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Journal of General Physiology

Eric J Hsu, Wandi Zhu, Angela R Schubert, Taylor Voelker, Zoltan Varga, Jonathan R Silva
Functional eukaryotic voltage-gated Na(+) (NaV) channels comprise four domains (DI-DIV), each containing six membrane-spanning segments (S1-S6). Voltage sensing is accomplished by the first four membrane-spanning segments (S1-S4), which together form a voltage-sensing domain (VSD). A critical NaV channel gating process, inactivation, has previously been linked to activation of the VSDs in DIII and DIV. Here, we probe this interaction by using voltage-clamp fluorometry to observe VSD kinetics in the presence of mutations at locations that have been shown to impair NaV channel inactivation...
February 23, 2017: Journal of General Physiology
Richard L Moss, Thomas L Lynch, Daniel P Fitzsimons
No abstract text is available yet for this article.
February 17, 2017: Journal of General Physiology
Anthony J Bakker, Tanya R Cully, Catherine D Wingate, Christopher J Barclay, Bradley S Launikonis
Fast-twitch skeletal muscle fibers are often exposed to motor neuron double discharges (≥200 Hz), which markedly increase both the rate of contraction and the magnitude of the resulting force responses. However, the mechanism responsible for these effects is poorly understood, likely because of technical limitations in previous studies. In this study, we measured cytosolic Ca(2+) during doublet activation using the low-affinity indicator Mag-Fluo-4 at high temporal resolution and modeled the effects of doublet stimulation on sarcoplasmic reticulum (SR) Ca(2+) release, binding of Ca(2+) to cytosolic buffers, and force enhancement in fast-twitch fibers...
February 16, 2017: Journal of General Physiology
Caitlin Sedwick
A new JGP study shows that the gating ring helps the voltage-sensing domain open the BK channel's pore.
February 15, 2017: Journal of General Physiology
Guohui Zhang, Yanyan Geng, Yakang Jin, Jingyi Shi, Kelli McFarland, Karl L Magleby, Lawrence Salkoff, Jianmin Cui
Large conductance Ca(2+)-activated K(+) channels (BK channels) gate open in response to both membrane voltage and intracellular Ca(2+) The channel is formed by a central pore-gate domain (PGD), which spans the membrane, plus transmembrane voltage sensors and a cytoplasmic gating ring that acts as a Ca(2+) sensor. How these voltage and Ca(2+) sensors influence the common activation gate, and interact with each other, is unclear. A previous study showed that a BK channel core lacking the entire cytoplasmic gating ring (Core-MT) was devoid of Ca(2+) activation but retained voltage sensitivity (Budelli et al...
February 14, 2017: Journal of General Physiology
Che-Wei Chang, Chung-Wei Chiang, Meyer B Jackson
Ca(2+)-triggered exocytosis functions broadly in the secretion of chemical signals, enabling neurons to release neurotransmitters and endocrine cells to release hormones. The biological demands on this process can vary enormously. Although synapses often release neurotransmitter in a small fraction of a millisecond, hormone release can be orders of magnitude slower. Vesicles usually contain multiple signaling molecules that can be released selectively and conditionally. Cells are able to control the speed, concentration profile, and content selectivity of release by tuning and tailoring exocytosis to meet different biological demands...
February 6, 2017: Journal of General Physiology
Xiwu Zhao, Aaron N Reifler, Melanie M Schroeder, Elizabeth R Jaeckel, Andrew P Chervenak, Kwoon Y Wong
Retinal neurons use sustained and transient light responses to encode visual stimuli of different frequency ranges, but the underlying mechanisms remain poorly understood. In particular, although earlier studies in retinal ganglion cells (RGCs) proposed seven potential mechanisms, all seven have since been disputed, and it remains unknown whether different RGC types use different mechanisms or how many mechanisms are used by each type. Here, we conduct a comprehensive survey in mice and rats of 12 candidate mechanisms that could conceivably produce tonic rod/cone-driven ON responses in intrinsically photosensitive RGCs (ipRGCs) and transient ON responses in three types of direction-selective RGCs (TRHR+, Hoxd10+ ON, and Hoxd10+ ON-OFF cells)...
February 2, 2017: Journal of General Physiology
Sharona E Gordon
Amid a difficult year for science and scientists, The Journal of General Physiology is thriving and gearing up for its 100th anniversary celebrations.
February 2017: Journal of General Physiology
Yaxian Zhao, Marcel P Goldschen-Ohm, João H Morais-Cabral, Baron Chanda, Gail A Robertson
Channels in the ether-à-go-go or KCNH family of potassium channels are characterized by a conserved, C-terminal domain with homology to cyclic nucleotide-binding homology domains (CNBhDs). Instead of cyclic nucleotides, two amino acid residues, Y699 and L701, occupy the binding pocket, forming an "intrinsic ligand." The role of the CNBhD in KCNH channel gating is still unclear, however, and a detailed characterization of the intrinsic ligand is lacking. In this study, we show that mutating both Y699 and L701 to alanine, serine, aspartate, or glycine impairs human EAG1 channel function...
February 2017: Journal of General Physiology
Caitlin Sedwick
A new JGP study shows how a disease-causing mutation in RyR2 dramatically alters channel behavior.
February 2017: 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...
February 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...
February 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)...
February 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...
February 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...
February 2017: Journal of General Physiology
Gail A Robertson
No abstract text is available yet for this article.
February 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...
February 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
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