Statistical mechanics of the human placenta : a stationary state of a near-equilibrium system in a linear regime

All near-equilibrium systems under linear regime evolve to stationary states in which there is constant entropy production rate. In an open chemical system that exchanges matter and energy with the exterior, we can identify both the energy and entropy flows associated with the exchange of matter and energy. This can be achieved by applying statistical mechanics (SM), which links the microscopic properties of a system to its bulk properties. In the case of contractile tissues such as human placenta, Huxley's equations offer a phenomenological formalism for applying SM. SM was investigated in human placental stem villi (PSV) (n = 40). PSV were stimulated by means of KCl exposure (n = 20) and tetanic electrical stimulation (n = 20). This made it possible to determine statistical entropy (S), internal energy (E), affinity (A), thermodynamic force (A / T) (T: temperature), thermodynamic flow (v) and entropy production rate (A / T x v). We found that PSV operated near equilibrium, i.e., A ≺≺ 2500 J/mol and in a stationary linear regime, i.e., (A / T) varied linearly with v. As v was dramatically low, entropy production rate which quantified irreversibility of chemical processes appeared to be the lowest ever observed in any contractile system

Comparative statistical mechanics of muscle and non-muscle contractile systems : stationary states of near-equilibrium systems in a linear regime

A. Huxley’s equations were used to determine the mechanical properties of muscle myosin II (MII) at the molecular level, as well as the probability of the occurrence of the different stages in the actin–myosin cycle. It was then possible to use the formalism of statistical mechanics with the grand canonical ensemble to calculate numerous thermodynamic parameters such as entropy, internal energy, affinity, thermodynamic flow, thermodynamic force, and entropy production rate. This allows us to compare the thermodynamic parameters of a non-muscle contractile system, such as the normal human placenta, with those of different striated skeletal muscles (soleus and extensor digitalis longus) as well as the heart muscle and smooth muscles (trachea and uterus) in the rat. In the human placental tissues, it was observed that the kinetics of the actin–myosin crossbridges were considerably slow compared with those of smooth and striated muscular systems. The entropy production rate was also particularly low in the human placental tissues, as compared with that observed in smooth and striated muscular systems. This is partly due to the low thermodynamic flow found in the human placental tissues. However, the unitary force of non-muscle myosin (NMII) generated by each crossbridge cycle in the myofibroblasts of the human placental tissues was similar in magnitude to that of MII in the myocytes of both smooth and striated muscle cells. Statistical mechanics represents a powerful tool for studying the thermodynamics of all contractile muscle and non-muscle systems

Prospective study of Hepatitis E Virus infection among pregnant women in France.

International audienceBACKGROUND: Hepatitis E Virus (HEV) infection has a poor prognosis among pregnant women from high endemic countries. HEV-prevalence and incidence among pregnant women is unknown in high-income countries such as France. This prospective study was conducted to assess HEV infection in this setting. FINDINGS: An overall HEV prevalence of 7.74% was observed among 315 pregnant women. Seroprevalence was higher in south than in north of France (29.3% vs. 3.6%, p < 0.0001), and women with detectable IgG were older. No IgG seroconversion or IgM detection were observed during pregnancy. CONCLUSIONS: Data suggest that HEV infection is a rare occurrence during pregnancy even in regions of western countries with high seroprevalence rates

Ultraslow Myosin Molecular Motors of Placental Contractile Stem Villi in Humans

Human placental stem villi (PSV) present contractile properties. In vitro mechanics were investigated in 40 human PSV. Contraction of PSV was induced by both KCl exposure (n = 20) and electrical tetanic stimulation (n = 20). Isotonic contractions were registered at several load levels ranging from zero-load up to isometric load. The tension-velocity relationship was found to be hyperbolic. This made it possible to apply the A. Huxley formalism for determining the rate constants for myosin cross-bridge (CB) attachment and detachment, CB single force, catalytic constant, myosin content, and maximum myosin ATPase activity. These molecular characteristics of myosin CBs did not differ under either KCl exposure or tetanus. A comparative approach was established from studies previously published in the literature and driven by mean of a similar method. As compared to that described in mammalian striated muscles, we showed that in human PSV, myosin CB rate constants for attachment and detachment were about 103 times lower whereas myosin ATPase activity was 105 times lower. Up to now, CB kinetics of contractile cells arranged along the long axis of the placental sheath appeared to be the slowest ever observed in any mammalian contractile tissue

Thermodynamic force versus PD3 probability relationship.

<p>There was a negative linear relationship between thermodynamic force and PD3 probability. Thermodynamic force = 1.2–12.2 PD3; r = 0.99.</p

Entropy production rate versus microcanonical partition function.

<p>There was a curvilinear relationship between entropy production rate and microcanonical partition function.</p

Thermodynamic parameters of human placental stem villi (PSV) under electrical tetanus and KCl [0.05M].

<p>Affinity of the CB cycle (J/mol); Thermodynamic force (J/mol/T); Thermodynamic flow (mol/L/s); EPR: Entropy production rate (J/T/L/s); S: Statistical entropy (J/mol/T); E: Internal energy (J/mol)); z: microcanonical partition function (dimensionless); k_cat: catalytic constant (s^-1); myosin content (nM/L). Values are means ± SD. For all parameters presented in Table 1, there were no statistical differences between tetanus and KCl exposure by applying the unpaired t test, as attested by the p-values.</p><p>Thermodynamic parameters of human placental stem villi (PSV) under electrical tetanus and KCl [0.05M].</p

Entropy production rate versus thermodynamic force.

<p>There was a curvilinear relationship between entropy production rate and thermodynamic force.</p