Spatial heterogeneity enhances and modulates excitability in a mathematical model of the myometrium

The muscular layer of the uterus (myometrium) undergoes profound changes in global excitability prior to parturition. Here, a mathematical model of the myocyte network is developed to investigate the hypothesis that spatial heterogeneity is essential to the transition from local to global excitation which the myometrium undergoes just prior to birth. Each myometrial smooth muscle cell is represented by an element with FitzHugh–Nagumo dynamics. The cells are coupled through resistors that represent gap junctions. Spatial heterogeneity is introduced by means of stochastic variation in coupling strengths, with parameters derived from physiological data. Numerical simulations indicate that even modest increases in the heterogeneity of the system can amplify the ability of locally applied stimuli to elicit global excitation. Moreover, in networks driven by a pacemaker cell, global oscillations of excitation are impeded in fully connected and strongly coupled networks. The ability of a locally stimulated cell or pacemaker cell to excite the network is shown to be strongly dependent on the local spatial correlation structure of the couplings. In summary, spatial heterogeneity is a key factor in enhancing and modulating global excitability

Reconstruction of cell surface densities of ion pumps, exchangers, and channels from mRNA expression, conductance kinetics, whole-cell calcium, and current-clamp voltage recordings, with an application to human uterine smooth muscle cells

Uterine smooth muscle cells remain quiescent throughout most of gestation, only generating spontaneous action potentials immediately prior to, and during, labor. This study presents a method that combines transcriptomics with biophysical recordings to characterise the conductance repertoire of these cells, the ‘conductance repertoire’ being the total complement of ion channels and transporters expressed by an electrically active cell. Transcriptomic analysis provides a set of potential electrogenic entities, of which the conductance repertoire is a subset. Each entity within the conductance repertoire was modeled independently and its gating parameter values were fixed using the available biophysical data. The only remaining free parameters were the surface densities for each entity. We characterise the space of combinations of surface densities (density vectors) consistent with experimentally observed membrane potential and calcium waveforms. This yields insights on the functional redundancy of the system as well as its behavioral versatility. Our approach couples high-throughput transcriptomic data with physiological behaviors in health and disease, and provides a formal method to link genotype to phenotype in excitable systems. We accurately predict current densities and chart functional redundancy. For example, we find that to evoke the observed voltage waveform, the BK channel is functionally redundant whereas hERG is essential. Furthermore, our analysis suggests that activation of calcium-activated chloride conductances by intracellular calcium release is the key factor underlying spontaneous depolarisations

The inwardly rectifying K+ channel KIR7.1 controls uterine excitability throughout pregnancy

Abnormal uterine activity in pregnancy causes a range of important clinical disorders, including preterm birth, dysfunctional labour and post-partum haemorrhage. Uterine contractile patterns are controlled by the generation of complex electrical signals at the myometrial smooth muscle plasma membrane. To identify novel targets to treat conditions associated with uterine dysfunction, we undertook a genome-wide screen of potassium channels that are enriched in myometrial smooth muscle. Computational modelling identified Kir7.1 as potentially important in regulating uterine excitability during pregnancy. We demonstrate Kir7.1 current hyper-polarizes uterine myocytes and promotes quiescence during gestation. Labour is associated with a decline, but not loss, of Kir7.1 expression. Knockdown of Kir7.1 by lentiviral expression of miRNA was sufficient to increase uterine contractile force and duration significantly. Conversely, overexpression of Kir7.1 inhibited uterine contractility. Finally, we demonstrate that the Kir7.1 inhibitor VU590 as well as novel derivative compounds induces profound, long-lasting contractions in mouse and human myometrium; the activity of these inhibitors exceeds that of other uterotonic drugs. We conclude Kir7.1 regulates the transition from quiescence to contractions in the pregnant uterus and may be a target for therapies to control uterine contractility

Voltage-dependent Ca2+ currents contribute to spontaneous Ca2+ waves in rabbit corpus cavernosum myocytes

Introduction.  Corpus cavernosum myocytes generate spontaneous tone that contributes to penile detumescence. It is essential to elucidate how tone is generated to fully understand the processes involved in erection. Tissue experiments have shown that blockers of voltage-dependent Ca2+ channels (VDCCs) reduce tone. However, there is also a widespread belief that these channels are poorly expressed in this tissue. Furthermore, it is unclear how VDCC would interact with recently described intracellular Ca2+ waves, which initiate contractions. Aims.  (i) To directly examine VDCC currents in freshly isolated corpus cavernosum myocytes; and (ii) to study the relationship between VDCC and intracellular Ca2+ waves. Main Outcome Measures.  VDCC and cytosolic Ca2+ were measured using patch clamp and confocal microscopy. Methods.  Male New Zealand white rabbits were euthanized and corpus cavernosum myocytes dispersed enzymatically for patch clamp recording and confocal Ca2+ imaging (using fluo-4AM). Results.  Isolated myocytes developed robust VDCC that could be separated into two components. One activated at −45 mV, reversed at +40 mV, inactivated with a V1/2 of −27 mV and was enhanced by Ba2+. This component was blocked with nifedipine, but not Ni2+ or mibefradil. The other component inactivated with a V1/2 of −87 mV, was unchanged in Ba2+, and was blocked by Ni2+ or mibefradil, but not nifedipine. Even though Ni2+ had no effect on intracellular Ca2+ waves, nifedipine blocked them, although localized Ca2+ events remained. Conclusions.  At least two VDCC are expressed in rabbit corpus cavernousum myocytes. One may be designated L-type Ca2+ current, whereas the other is a putative T-type current. The L-current facilitates conversion of local Ca2+ events into global Ca2+ waves, whereas the putative T-current plays little part in this process. These results provide a new basis for understanding the role of L-type Ca2+ current in generating detumescent tone in the corpus cavernosum. McCloskey C, Cagney V, Large R, Hollywood M, Sergeant G, McHale N, and Thornbury K. Voltage-dependent Ca2+ currents contribute to spontaneous Ca2+ waves in rabbit corpus cavernosum myocytes. J Sex Med 2009;6:3019–3031

CACNA1D overexpression and voltage‑gated calcium channels in prostate cancer during androgen deprivation

Prostate cancer is often treated by perturbing androgen receptor signalling. CACNA1D, encoding CaV1.3 ion channels is upregulated in prostate cancer. Here we show how hormone therapy affects CACNA1D expression and CaV1.3 function. Human prostate cells (LNCaP, VCaP, C4-2B, normal RWPE-1) and a tissue microarray were used. Cells were treated with anti-androgen drug, Enzalutamide (ENZ) or androgen-removal from media, mimicking androgen-deprivation therapy (ADT). Proliferation assays, qPCR, Western blot, immunofluorescence, Ca2+-imaging and patch-clamp electrophysiology were performed. Nifedipine, Bay K 8644 (CaV1.3 inhibitor, activator), mibefradil, Ni2+ (CaV3.2 inhibitors) and high K+ depolarising solution were employed. CACNA1D and CaV1.3 protein are overexpressed in prostate tumours and CACNA1D was overexpressed in androgen-sensitive prostate cancer cells. In LNCaP, ADT or ENZ increased CACNA1D time-dependently whereas total protein showed little change. Untreated LNCaP were unresponsive to depolarising high K+/Bay K (to activate CaV1.3); moreover, currents were rarely detected. ADT or ENZ-treated LNCaP exhibited nifedipine-sensitive Ca2+-transients; ADT-treated LNCaP exhibited mibefradil-sensitive or, occasionally, nifedipine-sensitive inward currents. CACNA1D knockdown reduced the subpopulation of treated-LNCaP with CaV1.3 activity. VCaP displayed nifedipine-sensitive high K+/Bay K transients (responding subpopulation was increased by ENZ), and Ni2+-sensitive currents. Hormone therapy enables depolarization/Bay K-evoked Ca2+-transients and detection of CaV1.3 and CaV3.2 currents. Physiological and genomic CACNA1D/CaV1.3 mechanisms are likely active during hormone therapy—their modulation may offer therapeutic advantage

Spruce bark beetle (Ips typographus) on the territory of the Šumava national park - biology, occurrence and methods of forest protection

<p>(A) Simulated voltage clamp traces of homomeric Kv7.4 channel at 28°C from holding potential of −90 mV, where the voltage was stepped to values up to +40 mV in increments of 10 mV, subsequently stepped down to −120 mV. (B) Steady state activation curves from Miceli et al [<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1004828#pcbi.1004828.ref096" target="_blank">96</a>]. (C) Simulated activation fast time constant derived from experimental data (filled circles) from Schröder et al [<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1004828#pcbi.1004828.ref034" target="_blank">34</a>].</p

Pilot scale production and demonstration of low cost MOFs for chilling applications

SSCI-VIDE+ING+DFA:CDAInternational audienceWe present here the results of a 3-year project aiming at the development of pilot scale production and shaping of MOFs and at their demonstration in Heat-Pump application at kilogram scale in relevant process conditions.Although MOFs outperform commercial adsorbents for heat-pump application in terms of higher water uptake and cyclability, their commercialisation was until now strongly penalized by their price due to high production process costs. The objective of this program was to develop low cost manufacture processes allowing the production of advanced and cost-competitive adsorbents. We have developed innovative and scalable MOF production processes including synthesis and shaping, for which (i) manufacturing equipment’s are readily available at industrial scale, and (ii) enable upscaling at high production rates whilst achieving high yields, product (sorbent) quality and higher operational safety. We will present three main technological innovations: (i) aqueous synthesis of UiO-66 without the use of corrosive acid modulator (ii) continuous mechano-chemical synthesis on Al-fumarate without solvent and (iii) original scalable shaping process enabling continuous production of robust and size-controlled spheres (beads). In contrast to other adsorbents, we discovered that performances of MOF were jeopardized due to severe mass transport limitations likely due to the organic binder. In order to overcome this limitation small spheres of 0.4 mm (0.3 mm – 0.7 mm) of Al- and Zr-MOF were produced at multi-kg scale. The performances of MOFs were evaluated in 3 liter adsorber demonstrator. We will show that MOFs outperform commercial Silica Gel under standard cycling conditions with stability over 10.000 cycles. Results in extremely low regeneration temperature will be presented and discussed in the frame application market requirements.This work has received funding from the EU under grant agreement No 685727