Extracellular acidification increases uterine contraction in pregnant mouse by increasing intracellular calcium.

AIMS: As uterine extracellular pH decreases during the ischemic conditions of labor, but its effects on myometrial contraction are largely unknown, there is a need to elucidate its physiological effects and mechanisms of action. Furthermore, it is not known if any of the effects of extracellular acidification are affected by pregnancy, thus we also determined how gestation affects the response to acidification. METHODS: Nonpregnant, mid-, and term-pregnant myometrial strips were obtained from humanely killed mice. Contractions were recorded under spontaneous, depolarized, and oxytocin-stimulated conditions. The extracellular pH of the perfusate was changed from 7.4 to 6.9 or 7.9 in HEPES-buffered physiological saline. Intracellular pH was measured using SNARF, and intracellular calcium was measured using Indo-1. Statistical differences were tested using the appropriate t-test. RESULTS: Extracellular acidification significantly increased the frequency and amplitude of spontaneous contractions in pregnant, but not nonpregnant, myometrium, whereas alkalinization decreased contractions. Intracellular acidification, via Na-butyrate, transiently increased force in pregnant tissue. Intracellular pH was gradually acidified when extracellular pH was acidified, but extracellular acidification increased contractility before any significant change in intracellular pH. If myometrial force was driven by oxytocin or high-K depolarization, then extracellular pH did not further increase force. Intracellular calcium changes mirrored those of force in the spontaneously contracting pregnant myometrium, and if calcium entry was prevented by nifedipine, extracellular acidification could not induce a rise in force. CONCLUSION: Extracellular acidification increases excitability, calcium entry, and thus force in pregnant mouse myometrium, and this may contribute to increasing contractions during labor when ischemic conditions and acidemia occur.

Adult brain tumour research in 2024: Status, challenges and recommendations.

In 2015, a groundswell of brain tumour patient, carer and charity activism compelled the UK Minister for Life Sciences to form a brain tumour research task and finish group. This resulted, in 2018, with the UK government pledging £20m of funding, to be paralleled with £25m from Cancer Research UK, specifically for neuro-oncology research over the subsequent 5 years. Herein, we review if and how the adult brain tumour research landscape in the United Kingdom has changed over that time and what challenges and bottlenecks remain. We have identified seven universal brain tumour research priorities and three cross-cutting themes, which span the research spectrum from bench to bedside and back again. We discuss the status, challenges and recommendations for each one, specific to the United Kingdom.

Lecture Capture: Friend or Foe?

Lecture capture (LC)-a recording of the live lecture provided as a supplementary resource-is accepted as a standard provision in UK higher education. Previous research has shown it to be very popular with students, although there have been conflicting findings in terms of its impact on attendance and attainment, and suggestions that student engagement with this resource varies depending on their own preferences and approaches. The aim of the present study was to determine the impact of LC on students in a wider sense, encompassing pedagogic and pastoral aspects of student development. This mixed-methods study analyzed focus group and questionnaire data from first- and second-year veterinary students at one UK university. Results demonstrated the student belief that LC is important for learning and well-being but highlighted the facilitation of passive and surface learning that this resource offers. More worryingly, this study identified a group of students for whom this resource may be particularly unhelpful. This group, relied excessively upon LC for learning, felt overwhelmed by their workload despite working fewer hours, and subsequently achieved poorer exam results. A key theme in this negative relationship appeared to be low self-efficacy. The findings enable educators to consider how resources are provided and to encourage implementing mechanisms to help students make better choices, and take control of their learning.

Peer-assisted learning - an antidote for spoonfeeding? Reflections on peer-assisted learning activites in a veterinary curriculum.

This article was migrated. The article was marked as recommended. Peer-assisted learning (PAL) is a potentially valuable teaching tool for students on veterinary and medical curricula, helping them to develop crucial learning, teaching and meta-adaptive skills ( Lizzio & Wilson, 2004) which will serve them during their undergraduate studies and throughout their future careers. This reflective article describes experiences of PAL activities on a UK veterinary degree course, and discusses potential reasons for success and failure of such activities. Advice is given for anyone planning to implement, or reviewing their own experiences of PAL.

Inhibitory effect of visfatin and leptin on human and rat myometrial contractility.

AIMS: The purpose of this study was to investigate the effect of visfatin on in vitro myometrial contractility in human and rat, and compare it to leptin. MAIN METHODS: Myometrial strips from term pregnant women having a caesarean section or rats were dissected, superfused with physiological saline and the effects of visfatin (500pM-25nM) or leptin (1nM-1µM), on spontaneous and oxytocin-induced contractions were studied. After establishment of regular contractions, tissues were incubated for control and test response at 37°C for 20min, and then contractility was assayed. KEY FINDINGS: In human and rat myometrium, visfatin had similar dose dependent effects on contractility. In the human myometrium, compared with that of controls (100%), 10nM produced a significant (paired t-test) decrease in the 20min integral of spontaneous (64±8%, n=13) and oxytocin-induced contractions (55±9%, n=5), mean±SEM. In rat tissue the decrease was also significant (spontaneous, 76±7%, n=7; oxytocin-induced 68±6%, n=3). Leptin at this concentration (10nM) had no effect in rat or human, and even at a higher concentration (1µM) produced only a small inhibitory effect (~ 80%) on contractions. SIGNIFICANCE: These data are the first to show that visfatin inhibits myometrial contractility and does so more potently than leptin. Our data suggest that increased output of visfatin and leptin in obese pregnant women may impair uterine contractility resulting in an unplanned Caesarean delivery.

Myometrial physiology--time to translate?

In this short review, we discuss how recent insights into myometrial physiology may be taken forward and translated into much-needed novel therapies for problems associated with labour. We consider excitation-contraction coupling in the myometrium and how this relates to our understanding of the changes that occur to produce myometrial contractions and successful labour. We then discuss how this information has already been used in the development of drugs to either stimulate or relax the myometrium, to address the needs of women with either slow (dystocic) labours or threatened preterm labours, respectively. We next present the data showing how basic physiological findings pertaining to hypoxia and lactate production have been taken and translated into a tool for predicting and thus better managing difficult labours. We then highlight examples of where physiological research has started to provide mechanistic insight into clinical problems associated with labour and parturition (obesity, diabetes, advanced maternal age, postdate and twin pregnancies) and suggest how these findings could be translated into new therapies for difficult labours.

What do we know about what happens to myometrial function as women age?

Much has been written about the effects of aging on reproductive function, especially female fertility. Much less is known about how aging may affect the contractility of the smooth muscle within the uterus, the myometrium. The myometrium is active through a woman's entire life, not just during pregnancy. Here we will discuss briefly the contractile functions of the uterus and the changes it undergoes throughout the stages of a woman's life from menstruation and the menopause, before evaluating the evidence for any changes in myometrial contractility and responses as women age, with a particular focus on women of advanced maternal age. We present original contractility analysis for the widest data set for human myometrium so far examined, and determine inherent spontaneous activity as well as responses to depolarisation and stimulation with oxytocin. Our data show that in the non-pregnant state there is a significant decrease in contractility for both spontaneous and depolarised-induced contractions, with age. We suggest that muscle atrophy and down regulation of Ca channels may account for this. Interestingly in pregnant myometrium we found a wide range of contractile ability between women and little evidence for decreased spontaneous activity between the ages of 25-40. Oxytocin responses appear to be more affected by aging, a finding that is consistent with previously reported clinical findings, and may partly be the result of membrane lipids such as cholesterol, increasing as women age. The marked differences between the age-related decline of force beyond age 30 in non-pregnant uterus, and the lack of difference in the pregnant state over this period, shows that the uterus retains its ability to respond to gestational hormones. The growth of the pregnant uterus and increase in content of myofibrillar proteins, may abolish any previous age-related force deficit. This finding is consistent with what is apparent for postmenopausal women in their 50s and 60s; that with the appropriate hormonal stimulation the uterus can allow an embryo to implant, and then without further intervention, carry the foetus to term. It is tempting therefore to speculate that unlike other well documented declines in female reproductive functions with age, the myometrium remains able to function into a woman's 7th decade.

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.

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

The uterine sacroplasmic reticulum (SR) takes up and stores calcium [Ca], using an ATPase (SERCA) and the Ca-buffering proteins, calsequestrin and calreticulin. This stored Ca can be released via IP(3)-gated Ca channels. Decreases in luminal Ca concentration [Ca] have been directly measured following agonist stimulation. During spontaneous contractions however, there appears to be no involvement of the SR, as Ca entry and efflux across the plasma membrane account for these phasic contractions. After over-viewing current knowledge concerning SR structure and function, we highlight three areas of research which suggest new ways of looking at the role of the SR in the uterus, although they may be controversial or speculative at the moment. Firstly, we review the evidence for the function, if any, of Ca-induced SR Ca release channels, the ryanodine receptor (RyR) and the lack of Ca sparks (the elemental release events from RyRs), in the uterus. Secondly, we ask does regulation of SERCA by the accessory protein, phospholamban, occur in the uterus and what is the effect of knocking out phospholamban on uterine activity? Thirdly, we address the question of when and how store-operated Ca entry occurs in the myometrium. By analogy with other, usually less excitable tissues, is there a mechanism that links store Ca depletion to plasma membrane Ca entry in smooth muscle cells within intact uterus and is it physiologically relevant and regulated? Are the recently described proteins ORAI and STIM-1 involved in uterine store-operated Ca entry? We end the review by integrating these new insights with previous data to present a new working model of the SR in the uterus.

In situ calcium signaling: no calcium sparks detected in rat myometrium.

Controlled uterine smooth muscle activity is essential for our reproductive health. While we understand reasonably well the steps that produce contraction following a rise in intracellular [Ca], the mechanism controlling excitability and thus the rise of Ca, is less well understood. Here we examine the role of the internal Ca sore, the sarcoplasmic reticulum (SR), and its relation to surface membrane ion channels. We show that despite having a well-developed SR, the rat uterus does not produce the elemental and local Ca signals, known as Ca sparks. This in turn has consequences for excitability, as the negative feedback loop between these Ca signals and Ca-activated K (BK) channels on the surface membrane is lost. This may be important for producing the powerful long-lasting contractions of the uterus required during labor.

Lipid rafts, the sarcoplasmic reticulum and uterine calcium signalling: an integrated approach.

The pathways involved in Ca2+ signalling in the uterus remain incompletely understood, impairing our ability to prevent preterm and difficult labours. In this review we focus on two elements in the pathway of Ca2+ signalling that have recently emerged as playing important roles: membrane lipid rafts and the sarcoplasmic reticulum. We examine the evidence for lipid rafts in the uterus and discuss their functional role. We suggest that the increases in cytosolic [Ca2+] and contractility that occur with raft disruption are due, at least in part, to effects on large conductance Ca2+-activated K+ (BK) channels that are localized to rafts. The role of the SR in contributing to subsarcolemmal cytosolic microdomains in uterus is evaluated, along with its interactions with ion channels on the plasma membrane. Thus, signalling microdomains play an important, but incompletely understood, role in the uterus, and integrating them into other Ca2+ signalling pathways is a challenge for further research. We suggest that the role of the SR changes in pregnancy, from promoting quiescence via BK channels or SR Ca2+ uptake, to promoting Ca2+ entry and contractility at term, and relate data on lipid rafts to clinical outcome in obese pregnant women.

Calcium signalling in smooth muscle.

Calcium signalling in smooth muscles is complex, but our understanding of it has increased markedly in recent years. Thus, progress has been made in relating global Ca2+ signals to changes in force in smooth muscles and understanding the biochemical and molecular mechanisms involved in Ca2+ sensitization, i.e. altering the relation between Ca2+ and force. Attention is now focussed more on the role of the internal Ca2+ store, the sarcoplasmic reticulum (SR), global Ca2+ signals and control of excitability. Modern imaging techniques have shown the elaborate SR network in smooth muscles, along with the expression of IP3 and ryanodine receptors. The role and cross-talk between these two Ca(2+) release mechanisms, as well as possible compartmentalization of the SR Ca2+ store are discussed. The close proximity between SR and surface membrane has long been known but the details of this special region to Ca2+ signalling and the role of local sub-membrane Ca2+ concentrations and membrane microdomains are only now emerging. The activation of K+ and Cl- channels by local Ca2+ signals, can have profound effects on excitability and hence contraction. We examine the evidence for both Ca2+ sparks and puffs in controlling ion channel activity, as well as a fundamental role for Ca2+ sparks in governing the period of inexcitability in smooth muscle, i.e. the refractory period. Finally, the relation between different Ca2+ signals, e.g. sparks, waves and transients, to smooth muscle activity in health and disease is becoming clearer and will be discussed.

The role of the sarcoplasmic reticulum in neonatal uterine smooth muscle: enhanced role compared to adult rat.

Little is known about contractile activity, response to agonists or excitation-contraction coupling in neonatal smooth muscle. We have therefore investigated 10-day rat uterus to better understand these processes, and compared it to adult uterus to elucidate how control of contractility develops. Spontaneous contractions are present in the 10-day neonatal uterus, although they are not as large or as regular as those present in adult tissues. External Ca(2+) entry via L-type Ca(2+) channels is the sole source of Ca(2+) and is essential for the spontaneous activity. The neonatal uterus was responsive to carbachol or prostaglandin F(2alpha) application; it showed a marked stimulation and a clear dissociation between the force and Ca(2+) changes. Such sensitization was not apparent in adult rat myometrium. The sarcoplasmic reticulum (SR) had more releasable Ca(2+) and contributed more to the response to agonists in neonatal compared to adult tissues. Thus, Ca(2+) entry as opposed to SR Ca(2+) release contributed much less to the uterine response to agonists in the neonatal, compared to adult tissues. Inhibition of the SR by cyclopiazonic acid also caused a more vigorous increase in Ca(2+) and contractile activity, particularly frequency, in the neonatal compared to the adult uterus. Taken together these data suggest that: (1) spontaneous activity is already present by day 10, (2) receptor-coupling and excitation-contraction signalling pathways are functional, (3) the SR and Ca(2+) sensitization mechanisms play a more prominent role in the neonate, and (4) there is a shift to a greater reliance on Ca(2+) entry and excitability with development of the myometrium.