk of breast fullness/tenderness (EAGeR RR 1.27, 95% CI 1.03, 1.55; BioCycle RR 1.37, 95% CI 0.56, 3.32) and generalized aches and pains (EAGeR RR 1.33, 95% CI 1.01, 1.78; BioCycle 1.36, 95% CI 0.41, 4.45), though results were imprecise in the BioCycle study. No associations were observed between insufficient 25(OH)D and psychological symptoms in either cohort. In BioCycle, iPTH, Ca, FGF23, and 1,25(OH) 2D were not associated with any premenstrual symptoms.

LIMITATIONS, REASONS FOR CAUTION

Results from the EAGeR study were limited by the study design, which assessed both 25(OH)D at baseline and individual premenstrual symptoms over the past year at the baseline. As such, reverse causality is a potential concern. Though premenstrual symptoms were assessed prospectively in the BioCycle cohort, the power was limited due to small sample size. However, results were fairly consistent across both studies.

WIDER IMPLICATIONS OF THE FINDINGS

Serum 25(OH)D may be associated with risk and severity of specific physical premenstrual symptoms.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the Intramural Research Program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland (Contract nos. HHSN267200603423, HHSN267200603424, and HHSN267200603426). JG.R. and D.L.K. have been funded by the NIH Medical Research Scholars Program, a public-private partnership jointly supported by the NIH and generous contributions to the Foundation for the NIH by the Doris Duke Charitable Foundation (Grant #2014194), the American Association for Dental Research, the Colgate Palmolive Company, Genentech, and other private donors. For a complete list, visit the foundation website at http://www.fnih.org. The authors have no conflicts of interest to disclose.

TRIAL REGISTRATION NUMBER

Clinicaltrials.gov NCT00467363.

Uterine contractions in rodent models and humans

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.

Smooth muscle cell-specific TMEM16A deletion does not alter Ca2+ signaling, uterine contraction, gestation length, or litter size in mice†

Ion channels in myometrial cells play critical roles in spontaneous and agonist-induced uterine contraction during the menstrual cycle, pregnancy maintenance, and parturition; thus, identifying the genes of ion channels in these cells and determining their roles are essential to understanding the biology of reproduction. Previous studies with in vitro functional and pharmacological approaches have produced controversial results regarding the presence and role of TMEM16A Ca2+-activated Cl- channels in myometrial cells. To unambiguously determine the function of this channel in these cells, we employed a genetic approach by using smooth muscle cell-specific TMEM16A deletion (i.e. TMEM16ASMKO) mice. We found that myometrial cells from TMEM16ASMKO mice generated the same pattern and magnitude in Ca2+ signals upon stimulation with KCl, oxytocin, and PGF2α compared to the isogenic control myometrial cells. At the uterine tissue level, TMEM16A deletion also did not cause detectable changes in either spontaneous or agonist (i.e. KCl, oxytocin, and PGF2α)-induced contractions. Moreover, in vivo the TMEM16ASMKO mice gave birth at full term with the same litter size as genetically identical control mice. Finally, TMEM16A immunostaining in both control and TMEM16ASMKO mice revealed that this protein was highly expressed in the endometrial stroma, but did not co-localize with a smooth muscle specific marker MYH11. Collectively, these results unequivocally demonstrate that TMEM16A does not serve as a pacemaking channel for spontaneous uterine contraction, neither does it function as a depolarizing channel for agonist-evoked uterine contraction. Yet these two functions could underlie the normal gestation length and litter size in the TMEM16ASMKO mice.

Marantodes pumilum (Blume) Kuntze (Kacip Fatimah) stimulates uterine contraction in rats in post-partum period

ETHNOPHARMACOLOGICAL RELEVANCE

Marantodes pumilum (Blume) Kuntze has traditionally been used to firm the uterus after delivery, however scientific evidences behind this claim is still lacking.

AIMS OF STUDY

To demonstrate Marantodes pumilum leaves aqueous extract (MPE) has an effect on uterine contraction after delivery and to elucidate the molecular mechanisms involved.

METHODS

Day-1 post-delivery female rats were given MPE (100, 250 and 500 mg/kg/day) orally for seven consecutive days. A day after the last treatment (day-8), rats were sacrificed and uteri were harvested and subjected for ex-vivo contraction study using organ bath followed by protein expression and distribution study by Western blotting and immunohistochemistry techniques, respectively. The proteins of interest include calmodulin-CaM, myosin light chain kinase-MLCK, sarcoplasmic reticulum Ca²⁺-ATPase (SERCA), G-protein α and β (Gα and Gβ), inositol-triphosphate 3-kinase (IP3K), oxytocin receptor-OTR, prostaglandin (PGF)2α receptor-PGFR, muscarinic receptor-MAChR and estrogen receptor (ER) isoforms α and β. Levels of estradiol and progesterone in serum were determined by enzyme-linked immunoassay (ELISA).

RESULTS

Ex-vivo contraction study revealed the force of uterine contraction increased with increasing doses of MPE. In addition, expression of CaM, MLCK, SERCA, Gα, Gβ, IP3K, OTR, PGF2α, MAChR, Erα and ERβ in the uterus increased with increasing doses of MPE. Serum analysis indicate that estradiol levels decreased while progesterone levels remained low at day-8 post-partum in rats receiving 250 and 500 mg/kg/day MPE.

CONCLUSIONS

These findings support the claims that MPE help to firm the uterus and pave the way for its use as a uterotonic agent after delivery.

The Myometrium: From Excitation to Contractions and Labour

We start by describing the functions of the uterus, its structure, both gross and fine, innervation and blood supply. It is interesting to note the diversity of the female's reproductive tract between species and to remember it when working with different animal models. Myocytes are the overwhelming cell type of the uterus (>95%) and our focus. Their function is to contract, and they have an intrinsic pacemaker and rhythmicity, which is modified by hormones, stretch, paracrine factors and the extracellular environment. We discuss evidence or not for pacemaker cells in the uterus. We also describe the sarcoplasmic reticulum (SR) in some detail, as it is relevant to calcium signalling and excitability. Ion channels, including store-operated ones, their contributions to excitability and action potentials, are covered. The main pathway to excitation is from depolarisation opening voltage-gated Ca²⁺ channels. Much of what happens downstream of excitability is common to other smooth muscles, with force depending upon the balance of myosin light kinase and phosphatase. Mechanisms of maintaining Ca²⁺ balance within the myocytes are discussed. Metabolism, and how it is intertwined with activity, blood flow and pH, is covered. Growth of the myometrium and changes in contractile proteins with pregnancy and parturition are also detailed. We finish with a description of uterine activity and why it is important, covering progression to labour as well as preterm and dysfunctional labours. We conclude by highlighting progress made and where further efforts are required.

Serum vitamin D concentrations in young Turkish women with primary dysmenorrhea: A randomized controlled study

OBJECTIVE

This study aims to investigate the possible role of vitamin D deficiency in primary dysmenorrhea by assessing serum 25-hydroxyvitamin D₃ levels in a cohort which includes young Turkish women with primary dysmenorrhea and healthy controls.

MATERIALS AND METHODS

A total of 683 women who were aged between 18 and 25 years and who were consecutively admitted to the study center were eligible. After the exclusion of 55 women, 184 women with primary dysmenorrhea were randomly assigned into the dysmenorrhea group and 184 women without dysmenorrhea were randomly allocated into the control group.

RESULTS

The dysmenorrhea group had significantly less consumption of dairy products (p = 0.001), lower serum calcium (p = 0.001), lower serum vitamin D (p = 0.001) and higher serum parathyroid hormone (p = 0.001) than those of the control group. Hyperparathyroidism was significantly less frequent whereas vitamin D deficiency was significantly more frequent in the dysmenorrhea group (p = 0.001 for each). The dysmenorrhea patients with vitamin D deficiency had significantly higher visual analogue scale (VAS) scores (p = 0.001). Depression, irritability, mood swings, fatigue, headache and breast tenderness were significantly more frequent in the vitamin D deficiency group (p < 0.05 for all). The VAS scores of the dysmenorrhea patients correlated positively and significantly with serum parathyroid hormone levels (r = 0.666, p = 0.001) whereas these VAS scores correlated negatively and significantly with serum vitamin D levels (r = -0.713, p = 0.001).

DISCUSSION

The significant and positive correlation between vitamin D levels and VAS scores and the significant reduction in serum vitamin D levels of the dysmenorrhea patients designate the possible role of vitamin D deficiency in the primary dysmenorrhea.

Gestation changes sodium pump isoform expression, leading to changes in ouabain sensitivity, contractility, and intracellular calcium in rat uterus

Developmental and tissue‐specific differences in isoforms allow Na⁺, K⁺‐ATPase function to be tightly regulated, as they control sensitivity to ions and inhibitors. Uterine contraction relies on the activity of the Na⁺, K⁺ATPase, which creates ionic gradients that drive excitation‐contraction coupling. It is unknown whether Na⁺, K⁺ATPase isoforms are regulated throughout pregnancy or whether they have a direct role in modulating uterine contractility. We hypothesized that gestation‐dependent differential expression of isoforms would affect contractile responses to Na⁺, K⁺ATPase α subunit inhibition with ouabain. Our aims were therefore: (1) to determine the gestation‐dependent expression of mRNA transcripts, protein abundance and tissue distribution of Na⁺, K⁺ATPase isoforms in myometrium; (2) to investigate the functional effects of differential isoform expression via ouabain sensitivity; and (3) if changes in contractile responses can be explained by changes in intracellular [Ca²⁺]. Changes in abundance and distribution of the Na⁺, K⁺ATPase α, β and FXYD1 and 2 isoforms, were studied in rat uterus from nonpregnant, and early, mid‐, and term gestation. All α, β subunit isoforms (1,2,3) and FXYD1 were detected but FXYD2 was absent. The α1 and β1 isoforms were unchanged throughout pregnancy, whereas α2 and α3 significant decreased at term while β2 and FXYD1 significantly increased from mid‐term onwards. These changes in expression correlated with increased functional sensitivity to ouabain, and parallel changes in intracellular Ca²⁺, measured with Indo‐1. In conclusion, gestation induces specific regulatory changes in expression of Na⁺, K⁺ATPase isoforms in the uterus which influence contractility and may be related to the physiological requirements for successful pregnancy and delivery.

Seipin deficiency leads to defective parturition in mice

Seipin is an integral endoplasmic reticulum membrane protein encoded by Berardinelli-Seip congenital lipodystrophy type 2 (BSCL2/Bscl2) gene. Seipin deficiency results in lipodystrophy, diabetes, muscle hypertrophy, and male infertility in both human and mouse. Seipin function in female reproduction is unknown. Bscl2-/- dams had normal embryo implantation and body weight gain during pregnancy but reduced delivery rates from 2nd to 4th pregnancies and reduced numbers of pups delivered from 1st to 4th pregnancies. Characterization of first pregnancy revealed increased gestation period and parturition problems, including uterine prolapse, difficulty in delivery, undelivered fetuses, and undelivered tissues in Bscl2-/- females. Bscl2-/- uterine weight was comparable to control at 3 weeks old but significantly increased with myometrial hypertrophy at 10 months old. In situ hybridization revealed relatively low level of Bscl2 mRNA expression in myometrium throughout pregnancy and postpartum but high level of expression in uterine luminal epithelium, suggesting that systemic effect (e.g. elevated glucose and insulin levels) rather than local seipin-deficiency in myometrium might be a main contributing factor to myometrial hypertrophy. On near-term gestation day 18.5 (D18.5), Bscl2-/- females had normal levels of serum progesterone and 17β-estradiol, indicating functional ovary and placenta. Proliferating Cell Nuclear Antigen (PCNA) staining showed minimal myometrial cell proliferation in both D18.5 Bscl2+/+ and Bscl2-/- uteri. There was strong LC3 immunostaining in Bscl2+/+ and Bscl2-/- peripartum myometrium and increased LC3 staining in Bscl2-/- peripartum uterine luminal epithelium, suggesting a potential role of seipin in regulating autophagy in uterine luminal epithelium but not myometrium. This study demonstrates an association of seipin with myometrium and parturition.

Pharmacological characterization of store-operated calcium channels (SOCC) in myometrium of non-pregnant buffaloes (Bubalus bubalis)

Present study unravels the existence and functional involvement of store-operated calcium channels in myometrium of non-pregnant buffaloes. Uteri along with ovaries were collected from nondescript adult cyclic buffaloes immediately after their slaughter from the local abattoir. Under a resting tension of 2 gm, effect of CaCl2 in the absence and presence of different blockers/modulators of calcium regulatory pathways was recorded. CaCl2 produced concentration-dependent contraction and the DRCs of CaCl2 were significantly (P < 0.05) shifted to right in the presence of nifedipine (1 μM) + CPA (10 μM) and nifedipine (1 μM) + CPA (10 μM) + 2-APB (10 μM). After incubation of myometrial strips with nifedipine + CPA in Ca2+ free RLS (-Ca2+), histamine was added to the tissue bath to allow the release of Ca2+ from SR while having already blocked the SERCA by CPA (10 μM) to prevent the Ca2+ reuptake into SR and nifedipine was used to prevent entry of Ca2+ from VDCC when calcium chloride was added and 2-aminoethoxydiphenyl borate (2-APB) (10 μM) was used as a non-specific blocker of store-operated calcium channels (SOCC). In the presence of nifedipine + CPA + 2-APB, calcium chloride produced contractile effect and the maximal contraction observed was only 0.62±0.14 g (n=6) which was significantly (P<0.05) lower compared to that of 1.20±0.10 g (n=6) in the presence of nifedipine + CPA in normal Ca2+ free RLS. This observation indicated that after depletion of Ca2+ from Sarcoplasmic reticular, SOCC got activated and in the presence of 2- APB, response was significantly reduced. Thus implying the functional involvement of store-operated calcium channels in myometrium of non-pregnant buffaloes.

Influence of smooth muscle contractility by inhibition of crac channels activity

The present in vitro study was focused on the differences in expression and activity of calcium release-activated calcium (CRAC) channels of human term-pregnant and non-pregnant myometrium. The expression of Orai1 protein, as a functional subunit of CRAC channel, was significantly higher than in non-pregnant myometrium. Lower Orai1 protein expression did not influence the amplitude of contractile response of term-pregnant myometrium, but higher Orai1 expression observed in non-pregnant myometrium was related to the different influence of CRAC blocker on contraction frequency.

Biomechanics of the human uterus

The appropriate biomechanical function of the uterus is required for the execution of human reproduction. These functions range from aiding the transport of the embryo to the implantation site, to remodeling its tissue walls to host the placenta, to protecting the fetus during gestation, to contracting forcefully for a safe parturition and postpartum, to remodeling back to its nonpregnant condition to renew the cycle of menstruation. To serve these remarkably diverse functions, the uterus is optimally geared with evolving and contractile muscle and tissue layers that are cued by chemical, hormonal, electrical, and mechanical signals. The relationship between these highly active biological signaling mechanisms and uterine biomechanical function is not completely understood for normal reproductive processes and pathological conditions such as adenomyosis, endometriosis, infertility and preterm labor. Animal studies have illuminated the rich structural function of the uterus, particularly in pregnancy. In humans, medical imaging techniques in ultrasound and magnetic resonance have been combined with computational engineering techniques to characterize the uterus in vivo, and advanced experimental techniques have explored uterine function using ex vivo tissue samples. The collective evidence presented in this review gives an overall perspective on uterine biomechanics related to both its nonpregnant and pregnant function, highlighting open research topics in the field. Additionally, uterine disease and infertility are discussed in the context of tissue injury and repair processes and the role of computational modeling in uncovering etiologies of disease. WIREs Syst Biol Med 2017, 9:e1388. doi: 10.1002/wsbm.1388 For further resources related to this article, please visit the WIREs website.

The role of STIM1 and SOCE in smooth muscle contractility

Contraction is a central feature for skeletal, cardiac and smooth muscle; this unique feature is largely dependent on calcium (Ca²⁺) signaling and therefore maintenance of internal Ca²⁺ stores. Stromal interaction molecule 1 (STIM1) is a single-pass transmembrane protein that functions as a Ca²⁺ sensor for the activation store-operated calcium channels (SOCCs) on the plasma membrane in response to depleted internal sarco(endo)plasmic (S/ER) reticulum Ca²⁺ stores. STIM1 was initially characterized in non-excitable cells; however, evidence from both animal models and human mutations suggests a role for STIM1 in modulating Ca²⁺ homeostasis in excitable tissues as well. STIM1-dependent SOCE is particularly important in tissues undergoing sustained contraction, leading us to believe STIM1 may play a role in smooth muscle contraction. To date, the role of STIM1 in smooth muscle is unknown. In this review, we provide a brief overview of the role of STIM1-dependent SOCE in striated muscle and build off that knowledge to investigate whether STIM1 contributes to smooth muscle contractility. We conclude by discussing the translational implications of targeting STIM1 in the treatment of smooth muscle disorders.

Ryanodine receptor type 3 does not contribute to contractions in the mouse myometrium regardless of pregnancy

Ryanodine receptor type 3 (RyR3) is expressed in myometrial smooth muscle cells (MSMCs). The short isoform of RyR3 is a dominant negative variant (DN-RyR3) and negatively regulates the functions of RyR2 and full-length (FL)-RyR3. DN-RyR3 has been suggested to function as a major RyR3 isoform in non-pregnant (NP) mouse MSMCs, and FL-RyR3 may also be upregulated during pregnancy (P). This increase in the FL-RyR3/DN-RyR3 ratio may contribute to the strong contractions by MSMCs for parturition. In the present study, spontaneous contractions by the myometrium in NP and P mice were highly susceptible to nifedipine but were not affected by ryanodine. Ca²⁺ image analyses under a voltage clamp revealed that the influx of Ca²⁺ through voltage-dependent Ca²⁺ channels did not cause the release of Ca²⁺ from the sarcoplasmic reticulum (SR). Cytosolic Ca²⁺ concentrations ([Ca²⁺]_cyt) in MSMCs were not affected by caffeine. Despite the abundant expression of large conductance Ca²⁺-activated K⁺ channels in MSMCs, spontaneous transient outward currents were not observed in the resting state because of the substantive lack of Ca²⁺ sparks. Quantitative PCR and Western blot analyses indicated that DN-RyR3 was strongly expressed in the NP myometrium, while the expression of FL-RyR3 and DN-RyR3 was markedly reduced in the P myometrium. The messenger RNA (mRNA) expression of RyR2 and RyR1 was negligible in the NP and P myometria. Moreover, RyR3 knockout mice may become pregnant and deliver normally. Thus, we concluded that none of the RyR subtypes, including RyR3, play a significant role in the regulation of [Ca²⁺]_cyt in or contractions by mouse MSMCs regardless of pregnancy.

Vitamin K3 inhibits mouse uterine contraction in vitro via interference with the calcium transfer and the potassium channels

Previous studies have demonstrated vitamin K3 had a great relief to smooth muscle spastic disorders, but no researches have yet pinpointed its possible anti-contractile activity in the uterus. Here, we evaluated the effect of vitamin K3 on myometrial contractility and explored the possible mechanisms of vitamin K3 action. Myograph apparatus were used to record the changes in contractility of isolated mouse uterine strips in a tissue bath. Uterine strips were exposed to vitamin K3 or vehicle. Vitamin K3 suppressed spontaneous contractions in a concentration dependent manner. It significantly decreased the contractile frequency induced by PGF2ɑ but not their amplitude (expect 58.0 μM). Prior incubation with vitamin K3 reduced the effectiveness of PGF2ɑ-induced contraction. The antispasmodic effect of vitamin K3 was also sensitive to potassium channel blockers, such as tetraethylammonium, 4-aminopyridine, iberiotoxin) but not to the nitric oxide related pathway blockers. High concentrations (29.0, 58.0 μM) of vitamin K3 weakened the Ca(2+) dose response and inhibited phase 1 contraction (intracellular stored calcium release). These dates suggest that vitamin K3 specifically suppresses myometrial contractility by affecting calcium and potassium channels; thus, this approach has potential therapy for uterine contractile activity related disorders.

A short review of adipokines, smooth muscle and uterine contractility

Obesity is a major health problem worldwide. The prevalence of obesity is increasing in both developed and developing countries. In the UK, for example, 60% of adults are overweight and 25% are obese. Obesity is associated with many pathological complications including respiratory, cardiovascular and endocrine, but it also affects fertility and is associated with many reproductive complications. This has led us and others to investigate links between women with high BMI, pregnancy outcome and uterine function. These studies in turn have led investigators to ask how obesity can have such an impact on reproduction and, as part of this, to consider the role of the adipokines released from adipose tissues. Our focus in this short review is on adipokines and myometrial activity, and for completeness we overview their effects on other smooth muscles. To date four adipokines (leptin, visfatin, apelin and ghrelin) have been investigated and all affect myometrial contractility, but some more potently than others. We consider the possible mechanisms involved in how adipokines may modify uterine contractility, and discuss the potential impact on labor and delivery.

Progress in understanding electro-mechanical signalling in the myometrium

In this review, we give a state-of-the-art account of uterine contractility, focussing on excitation-contraction (electro-mechanical) coupling (ECC). This will show how electrophysiological data and intracellular calcium measurements can be related to more modern techniques such as confocal microscopy and molecular biology, to advance our understanding of mechanical output and its modulation in the smooth muscle of the uterus, the myometrium. This new knowledge and understanding, for example concerning the role of the sarcoplasmic reticulum (SR), or stretch-activated K channels, when linked to biochemical and molecular pathways, provides a clearer and better informed basis for the development of new drugs and targets. These are urgently needed to combat dysfunctions in excitation-contraction coupling that are clinically challenging, such as preterm labour, slow to progress labours and post-partum haemorrhage. It remains the case that scientific progress still needs to be made in areas such as pacemaking and understanding interactions between the uterine environment and ion channel activity.

Orai1 protein expression and the role of calcium release-activated calcium channels in the contraction of human term-pregnant and non-pregnant myometrium

AIM

This experimental in vitro study examined differences in the expression and activity of calcium release-activated calcium (CRAC) channels of human term-pregnant and non-pregnant myometrium.

MATERIAL AND METHODS

The tissue samples were obtained from term-pregnant myometrium in labor of women undergoing cesarean section and from non-pregnant myometrium of women undergoing total hysterectomy due to uterine myoma. The expression of Orai1 protein, a pore-forming subunit of CRAC channels, in human myometrium was examined using immunohistochemistry. CRAC channel involvement in the amplitude and frequency of myometrial contractions was evaluated in vitro using a tissue bath method with a CRAC ion channel blocker 3-fluropyridine-4-carboxylic acid (FPCA).

RESULTS

Decreased Orai1 expression was observed in human term-pregnant laboring myometrium compared with non-pregnant myometrium. However, the initial oxytocin-induced contraction of myometrium was significantly suppressed at different doses of FPCA in both non-pregnant human isolated myometrium and non-pregnant myometrium. The frequency of contractions was the most significantly reduced at the lowest dose of FPCA in non-pregnant myometrium and remained suppressed at all doses of FPCA in term-pregnant myometrium. Salbutamol was shown as more effective in suppression of amplitude in term-pregnant isolated myometrium.

CONCLUSION

Our results provide the first information about the changes in the Orai1 protein expression and activity of human myometrial CRAC channels in term-pregnant laboring myometrium.

The effects of Ginseng Java root extract on uterine contractility in nonpregnant rats

Ginseng Java or Talinum paniculatum (Jacq.) Geartn has long been used in herbal recipes because of its various therapeutic properties. Ginseng Java is believed to be beneficial to the female reproductive system by inducing lactation and restoring uterine functions after the postpartum period. There are, however, no scientific data on verifying the effects on the uterus to support its therapeutic relevance. Therefore, the purpose of this study was to investigate the effects of Ginseng Java root extract and its possible mechanism(s) of action on uterine contractility. Female virgin rats were humanely killed by CO₂ asphyxia and uteri removed. Isometric force was measured in strips of longitudinal myometrium. The effects of Ginseng Java root extract at its IC₅₀ concentration (0.23 mg/mL) on spontaneous, oxytocin‐induced (10 nmol/L), and depolarized (KCl 40 mmol/L) contraction were investigated. After establishing regular phasic contractions, the application of Java root extract significantly inhibited spontaneous uterine contractility (n =5). The extract also significantly inhibited the contraction induced by high KCl solution (n =5) and oxytocin (n =5). The extract also inhibited oxytocin‐induced contraction in the absence of external Ca entry (n =7) and the tonic force induced by oxytocin in the presence of high KCl solution. Taken together, the data demonstrate a potent and consistent ability of extract from Ginseng Java root to reduce myometrial contractility. The tocolytic effects were demonstrated on both spontaneous and agonist‐induced contractions. The fact that force was inhibited in depolarized conditions suggests that the possible mechanisms may be blockade of Ca influx via L‐type Ca channels. The data in Ca‐free solutions suggest that the extract also reduces IP₃‐induced Ca release from the internal store. These tocolytic effects do not support the use of ginseng to help with postpartum contractility, but instead suggest it may be helpful in reducing inappropriate uterine contractions, such as in threatened preterm delivery.

The data demonstrate a potent and consistent ability of extract from Ginseng Java root to reduce myometrial contractility. The tocolytic effects were demonstrated on both spontaneous and agonist‐induced contractions.

Store-operated Ca²⁺ entry and depolarization explain the anomalous behaviour of myometrial SR: effects of SERCA inhibition on electrical activity, Ca²⁺ and force

•

SERCA pump inhibition by CPA caused membrane depolarization, activation of action potentials, Ca²⁺ spikes and force.

•

Depletion of Ca²⁺ store by agonists leads to membrane depolarization and activation of electrical and mechanical activity.

•

Ca²⁺ release/Ca²⁺ entry coupling is playing a key role in control of spontaneous electrical and mechanical activity in rat pregnant myometrium.

In the myometrium SR Ca²⁺ depletion promotes an increase in force but unlike several other smooth muscles, there is no Ca²⁺ sparks-STOCs coupling mechanism to explain this. Given the importance of the control of contractility for successful parturition, we have examined, in pregnant rat myometrium, the effects of SR Ca²⁺-ATPase (SERCA) inhibition on the temporal relationship between action potentials, Ca²⁺ transients and force. Simultaneous recording of electrical activity, calcium and force showed that SERCA inhibition, by cyclopiazonic acid (CPA 20 μM), caused time-dependent changes in excitability, most noticeably depolarization and elevations of baseline [Ca²⁺]_i and force. At the onset of these changes there was a prolongation of the bursts of action potentials and a corresponding series of Ca²⁺ spikes, which increased the amplitude and duration of contractions. As the rise of baseline Ca²⁺ and depolarization continued a point was reached when electrical and Ca²⁺ spikes and phasic contractions ceased, and a maintained, tonic force and Ca²⁺ was produced. Lanthanum, a non-selective blocker of store-operated Ca²⁺ entry, but not the L-type Ca²⁺ channel blocker nifedipine (1–10 μM), could abolish the maintained force and calcium. Application of the agonist, carbachol, produced similar effects to CPA, i.e. depolarization, elevation of force and calcium. A brief, high concentration of carbachol, to cause SR Ca²⁺ depletion without eliciting receptor-operated channel opening, also produced these results. The data obtained suggest that in pregnant rats SR Ca²⁺ release is coupled to marked Ca²⁺ entry, via store operated Ca²⁺ channels, leading to depolarization and enhanced electrical and mechanical activity.

Combination of tocolytic agents for inhibiting preterm labour

BACKGROUND

Preterm birth represents the single largest cause of mortality and morbidity for newborns and a major cause of morbidity for pregnant women. Tocolytic agents include a wide range of drugs that can inhibit labour to prolong pregnancy. This may gain time to allow the fetus to mature further before being born, permit antenatal corticosteroid administration for lung maturation, and allow time for intra-uterine transfer to a hospital with neonatal intensive care facilities. However, some tocolytic drugs are associated with severe side effects. Combinations of tocolytic drugs may be more effective over single tocolytic agents or no intervention, without adversely affecting the mother or neonate.

OBJECTIVES

To assess the effects on maternal, fetal and neonatal outcomes of any combination of tocolytic drugs for the treatment of preterm labour when compared with any other treatment, no treatment or placebo.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 January 2014) and reference lists of retrieved studies.

SELECTION CRITERIA

We included randomised controlled trials comparing a combination of tocolytic agents, administered by any route or any dose, for inhibiting preterm labour versus any other treatment (including other combinations of tocolytics or single tocolytics), no intervention or placebo.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed study reports for eligibility, carried out data extraction and assessed risk of bias.

MAIN RESULTS

Eleven studies met our inclusion criteria. Two studies did not report any outcome data relevant to the review, so the results of the review are based on nine trials that contributed data. Primary outcomes were perinatal mortality, serious maternal or infant outcomes, adverse drug reactions, birth before 48 hours of trial entry, birth before 34 weeks' gestation and preterm neonates delivered without a full course of antenatal steroids completed 24 hours before birth. The quality of evidence in included trials was mixed; only three of the trials were placebo controlled.The included trials examined seven different comparisons: intravenous (IV) ritodrine plus oral or IV magnesium (sulphate or gluconate) versus IV ritodrine alone (three trials, 231 women); IV ritodrine plus indomethacin suppositories versus IV ritodrine alone (one trial, 208 women); IV ritodrine plus vaginal progesterone versus IV ritodrine alone (one trial, 83 women); IV hexoprenaline sulphate plus IV magnesium hydrochloride versus IV hexoprenaline sulphate alone (one trial, 24 women); IV fenoterol plus oral naproxen versus IV fenoterol alone (one trial, 72 women); oral pentoxifylline plus IV magnesium sulphate plus IV fenoterol versus IV magnesium sulphate plus IV fenoterol (one trial, 125 women); and, IV terbutaline plus oral metoprolol versus IV terbutaline alone (one trial, 17 women). Few studies with small numbers of women were available for each comparison, hence very little data were pooled in meta-analysis. In all trials, not many of the primary outcomes were reported.Three trials examined intravenous (IV) ritodrine plus IV or oral magnesium (sulphate or gluconate) compared with IV ritodrine alone. One study, with 41 women, reported more adverse drug reactions in the group receiving the combined tocolytics (risk ratio (RR) 7.79, 95% confidence interval (CI) 1.11 to 54.80). Two trials reported discontinuation of therapy due to severe side effects (results were not combined due to high statistical heterogeneity, I² = 83%); one trial reported increased severe side effects in the group receiving IV ritodrine alone (RR 7.79, 95% CI 1.11 to 54.80, 41 women); in the other trial there was no clear difference between groups (RR 0.23, 95% CI 0.03 to 1.97, 107 women). Other primary outcomes were not reported.One trial assessed IV ritodrine plus indomethacin suppositories versus IV ritodrine alone. There were no significant differences between groups for perinatal mortality or serious neonatal morbidity. Results for other primary outcomes were not reported.There were no significant differences between groups receiving IV ritodrine plus vaginal progesterone compared with IV ritodrine alone for most outcomes reported, although the latency period (time from recruitment to delivery) was increased in the group receiving the combination of tocolytics.For other combinations of tocolytic agents, primary outcomes were rarely reported and for secondary outcomes results did not demonstrate differences between groups.

AUTHORS' CONCLUSIONS

It is unclear whether a combination of tocolytic drugs for preterm labour is more advantageous for women and/or newborns due to a lack of large, well-designed trials including the outcomes of interest. There are no trials of combination regimens using widely used tocolytic agents, such as calcium channel blockers (nifedipine) and/or oxytocin receptor antagonists (atosiban). Further trials are needed before specific conclusions on use of combination tocolytic therapy for preterm labour can be made.

STIM and Orai isoform expression in pregnant human myometrium: a potential role in calcium signaling during pregnancy

Store-operated calcium (Ca(2+)) entry (SOCE) can be mediated by two novel proteins, STIM/Orai. We have previously demonstrated that members of the TRPC family, putative basal and store operated calcium entry channels, are present in human myometrium and regulated by labor associated stimuli IL-1β and mechanical stretch. Although STIM and Orai isoforms (1-3) have been reported in other smooth muscle cell types, there is little known about the expression or gestational regulation of STIM and Orai expression in human myometrium. Total RNA was isolated from lower segment human myometrial biopsies obtained at Cesarean section from women at the time of preterm no labor (PTNL), preterm labor (PTL), term non-labor (TNL), and term with labor (TL); primary cultured human uterine smooth muscle cells, and a human myometrial cell line (hTERT-HM). STIM1-2, and Orai1-3 mRNA expression was assessed by quantitative real-time PCR. All five genes were expressed in myometrial tissue and cultured cells. STIM1-2 and Orai2-3 expression was significantly lower in cultured cells compared tissue. This has implications with regard investigation of the contribution of these proteins in cultured cells. Orai2 was the most abundant Orai isoform in human myometrium. Expression of STIM1-2/Orai1-3 did not alter with the onset of labor. Orai1 mRNA expression in cultured cells was enhanced by IL-1β treatment. This novel report of STIM1-2 and Orai1-3 mRNA expression in pregnant human myometrium and Orai1 regulation by IL-1β indicates a potential role for these proteins in calcium signaling in human myometrium during pregnancy.

Androgens in pregnancy: roles in parturition

BACKGROUND

Understanding the physiology of pregnancy enables effective management of pregnancy complications that could otherwise be life threatening for both mother and fetus. A functional uterus (i) retains the fetus in utero during pregnancy without initiating stretch-induced contractions and (ii) is able to dilate the cervix and contract the myometrium at term to deliver the fetus. The onset of labour is associated with successful cervical remodelling and contraction of myometrium, arising from concomitant activation of uterine immune and endocrine systems. A large body of evidence suggests that actions of local steroid hormones may drive changes occurring in the uterine microenvironment at term. Although there have been a number of studies considering the potential role(s) played by progesterone and estrogen at the time of parturition, the bio-availability and effects of androgens during pregnancy have received less scrutiny. The aim of this review is to highlight potential roles of androgens in the biology of pregnancy and parturition.

METHODS

A review of published literature was performed to address (i) androgen concentrations, including biosynthesis and clearance, in maternal and fetal compartments throughout gestation, (ii) associations of androgen concentrations with adverse pregnancy outcomes, (iii) the role of androgens in the physiology of cervical remodelling and finally (iv) the role of androgens in the physiology of myometrial function including any impact on contractility.

RESULTS

Some, but not all, androgens increase throughout gestation in maternal circulation. The effects of this increase are not fully understood; however, evidence suggests that increased androgens might regulate key processes during pregnancy and parturition. For example, androgens are believed to be critical for cervical remodelling at term, in particular cervical ripening, via regulation of cervical collagen fibril organization. Additionally, a number of studies highlight potential roles for androgens in myometrial relaxation via non-genomic, AR-independent pathways critical for the pregnancy reaching term. Understanding of the molecular events leading to myometrial relaxation is an important step towards development of novel targeted tocolytic drugs.

CONCLUSIONS

The increase in androgen levels throughout gestation is likely to be important for establishment and maintenance of pregnancy and initiation of parturition. Further investigation of the underlying mechanisms of androgen action on cervical remodelling and myometrial contractility is needed. The insights gained may facilitate the development of new therapeutic approaches to manage pregnancy complications such as preterm birth.

Dexmedetomidine modifies uterine contractions in pregnancy terms of rats

OBJECTIVES

The present study was aimed at determining the effective doses of Dexmedetomidine (Dex) involved in amplitude of contraction-force and frequency of uterine rings in pregnancy terms of rats. All experiments involving animal subjects were carried out with the approval of animal care and use Ethical Committee of Cukurova University. Experiments were performed on female Albino-Wistar rats (200-260 g; n = 40).

MATERIALS AND METHODS

Uterine rings from pregnant rats were placed in organ bath with Krebs and calcium ion (Ca(2+))-free solutions to record and exposed to serially increasing log10 concentrations of Dex.

RESULTS

In Krebs solution, while Dex caused an increase in the spontaneous contraction-forces in all pregnancy terms of rats in a significant dose-dependent manner, it led to a decrease in contraction-frequency in late-pregnancy term of rats. In Ca(2+)-free, the spontaneous contraction-force decreased in late-pregnancy term and increased in early and middle-pregnancy terms. In addition, while Dex increased the contraction-frequency in early and middle-pregnancy terms, it decreased in late-pregnancy term in a dose-dependent manner.

STATISTICAL ANALYSIS USED

The data were subjected to one-way analysis of variance. Repeated measures were employed for comparison of several group means through the Tukey post-hoc test (SPSS 10.00 Inc., Chicago, Ill, USA). P < 0.05 was considered statistically significant.

CONCLUSIONS

This study suggested that Dex might differently alter the spontaneous contraction-forces and contraction-frequencies of uterine rings in all pregnancy terms of rats in Krebs and Ca(2+)-free solutions.

Characterization of the myometrial transcriptome in women with an arrest of dilatation during labor

OBJECTIVE

The molecular basis of failure to progress in labor is poorly understood. This study was undertaken to characterize the myometrial transcriptome of patients with an arrest of dilatation (AODIL).

STUDY DESIGN

Human myometrium was prospectively collected from women in the following groups: (1) spontaneous term labor (TL; n=29) and (2) arrest of dilatation (AODIL; n=14). Gene expression was characterized using Illumina® HumanHT-12 microarrays. A moderated Student's t-test and false discovery rate adjustment were used for analysis. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) of selected genes was performed in an independent sample set. Pathway analysis was performed on the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway database using Pathway Analysis with Down-weighting of Overlapping Genes (PADOG). The MetaCore knowledge base was also searched for pathway analysis.

RESULTS

(1) Forty-two differentially expressed genes were identified in women with an AODIL; (2) gene ontology analysis indicated enrichment of biological processes, which included regulation of angiogenesis, response to hypoxia, inflammatory response, and chemokine-mediated signaling pathway. Enriched molecular functions included transcription repressor activity, heat shock protein (Hsp) 90 binding, and nitric oxide synthase (NOS) activity; (3) MetaCore analysis identified immune response chemokine (C-C motif) ligand 2 (CCL2) signaling, muscle contraction regulation of endothelial nitric oxide synthase (eNOS) activity in endothelial cells, and triiodothyronine and thyroxine signaling as significantly overrepresented (false discovery rate <0.05); (4) qRT-PCR confirmed the overexpression of Nitric oxide synthase 3 (NOS3); hypoxic ischemic factor 1A (HIF1A); Chemokine (C-C motif) ligand 2 (CCL2); angiopoietin-like 4 (ANGPTL4); ADAM metallopeptidase with thrombospondin type 1, motif 9 (ADAMTS9); G protein-coupled receptor 4 (GPR4); metallothionein 1A (MT1A); MT2A; and selectin E (SELE) in an AODIL.

CONCLUSION

The myometrium of women with AODIL has a stereotypic transcriptome profile. This disorder has been associated with a pattern of gene expression involved in muscle contraction, an inflammatory response, and hypoxia. This is the first comprehensive and unbiased examination of the molecular basis of an AODIL.

Calcium channel blockers as tocolytics: principles of their actions, adverse effects and therapeutic combinations

Dihydropyridine Ca²⁺ channel blockers (CCBs) are widely accepted in the treatment of premature labour. Their mechanism of action in tocolysis involves the blockade of L-type Ca²⁺ channels, influenced by the Ca²⁺-activated K⁺ channels, beta-adrenergic receptors (β-ARs) and sexual hormones. In clinical practice, most experience has been gained with the use of nifedipine, whose efficacy is superior or comparable to those of β-agonists and oxytocin antagonists. Additionally, it has a favourable adverse effect profile as compared with the majority of other tocolytics. The most frequent and well-tolerated side-effects of CCBs are tachycardia, headache and hypotension. In tocolytic therapy efforts are currently being made to find combinations of tocolytic agents that yield better therapeutic action. The available human and animal studies suggest that the combination of CCBs with β-AR agonists is beneficial, although such combinations can pose risk of pulmonary oedema in multiple pregnancies and maternal cardiovascular diseases. Preclinical data indicate the potential benefit of combinations of CCBs and oxytocin antagonists. However, the combinations of CCBs with progesterone or cyclooxygenase inhibitors may decrease their efficacy. The CCBs are likely to remain one of the most important groups of drugs for the rapid inhibition of premature uterine contractions. Their significance may be magnified by further clinical studies on their combined use for tocolysis.

Complex effects of imatinib on spontaneous and oxytocin-induced contractions in human non-pregnant myometrium

Human myometrium includes two important cell populations involved in its contractility: smooth muscle fibers and interstitial cells. The pacemaking mechanism is not yet identified, but it is possible that myometrial smooth muscle cells contract in response to a signal generated by c-kit positive interstitial cells. The aim of this study was to investigate the effects of imatinib as a c-kit receptor antagonist on the spontaneous or oxytocin (OT) induced contractions of human non-pregnant myometrium in vitro. Myometrial strips were obtained from non-pregnant women (reproductive age) undergoing hysterectomy for benign indications. The strips were suspended in organ baths for recording of isometric tension. Imatinib effects were assessed on spontaneous contraction and after preexposure to OT.Direct exposure of myometrial strips to imatinib inhibits both amplitude and frequency of contractions (80-320 μM) in a dose dependent manner. Amplitude reverted back to 90% of the baseline amplitude by consequent addition of imatinib (until 480 μM). Total inhibition of myometrial contraction was obtained after addition of OT 60 nM. If myometrium was pre-exposed to OT (320 nM), imatinib 80-160 μm increased amplitude, while decreasing frequency. These data provide evidence that telocytes may be involved as modulators of the spontaneous contractions of the non-pregnant human uterus, via a tyrosine-kinase independent signaling pathway.

Mechanics and energetics of myosin molecular motors from nonpregnant human myometrium

Mechanical properties of spontaneously contracting isolated nonpregnant human myometrium (NPHM) were investigated throughout the whole continuum of load from zero load up to isometry. This made it possible to assess the three-dimensional tension-velocity-length (T-V-L) relationship characterizing the level of contractility and to determine crossbridge (CB) kinetics of myosin molecular motors. Seventy-seven muscle strips were obtained from hysterectomy in 42 nonpregnant patients. Contraction and relaxation parameters were measured during spontaneous mechanical activity. The isotonic tension-peak velocity (T-V) relationship was hyperbolic in 30 cases and nonhyperbolic in 47 cases. When the T-V relationship was hyperbolic, the Huxley formalism could be used to calculate CB kinetics and CB unitary force. At the whole muscle level and for a given isotonic load level, part of the V-L phase plane showed a common pathway, so that a given instantaneous length corresponded to only one possible instantaneous velocity, independent of time and initial length. At the molecular level, rate constants for CB attachment and detachment were dramatically low, ∼100 times lower than those of striated muscles, and ∼5 to 10 times lower than those of other smooth muscles. The CB unitary force was ∼1.4 ± 0.1 pN. NPHM shared similar basic contractile properties with striated muscles, reflected in the three-dimensional T-V-L relationship characterizing the contractile level. Low CB attachment and detachment rate constants made it possible to generate normal CB unitary force and normal muscle tension in NPHM, even though it contracted extremely slowly compared with other muscles.

TRPC1, STIM1, and ORAI influence signal-regulated intracellular and endoplasmic reticulum calcium dynamics in human myometrial cells

To explore the relationship between signal-stimulated increases in intracellular calcium ([Ca(2+)](i)) and depletion and refilling of the endoplasmic reticulum (ER) Ca(2+) stores ([Ca(2+)](L)) in human myometrial cells, we measured simultaneous changes in [Ca(2+)](i) and [Ca(2+)](L) using Fura-2 and Mag-fluo-4, respectively, in PHM1-41 immortalized and primary cells derived from pregnant myometrium and in primary cells derived from nonpregnant tissue. Signal- and extracellular Ca(2+)-dependent increases in [Ca(2+)](i) (SRCE) and ER refilling stimulated by oxytocin and cyclopiazonic acid were not inhibited by voltage-operated channel blocker nifedipine or mibefradil, inhibition of Na(+)/Ca(2+) exchange with KB-R7943, or zero extracellular Na(+) in PHM1-41 cells. Gadolinium-inhibited oxytocin- and cyclopiazonic acid-induced SRCE and slowed ER store refilling. TRPC1 mRNA knockdown specifically inhibited oxytocin-stimulated SRCE but had no statistically significant effect on ER store refilling and no effect on either parameter following cyclopiazonic acid treatment. Dominant negative STIMΔERM expression attenuated oxytocin- and thapsigargin-stimulated SRCE. Both STIM1 and ORAI1-ORAI3 mRNA knockdowns significantly attenuated oxytocin- and cyclopiazonic acid-stimulated SRCE. The data also suggest that reduction in STIM1 or ORAI1-ORAI3 mRNA can impede the rate of ER store refilling following removal of SERCA inhibition. These data provide evidence for both distinct and overlapping influences of TRPC1, STIM1, and ORAI1-ORAI3 on SRCE and ER store refilling in human myometrial cells that may contribute to the regulation of myometrial Ca(2+) dynamics. These findings have important implications for understanding the control of myometrial Ca(2+) dynamics in relation to myometrial contractile function.

A molecular signature of an arrest of descent in human parturition

OBJECTIVE

This study was undertaken to identify the molecular basis of an arrest of descent.

STUDY DESIGN

Human myometrium was obtained from women in term labor (TL; n = 29) and arrest of descent (AODes; n = 21). Gene expression was characterized using Illumina HumanHT-12 microarrays. A moderated Student t test and false discovery rate adjustment were applied for analysis. Confirmatory quantitative reverse transcription-polymerase chain reaction and immunoblot were performed in an independent sample set.

RESULTS

Four hundred genes were differentially expressed between women with an AODes compared with those with TL. Gene Ontology analysis indicated enrichment of biological processes and molecular functions related to inflammation and muscle function. Impacted pathways included inflammation and the actin cytoskeleton. Overexpression of hypoxia inducible factor-1a, interleukin -6, and prostaglandin-endoperoxide synthase 2 in AODes was confirmed.

CONCLUSION

We have identified a stereotypic pattern of gene expression in the myometrium of women with an arrest of descent. This represents the first study examining the molecular basis of an arrest of descent using a genome-wide approach.

A functional role for nicotinic acid adenine dinucleotide phosphate in oxytocin-mediated contraction of uterine smooth muscle from rat

Conventionally, G protein-coupled receptors are thought to increase calcium via inositol 1,4,5-trisphosphate (InsP(3)). More recent evidence shows that an alternative second messenger, nicotinic acid adenine dinucleotide phosphate (NAADP), also has a role to play, causing researchers to question established calcium releasing pathways. With the recent development, by our group, of cell-permeant NAADP (NAADP-aceteoxymethyl ester) and a selective NAADP receptor antagonist (Ned-19; 1-(3-((4-(2-fluorophenyl)piperazin-1-yl)methyl)-4-methoxyphenyl)-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole-3-carboxylic acid),the ability to investigate this signaling pathway has improved. Therefore, we investigated a role for NAADP in oxytocin-mediated responses in the rat uterus. Oxytocin- and NAADP-mediated effects were investigated by using contractile measurements of whole uterine strips from rat in organ baths. Responses were correlated to calcium release in cultured rat uterine smooth muscle cells measured by fluorescence microscopy. Inhibition of both oxytocin-induced contraction and calcium release by the traditional NAADP-signaling disrupter bafilomycin and the NAADP receptor antagonist Ned-19 clearly demonstrated a role for NAADP in oxytocin-induced signaling. A cell-permeant form of NAADP was able to produce both uterine contractions and calcium release. This response was unaffected by depletion of sarcoplasmic reticulum stores with thapsigargin, but was abolished by both bafilomycin and Ned-19. Crucially, oxytocin stimulated an increase in NAADP in rat uterine tissue. The present study demonstrates directly that NAADP signaling plays a role in rat uterine contractions. Moreover, investigation of this signaling pathway highlights yet another component of oxytocin-mediated signaling, stressing the need to consider the action of new components as they are discovered, even in signaling pathways that are thought to be well established.

Sarcoplasmic reticulum function in smooth muscle

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.

Minding the calcium store: Ryanodine receptor activation as a convergent mechanism of PCB toxicity

Chronic low-level polychlorinated biphenyl (PCB) exposures remain a significant public health concern since results from epidemiological studies indicate that PCB burden is associated with immune system dysfunction, cardiovascular disease, and impairment of the developing nervous system. Of these various adverse health effects, developmental neurotoxicity has emerged as a particularly vulnerable endpoint in PCB toxicity. Arguably the most pervasive biological effects of PCBs could be mediated by their ability to alter the spatial and temporal fidelity of Ca2+ signals through one or more receptor-mediated processes. This review will focus on our current knowledge of the structure and function of ryanodine receptors (RyRs) in muscle and nerve cells and how PCBs and related non-coplanar structures alter these functions. The molecular and cellular mechanisms by which non-coplanar PCBs and related structures alter local and global Ca2+ signaling properties and the possible short and long-term consequences of these perturbations on neurodevelopment and neurodegeneration are reviewed.

Distribution, expression and functional effects of small conductance Ca-activated potassium (SK) channels in rat myometrium

Calcium-activated potassium channels are important in a variety of smooth muscles, contributing to excitability and contractility. In the myometrium previous work has focussed on the large conductance channels (BK), and the role of small conductance channels (SK) has received scant attention, despite the finding that over-expression of an SK channel isoform (SK3) results in uterine dysfunction and delayed parturition. This study therefore characterises the expression of the three SK channel isoforms (SK1-3) in rat myometrium throughout pregnancy and investigates their effect on cytosolic [Ca] and force and compares this with that of BK channels. Consistent expression of all SK isoform transcripts and clear immunostaining of SK1-3 was found. Inhibition of SK1-3 channels (apamin, scyllatoxin) significantly inhibited outward current, caused membrane depolarisation and elicited action potentials in previously quiescent cells. Apamin or scyllatoxin increased the amplitude of [Ca] and force in spontaneously contracting myometrial strips throughout gestation. The functional effect of SK inhibition was larger than that of BK channel inhibition. Thus we show for the first time that SK1-3 channels are expressed and translated throughout pregnancy and contribute to outward current, regulate membrane potential and hence Ca signals in pregnant rat myometrium. They contribute more to quiescence that BK channels.

Modification of the effect of nifedipine in the pregnant rat myometrium: the influence of progesterone and terbutaline

AIMS

The aims of the study were to investigate the effects of nifedipine on potassium chloride (KCl)-evoked rat uterine contractions on different days of pregnancy in vitro, and the alterations in the effects of nifedipine on combination with terbutaline or progesterone.

MAIN METHODS

In rat myometrial rings taken on different days of pregnancy, rhythmic contractions were evoked with KCl in an isolated organ bath.

KEY FINDINGS

The relaxing effect of nifedipine was most expressed in the 25 mM KCl-induced uterine contractions, reaching the maximum on the last day of pregnancy (day 22). This effect was decreased by progesterone pretreatment in vivo. Synergism was observed in the uterus-relaxing effect of nifedipine+terbutaline, though the extent of potentiation depended on the sequence of administration of the two compounds. When terbutaline was added first in a single dose, the maximal inhibitory effect of nifedipine was lower. This decrease in the inhibition was suspended by a Ca(2+)-poor buffer, indicating the role of Ca(2+) channel activating effect of terbutaline.

SIGNIFICANCE

It is concluded that the uterus-relaxing effect of nifedipine is weakened by progesterone and may be enhanced by low concentrations of beta-mimetics. However, the administration of terbutaline cannot precede the administration of nifedipine.

Diminished sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) expression contributes to airway remodelling in bronchial asthma

Phenotypic modulation of airway smooth muscle (ASM) is an important feature of airway remodeling in asthma that is characterized by enhanced proliferation and secretion of pro-inflammatory chemokines. These activities are regulated by the concentration of free Ca(2+) in the cytosol ([Ca(2+)](i)). A rise in [Ca(2+)](i) is normalized by rapid reuptake of Ca(2+) into sarcoplasmic reticulum (SR) stores by the sarco/endoplasmic reticulum Ca(2+) (SERCA) pump. We examined whether increased proliferative and secretory responses of ASM from asthmatics result from reduced SERCA expression. ASM cells were cultured from subjects with and without asthma. SERCA expression was evaluated by western blot, immunohistochemistry and real-time PCR. Changes in [Ca(2+)](i), cell spreading, cellular proliferation, and eotaxin-1 release were measured. Compared with control cells from healthy subjects, SERCA2 mRNA and protein expression was reduced in ASM cells from subjects with moderately severe asthma. SERCA2 expression was similarly reduced in ASM in vivo in subjects with moderate/severe asthma. Rises in [Ca(2+)](i) following cell surface receptor-induced SR activation, or inhibition of SERCA-mediated Ca(2+) re-uptake, were attenuated in ASM cells from asthmatics. Likewise, the return to baseline of [Ca](i) after stimulation by bradykinin was delayed by approximately 50% in ASM cells from asthmatics. siRNA-mediated knockdown of SERCA2 in ASM from healthy subjects increased cell spreading, eotaxin-1 release and proliferation. Our findings implicate a deficiency in SERCA2 in ASM in asthma that contributes to its secretory and hyperproliferative phenotype in asthma, and which may play a key role in mechanisms of airway remodeling.