The effect of extracellular ATP on rat uterine contraction from different gestational stages and its possible mechanisms of action

Golgi Reassembly Stacking Protein 2 Modulates Myometrial Contractility during Labor by Affecting ATP Production

The mechanism of maintaining myometrial contractions during labor remains unclear. Autophagy has been reported to be activated in laboring myometrium, along with the high expression of Golgi reassembly stacking protein 2 (GORASP2), a protein capable of regulating autophagy activation. This study aimed to investigate the role and mechanism of GORASP2 in uterine contractions during labor. Western blot confirmed the increased expression of GORASP2 in laboring myometrium. Furthermore, the knockdown of GORASP2 in primary human myometrial smooth muscle cells (hMSMCs) using siRNA resulted in reduced cell contractility. This phenomenon was independent of the contraction-associated protein and autophagy. Differential mRNAs were analyzed using RNA sequencing. Subsequently, KEGG pathway analysis identified that GORASP2 knockdown suppressed several energy metabolism pathways. Furthermore, reduced ATP levels and aerobic respiration impairment were observed in measuring the oxygen consumption rate (OCR). These findings suggest that GORASP2 is up-regulated in the myometrium during labor and modulates myometrial contractility mainly by maintaining ATP production.

Pimpinella anisum extract attenuates spontaneous and agonist-induced uterine contraction in term-pregnant rats

ETHNOPHARMACOLOGY RELEVANCE

Pimpinella anisum is a well-known traditional medicinal herb which has been used in folk medicine as an antiulcer, anticancer, antibacterial and as a muscle relaxant.

AIM OF THE STUDY

This study was performed to explore the modulatory effects of Pimpinella anisum on term-pregnant rat uterine contractility and to investigate its possible underlying mechanisms.

MATERIAL AND METHODS

Intact uterine strips without endometrial layer were isolated from female term-pregnant Wistar rats (22 days of gestation) and mounted in a tissue bath apparatus for in vitro isometric force recording. The effects of different concentrations of Pimpinella anisum extract (PAE) (1, 3, 5, and 7 mg/mL) were examined on uterine contractions generated spontaneously or induced with oxytocin (5 nmol/L), Bay K8644 (1 μmol/L), and carbachol (10 μmol/L). In some experiments, PAE was applied on depolarized myometrium in the presence of high-KCl solution (60 mmol/L). The effect on Ca²⁺ release was also examined.

RESULTS

Application of PAE significantly reduced uterine contractions generated spontaneously or induced with oxytocin, Bay K8644, and carbachol in a concentration-dependent manner (n = 7; P < 0.01). In depolarized myometrium, PAE significantly reduced the tonic force induced by high-KCl solution (n = 7; P < 0.01). PAE prevented oxytocin-induced transient contraction in the entire absence of external calcium (n = 7; P < 0.01).

CONCLUSION

The present findings demonstrate the potentials of PAE to relax pregnant uterine contractions possibly by blocking Ca²⁺ entry via L-type calcium channels and inhibiting Ca²⁺ release from the internal store. The tocolytic effects of PAE may be a potential adjuvant against strong premature uterine contractions which threaten early pregnancy although clinical studies are required.

Electro-Mechanical Ionic Channel Modeling for Uterine Contractions and Oxytocin Effect during Pregnancy

Uterine contractions during normal pregnancy and preterm birth are an important physiological activity. Although the cause of preterm labor is usually unknown, preterm birth creates very serious health concerns in many cases. Therefore, understanding normal birth and predicting preterm birth can help both newborn babies and their families. In our previous work, we developed a multiscale dynamic electrophysiology model of uterine contractions. In this paper, we mainly focus on the cellular level and use electromyography (EMG) and cell force generation methods to construct a new ionic channel model and a corresponding mechanical force model. Specifically, the ionic channel model takes into consideration the knowledge of individual ionic channels, which include the electrochemical and bioelectrical characteristics of individual myocytes. We develop a new sodium channel and a new potassium channel based on the experimental data from the human myometrium and the average correlations are 0.9946 and 0.9945, respectively. The model is able to generate the single spike, plateau type and bursting type of action potentials. Moreover, we incorporate the effect of oxytocin on changing the properties of the L-type and T-type calcium channels and further influencing the output action potentials. In addition, we develop a mechanical force model based on the new ionic channel model that describes the detailed ionic dynamics. Our model produces cellular mechanical force that propagates to the tissue level. We illustrate the relationship between the cellular mechanical force and the intracellular ionic dynamics and discuss the relationship between the application of oxytocin and the output mechanical force. We also propose a simplified version of the model to enable large scale simulations using sensitivity analysis method. Our results show that the model is able to reproduce the bioelectrical and electromechanical characteristics of uterine contractions during pregnancy.

A computational model of excitation and contraction in uterine myocytes from the pregnant rat

Aberrant uterine myometrial activities in humans are major health issues. However, the cellular and tissue mechanism(s) that maintain the uterine myometrium at rest during gestation, and that initiate and maintain long-lasting uterine contractions during delivery are incompletely understood. In this study we construct a computational model for describing the electrical activity (simple and complex action potentials), intracellular calcium dynamics and mechanical contractions of isolated uterine myocytes from the pregnant rat. The model reproduces variant types of action potentials - from spikes with a smooth plateau, to spikes with an oscillatory plateau, to bursts of spikes - that are seen during late gestation under different physiological conditions. The effects of the hormones oestradiol (via reductions in calcium and potassium selective channel conductance), oxytocin (via an increase in intracellular calcium release) and the tocolytic nifedipine (via a block of L-type calcium channels currents) on action potentials and contractions are also reproduced, which quantitatively match to experimental data. All of these results validated the cell model development. In conclusion, the developed model provides a computational platform for further investigations of the ionic mechanism underlying the genesis and control of electrical and mechanical activities in the rat uterine myocytes.

The Effects of Ibogaine on Uterine Smooth Muscle Contractions: Relation to the Activity of Antioxidant Enzymes

Ibogaine is an indole alkaloid originally extracted from the root bark of the African rainforest shrub Tabernanthe iboga. It has been explored as a treatment for substance abuse because it interrupts drug addiction and relieves withdrawal symptoms. However, it has been shown that ibogaine treatment leads to a sharp and transient fall in cellular ATP level followed by an increase of cellular respiration and ROS production. Since contractile tissues are sensitive to changes in the levels of ATP and ROS, here we investigated an ibogaine-mediated link between altered redox homeostasis and uterine contractile activity. We found that low concentrations of ibogaine stimulated contractile activity in spontaneously active uteri, but incremental increase of doses inhibited it. Inhibitory concentrations of ibogaine led to decreased SOD1 and elevated GSH-Px activity, but doses that completely inhibited contractions increased CAT activity. Western blot analyses showed that changes in enzyme activities were not due to elevated enzyme protein concentrations but posttranslational modifications. Changes in antioxidant enzyme activities point to a vast concentration-dependent increase in H₂O₂ level. Knowing that extracellular ATP stimulates isolated uterus contractility, while H₂O₂ has an inhibitory effect, this concentration-dependent stimulation/inhibition could be linked to ibogaine-related alterations in ATP level and redox homeostasis.

Changes in expression of P2X7 receptors in rat myometrium at different gestational stages and the mechanism of ATP-induced uterine contraction

AIMS

Given the importance of ATP in the control of uterine activity for successful labor and involution, this study was performed to measure the level of P2X7 receptors (P2X7Rs) in rat myometrium at different gestational stages and to investigate the mechanisms of ATP-induced uterine contraction.

MATERIALS AND METHODS

Myometrial tissues were obtained from rats at different gestational stages and the level of P2X7Rs was measured by ELISA. In other experiments, the effect of 1 mM ATP was tested on spontaneous contraction and the underlying mechanisms were investigated.

KEY FINDINGS

P2X7Rs were expressed in nonpregnant uterine tissues, progressively increased throughout pregnancy, and markedly peaked during postpartum involution. ATP significantly increased the force of spontaneous contraction in all uterine strips from different gestational stages with marked increase during labor and postpartum. ATP could not maintain the force when external Ca²⁺ was removed. In addition, ATP was able to cause tonic transient contraction in the absence of external Ca²⁺.

SIGNIFICANCE

P2X7Rs are functionally regulated and contributed to ATP-induced uterine contraction. The sensitivity of the myometrium to ATP increases as pregnancy progresses and it involves Ca²⁺ influx and Ca²⁺ release pathways. The clear effects of ATP on contractility suggest its physiological requirement for successful labor and postpartum involution.

Purinergic Signalling: Therapeutic Developments

Purinergic signalling, i.e., the role of nucleotides as extracellular signalling molecules, was proposed in 1972. However, this concept was not well accepted until the early 1990's when receptor subtypes for purines and pyrimidines were cloned and characterised, which includes four subtypes of the P1 (adenosine) receptor, seven subtypes of P2X ion channel receptors and 8 subtypes of the P2Y G protein-coupled receptor. Early studies were largely concerned with the physiology, pharmacology and biochemistry of purinergic signalling. More recently, the focus has been on the pathophysiology and therapeutic potential. There was early recognition of the use of P1 receptor agonists for the treatment of supraventricular tachycardia and A2A receptor antagonists are promising for the treatment of Parkinson's disease. Clopidogrel, a P2Y12 antagonist, is widely used for the treatment of thrombosis and stroke, blocking P2Y12 receptor-mediated platelet aggregation. Diquafosol, a long acting P2Y2 receptor agonist, is being used for the treatment of dry eye. P2X3 receptor antagonists have been developed that are orally bioavailable and stable in vivo and are currently in clinical trials for the treatment of chronic cough, bladder incontinence, visceral pain and hypertension. Antagonists to P2X7 receptors are being investigated for the treatment of inflammatory disorders, including neurodegenerative diseases. Other investigations are in progress for the use of purinergic agents for the treatment of osteoporosis, myocardial infarction, irritable bowel syndrome, epilepsy, atherosclerosis, depression, autism, diabetes, and cancer.