Gap junctions: their presence and necessity in myometrium during parturition

The oxytocin-oxytocin receptor system and its antagonists as tocolytic agents

Oxytocin, a hormone involved in numerous physiologic processes, plays a central role in the mechanisms of parturition and lactation. It acts through its receptor, which belongs to the G-protein-coupled receptor superfamily, while Gq/phospholipase C (PLC)/inositol 1,4,5-triphosphate (InsP3) is the main pathway via which it exerts its action in the myometrium. Changes in receptor levels, receptor desensitization, and locally produced oxytocin are factors that influence the effect of oxytocin on uterine contractility in labor. Activation of oxytocin receptor causes myometrial contractions by increasing intracellular Ca(+2) and production of prostaglandins. Since oxytocin induces contractions, the inhibition of its action has been a target in the management of preterm labor. Atosiban is today the only oxytocin receptor antagonist that is available as a tocolytic. However, the quest for oxytocin receptor antagonists with a better pharmacological profile has led to the synthesis of peptide and nonpeptide molecules such as barusiban, retosiban, L-368,899, and SSR-126768A. Many of these oxytocin receptor antagonists are used only as pharmacological tools, while others have tocolytic action. In this paper, we summarize the action of oxytocin and its receptor and we present an overview of the clinical and experimental data of oxytocin antagonists and their tocolytic action.

Decrement of uterine myometrial burst duration as a correlate to active labor: a Hilbert phase approach

We propose a novel approach based on Hilbert phase to identify the burst in the uterine myometrial activity. We apply this approach to 24 serial magnetomyographic signals recorded from four pregnant women using a 151 SQUID array system. The bursts identified with this approach are evaluated for duration and are correlated with the gestational age. In all four subjects, we find a decrease in the duration of burst as the subject approaches active labor. As was shown in animal studies, this result indicates a faster conduction time between the muscle cells which activate a larger number of muscle units in a synchronous manner.

The effects of a high-fat, high-cholesterol diet on markers of uterine contractility during parturition in the rat

Increasing levels of obesity within women of reproductive age is a major concern in the UK. Approximately, 13% of women aged <30 and 22% of 31- to 40-year-old women are obese. Obesity increases complications during pregnancy and the risk of caesarean section due to prolonged labour and poor uterine activity. The aim was to investigate whether a high-fat, high-cholesterol (HFHC) diet decreases markers of uterine contractility during parturition in the rat. Female Wistar rats were fed control (CON, n=10) or HFHC (n=10) diets for 6 weeks. Animals were mated and, once pregnant, maintained on their diet throughout gestation. On gestational day 19, rats were monitored continuously and killed at the onset of parturition. Body and fat depot weights were recorded. Myometrial tissue was analysed for cholesterol (CHOL), triglycerides (TAG), and expression of the contractile associated proteins gap junction protein alpha 1 (GJA1; also known as connexin-43, CX-43), prostaglandin-endoperoxide synthase 2 (PTGS2; also known as cyclo-oxygenase-2, COX-2) and caveolin-1 (CAV1) and maternal plasma for prostaglandin F(2)(α) (PGF(2)(α)) and progesterone. HFHC fed rats gained greater weight than CON (P<0.003) with significant increases in peri-renal fat (P<0.01). The HFHC diet increased plasma CHOL, TAG and progesterone, but decreased PGF(2)(α) versus CON (P<0.01, P<0.01, P=0.05 and P<0.02 respectively). Total CHOL and TAG levels of uterine tissue were similar. However, HFHC fed rats showed significant increases in PTGS2 (P<0.037), but decreases in GJA1 and CAV1 (P=0.059). In conclusion, a HFHC diet significantly increases body weight and alters lipid profiles that correlate with decreases in key markers of uterine contractility. Further work is required to ascertain whether these changes have adverse effects on uterine activity.

Emergent behaviors in a deterministic model of the human uterus

The human birth process is powered by uterine contractions that have observable patterns that depend on the physiology of muscular activity. We explored a previously designed model(1) simulating the uterus to assess global contractile patterns. The model is a cellular automaton that simulates the complexities of uterine activity from a few simple rules of cellular interaction and uterine geometry. Multiple experiments using the cellular automaton involved different uterine shapes, cell numbers, and initial distributions of active and resting cells. Results demonstrate complex contraction patterns similar to those observed in human labor. At least 2 modes of behavior appear in the simulations, one consistent with effective labor and one not. Experiments with cellular automata provide insights into stereotypic and disordered labor patterns that produce patient discomfort without progress in labor. We hypothesize that complex uterine contraction patterns may have other roles in the preparation for labor and birth.

Preventing preterm birth: the past limitations and new potential of animal models

The high rate of preterm birth in the USA and many other countries is a potential target for improving children’s immediate health and reducing the medical problems they face as adults. The acute complications for infants born prematurely often require intensive care management and are followed by long-lasting cognitive, sensory, motor, and cardiovascular deficits that substantially limit adult capabilities and survival. The inability to effectively reduce preterm birth stems from the failure to understand normal mechanisms of parturition in humans. Although studies from several model organisms help define the physiology of maintenance and termination of pregnancy, there are fundamental differences between species. For example, species regulate their production of progesterone, the crucial hormone in sustaining pregnancy, differently. This limits the extent to which models can provide meaningful information about the physiological mechanisms of human gestation. The growing wealth of sequenced mammalian genomes, computational comparative genomic tools and systems biology approaches provides new potential to utilize the divergence of DNA sequences and physiology between species to understand the genetic underpinnings of preterm birth.

Noninvasive estimation of the electrohysterographic action-potential conduction velocity

Electrophysiological monitoring of the fetal-heart and the uterine-muscle activity, referred to as an electrohysterogram, is essential to permit timely treatment during pregnancy. While remarkable progress is reported for fetal-cardiac-activity monitoring, the electrohysterographic (EHG) measurement and interpretation remain challenging. In particular, little attention has been paid to the analysis of the EHG propagation, whose characteristics might be predictive of the preterm delivery. Therefore, this paper focuses, for the first time, on the noninvasive estimation of the conduction velocity of the EHG-action potentials. To this end, multichannel EHG recording and surface high-density electrodes are used. A maximum-likelihood method is employed for analyzing the EHG-action-potential propagation in two dimensions. The use of different weighting strategies of the derived cost function is introduced to deal with the poor signal similarity between different channels. The presented methods were evaluated by specific simulations proving the best weighting strategy to lead to an accuracy improvement of 56.7%. EHG measurements on ten women with uterine contractions confirmed the feasibility of the method by leading to conduction velocity values within the expected physiological range.

Functional expression of purinergic P2X7 receptors in pregnant rat myometrium

ATP has been reported to enhance the membrane conductance of myometrial cells and uterine contractility. Purinergic P2 receptor expression has been reported in the myometrium, using molecular biology, but the functional identity of the receptor subtype has not been determined. In this study, ATP-induced currents were recorded and characterized in single myometrial cells from pregnant rats using whole cell patch clamping. Extracellular ATP was applied in the range of 10 muM-1 mM and induced currents with an EC(50) of 74 muM, with no desensitization, time dependency, or voltage dependency. The currents induced carried multiple monovalent cations, with conductances ranked as K(+) > Cs(+) > Li(+) > Na(+). They were activated by P2X receptor agonists, with their effectiveness ranked as 2',3'-O-(4-benzoylbenzoyl)-ATP >> ATP > alphabeta-methylene-ATP > 2-methylthio ATP > or = UTP > or = GTP > ADP. These currents were blocked by the selective P2X7 receptor antagonist 3-[5-(2,3-dichlorophenyl)-1 H-tetrazol-1-yl]methyl pyridine (A-438079). We therefore concluded that ATP-induced currents in rat myometrial cells crossed cell membranes via P2X7 receptors. We further showed that the ATP-induced currents were blocked by extracellular Mg(2+) (IC(50) = 0.26 mM). Clinically, administering extracellular Mg(2+) is known to inhibit uterine contraction. It therefore seems likely that uterine contraction may be induced by raised extracellular ATP and suppressed via Mg(2+) inhibiting P2X7 receptors. Further research is needed into the P2X7 receptor as a therapeutic target in abnormal uterine contraction, as a possible treatment for premature labor.

Modeling and identification of the electrohysterographic volume conductor by high-density electrodes

The surface electrohysterographic (EHG) signal represents the bioelectrical activity that triggers the mechanical contraction of the uterine muscle. Previous work demonstrated the relevance of the EHG signal analysis for fetal and maternal monitoring as well as for prognosis of preterm labor. However, for the introduction in the clinical practice of diagnostic and prognostic EHG techniques, further insights are needed on the properties of the uterine electrical activation and its propagation through biological tissues. An important contribution for studying these phenomena in humans can be provided by mathematical modeling. A five-parameter analytical model of the EHG volume conductor and the cellular action potential (AP) is proposed here and tested on EHG signals recorded by a grid of 64 high-density electrodes. The model parameters are identified by a least-squares optimization method that uses a subset of electrodes. The parameters representing fat and abdominal muscle thickness are also measured by echography. The mean correlation coefficient and standard deviation of the difference between the echographic and EHG estimates were 0.94 and 1.9 mm, respectively. No bias was present. These results suggest that the model provides an accurate description of the EHG AP and the volume conductor, with promising perspectives for future applications.

Magnetomyographic recording and identification of uterine contractions using Hilbert-wavelet transforms

We propose a multi-stage approach using Wavelet and Hilbert transforms to identify uterine contraction bursts in magnetomyogram (MMG) signals measured using a 151 magnetic sensor array. In the first stage, we decompose the MMG signals by wavelet analysis into multilevel approximate and detail coefficients. In each level, the signals are reconstructed using the detail coefficients followed by the computation of the Hilbert transform. The Hilbert amplitude of the reconstructed signals from different frequency bands (0.1-1 Hz) is summed up over all the sensors to increase the signal-to-noise ratio. Using a novel clustering technique, affinity propagation, the contractile bursts are distinguished from the noise level. The method is applied on simulated MMG data, using a simple stochastic model to determine its robustness and to seven MMG datasets.

Myometrial interstitial cells and the coordination of myometrial contractility

A strict regulation of contractility in the uterus and fallopian tube is essential for various reproductive functions. The uterus contributes, through either increased contractility or periods of relative quiescence, to: (i) expulsion of menstrual debris, (ii) sperm transport, (iii) adequate embryo placement during implantation, (iv) enlarging its capacity during pregnancy and (v) parturition. The dominant cell population of the uterine wall consists of smooth muscle cells that contain the contractile apparatus responsible for the generation of contractile force. Recent interest has focused on a new population of cells located throughout the myometrium on the borders of smooth muscle bundles. These cells are similar to interstitial cells of Cajal (ICC) in the gut that are responsible for the generation of electrical slow waves that control peristalsis. A precise role for myometrial Cajal-like interstitial cells (m-ICLC) has not been identified. m-ICLC express the c-kit receptor, involved in creating and maintaining the ICC phenotype in the gastrointestinal tract. However, both acute and prolonged inhibition of this receptor with the c-kit antagonist imatinib mesylate does not appear to affect the spontaneous contractility of myometrium. Calcium imaging of live tissue slices suggests that contractile signalling starts on the borders of smooth muscle bundles where m-ICLC are located and recently the possible role of extracellular ATP signalling from m-ICLC has been studied. This manuscript reviews the evidence regarding tissue-level signalling in the myometrium with a particular emphasis on the anatomical and possible functional aspects of m-ICLC as new elements of the contractile mechanisms in the uterus.

Regulation of oxytocin receptor responsiveness by G protein-coupled receptor kinase 6 in human myometrial smooth muscle

Oxytocin plays an important role in the progression, timing, and modulation of uterine contraction during labor and is widely used as an uterotonic agent. We investigated the mechanisms regulating oxytocin receptor (OTR) signaling in human primary myometrial smooth muscle cells and the ULTR cell-line. Oxytocin produced concentration-dependent increases in both total [(3)H]inositol phosphate accumulation and intracellular Ca(2+) concentration ([Ca(2+)](i)); however, responses were greater and more reproducible in the ULTR cell line. Assessment of phospholipase C activity in single cells revealed that the OTR desensitizes rapidly (within 5 min) in the presence of oxytocin (100 nm). To characterize OTR desensitization further, cells were stimulated with a maximally effective concentration of oxytocin (100 nm, 30 sec) followed by a variable washout period and a second identical application of oxytocin. This brief exposure to oxytocin caused a marked decrease (>70%) in OTR responsiveness to rechallenge and was fully reversed by increasing the time period between agonist challenges. To assess involvement of G protein-coupled receptor kinases (GRKs) in OTR desensitization, cells were transfected with small interfering RNAs to cause specific > or =75% knockdown of GRKs 2, 3, 5, or 6. In both primary myometrial and ULTR cells, knockdown of GRK6 largely prevented oxytocin-induced OTR desensitization; in contrast, selective depletion of GRKs 2, 3, or 5 was without effect. These data indicate that GRK6 recruitment is a cardinal effector of OTR responsiveness and provide mechanistic insight into the likely in vivo regulation of OTR signaling in uterine smooth muscle.

Temporal and spatial variations in spontaneous Ca events and mechanical activity in pregnant rat myometrium

OBJECTIVES

The aim of this study was to investigate the temporal and spatial characteristics of spontaneous Ca signals in pregnant rat myometrium.

STUDY DESIGN

Confocal imaging of longitudinal strips of 21-day pregnant rats loaded with the Ca sensitive indicator Fluo-4, was combined with measurements of mechanical activity in uterine smooth muscle cells, in situ and freshly isolated.

RESULTS

Our results show that the Ca transients in pregnant uterine tissue are composed of Ca spikes, which are associated with the spike-like action potentials. There is large variation in the pattern of spontaneous activity in myometrium, ranging from non-propagating Ca spikes confined to individual smooth muscle cells, through to regional and global propagating Ca spikes. Irrespective of the pattern of activity displayed, the Ca signals were always in the form of Ca spikes, singularly or in bursts. These Ca spikes did not show fixed initiations sites, propagated in longitudinal and transverse directions from the initiation regions, and had a variable pattern of propagation in preparations which were not synchronously active. In preparations which showed synchronous activity, Ca spikes singularly or bursts propagated mainly in the transverse direction from the initiation regions. The amplitude of force generated by single spikes was dependent on the number of bundles recruited by the propagating Ca spike within the strip, and was about 30-40% of the maximal force produced by carbachol or high-K stimulation. If Ca spikes appeared in the form of bursts they generated longer lasting fused contractions, the amplitudes of which were dependent on the number and the frequency of Ca spikes in the burst.

CONCLUSIONS

Longitudinal myometrium from pregnant rats generates spontaneous Ca spikes which vary in their initiation sites, spatial spread and frequency and are associated with the spike-like action potentials. They are sensitive to the L-type Ca channel blocker, nifedipine. Contractile activity was dependent on the spatial spread of individual Ca spikes and when fully synchronized, produced single submaximal phasic contraction. The number and frequency of bursts of Ca spikes controlled the amplitude and duration of contraction.

The genetics of birth timing: insights into a fundamental component of human development

The timing of birth necessitates the coupling of fetal maturation with the onset of parturition, and occurs at characteristic, but divergent gestations between mammals. Preterm birth in humans is an important but poorly understood outcome of pregnancy that uncouples fetal maturation and birth timing. The etiology of preterm birth is complex, involving environmental and genetic factors whose underlying molecular and cellular pathogenic mechanisms remain poorly understood. Animal models, although limited by differences with human physiology, have been crucial in exploring the role of various genetic pathways in mammalian birth timing. Studies in humans of both familial aggregation and racial disparities in preterm birth have contributed to the understanding that preterm birth is heritable. A significant portion of this heritability is due to polygenic causes with few true Mendelian disorders contributing to preterm birth. Thus far, studies of the human genetics of preterm birth using a candidate gene approach have met with limited success. Emerging research efforts using unbiased methods may yield promising results if concerns about study design can be adequately addressed. The findings from this frontier of research may have direct implications for the allocation of public health and clinical resources as well as spur the development of more effective therapeutics.

Insights into parturition biology from genetically altered mice

With the growing frequency of preterm birth, increased effort has been made to elucidate the physiology of normal and aberrant parturition. As with many developmental processes, the study of genetically altered mice has led to an increased understanding of mechanisms controlling the maintenance and resolution of pregnancy. Studies in genetically altered mice have implicated critical roles for both prostaglandin synthesis and degradation in luteolysis and the progression of labor. The importance of local modulation of progesterone activity to cervical ripening has also been demonstrated. Although a decline in levels of serum progesterone is a part of normal labor initiation in mice but not humans, murine labor without progesterone withdrawal has been reported in some cases. These findings emphasize the importance of other components of the parturition cascade that are shared in mice and humans and highlights the importance of an increased understanding of the physiology of mouse parturition.

Prostacyclin primes pregnant human myometrium for an enhanced contractile response in parturition

An incomplete understanding of the molecular events that regulate the myometrial transition from the quiescent pregnant state to the active contractile state during labor has hindered the development of improved therapies for preterm labor. During myometrial activation, proteins that prime the smooth muscle for contraction are upregulated, allowing maximal responsiveness to contractile agonists and thereby producing strong phasic contractions. Upregulation of one such protein, COX-2, generates PGs that induce contractions. Intriguingly, the predominant myometrial PG produced just prior to labor is prostacyclin (PGI2), a smooth muscle relaxant. However, here we have shown that activation of PGI2 receptor (IP) upregulated the expression of several contractile proteins and the gap junction protein connexin 43 through cAMP/PKA signaling in human myometrial tissue in organ and cell culture. Functionally, these IP-dependent changes in gene expression promoted an enhanced contractile response to oxytocin in pregnant human myometrial tissue strips, which was inhibited by the IP antagonist RO3244794. Furthermore, contractile protein induction was dependent on the concentration and time of exposure to the PGI2 analog iloprost and was blocked by both RO3244794 and PKA knockdown. We therefore propose that PGI2-mediated upregulation of contractile proteins and connexin 43 is a critical step in myometrial activation, allowing for a maximal contractile response. Our observations have important implications regarding activation of the myometrium prior to the onset of labor.

Physiology of myometrial function: intercellular coupling and its role in uterine contractility

The mammalian uterus is composed of a preponderance of small smooth muscle cells usually aligned in two layers. The number of muscle cells in the human uterus at term is estimated at 200 billion, each minute fusiform cell measuring about 5–10μm in diameter and about 200μm in length. The main function of the uterus is to harbour the developing fetus during pregnancy and then to contract vigorously during labour to expel the products of conception. In order for the uterus to contract rhythmically and forcefully, a mechanism must exist to allow interaction between muscle cells in order to achieve synchronous activity. Phasic or cyclical patterns of contractile activity of the uterus cannot be accounted for by stimulation or inhibition from the nervous or endocrine systems. Since myometrial cells are dependent upon action potentials for their contractile processes, some system must be present between the muscle cells for the propagation of action potentials between them. The observation that gap junctions occur in large numbers between myometrial cells during parturition is thought to be significant in this regard and they are considered to play an essential role in parturition and in the control and co-ordination of uterine contractility. In this brief review, we will discuss the role of gap junctions in the modulation of myometrial contractility and the mechanisms that regulate their synthesis and permeability.

Effect of prolonged c-kit receptor inhibition by imatinib mesylate on the uterine contractility of pregnant rabbits

BACKGROUND

The c-kit receptor expressed by interstitial cells in the gastrointestinal tract is crucial to their pacemaking function. The function of similar c-kit-expressing myometrial cells is unknown.

METHODS

Imatinib mesylate, a specific c-kit receptor antagonist, was administered to pregnant New Zealand white rabbits (term = 31 days, n = 35) from day 27 gestation by intramuscular injection twice daily at high (50 microg/kg) or medium (10 microg/kg) dose and compared with a control group injected with vehicle only. In a second phase, two further groups received imatinib at medium or low (1 mug/kg) dose for a longer duration starting from day 18 until delivery. Three does from the latter groups as well as controls underwent myometrial biopsy under general anesthesia after spontaneous vaginal birth. Contractility was recorded by isometric tensiometry. The outcome measures were delay of parturition and in vitro contractility characteristics.

RESULTS

High-dose imatinib induced early delivery when compared with the control group (28.6 vs. 30.7 days, p < 0.001). The other groups delivered at term. No effect on in vitro contractility was apparent in any of the groups.

CONCLUSIONS

c-kit receptor inhibition in pregnant rabbits does not delay significantly the length of gestation or change myometrial contractility in vitro.

Preterm labour. Myometrial function in prematurity

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.

Spatial-temporal analysis of uterine smooth muscle activity recorded during pregnancy

We performed recording of the magnetic fields (Magnetomyography - MMG) corresponding to the electrical activity of the uterine smooth muscle with a device called SARA, (SQuid Array for Reproductive Assessment). Past studies suggest that the uterus passes through a preparatory process before entering labor and resulting in delivery of the fetus. But the electrophysiological mechanism of this process is not completely understood. We propose four parameters that will allow us quantify the characteristics of the uterine MMG signal obtained from 151 sensors spread over the pregnant abdomen. In summary, we believe that spatial-temporal analysis mapping of uterine activity will help us better understand the process of labor.

Placental site does not change background uterine electromyographic activity in the middle trimester of pregnancy

OBJECTIVE

This study was performed in order to assess the potential influence of placental implantation site on transabdominal electromyographic (EMG) assessment of the uterine electrical activity in the middle trimester of pregnancy.

STUDY DESIGN

In this prospective study 251 unselected, nulliparous asymptomatic women with a singleton pregnancy underwent transabdominal uterine EMG. Uterine electrical activity was recorded using bipolar electrodes placed on the abdominal surface for 20min. Regarding the placental implantation site and presence of action potentials (AP) pregnant women were divided into two groups: the anterior placenta group (APG) and the posterior placenta group (PPG). Outcome measures were differences in the median frequency (MF) and median amplitude (MA) of AP between the two groups.

RESULTS

Action potentials were detected in 56 women: 33/56 in the APG versus 23/56 in the PPG. The parameters analyzed (MF, p=0.527, Fisher's exact test, and MA, p=0.255, Fisher's exact test) did not produce any statistical significant differences between the two groups.

CONCLUSION

Background uterine EMG activity measured from the abdominal surface in the middle trimester of pregnancy does not depend on the placental implantation site.

Prolonged labour associated with lower expression of syndecan 3 and connexin 43 in human uterine tissue

BACKGROUND

Prolonged labour is associated with greater morbidity and mortality for mother and child. Connexin 43 is a major myometrial gap junction protein found in human myometrium. Syndecan 3 seems to prevail in the human uterus among heparan sulphate proteoglycans, showing the most significant increase during labour. The aims of the present study were to investigate syndecan 3 and connexin 43 mRNA expressions and protein distributions in human uterine tissue during normal and prolonged labour.

METHODS

Uterine isthmic biopsies were collected from non-pregnant (n = 7), term pregnant women not in labour (n = 14), in normal labour (n = 7) and in prolonged labour (n = 7). mRNA levels of syndecan 3 and connexin 43 were determined by real time RT-PCR. The localization and expression were demonstrated by immunohistochemistry and confocal microscopy.

RESULTS

In women with prolonged labour, the mRNA expressions of syndecan 3 and Connexin 43 were considerably lower than the expression level at normal labour (p < 0.05). In term-pregnant tissue, the expression of syndecan 3 and connexin 43 did not differ significantly compared to non-pregnant and normal labour. The immunoreactivity of syndecan 3 was strong at normal labour, in contrast to prolonged labour, where both a weaker expression and an irregular distribution were detected. The immunoreactivity of connexin 43 increased until term and further stronger staining occurred at normal labour. At prolonged labour, the immunoreactivity was weaker and more unevenly distributed. At labour, a co-localization of syndecan 3 and connexin 43 could be demonstrated in the smooth muscle by confocal microscopy.

CONCLUSION

The high expression of syndecan 3 and connexin 43 and their co-localization to the smooth muscle bundles during normal labour, together with the significant reduction in prolonged labour, may indicate a role for these proteins in the co-ordination of myometrial contractility.

Fifty-eight years in science--a commentary

After 58 years in science, mostly in pharmacology, one gains perspective. Mine is that there have been important changes over this time, some good and some questionable. In this commentary, I try to reveal how I got to this stage, partially explaining my biases, and possibly helping others learn from my experiences including mistakes. Changing from seeking an M.D. to cellular biology and then to pharmacology early in my career were the best moves I made. The next best move was migration to Canada, away from the McCarthy-McCarran hysteria. Arriving at a time after the end of World War II when science in Canada was expanding was very good luck. I had an excellent opportunity to enjoy both the administration (as Chair of the first independent Department of Pharmacology at the University of Alberta) and the practice of pharmacology (as a practitioner of research on smooth muscle in health and disease). For me, the practice of research has always won over administration when a choice had to be made. Early on, I began to ask questions about educational practices and tried to evaluate them. This led me to initiate changes in laboratories and to seek nondidactic educational approaches such as problem-based learning. I also developed questions about the practice of anonymous peer review. After moving to McMaster in 1975, I was compelled to find a solution for a failed "Pharmacology Program" and eventually developed the first "Smooth Muscle Research Program". Although that was a good solution for the research component, it did not solve the educational needs. This led to the development of "therapeutic problems", which were used to help McMaster medical students educate themselves about applied pharmacology. Now these problems are being used to educate pharmacology honours and graduate students at the University of Alberta. The best part of all these activities is the colleagues and friends that I have interacted with and learned from over the years, and the realization that many of them have collaborated with me again in this volume.

2,2'-Dichlorobiphenyl decreases amplitude and synchronization of uterine contractions through MAPK1-mediated phosphorylation of GJA1 (connexin43) and inhibition of myometrial gap junctions

The present study examined the hypothesis that inhibition of myometrial gap junctions through MAPK1-induced phosphorylation of GJA1 (connexin43) leads to inhibition of spontaneous phasic uterine contractions by 2,2'-dichlorobiphenyl (2,2'-DCB). Uterine strips from Gestation Day 10-pregnant rats exposed in muscle baths to 2,2'-DCB exhibited increased oscillatory frequency and decreased amplitude and synchronization of contractions. To assess effects on gap junctions, Lucifer yellow was injected into myometrial cells and transfer to adjacent cells was scored. After a 1-h treatment, 100 microM 2,2'-DCB decreased Lucifer yellow intercellular transfer in a concentration-dependent manner. The MAP2K1 inhibitor PD98059 increased percentage of dye transfer to adjacent myometrial cells from 18% in cultures exposed for 1 h to 100 microM 2,2'-DCB alone to 48% in cultures cotreated with 50 microM PD98059 and 100 microM 2,2'-DCB. In contrast, the conventional PRKC inhibitor Gö6976 (10 microM) had no significant effect on 2,2'-DCB-induced inhibition of dye transfer. Western blotting showed about a 4.5-fold increase in phosphorylation of GJA1 at S255, a MAPK1 site, after exposure to 100 microM 2,2'-DCB compared to untreated and solvent controls. However, there was no difference in phosphorylation of GJA1 at S368, a PRKC site. Cells treated with 2,2'-DCB increased phosphorylated MAPK1, implicating the increase of activation of MAPK1. Cotreatment with 100 microM 2,2'-DCB and 5 microM PD98059 reversed 2,2'-DCB-induced modification of uterine contractions and increase of pGJA1(S255) in uterine strips. Therefore, this study suggests that 2,2'-DCB decreases amplitude and synchronization of uterine contractions mediated through MAPK1-mediated phosphorylation of GJA1 and subsequent inhibition of myometrial gap junctions.

Normal Labor: Mechanism and Duration

Labor is refers to the chain of physiologic events that allows a fetus to undertake its journey from the uterus to the outside world. The mean duration of a singleton preganancy is 40.0 weeks (280 days), which is dated from the first day of the last normal menstrual period. The period from 37.0 weeks (259 days) to 42.0 weeks (294 days) of gestation is regarded as "term". This article focuses on the onset progress, and mechanics of normal labor term. Topics such as preterm labor (labor before 37 weeks), postterm labor (labor after 42 weeks), and abnormal labor and delivery have not been addressed and are discussed in detail elsewhere in this issue.

Divergent roles for glutathione in lindane-induced acute and delayed-onset inhibition of rat myometrial gap junctions

Previous studies have shown that the insecticide lindane (gamma-hexachlorocyclohexane) induces a biphasic inhibition of gap junction intercellular communication that is accompanied by oxidative stress. The present study investigates the hypothesis that depletion of cellular glutathione (GSH) is a mechanistic link between lindane-induced oxidative stress and inhibition of myometrial gap junctions. Exposure to 100 or 200 microM lindane rapidly (within 1 min) increased myometrial cell generation of superoxide, as measured by superoxide dismutase-inhibitable cytochrome c reduction, and superoxide production remained elevated for up to 60 min of exposure. To measure gap junction communication, Lucifer yellow dye was injected into myometrial cells, and dye transfer to adjoining cells was monitored. Cells were exposed to lindane with or without GSH modulators, and dye transfer was determined at the end of a 1-h exposure to 100 microM lindane (acute phase) and 24 h after termination of lindane exposure (secondary phase). The acute phase of lindane-induced inhibition of dye transfer was prevented by GSH depletion with L-buthionine-[S,R]-sulfoximine (BSO) and enhanced by GSH augmentation with GSH monoethyl ester or L-2-oxothiazolidine-4-carboxylate (OTC). In contrast, the secondary, delayed-onset phase of lindane-induced inhibition of dye transfer was enhanced by GSH depletion with BSO and prevented by GSH augmentation with GSH monoethyl ester or OTC. Changes in cellular GSH by the pharmacological modulators were confirmed by high performance liquid chromatography. These results suggest that GSH is required in the acute phase but protects against the secondary phase of lindane-induced inhibition of myometrial gap junctions.

The effects of connexin phosphorylation on gap junctional communication

Gap junctions are specialized membrane domains composed of collections of channels that directly connect neighboring cells providing for the cell-to-cell diffusion of small molecules, including ions, amino acids, nucleotides, and second messengers. Vertebrate gap junctions are composed of proteins encoded by the "connexin" gene family. In most cases examined, connexins are modified post-translationally by phosphorylation. Phosphorylation has been implicated in the regulation of gap junctional communication at several stages of the connexin "lifecycle", such as the trafficking, assembly/disassembly, degradation, as well as, the gating of gap junction channels. Since connexin43 (Cx43) is widely expressed in tissues and cell lines, we understand the most about how it is regulated, and thus, connexin43 phosphorylation is a major focus of this review. Recent reports utilizing new methodologies combined with the latest genome information have shown that activation of several kinases including protein kinase A, protein kinase C, p34(cdc2)/cyclin B kinase, casein kinase 1, mitogen-activated protein (MAP) kinase and pp60(src) kinase can lead to phosphorylation at 12 of the 21 serine and two of the six tyrosine residues in the C-terminal region of connexin43. In several cases, use of site-directed mutants of these sites have shown that these specific phosphorylation events can be linked to changes in gap junctional communication.

Plasma membrane channels formed by connexins: their regulation and functions

Members of the connexin gene family are integral membrane proteins that form hexamers called connexons. Most cells express two or more connexins. Open connexons found at the nonjunctional plasma membrane connect the cell interior with the extracellular milieu. They have been implicated in physiological functions including paracrine intercellular signaling and in induction of cell death under pathological conditions. Gap junction channels are formed by docking of two connexons and are found at cell-cell appositions. Gap junction channels are responsible for direct intercellular transfer of ions and small molecules including propagation of inositol trisphosphate-dependent calcium waves. They are involved in coordinating the electrical and metabolic responses of heterogeneous cells. New approaches have expanded our knowledge of channel structure and connexin biochemistry (e.g., protein trafficking/assembly, phosphorylation, and interactions with other connexins or other proteins). The physiological role of gap junctions in several tissues has been elucidated by the discovery of mutant connexins associated with genetic diseases and by the generation of mice with targeted ablation of specific connexin genes. The observed phenotypes range from specific tissue dysfunction to embryonic lethality.

Ini, a small nuclear protein that enhances the response of the connexin43 gene to estrogen

This article describes the structural and functional characterization of Ini (AF495522), a novel highly conserved zinc-finger protein that had been identified by screening an estrogen-induced rat myometrial expression library. Ini localizes to the nucleus of HeLa cells and binds to the proximal connexin43 (cx43) promoter, as demonstrated by EMSA. In addition, transient transfection experiments performed with estrogen receptor alpha (ERalpha) cDNA show that overexpression of Ini enhances, in a dose-dependent fashion, the up-regulation of the cx43 gene by estrogen. On binding to the cx43 promoter, Ini stimulates the transcriptional activating function (AF)-1, but not the AF-2, of the ERalpha. This makes Ini one of the few known coactivators specific for AF-1. Because estrogen up-regulates Ini mRNA in the myometrium, it is likely that Ini's physiological role in this tissue is to modulate the response of the cx43 gene to estrogen. Transfection studies with an Ini antisense construct seem to indicate that Ini plays an additional role in the cellular response to estrogen affecting both AF-1 and AF-2 activities of the ERalpha. This broader effect may be associated with cell cycle progression that in yeast has been shown to require Ini.

The impact of estrogen and progesterone on asthma

OBJECTIVE

This paper describes evidence of a positive effect of both endogenous and exogenous estrogen and progesterone on lung function across the life span in women.

DATA SOURCES

Articles were identified using the keywords asthma, pulmonary function, menarche, menopause, estrogen, progesterone, hormone replacement therapy, oral contraceptives, and menstrual cycle from years 1966 to 2001 in MEDLINE. Additional studies were identified from article reference lists.

STUDY SELECTION

Relevant, peer-reviewed original research articles in the English language were selected.

RESULTS

Estrogen and/or progesterone may alter pulmonary function and asthma. Premenopausal women experience decreases in pulmonary function and increases in asthma exacerbations and hospitalizations during the premenstrual and menstrual phases. Oral contraceptives and hormone replacement therapy are associated with improved pulmonary function and decrease in asthma exacerbation. Some asthmatic patients experience improved pulmonary function and reduced asthma medication requirement during pregnancy.

CONCLUSIONS

Estrogen and progesterone modify airway responsiveness. Further research is needed to elucidate the clinical relevance of estrogen and progesterone in the pathophysiology and therapy of asthma.

The effects of sex steroids on the formation of gap junctions between folliculo-stellate cells; a study in castrated male rats and ovariectomized female rats

We investigated the relationship between gap junction formation and the sex steroids testosterone, progesterone and 17beta-estradiol in the anterior pituitary glands of castrated male rats and ovariectomized female rats. Male and female 30-day-old Wistar-Imamichi strain rats were castrated or ovariectomized, and 30 days later they were subcutaneously injected with the above sex steroids. They were divided into six groups according to the injected materials: sesame oil (control), testosterone, progesterone, 17beta-estradiol, testosterone with 17beta-estradiol, and progesterone with 17beta-estradiol. Five rats from each group were sacrificed 1, 2, 3, 4 and 5 days after the injections, and the anterior pituitary glands were prepared for observation by transmission electron microscopy. We quantified the number of follicles and gap junctions and calculated the rate of occurrence of gap junctions as the ratio of the number of gap junctions existing between folliculo-stellate cells per intersected follicle profile in electron photomicrographs. The administration of testosterone to castrated male rats increased the rate of gap junctions between folliculo-stellate cells; however, progesterone and 17beta-estradiol did not affect the formation of gap junctions. The administration of progesterone to ovariectomized female rats increased the rate of gap junctions between folliculo-stellate cells; this progesterone effect was prevented by the simultaneous administration of 17beta-estradiol, which by itself did not affect the rate of gap junctions between folliculo-stellate cells. These observations indicate that the formation of gap junctions within the anterior pituitary gland is regulated differently by sex steroids in castrated male and ovariectomized female rats.

The Caenorhabditis elegans ortholog of human PHF5a shows a muscle-specific expression domain and is essential for C. elegans morphogenetic development

We have recently described a novel human and murine multigene-family that is highly conserved during evolution and shows a PHD-finger-like domain present in the deduced protein sequences. Here, we describe the cloning and characterization of the Caenorhabditis elegans ortholog of human PHF5a. Transgenic phf-5::yfp-reporter techniques in C. elegans identified temporal C. elegans phf-5 expression being restricted to late C. elegans development. The phf-5::yfp expression starts within the morphogenetic phase of embryonic development and lasts to the stage of adult worms. Spatial phf-5 expression is muscle-specific with an expression in the developing pharynx, in body wall muscular structures, and in the anal muscles. By phf-5 RNAi we further demonstrated that PHF-5 is essential in the morphogenetic phase of C. elegans embryonic development as well as in young larvae. In contrast, phf-5 RNAi does not show an evident phenotype to adult worms. Taken together, this is the first report providing evidence for a tissue and stage-specific expression of a PHF5a ortholog, named phf-5, in C. elegans while our data further suggest an essential role of the encoded PHF-5 protein in morphogenetic development and muscle function.

Regulation of connexin 43 by nitric oxide in primary uterine myocytes from term pregnant women

OBJECTIVE

Our purpose was to test the hypothesis that nitric oxide signals regulate the expression of the gap-junction protein connexin 43 in primary uterine myocytes from pregnant women at term.

STUDY DESIGN

Northern analysis and immunoblotting were used to determine the expression of connexin 43 in myocytes cultured in the presence of the nitric oxide donors S -nitroso-N -acetyl-penicillamine (SNAP) (100 micromol/L) and (Z)-1-[2-(2-aminoethyl)-N -(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate diethylenetriamine (NOC-18) (100 micromol/L). We also tested the effect of the NO stimulants 8-bromo-cyclic adenosine 3',5'-monophosphate (cAMP) (100 micromol/L) and 8-bromo-cyclic guanosine 3',5'-monophosphate (cGMP) (200 micromol/L), and the nitric oxide synthase inhibitors N -nitro-L-arginine methyl ester (NAME) (100 micromol/L) and L -N (1-iminoethyl)lysine (NIL) (50 micromol/L).

RESULTS

Nitric oxide and 8-bromo-cAMP reduced the level of connexin 43 expression, and 8-bromo-cGMP had no effect. In contrast, NIL, but not NAME, increased the levels of connexin 43 protein without affecting the level of connexin 43 messenger RNA. With immunoblotting, expression of inducible nitric oxide synthase was not detected in these cells.

CONCLUSION

Nitric oxide down-regulates the expression of connexin 43 in cultured human myocytes. We speculate that this effect may decrease the efficacy of intermyocyte signaling and thus contribute to uterine quiescence during human pregnancy.

Gap junctions, homeostasis, and injury

Gap junctions (Gj) play an important role in the communication between cells of many tissues. They are composed of channels that permit the passage of ions and low molecular weight metabolites between adjacent cells, without exposure to the extracellular environment. These pathways are formed by the interaction between two hemichannels on the surface of opposing cells. These hemichannels are formed by the association of six identical subunits, named connexins (Cx), which are integral membrane proteins. Cell coupling via Gj is dependent on the specific pattern of Cx gene expression. This pattern of gene expression is altered during several pathological conditions resulting in changes of cell coupling. The regulation of Cx gene expression is affected at different levels from transcription to post translational processes during injury. In addition, Gj cellular communication is regulated by gating mechanisms. The alteration of Gj communication during injury could be rationalized by two opposite theories. One hypothesis proposes that the alteration of Gj communication attenuates the spread of toxic metabolites from the injured area to healthy organ regions. The alternative proposition is that a reduction of cellular communication reduces the loss of important cellular metabolisms, such as ATP and glucose.

Connexin 43 expression in normal versus dysfunctional labor

OBJECTIVE

We sought to determine whether connexin 43 (Cx43), the major myometrial gap junction protein, is differentially expressed in normal versus dysfunctional labor.

STUDY DESIGN

Myometrial biopsies were obtained from 28 patients undergoing cesarean section and grouped into the following categories: (1) no labor, (2) dysfunctional labor, and (3) normal labor. Northern and Western analyses were performed to determine Cx43 messenger RNA (mRNA) and protein expression, respectively. Localization of Cx43 protein was determined by immunohistochemistry.

RESULTS

Labor was associated with increased Cx43 mRNA expression (P <.05). This association was not true for protein. There was no difference in mRNA or protein expression between patients with normal labor versus those with dysfunctional labor. The extent of Cx43 immunohistochemical staining was not significantly different among the groups (P >.05).

CONCLUSION

Dysfunctional labor is not associated with aberrant Cx43 mRNA or protein expression or with a reduction in immunodetectable Cx43 gap junctions.

Oestriol and oestradiol increase cell to cell communication and connexin43 protein expression in human myometrium

Oestradiol increases the protein expression of connexin43 (Cx43) gap junctions in myometrium but the effect of oestriol on gap junction expression has not been described previously. Oestriol is the most abundant free oestrogen in pregnant women and there is a marked surge in oestriol concentrations before term and idiopathic preterm labour. In order to determine whether oestriol may have a physiological action on the myometrium, cultured human myometrial cells obtained from non-pregnant hysterectomy specimens were exposed to 10 nmol/l oestradiol or oestriol. Intercellular communication between myometrial cells was investigated by microinjection of confluent cultured cells with the gap junction-permeant tracer Cascade Blue. There was a progressive increase in coupling after exposure to oestradiol or oestriol (P < 0.0005). An increase in Cx43 protein expression was demonstrated by immunocytochemistry after 1 h (P < 0.01) and 3 days (P < 0.01) exposure, and by Western blotting after 1 h (P < 0.01) and 3 days (P < 0.05) exposure, to both oestradiol and to oestriol. We conclude that oestriol increases gap junction communication in human myometrium by increasing gap junction expression. Elevated oestriol concentrations may thus play a role in the initiation of labour in women, by increasing cell-cell communication in the myometrium.

Antioxidants prevent gamma-hexachlorocyclohexane-induced inhibition of rat myometrial gap junctions and contractions

Lindane (gamma-hexachlorocyclohexane) is a commonly used pesticide that bioaccumulates in mammalian adipose tissue. Lindane inhibits gap junctional intercellular communication and oscillatory contractions of pregnant rat myometrium in vitro. The present study investigated the role of oxidative stress in lindane's inhibition of myometrial function in mid-gestation pregnant rat uteri. Lucifer yellow dye was microinjected into cultured myocytes to assess gap junctional intercellular communication. Lindane exposure (100 microM) resulted in a time-dependent, biphasic inhibition of dye transfer. This pattern of inhibition was also seen upon cell exposure to the pro-oxidant, tert-butyl hydroperoxide (100 microM). Lindane's initial and secondary-onset dye transfer inhibitions were reversed by cotreatment and pretreatment with the antioxidants, alpha-tocopherol (25-100 microM), diphenyl-1,4-phenylene diamine (10-30 microM), and superoxide dismutase (100-400 U/ml). D-mannitol (100-300 mM) also reversed lindane's initial dye transfer inhibition. Nitro blue tetrazolium reduction to formazan (measured spectrophotometrically) was elevated upon exposure of cultured cells to lindane or tert-butyl hydroperoxide, indicating the presence of reducing agents. Lipid peroxidation, assessed as thiobarbituric acid-reactive substances, was also elevated in lindane-exposed cell cultures. alpha-Tocopherol reversed this elevation. Finally, uterine contractility was assessed by measuring isometric contractions of uterine strips hung in standard muscle baths. Pretreatment with alpha-tocopherol prevented lindane's abolishment of uterine contractions in vitro. These data support the hypothesis that lindane inhibits uterine contractility and myometrial gap junctions by establishing an oxidative stress environment.

Regulation of gap junctions by phosphorylation of connexins

Gap junctions are a unique type of intercellular junction found in most animal cell types. Gap junctions permit the intercellular passage of small molecules and have been implicated in diverse biological processes, such as development, cellular metabolism, and cellular growth control. In vertebrates, gap junctions are composed of proteins from the "connexin" gene family. The majority of connexins are modified posttranslationally by phosphorylation, primarily on serine amino acids; however, phosphotyrosine has also been detected in connexin from cells coexpressing nonreceptor tyrosine protein kinases. Connexins are targeted by numerous protein kinases, of which some have been identified: protein kinase C, mitogen-activated protein kinase, and the v-Src tyrosine protein kinase. Phosphorylation has been implicated in the regulation of a broad variety of connexin processes, such as the trafficking, assembly/disassembly, degradation, as well as the gating of gap junction channels. This review examines the consequences of connexin phosphorylation for the regulation of gap junctional communication.

Lessons from pregnancy and parturition: uterine leiomyomas result from discordant differentiation and dedifferentiation responses in smooth muscle cells

Leiomyomas, benign smooth muscle tumors of the uterus, are the most common gynecological neoplasm in women. Studies with human tissues and primary cultures have revealed little about the development of leiomyomas, although several genes have been shown to be differentially expressed in leiomyomas compared to matched normal myometrium. We propose that uterine smooth muscle tumor cells mimic a differentiated myometrial cell of pregnancy, and are associated with a hypersensitivity to sex steroid hormones, preventing the cells from responding to normal apoptotic or dedifferentiation signals which would return the cells to a nongravid phenotype. Support of this hypothesis is derived from experimental studies in female Eker rats which develop uterine leiomyoma with many similarities to the human disease. Members of the steroid receptor superfamily as well as the binding partners and co-regulators necessary for transactivation and gene transcription, may be involved in the altered pathway of cellular differentiation and regulation observed in uterine leiomyomas.

Connexin43 in porcine myocardium and non-pregnant myometrium

It is generally accepted that connexin43 (Cx43) is a major constituent of heart and myometrial gap junctions. However, the presence of Cx43 gap junctions in non-pregnant myometrium is still poorly documented. Tissue sections of porcine heart and non-pregnant uterus and myometrial smooth muscle cell cultures were immunostained with monoclonal antibody against Cx43. In the heart, intensive immunostaining was confined to the intercalated discs as previously reported. In the non-pregnant uterus, punctuate immunostaining of Cx43 was seen throughout the myometrium along cell interfaces between myocytes. The expression of Cx43 was sustained in cultured smooth muscle cells isolated from non-pregnant myometrium. Western blotting has detected single isoform of Cx43 in both, cardiac and myometrial tissues. The electrophoretic mobility of porcine heart Cx43 was similar to that of myometrial isoform but different from the pattern of mobility of Cx43 of the rat heart. Hence, porcine myometrium may provide attractive model for studying cellular mechanisms triggering expression of gap junction protein in normal (non-pregnant) uterus.

Sensitivity of myometrium to CGRP varies during mouse estrous cycle and in response to progesterone

Calcitonin gene-related peptide (CGRP) inhibits contractions of the myometrium. Isometric force measurements on myometrial strips were carried out to monitor the inhibitory capacity of CGRP in the myometrium during the estrous cycle and in response to estrogen and progesterone in ovariectomized mice. CGRP inhibition of KCl-induced contractions was lowest at estrus and significantly increased during metestrus and diestrus. Progesterone treatment of ovariectomized mice resulted in a significant increase in the responsiveness of the myometrium to CGRP. Expression of CGRP-receptor component protein (CGRP-RCP), a marker of CGRP-receptor expression, was quantitated by Western and Northern blot analyses. The levels of inhibition exerted by CGRP during the various stages of the estrous cycle and in response to steroid hormone treatment correlated with the protein levels of CGRP-RCP. The mRNA levels did not change significantly during the estrous cycle or in response to hormone treatment, indicating that the regulation of CGRP-RCP protein does not occur at the transcriptional level. CGRP had an inhibitory effect both when applied before the stimulus for contraction and when applied during a sustained contracture induced by KCl. This suggests that CGRP-induced generation of second messengers can influence late events in electro-/chemomechanical coupling and/or the contractile machinery directly.

Connexin and gap junction degradation

Many of the subunit proteins (connexins) that form gap junctions are rather dynamic, with half-lives of only a few hours. Thus, alterations in connexin turnover and degradation may represent significant mechanisms for the regulation of intercellular communication. We describe a pharmacological approach to determining pathways of connexin degradation. Cell cultures are left untreated or treated with inhibitors of lysosomal or proteasomal proteolysis. Changes in connexin levels, localization, or decay curves (derived from pulse-chase experiments) are assessed by immunoblotting, immunofluorescence, and immunoprecipitation, respectively. Such experiments have provided evidence that connexin43 degradation involves both the lysosome and the proteasome.