The Journal of General Physiology最新文献

{"title":"Developmental changes in the cochlear hair cell mechanotransducer channel and their regulation by transmembrane channel-like proteins.","authors":"Kyunghee X Kim,&nbsp;Robert Fettiplace","doi":"10.1085/jgp.201210913","DOIUrl":"https://doi.org/10.1085/jgp.201210913","url":null,"abstract":"<p><p>Vibration of the stereociliary bundles activates calcium-permeable mechanotransducer (MT) channels to initiate sound detection in cochlear hair cells. Different regions of the cochlea respond preferentially to different acoustic frequencies, with variation in the unitary conductance of the MT channels contributing to this tonotopic organization. Although the molecular identity of the MT channel remains uncertain, two members of the transmembrane channel-like family, Tmc1 and Tmc2, are crucial to hair cell mechanotransduction. We measured MT channel current amplitude and Ca(2+) permeability along the cochlea's longitudinal (tonotopic) axis during postnatal development of wild-type mice and mice lacking Tmc1 (Tmc1-/-) or Tmc2 (Tmc2-/-). In wild-type mice older than postnatal day (P) 4, MT current amplitude increased ~1.5-fold from cochlear apex to base in outer hair cells (OHCs) but showed little change in inner hair cells (IHCs), a pattern apparent in mutant mice during the first postnatal week. After P7, the OHC MT current in Tmc1-/- (dn) mice declined to zero, consistent with their deafness phenotype. In wild-type mice before P6, the relative Ca(2+) permeability, P(Ca), of the OHC MT channel decreased from cochlear apex to base. This gradient in P(Ca) was not apparent in IHCs and disappeared after P7 in OHCs. In Tmc1-/- mice, P(Ca) in basal OHCs was larger than that in wild-type mice (to equal that of apical OHCs), whereas in Tmc2-/-, P(Ca) in apical and basal OHCs and IHCs was decreased compared with that in wild-type mice. We postulate that differences in Ca(2+) permeability reflect different subunit compositions of the MT channel determined by expression of Tmc1 and Tmc2, with the latter conferring higher P(Ca) in IHCs and immature apical OHCs. Changes in P(Ca) with maturation are consistent with a developmental decrease in abundance of Tmc2 in OHCs but not in IHCs.</p>","PeriodicalId":173753,"journal":{"name":"The Journal of General Physiology","volume":" ","pages":"141-8"},"PeriodicalIF":3.8,"publicationDate":"2013-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1085/jgp.201210913","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"40200940","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Action of nicotine and analogs on acetylcholine receptors having mutations of transmitter-binding site residue αG153.","authors":"Snehal Jadey,&nbsp;Prasad Purohit,&nbsp;Anthony Auerbach","doi":"10.1085/jgp.201210896","DOIUrl":"https://doi.org/10.1085/jgp.201210896","url":null,"abstract":"<p><p>A primary target for nicotine is the acetylcholine receptor channel (AChR). Some of the ability of nicotine to activate differentially AChR subtypes has been traced to a transmitter-binding site amino acid that is glycine in lower affinity and lysine in higher affinity AChRs. We studied the effects of mutations of this residue (αG153) in neuromuscular AChRs activated by nicotine and eight other agonists including nornicotine and anabasine. All of the mutations increased the unliganded gating equilibrium constant. The affinity of the resting receptor (K(d)) and the net binding energy from the agonist for gating (ΔG(B)) were estimated by cross-concentration fitting of single-channel currents. In all but one of the agonist/mutant combinations there was a moderate decrease in K(d) and essentially no change in ΔG(B). The exceptional case was nicotine plus lysine, which showed a large, >8,000-fold decrease in K(d) but no change in ΔG(B). The extraordinary specificity of this combination leads us to speculate that AChRs with a lysine at position αG153 may be exposed to a nicotine-like compound in vivo.</p>","PeriodicalId":173753,"journal":{"name":"The Journal of General Physiology","volume":" ","pages":"95-104"},"PeriodicalIF":3.8,"publicationDate":"2013-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1085/jgp.201210896","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"40202042","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Aquaporin-4-dependent K(+) and water transport modeled in brain extracellular space following neuroexcitation.","authors":"Byung-Ju Jin,&nbsp;Hua Zhang,&nbsp;Devin K Binder,&nbsp;A S Verkman","doi":"10.1085/jgp.201210883","DOIUrl":"https://doi.org/10.1085/jgp.201210883","url":null,"abstract":"<p><p>Potassium (K(+)) ions released into brain extracellular space (ECS) during neuroexcitation are efficiently taken up by astrocytes. Deletion of astrocyte water channel aquaporin-4 (AQP4) in mice alters neuroexcitation by reducing ECS [K(+)] accumulation and slowing K(+) reuptake. These effects could involve AQP4-dependent: (a) K(+) permeability, (b) resting ECS volume, (c) ECS contraction during K(+) reuptake, and (d) diffusion-limited water/K(+) transport coupling. To investigate the role of these mechanisms, we compared experimental data to predictions of a model of K(+) and water uptake into astrocytes after neuronal release of K(+) into the ECS. The model computed the kinetics of ECS [K(+)] and volume, with input parameters including initial ECS volume, astrocyte K(+) conductance and water permeability, and diffusion in astrocyte cytoplasm. Numerical methods were developed to compute transport and diffusion for a nonstationary astrocyte-ECS interface. The modeling showed that mechanisms b-d, together, can predict experimentally observed impairment in K(+) reuptake from the ECS in AQP4 deficiency, as well as altered K(+) accumulation in the ECS after neuroexcitation, provided that astrocyte water permeability is sufficiently reduced in AQP4 deficiency and that solute diffusion in astrocyte cytoplasm is sufficiently low. The modeling thus provides a potential explanation for AQP4-dependent K(+)/water coupling in the ECS without requiring AQP4-dependent astrocyte K(+) permeability. Our model links the physical and ion/water transport properties of brain cells with the dynamics of neuroexcitation, and supports the conclusion that reduced AQP4-dependent water transport is responsible for defective neuroexcitation in AQP4 deficiency.</p>","PeriodicalId":173753,"journal":{"name":"The Journal of General Physiology","volume":" ","pages":"119-32"},"PeriodicalIF":3.8,"publicationDate":"2013-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1085/jgp.201210883","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"40202044","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mitochondria-targeted cpYFP: pH or superoxide sensor?","authors":"Emilie Quatresous,&nbsp;Claude Legrand,&nbsp;Sandrine Pouvreau","doi":"10.1085/jgp.201210863","DOIUrl":"https://doi.org/10.1085/jgp.201210863","url":null,"abstract":"The JGP series Perspectives on: SGP Symposium on Mitochondrial Physiology and Medicine includes articles by [Wei and Dirksen (2012)][1] and by [Santo-Domingo and Demaurex (2012)][2], which highlight two fields of research in mitochondrial physiology experiencing renewed interest thanks to the","PeriodicalId":173753,"journal":{"name":"The Journal of General Physiology","volume":" ","pages":"567-70"},"PeriodicalIF":3.8,"publicationDate":"2012-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1085/jgp.201210863","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"30980165","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Basis for allosteric open-state stabilization of voltage-gated potassium channels by intracellular cations.","authors":"Samuel J Goodchild,&nbsp;Hongjian Xu,&nbsp;Zeineb Es-Salah-Lamoureux,&nbsp;Christopher A Ahern,&nbsp;David Fedida","doi":"10.1085/jgp.201210823","DOIUrl":"https://doi.org/10.1085/jgp.201210823","url":null,"abstract":"<p><p>The open state of voltage-gated potassium (Kv) channels is associated with an increased stability relative to the pre-open closed states and is reflected by a slowing of OFF gating currents after channel opening. The basis for this stabilization is usually assigned to intrinsic structural features of the open pore. We have studied the gating currents of Kv1.2 channels and found that the stabilization of the open state is instead conferred largely by the presence of cations occupying the inner cavity of the channel. Large impermeant intracellular cations such as N-methyl-d-glucamine (NMG(+)) and tetraethylammonium cause severe slowing of channel closure and gating currents, whereas the smaller cation, Cs(+), displays a more moderate effect on voltage sensor return. A nonconducting mutant also displays significant open state stabilization in the presence of intracellular K(+), suggesting that K(+) ions in the intracellular cavity also slow pore closure. A mutation in the S6 segment used previously to enlarge the inner cavity (Kv1.2-I402C) relieves the slowing of OFF gating currents in the presence of the large NMG(+) ion, suggesting that the interaction site for stabilizing ions resides within the inner cavity and creates an energetic barrier to pore closure. The physiological significance of ionic occupation of the inner cavity is underscored by the threefold slowing of ionic current deactivation in the wild-type channel compared with Kv1.2-I402C. The data suggest that internal ions, including physiological concentrations of K(+), allosterically regulate the deactivation kinetics of the Kv1.2 channel by impairing pore closure and limiting the return of voltage sensors. This may represent a primary mechanism by which Kv channel deactivation kinetics is linked to ion permeation and reveals a novel role for channel inner cavity residues to indirectly regulate voltage sensor dynamics.</p>","PeriodicalId":173753,"journal":{"name":"The Journal of General Physiology","volume":" ","pages":"495-511"},"PeriodicalIF":3.8,"publicationDate":"2012-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1085/jgp.201210823","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"30980166","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Purinergic regulation of inflammasome activation after central nervous system injury.","authors":"Louis-Philippe Bernier","doi":"10.1085/jgp.201210875","DOIUrl":"https://doi.org/10.1085/jgp.201210875","url":null,"abstract":"The body’s response to immune challenges and tissue damage involves a complex inflammatory process. The innate immune system acts as the initial barrier that protects from infectious agents and also senses endogenous danger molecules released after traumatic insults to mediate the response to","PeriodicalId":173753,"journal":{"name":"The Journal of General Physiology","volume":" ","pages":"571-5"},"PeriodicalIF":3.8,"publicationDate":"2012-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1085/jgp.201210875","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"31011675","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Open-state stabilization in Kv channels: voltage-sensor relaxation and pore propping by a bound ion.","authors":"Robert J French,&nbsp;Rocio K Finol-Urdaneta","doi":"10.1085/jgp.201210901","DOIUrl":"https://doi.org/10.1085/jgp.201210901","url":null,"abstract":"### Historical context and overview\u0000\u0000The [Hodgkin and Huxley (1952)][1] description of Na and K conductances underlying the action potential in squid giant axon is remarkable not only for its predictive accuracy in describing the shape and propagation velocity of the action potential but also for","PeriodicalId":173753,"journal":{"name":"The Journal of General Physiology","volume":" ","pages":"463-7"},"PeriodicalIF":3.8,"publicationDate":"2012-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1085/jgp.201210901","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"30980161","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Cellular context and multiple channel domains determine cAMP sensitivity of HCN4 channels: ligand-independent relief of autoinhibition in HCN4.","authors":"Zhandi Liao,&nbsp;Dean Lockhead,&nbsp;Joshua R St Clair,&nbsp;Eric D Larson,&nbsp;Courtney E Wilson,&nbsp;Catherine Proenza","doi":"10.1085/jgp.201210858","DOIUrl":"https://doi.org/10.1085/jgp.201210858","url":null,"abstract":"<p><p>Hyperpolarization-activated, cyclic nucleotide-sensitive (HCN) channels produce the I(f) and I(h) currents, which are critical for cardiac pacemaking and neuronal excitability, respectively. HCN channels are modulated by cyclic AMP (cAMP), which binds to a conserved cyclic nucleotide-binding domain (CNBD) in the C terminus. The unliganded CNBD has been shown to inhibit voltage-dependent gating of HCNs, and cAMP binding relieves this \"autoinhibition,\" causing a depolarizing shift in the voltage dependence of activation. Here we report that relief of autoinhibition can occur in the absence of cAMP in a cellular context- and isoform-dependent manner: when the HCN4 isoform was expressed in Chinese hamster ovary (CHO) cells, the basal voltage dependence was already shifted to more depolarized potentials and cAMP had no further effect on channel activation. This \"pre-relief\" of autoinhibition was specific both to HCN4 and to CHO cells; cAMP shifted the voltage dependence of HCN2 in CHO cells and of HCN4 in human embryonic kidney (HEK) cells. The pre-relief phenotype did not result from different concentrations of soluble intracellular factors in CHO and HEK cells, as it persisted in excised cell-free patches. Likewise, it did not arise from a failure of cAMP to bind to the CNBD of HCN4 in CHOs, as indicated by cAMP-dependent slowing of deactivation. Instead, a unique ∼300-amino acid region of the distal C terminus of HCN4 (residues 719-1012, downstream of the CNBD) was found to be necessary, but not sufficient, for the depolarized basal voltage dependence and cAMP insensitivity of HCN4 in CHO cells. Collectively, these data suggest a model in which multiple HCN4 channel domains conspire with membrane-associated intracellular factors in CHO cells to relieve autoinhibition in HCN4 channels in the absence of cAMP. These findings raise the possibility that such ligand-independent regulation could tune the activity of HCN channels and other CNBD-containing proteins in many physiological systems.</p>","PeriodicalId":173753,"journal":{"name":"The Journal of General Physiology","volume":" ","pages":"557-66"},"PeriodicalIF":3.8,"publicationDate":"2012-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1085/jgp.201210858","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"31011674","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Molecular mechanism for depolarization-induced modulation of Kv channel closure.","authors":"Alain J Labro,&nbsp;Jerome J Lacroix,&nbsp;Carlos A Villalba-Galea,&nbsp;Dirk J Snyders,&nbsp;Francisco Bezanilla","doi":"10.1085/jgp.201210817","DOIUrl":"https://doi.org/10.1085/jgp.201210817","url":null,"abstract":"<p><p>Voltage-dependent potassium (Kv) channels provide the repolarizing power that shapes the action potential duration and helps control the firing frequency of neurons. The K(+) permeation through the channel pore is controlled by an intracellularly located bundle-crossing (BC) gate that communicates with the voltage-sensing domains (VSDs). During prolonged membrane depolarizations, most Kv channels display C-type inactivation that halts K(+) conduction through constriction of the K(+) selectivity filter. Besides triggering C-type inactivation, we show that in Shaker and Kv1.2 channels (expressed in Xenopus laevis oocytes), prolonged membrane depolarizations also slow down the kinetics of VSD deactivation and BC gate closure during the subsequent membrane repolarization. Measurements of deactivating gating currents (reporting VSD movement) and ionic currents (BC gate status) showed that the kinetics of both slowed down in two distinct phases with increasing duration of the depolarizing prepulse. The biphasic slowing in VSD deactivation and BC gate closure was strongly correlated in time and magnitude. Simultaneous recordings of ionic currents and fluorescence from a probe tracking VSD movement in Shaker directly demonstrated that both processes were synchronized. Whereas the first slowing originates from a stabilization imposed by BC gate opening, the subsequent slowing reflects the rearrangement of the VSD toward its relaxed state (relaxation). The VSD relaxation was observed in the Ciona intestinalis voltage-sensitive phosphatase and in its isolated VSD. Collectively, our results show that the VSD relaxation is not kinetically related to C-type inactivation and is an intrinsic property of the VSD. We propose VSD relaxation as a general mechanism for depolarization-induced slowing of BC gate closure that may enable Kv1.2 channels to modulate the firing frequency of neurons based on the depolarization history.</p>","PeriodicalId":173753,"journal":{"name":"The Journal of General Physiology","volume":" ","pages":"481-93"},"PeriodicalIF":3.8,"publicationDate":"2012-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1085/jgp.201210817","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"30980163","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Unlocking the mechanisms of HCN channel gating with locked-open and locked-closed channels.","authors":"Matthew C Trudeau","doi":"10.1085/jgp.201210898","DOIUrl":"https://doi.org/10.1085/jgp.201210898","url":null,"abstract":"Ion channels are highly specialized to respond to a wide range of environmental stimuli, including transmembrane voltage and chemical ligands ([Hille, 2001][1]). The response of channels to external cues causes a change in their ion conduction, which, in turn, modifies the behavior of excitable and","PeriodicalId":173753,"journal":{"name":"The Journal of General Physiology","volume":" ","pages":"457-61"},"PeriodicalIF":3.8,"publicationDate":"2012-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1085/jgp.201210898","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"30980164","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}