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Journal of General Physiology

Peilin Yu, Xiwen Xue, Jianmin Zhang, Xupang Hu, Yan Wu, Lin-Hua Jiang, Hongwei Jin, Jianhong Luo, Liangren Zhang, Zhenming Liu, Wei Yang
Activation of the transient receptor potential melastatin 2 (TRPM2) channel occurs during the response to oxidative stress under physiological conditions as well as in pathological processes such as ischemia and diabetes. Accumulating evidence indicates that adenosine diphosphate ribose (ADPR) is the most important endogenous ligand of TRPM2. However, although it is known that ADPR binds to the NUDT9 homology (NUDT9-H) domain in the intracellular C-terminal region, the molecular mechanism underlying ADPR binding and activation of TRPM2 remains unknown...
January 20, 2017: Journal of General Physiology
Haidun Yan, Chaojian Wang, Steven O Marx, Geoffrey S Pitt
Increased "persistent" current, caused by delayed inactivation, through voltage-gated Na(+) (NaV) channels leads to cardiac arrhythmias or epilepsy. The underlying molecular contributors to these inactivation defects are poorly understood. Here, we show that calmodulin (CaM) binding to multiple sites within NaV channel intracellular C-terminal domains (CTDs) limits persistent Na(+) current and accelerates inactivation across the NaV family. Arrhythmia or epilepsy mutations located in NaV1.5 or NaV1.2 channel CTDs, respectively, reduce CaM binding either directly or by interfering with CTD-CTD interchannel interactions...
January 13, 2017: Journal of General Physiology
Cheon-Gyu Park, Yongsoo Park, Byung-Chang Suh
The β subunit of voltage-gated Ca(2+) (CaV) channels plays an important role in regulating gating of the α1 pore-forming subunit and its regulation by phosphatidylinositol 4,5-bisphosphate (PIP2). Subcellular localization of the CaV β subunit is critical for this effect; N-terminal-dependent membrane targeting of the β subunit slows inactivation and decreases PIP2 sensitivity. Here, we provide evidence that the HOOK region of the β subunit plays an important role in the regulation of CaV biophysics. Based on amino acid composition, we broadly divide the HOOK region into three domains: S (polyserine), A (polyacidic), and B (polybasic)...
January 13, 2017: Journal of General Physiology
Akira Uehara, Takashi Murayama, Midori Yasukochi, Michael Fill, Minoru Horie, Toru Okamoto, Yoshiharu Matsuura, Kiyoko Uehara, Takahiro Fujimoto, Takashi Sakurai, Nagomi Kurebayashi
Various ryanodine receptor 2 (RyR2) point mutations cause catecholamine-induced polymorphic ventricular tachycardia (CPVT), a life-threatening arrhythmia evoked by diastolic intracellular Ca(2+) release dysfunction. These mutations occur in essential regions of RyR2 that regulate Ca(2+) release. The molecular dysfunction caused by CPVT-associated RyR2 mutations as well as the functional consequences remain unresolved. Here, we study the most severe CPVT-associated RyR2 mutation (K4750Q) known to date. We define the molecular and cellular dysfunction generated by this mutation and detail how it alters RyR2 function, using Ca(2+) imaging, ryanodine binding, and single-channel recordings...
January 12, 2017: Journal of General Physiology
Emily J Sharpe, Eric D Larson, Catherine Proenza
Aerobic capacity decreases with age, in part because of an age-dependent decline in maximum heart rate (mHR) and a reduction in the intrinsic pacemaker activity of the sinoatrial node of the heart. Isolated sinoatrial node myocytes (SAMs) from aged mice have slower spontaneous action potential (AP) firing rates and a hyperpolarizing shift in the voltage dependence of activation of the "funny current," If Cyclic AMP (cAMP) is a critical modulator of both AP firing rate and If in SAMs. Here, we test the ability of endogenous and exogenous cAMP to overcome age-dependent changes in acutely isolated murine SAMs...
January 5, 2017: Journal of General Physiology
Gail A Robertson
No abstract text is available yet for this article.
January 5, 2017: Journal of General Physiology
Ping Lu, Cheng-Hai Zhang, Lawrence M Lifshitz, Ronghua ZhuGe
Bitter taste receptors (TAS2Rs or T2Rs) belong to the superfamily of seven-transmembrane G protein-coupled receptors, which are the targets of >50% of drugs currently on the market. Canonically, T2Rs are located in taste buds of the tongue, where they initiate bitter taste perception. However, accumulating evidence indicates that T2Rs are widely expressed throughout the body and mediate diverse nontasting roles through various specialized mechanisms. It has also become apparent that T2Rs and their polymorphisms are associated with human disorders...
January 4, 2017: Journal of General Physiology
Diana Pendin, Elisa Greotti, Konstantinos Lefkimmiatis, Tullio Pozzan
Cellular signaling networks are composed of multiple pathways, often interconnected, that form complex networks with great potential for cross-talk. Signal decoding depends on the nature of the message as well as its amplitude, temporal pattern, and spatial distribution. In addition, the existence of membrane-bound organelles, which are both targets and generators of messages, add further complexity to the system. The availability of sensors that can localize to specific compartments in live cells and monitor their targets with high spatial and temporal resolution is thus crucial for a better understanding of cell pathophysiology...
January 2017: Journal of General Physiology
Juan Lorenzo Pablo, Paul G DeCaen, David E Clapham
Mammalian cilia are ubiquitous appendages found on the apical surface of cells. Primary and motile cilia are distinct in both morphology and function. Most cells have a solitary primary cilium (9+0), which lacks the central microtubule doublet characteristic of motile cilia (9+2). The immotile primary cilia house unique signaling components and sequester several important transcription factors. In contrast, motile cilia commonly extend into the lumen of respiratory airways, fallopian tubes, and brain ventricles to move their contents and/or produce gradients...
January 2017: Journal of General Physiology
Thomas R Middendorf, Richard W Aldrich
Understanding the interactions of proteins with their ligands requires knowledge of molecular properties, such as binding site affinities and the effects that binding at one site exerts on binding at other sites (cooperativity). These properties cannot be measured directly and are usually estimated by fitting binding data with models that contain these quantities as parameters. In this study, we present a general method for answering the critical question of whether these parameters are identifiable (i.e., whether their estimates are accurate and unique)...
January 2017: Journal of General Physiology
Thomas R Middendorf, Richard W Aldrich
A critical but often overlooked question in the study of ligands binding to proteins is whether the parameters obtained from analyzing binding data are practically identifiable (PI), i.e., whether the estimates obtained from fitting models to noisy data are accurate and unique. Here we report a general approach to assess and understand binding parameter identifiability, which provides a toolkit to assist experimentalists in the design of binding studies and in the analysis of binding data. The partial fraction (PF) expansion technique is used to decompose binding curves for proteins with n ligand-binding sites exactly and uniquely into n components, each of which has the form of a one-site binding curve...
January 2017: Journal of General Physiology
Maria S Remedi, Jonathan B Friedman, Colin G Nichols
Gain-of-function (GOF) mutations in the pore-forming (Kir6.2) and regulatory (SUR1) subunits of KATP channels have been identified as the most common cause of human neonatal diabetes mellitus. The critical effect of these mutations is confirmed in mice expressing Kir6.2-GOF mutations in pancreatic β cells. A second KATP channel pore-forming subunit, Kir6.1, was originally cloned from the pancreas. Although the prominence of this subunit in the vascular system is well documented, a potential role in pancreatic β cells has not been considered...
January 2017: Journal of General Physiology
Martin Skov, Robert T Dirksen
No abstract text is available yet for this article.
January 2017: Journal of General Physiology
Shaweta Gupta, Srirupa Chakraborty, Ridhima Vij, Anthony Auerbach
Nicotinic acetylcholine receptors are allosteric proteins that generate membrane currents by isomerizing ("gating") between resting and active conformations under the influence of neurotransmitters. Here, to explore the mechanisms that link the transmitter-binding sites (TBSs) with the distant gate, we use mutant cycle analyses to measure coupling between residue pairs, phi value analyses to sequence domain rearrangements, and current simulations to reproduce a microsecond shut component ("flip") apparent in single-channel recordings...
January 2017: Journal of General Physiology
Anne C Wolfes, Saheeb Ahmed, Ankit Awasthi, Markus A Stahlberg, Ashish Rajput, Daniel S Magruder, Stefan Bonn, Camin Dean
Interactions between astrocytes and neurons rely on the release and uptake of glial and neuronal molecules. But whether astrocytic vesicles exist and exocytose in a regulated or constitutive fashion is under debate. The majority of studies have relied on indirect methods or on astrocyte cultures that do not resemble stellate astrocytes found in vivo. Here, to investigate vesicle-associated proteins and exocytosis in stellate astrocytes specifically, we developed a simple, fast, and economical method for growing stellate astrocyte monocultures...
January 2017: Journal of General Physiology
Daniel R Miranda, Monica Wong, Shannon H Romer, Cynthia McKee, Gabriela Garza-Vasquez, Alyssa C Medina, Volker Bahn, Andrew D Steele, Robert J Talmadge, Andrew A Voss
Huntington's disease (HD) patients suffer from progressive and debilitating motor dysfunction. Previously, we discovered reduced skeletal muscle chloride channel (ClC-1) currents, inwardly rectifying potassium (Kir) channel currents, and membrane capacitance in R6/2 transgenic HD mice. The ClC-1 loss-of-function correlated with increased aberrant mRNA processing and decreased levels of full-length ClC-1 mRNA (Clcn1 gene). Physiologically, the resulting muscle hyperexcitability may help explain involuntary contractions of HD...
January 2017: Journal of General Physiology
Srboljub M Mijailovich, Oliver Kayser-Herold, Boban Stojanovic, Djordje Nedic, Thomas C Irving, Michael A Geeves
The effect of molecule tethering in three-dimensional (3-D) space on bimolecular binding kinetics is rarely addressed and only occasionally incorporated into models of cell motility. The simplest system that can quantitatively determine this effect is the 3-D sarcomere lattice of the striated muscle, where tethered myosin in thick filaments can only bind to a relatively small number of available sites on the actin filament, positioned within a limited range of thermal movement of the myosin head. Here we implement spatially explicit actomyosin interactions into the multiscale Monte Carlo platform MUSICO, specifically defining how geometrical constraints on tethered myosins can modulate state transition rates in the actomyosin cycle...
December 2016: Journal of General Physiology
Byung-Ju Jin, Alex J Smith, Alan S Verkman
A "glymphatic system," which involves convective fluid transport from para-arterial to paravenous cerebrospinal fluid through brain extracellular space (ECS), has been proposed to account for solute clearance in brain, and aquaporin-4 water channels in astrocyte endfeet may have a role in this process. Here, we investigate the major predictions of the glymphatic mechanism by modeling diffusive and convective transport in brain ECS and by solving the Navier-Stokes and convection-diffusion equations, using realistic ECS geometry for short-range transport between para-arterial and paravenous spaces...
December 2016: Journal of General Physiology
Vanessa Leone, José D Faraldo-Gómez
Two subunits within the transmembrane domain of the ATP synthase-the c-ring and subunit a-energize the production of 90% of cellular ATP by transducing an electrochemical gradient of H(+) or Na(+) into rotational motion. The nature of this turbine-like energy conversion mechanism has been elusive for decades, owing to the lack of definitive structural information on subunit a or its c-ring interface. In a recent breakthrough, several structures of this complex were resolved by cryo-electron microscopy (cryo-EM), but the modest resolution of the data has led to divergent interpretations...
December 2016: Journal of General Physiology
Guruprasad Kuntamallappanavar, Alex M Dopico
In most mammalian tissues, Ca(2+)i/voltage-gated, large conductance K(+) (BK) channels consist of channel-forming slo1 and auxiliary (β1-β4) subunits. When Ca(2+)i (3-20 µM) reaches the vicinity of BK channels and increases their activity at physiological voltages, β1- and β4-containing BK channels are, respectively, inhibited and potentiated by intoxicating levels of ethanol (50 mM). Previous studies using different slo1s, lipid environments, and Ca(2+)i concentrations-all determinants of the BK response to ethanol-made it impossible to determine the specific contribution of β subunits to ethanol action on BK activity...
November 2016: Journal of General Physiology
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