Structural determinants at the M2 muscarinic receptor modulate the RGS4-GIRK response to pilocarpine by impairment of the receptor voltage sensitivity.

Membrane potential controls the response of the M2 muscarinic receptor to its ligands. Membrane hyperpolarization increases response to the full agonist acetylcholine (ACh) while decreasing response to the partial agonist pilocarpine. We previously have demonstrated that the regulator of G-protein signaling (RGS) 4 protein discriminates between the voltage-dependent responses of ACh and pilocarpine; however, the underlying mechanism remains unclear. Here we show that RGS4 is involved in the voltage-dependent behavior of the M2 muscarinic receptor-mediated signaling in response to pilocarpine. Additionally we revealed structural determinants on the M2 muscarinic receptor underlying the voltage-dependent response. By electrophysiological recording in Xenopus oocytes expressing M2 muscarinic receptor and G-protein-gated inwardly rectifying K+ channels, we quantified voltage-dependent desensitization of pilocarpine-induced current in the presence or absence of RGS4. Hyperpolarization-induced desensitization of the current required for RGS4, also depended on pilocarpine concentration. Mutations of charged residues in the aspartic acid-arginine-tyrosine motif of the M2 muscarinic receptor, but not intracellular loop 3, significantly impaired the voltage-dependence of RGS4 function. Thus, our results demonstrated that voltage-dependence of RGS4 modulation is derived from the M2 muscarinic receptor. These results provide novel insights into how membrane potential impacts G-protein signaling by modulating GPCR communication with downstream effectors

RGS4 regulates partial agonism of the M2 muscarinic receptor-activated K+ currents.

Partial agonists are used clinically to avoid overstimulation of receptor-mediated signalling, as they produce a submaximal response even at 100% receptor occupancy. The submaximal efficacy of partial agonists is due to conformational change of the agonist-receptor complex, which reduces effector activation. In addition to signalling activators, several regulators help control intracellular signal transductions. However, it remains unclear whether these signalling regulators contribute to partial agonism. Here we show that regulator of G-protein signalling (RGS) 4 is a determinant for partial agonism of the M2 muscarinic receptor (M2R). In rat atrial myocytes, pilocarpine evoked smaller G-protein-gated K(+) inwardly rectifying (KG) currents than those evoked by ACh. In a Xenopus oocyte expression system, pilocarpine acted as a partial agonist in the presence of RGS4 as it did in atrial myocytes, while it acted like a full agonist in the absence of RGS4. Functional couplings within the agonist-receptor complex/G-protein/RGS4 system controlled the efficacy of pilocarpine relative to ACh. The pilocarpine-M2R complex suppressed G-protein-mediated activation of KG currents via RGS4. Our results demonstrate that partial agonism of M2R is regulated by the RGS4-mediated inhibition of G-protein signalling. This finding helps us to understand the molecular components and mechanism underlying the partial agonism of M2R-mediated physiological responses

Some reactions of norcaranylidene with polar solvents

As part of our efforts to understand the chemistry of cyclopropylidenes in solution, the reactions of norcaranylidene in alcohols and nitriles have been studied;In alcohols (methanol or t-butanol), the partitioning of norcaranylidene between intramolecular insertion and intermolecular reaction with alcohols is a function of alcohol concentration. In methanol, an ylide intermediate is transformed into the product ether in a stepwise manner. However, in t-butanol, the corresponding ylide intermediate releases the t-butanol molecule to give the intramolecular insertion product, in competition with protonation to form the ether product;Methanol was found to react with norcaranylidene 2.5 times faster than t-butanol, irrespective of the total alcohol concentrations. A reasonable interpretation of the activation parameters is that norcaranylidene is solvated preferentially by t-butanol monomers at high alcohol concentration, but is solvated essentially equally by either methanol or t-butanol at low alcohol concentration. Thus at either low or high alcohol concentrations, the starting carbene is a single, albeit differently, solvated species;When nitriles are present in methanol, the nitrile ylide intermediate from the reaction norcaranylidene with nitriles reacts with methanol to yield a mixture of epimeric methanol insertion products. In acrylonitrile, the ylide is also captured by another molecule of acrylonitrile to give a 3 + 2 cycloadduct. And dipolarophiles also capture the diazo-precursor to norcaranylidene in acrylonitrile and methacrylonitrile;Pyrolysis of anti-7-bromo-syn-7-trimethylstannylbicyclo 4.1.0 heptane also generates norcaranylidene. This allows the high temperature study of the kinetic deuterium isotope effects for the reaction of norcaranylidene with methanol and t-butanol. Mechanisms to account for the isotope effects at low (diazo-precursor) and high (tin bromide precursor) temperatures are discussed. Two changes in mechanism are seen as the temperature is changed from -78(DEGREES) to 160(DEGREES)C

Efficient Volumetric Method of Moments for Modeling Plasmonic Thin-Film Solar Cells with Periodic Structures

Metallic nanoparticles (NPs) support localized surface plasmon resonances (LSPRs), which enable to concentrate sunlight at the active layer of solar cells. However, full-wave modeling of the plasmonic solar cells faces great challenges in terms of huge computational workload and bad matrix condition. It is tremendously difficult to accurately and efficiently simulate near-field multiple scattering effects from plasmonic NPs embedded into solar cells. In this work, a preconditioned volume integral equation (VIE) is proposed to model plasmonic organic solar cells (OSCs). The diagonal block preconditioner is applied to different material domains of the device structure. As a result, better convergence and higher computing efficiency are achieved. Moreover, the calculation is further accelerated by two-dimensional periodic Green's functions. Using the proposed method, the dependences of optical absorption on the wavelengths and incident angles are investigated. Angular responses of the plasmonic OSCs show the super-Lambertian absorption on the plasmon resonance but near-Lambertian absorption off the plasmon resonance. The volumetric method of moments and explored physical understanding are of great help to investigate the optical responses of OSCs.Comment: 11 pages, 6 figure

Efficient kinetic method for fluid simulation beyond the Navier-Stokes equation

We present a further theoretical extension to the kinetic theory based formulation of the lattice Boltzmann method of Shan et al (2006). In addition to the higher order projection of the equilibrium distribution function and a sufficiently accurate Gauss-Hermite quadrature in the original formulation, a new regularization procedure is introduced in this paper. This procedure ensures a consistent order of accuracy control over the non-equilibrium contributions in the Galerkin sense. Using this formulation, we construct a specific lattice Boltzmann model that accurately incorporates up to the third order hydrodynamic moments. Numerical evidences demonstrate that the extended model overcomes some major defects existed in the conventionally known lattice Boltzmann models, so that fluid flows at finite Knudsen number (Kn) can be more quantitatively simulated. Results from force-driven Poiseuille flow simulations predict the Knudsen's minimum and the asymptotic behavior of flow flux at large Kn

Diversification as a Value-Adding Strategy for Asian REITs: A Myth or Reality?

This study tests the impact of diversification strategies on the cash flows, expenses, risks and returns of REITs in Asia. Hirschman-Herfindahl indices (HHI) are computed based on 2281 properties owned by 63 sample Asian REITs for the periods from 2002 to 2007 to measure the levels of diversification by property type and geographical region. In our empirical tests that use weighted least square regressions, we find no significant effects of diversification by property types on cash flows, expenses and risk premiums of Asian REITs. However, significant variations in expenses and risk premiums of the REITs are explained by a geographical diversification strategy. REITs with assets distributed across different countries incur higher total expenses, interest expenses, general and administrative expenses and capital expenditure. Regionally diversified REITs have higher risk premiums. The results remain unchanged after controlling for country factor and simultaneity between the cash flows, expenses, risk and return variables.Diversification and focus strategies; Asian REITs; Illiquidity premiums

Facilitation of I Kr current by some hERG channel blockers suppresses early afterdepolarizations.

Drug-induced block of the cardiac rapid delayed rectifying potassium current (I Kr), carried by the human ether-a-go-go-related gene (hERG) channel, is the most common cause of acquired long QT syndrome. Indeed, some, but not all, drugs that block hERG channels cause fatal cardiac arrhythmias. However, there is no clear method to distinguish between drugs that cause deadly arrhythmias and those that are clinically safe. Here we propose a mechanism that could explain why certain clinically used hERG blockers are less proarrhythmic than others. We demonstrate that several drugs that block hERG channels, but have favorable cardiac safety profiles, also evoke another effect; they facilitate the hERG current amplitude in response to low-voltage depolarization. To investigate how hERG facilitation impacts cardiac safety, we develop computational models of I Kr block with and without this facilitation. We constrain the models using data from voltage clamp recordings of hERG block and facilitation by nifekalant, a safe class III antiarrhythmic agent. Human ventricular action potential simulations demonstrate the ability of nifekalant to suppress ectopic excitations, with or without facilitation. Without facilitation, excessive I Kr block evokes early afterdepolarizations, which cause lethal arrhythmias. When facilitation is introduced, early afterdepolarizations are prevented at the same degree of block. Facilitation appears to prevent early afterdepolarizations by increasing I Kr during the repolarization phase of action potentials. We empirically test this prediction in isolated rabbit ventricular myocytes and find that action potential prolongation with nifekalant is less likely to induce early afterdepolarization than action potential prolongation with dofetilide, a hERG channel blocker that does not induce facilitation. Our data suggest that hERG channel blockers that induce facilitation increase the repolarization reserve of cardiac myocytes, rendering them less likely to trigger lethal ventricular arrhythmias