Can selectivity be functionally modulated in ion channels?

In a two-electrode voltage-clamp study on the rat sympathetic neuron, the properties of the subsynaptic native neuronal AChR (nAChR) in response to the physiologically released ACh were shown to be modified within a few hours after denervation (Sacchi et al., 2008), suggesting that the nAChR ion selectivity switched from preferential permeability to potassium ions to scarce selectivity between K+ and Na+; the changes regarded synaptic, but not extrasynaptic, receptors and revealed an unexpected flexibility of the nicotinic channel in its permeation properties. Subsequently, a number of quite simple experimental procedures in intact ganglia were also shown to produce changes in conductance and ion selectivity properties of the nAChR; unlike denervation, such procedures (resting membrane potential shifts within a voltage range of physiological interest, ionic modifications, and the action of \u3b1-bungarotoxin) were very unlikely to acutely produce modifications in nAChR subunit composition or steric conformation (Sacchi et al., 2011). Posttranslational modifications of the channel protein might have occurred, but the consistency of those results with the idea that impermeant Cl 12 ions might affect cation binding and/or penetration into the pore raised the aforementioned question of whether extrinsic factors might contribute, together with the structural organization of the pore, to determine the permeability and ion selectivity of the channel. Actually, any change in the potential profile along the pore (and/or at its mouths) is bound to affect both the thermodynamic aspects of ion permeation (local field profile and ion binding to sites within the pore) and the kinetic aspects (ease of ion displacement and traveling among subsequent sites). These appear to constitute two distinct factors in determining ion selectivity, but the two aspects are strictly related. The electrical field across the membrane, determined by the membrane potential (Vm), may well be constant and produce a linear change in free energy along the pore. However, the thermodynamic profiles in ion-selective channels display nonlinear variations in the local potential seen by each ion, so that the energetic profile, \u394G(x) = G(x) 12 G(0) (where 0 refers to the extracellular bulk solution), is not simply a result of the presence of the membrane potential. At equilibrium, the probability for an ion to be located at x, p(x), is proportional to exp(\u2013\u394G(x)/RT); this determines the ratio between forward and backward velocities. As a purely qualitative, numerical example, an arbitrary pore energy profile has been simulated for the Na+ and K+ ions. The profiles for the ions are arbitrarily designed, based on the suggested differential coordination of Na+ and K+ with the charges lining the pore (Nimigean and Allen, 2011). From the same energy profile in the presence of a constant electrical field (Vm = \u20133RT/zF 48 \u201375 mV) the relative occupancy along the pore for Na+ and K+ has been computed, and the resulting permeability derived. It is shown that simple modifications of the profiles by Ca- concentration could account for the observed changes in cation selectivit

Scienza della Nutrizione

La scienza dell’alimentazione è una disciplina estremamente affascinante ed eterogenea che spazia dalla relazione stretta fra nutrizione e salute umana, ai meccanismi fisiologici, biomolecolari e cellulari che la regolano, coinvolgendo anche modelli comportamentali ed influenze sociali, comprendendo inoltre la relazione fra alimentazione ed ambiente, fino ad arrivare alla relazione fra il nostro genoma ed i nutrienti e fra i nostri simbionti e la salute. È necessario quindi tessere una rete che metta in relazione tutti gli ambiti di questa scienza in modo comprensibile, ma non superficiale, con l’attenzione rivolta alla scientificità delle affermazioni fatte e con lo scopo di indurre un approccio critico da parte dello studente, nei confronti delle informazioni di cui viene a conoscenza. Questo è stato l’obiettivo di questo testo. Esso tratta gli argomenti classici della scienza dell’alimentazione (biochimica dei nutrienti, classi di alimenti, fisiologia dell’apparato digerente, bilancio energetico) con un occhio attento alle ultime scoperte scientifiche riguardo ad essi. Per esempio alla classica trattazione delle varie categorie di alimenti viene associata una parte dedicata agli alimenti funzionali, argomento molto di moda e per questo facilmente soggetto a semplificazioni o male interpretazioni, ed un approfondimento dedicato agli OGM dando le principali informazioni sia strettamente legate alla salute che ai sistemi di controllo e all’impatto ambientale. Per quanto riguarda il bilancio energetico si è voluto introdurre accanto ad una visione antropocentrica dell’argomento, la valutazione ambientale dell’impatto del comportamento alimentare umano, utilizzando i vari misuratori di impatto ambientale che sono stati scientificamente formulati in questi anni. Non si può parlare di scienza dell’alimentazione senza parlare delle patologie correlate, alcune delle quali vere e proprie pandemie (obesità e diabete). Anche in questo caso si è cercato di completare le informazioni mediche con informazioni epidemiologiche ed ambientali e con i più recenti dati sulle terapie sperimentali in studio. Più volte nel testo si parla di terapia personalizzata, ed il capitolo sull’influenza dell’alimentazione sulla risposta immunitaria e quello sulla nutrigenomica sono quelli che meglio spiegano quale direzione dovrebbe prendere la scienza dell’alimentazione nel futuro: quella di una scienza che non solo detta le linee guida per non incorrere in un’alimentazione scorretta, ma una scienza che sa cogliere le capacità terapeutiche degli alimenti in riferimento al patrimonio genetico di ogni singolo individuo. Si tratta di un libro utilizzabile da studenti universitari di discipline di ambito biologico ed agroalimentare

Mindfulness based stress reduction (MBSR) program leads to a reduction in physiological evaluated stress

2noopenBackground: Oxidative stress has complex interactions with our lifestyle habits that negatively affect our health. Increasing evidence suggests that chronic psychosocial stress enhances oxidative stress, which in turn may contribute to aging and aetiology of many lifestyle-related degenerative diseases. Mindfulness practice is defined as “paying attention in an intentional and non-judgmental way to the present moment”. Past studies investigating the link between mindfulness and stress response demonstrated that Mindfulness-Based Stress Reduction (MBSR) program is an effective stress management technique which have beneficial effects on emotional and psychological responses to stressors. In contrast, there have been less studies of its effect on physiological parameters, such as oxidative stress. Methods: In this study, we evaluated the effectiveness of MBSR program on a sample of 42 people (age 30-66 years). In particular, we analyzed blood pressure, plasma concentration of carotenoids and salivary cortisol levels, before (baseline) and after an MBSR training (8 weeks). Cortisol was measured by an Enzyme Immunoassay kit. Carotenoid concentration was evaluated by Raman spectroscopic technique. Levels of perceived stress, anxiety and awareness were assessed by Perceived Stress Scale, State Anxiety Inventory, and Mindful Attention Awareness Scale questionnaires, respectively. Student’s t was used for statistical analysis (P < 0.05). Results: Mindfulness practice significantly reduced salivary levels of cortisol (P < 0.01), blood pressure in hypertensive people (P < 0.01) and increases blood concentration of carotenoids (P < 0.05). An increase in awareness and a decrease in perceived stress and anxiety were also observed. All the parameters analysed showed a statistically significant improvement (P < 0.01). Conclusions: These preliminary data are a first indication that the MBSR program is an effective tool to ameliorate antioxidant defence (as indicated by carotenoids data) confirming positive effects on blood pressure and psychological outcomes. Further studies on pro-inflammatory cytokine levels and overall redox related mechanisms are needed to better evaluate MBSR systemic effects.openCanella, Rita; Gardi, ConcettaCanella, Rita; Gardi, Concett

Nicotinic EPSCs in intact rat ganglia feature depression except if evoked during intermittent postsynaptic depolarization

The involvement of the postsynaptic membrane potential level in controlling synaptic strength at the ganglionic synapse was studied by recording nicotinic fast synaptic currents (EPSCs) from neurons in the intact, mature rat superior cervical ganglion, using the two-electrode voltage-clamp technique. EPSCs were evoked by 0.05-Hz supramaximal stimulation of the preganglionic sympathetic trunk over long periods; their peak amplitude (or synaptic charge transfer) over time appeared to depend on the potential level of the neuronal membrane where the nicotinic receptors are embedded. EPSC amplitude remained constant (n = 6) only if ACh was released within repeated depolarizing steps of the postganglionic neuron, which constantly varied between -50 and -20 mV in consecutive 10-mV steps, whereas it decreased progressively by 45% (n = 9) within 14 min when the sympathetic neuron was held at constant membrane potential. Synaptic channel activation, channel ionic permeation and depolarization of the membrane in which the nicotinic receptor is localized must occur simultaneously to maintain constant synaptic strength at the ganglionic synapse during low-rate stimulation (0.03-1 Hz). Different posttetanic (20 Hz for 10 s) behaviors were observed depending on the mode of previous stimulation. In the neuron maintained at constant holding potential during low-rate stimulation, the depressed EPSC showed posttetanic potentiation, recovering approximately 23% of the mean pretetanic values (n = 10). The maximum effect was immediate in 40% of the neurons tested and developed over a 3- to 6-min period in the others; thereafter potentiation vanished within 40 min of 0.05-Hz stimulation. In contrast, no statistically significant synaptic potentiation was observed when EPSC amplitudes were kept constant by repeated -50/-20-mV command cycles (n = 12). It is suggested that, under these conditions, posttetanic potentiation could represent an attempt at recovering the synaptic strength lost during inappropriate functioning of the ganglionic synapse

A model of signal processing at the isolated hair cell of the frog semicircular canal

A computational model has been developed to simulate the electrical behavior of the type II hair cell dissected from the crista ampullaris of frog semicircular canals. In its basolateral membrane, it hosts a system of four voltagedependent conductances (gA, gKV, gKCa, gCa). The conductance behavior was mathematically described using original patch-clamp experimental data. The transient K current, IA, was isolated as the difference between the currents obtained before and after removing IA inactivation. The remaining current, IKD, results from the summation of a voltage-dependent K current, IKV, a voltage-calcium-dependent K current, IKCa, and the calcium current, ICa. IKD was modeled as a single lumped current, since the physiological role of each component is actually not discernible. To gain a clear understanding of its prominent role in sustaining transmitter release at the cytoneural junction, ICa was modeled under different experimental conditions. The model includes the description of voltage- and time-dependent kinetics for each single current. After imposing any starting holding potential, the system sets the pertinent values of the variables and continually updates them in response to variations in membrane potential. The model reconstructs the individual I-V curves obtained in voltage-clamp experiments and simulations compare favorably with the experimental data. The model proves useful in describing the early steps of signal processing that results from the interaction of the apical receptor current with the basolateral voltage-dependent conductances. The program is thus helpful in understanding aspects of sensory transduction that are hard to analyze in the native hair cell of the crista ampullaris

The amplitude and inactivation properties of the delayed potassium currents are regulated by protein kinase activity in hair cells of the frog semicircular canals.

In hair cells dissected from the frog crista ampullaris, the combination of a calcium-dependent (IKCa) and a purely voltage-dependent component (IKV) gives rise to the delayed potassium current complex (IKD). These currents have been recently reported to display slow depolarization-induced inactivation and biphasic inactivation removal by hyperpolarization. The amplitude and inactivation kinetics of both IKCa and IKV are drastically modulated by a previously unrecognized mechanism of protein phosphorylation (sensitive to kinase inhibitors H89 and KT5823), which does not interfere with the transient potassium current (IA) or the calcium current (ICa). IKD amplitude was stable in cells patched with pipettes containing 8 mM ATP or under perforated-patch; under these conditions, a 10 min treatment with 10 µM H89 or 1-10 µM KT5823 reduced IKD amplitude by a mean of 67% at +40 mV. Similarly affected was the isolated IKV component (ICa blocked with Cd(2+)). Thus, a large potassium conductance can be activated by depolarization, but it is made available to the cell to a variable extent that depends on membrane potential and protein kinase activity. The total gKD ranged 4.6-44.0 nS in control cells, according to the level of steady-state inactivation, and was reduced to 1.4-2.7 nS after protein kinase inhibition. When sinusoidal membrane potential changes in the -70/-10 mV range were applied, to mimic receptor response to hair bundle deflection, IKD proved the main current dynamically activated and the only one regulated by PK: H89 decreased the total outward charge during each cycle by 60%. Phosphorylation appears to control both the amount of IKCa and IKV conductance activated by depolarization and the fraction thereof which can be rescued by removal of inactivation. The balance between the depolarizing transduction current and the repolarizing potassium current, and eventually the transmitter release at the cytoneural junction, are therefore modulated by a phosphorylation-mediated process