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The gating of the KCNQ1 potassium channel is drastically regulated by auxiliary subunit KCNE proteins. KCNE1, for example, slows the activation kinetics of KCNQ1 by two orders of magnitude. Like other voltage-gated ion channels, the opening of KCNQ1 is regulated by the voltage-sensing domain (VSD; S1–S4 segments). Although it has been known that KCNE proteins interact with KCNQ1 via the pore domain, some recent reports suggest that the VSD movement may be altered by KCNE. The altered VSD movement of KCNQ1 by KCNE proteins has been examined by site-directed mutagenesis, the scanning cysteine accessibility method (SCAM), voltage clamp fluorometry (VCF) and gating charge measurements. These accumulated data support the idea that KCNE proteins interact with the VSDs of KCNQ1 and modulate the gating of the KCNQ1 channel. In this review, we will summarize recent findings and current views of the KCNQ1 modulation by KCNE via the VSD. In this context, we discuss our recent findings that KCNE1 may alter physical interactions between the S4 segment (VSD) and the S5 segment (pore domain) of KCNQ1. Based on these findings from ourselves and others, we propose a hypothetical mechanism for how KCNE1 binding alters the VSD movement and the gating of the channel.

The purpose of this study was to test whether a Kv3 potassium channel modulator, AUT00063, has therapeutic potential for reversing noise-induced increases in spontaneous neural activity, a state that is widely believed to underlie noise-induced tinnitus. Recordings were conducted in noise exposed and control hamsters from dorsal cochlear nucleus (DCN) fusiform cells before and following intraperitoneal administration of AUT00063 (30 mg/kg). Fusiform cell spontaneous activity was increased in sound-exposed animals, approximating levels that were nearly 50% above those of controls. Administration of AUT00063 resulted in a powerful suppression of this hyperactivity. The first signs of this suppression began 13 min after AUT00063 administration, but activity continued to decline gradually until reaching a floor level which was approximately 60% of pre-drug baseline by 25 min after drug treatment. A similar suppressive effect of AUT00063 was observed in control animals, with onset of suppression first apparent at 13 min post-treatment, but continuing to decline toward a floor level that was 54% of pre-drug baseline and was reached 28 min after drug treatment. In contrast, no suppression of spontaneous activity was observed in animals given similar injections of vehicle (control) solution. The suppressive effect of AUT00063 was achieved without significantly altering heart rate and with minimal effects on response thresholds, supporting the interpretation that the reductions of hyperactivity were not a secondary consequence of a more general physiological suppression of the brain or auditory system. These findings suggest that Kv3 channel modulation may be an effective approach to suppressing spontaneous activity in the auditory system and may provide a future avenue for treatment of tinnitus resulting from exposure to intense sound.

Sequences of events are ubiquitous in sensory, motor, and cognitive function. Key computational operations, including pattern recognition, event prediction, and plasticity, involve neural discrimination of spatio-temporal sequences. Here, we show that synaptically-driven reaction-diffusion pathways on dendrites can perform sequence discrimination on behaviorally relevant time-scales. We used abstract signaling models to show that selectivity arises when inputs at successive locations are aligned with, and amplified by, propagating chemical waves triggered by previous inputs. We incorporated biological detail using sequential synaptic input onto spines in morphologically, electrically, and chemically detailed pyramidal neuronal models based on rat data. Again, sequences were recognized, and local channel modulation downstream of putative sequence-triggered signaling could elicit changes in neuronal firing. We predict that dendritic sequence-recognition zones occupy 5 to 30 microns and recognize time-intervals of 0.2 to 5 s. We suggest that this mechanism provides highly parallel and selective neural computation in a functionally important time range. DOI: http://dx.doi.org/10.7554/eLife.25827.001

Energy conservation in battery powered mobile devices that perform wireless multimedia streaming has been a significant research problem since last decade. This is because these mobile devices consume a lot of power while receiving, decoding and ultimately, presenting the multimedia content. What makes things worse is the fact that battery technologies have not evolved enough to keep up with the rapid advancement of mobile devices. This survey examines solutions that have been proposed during the last few years, to improve the energy efficiency of wireless multimedia streaming in mobile hand-held devices. We categorize the research work according to different layers of the Internet protocol stack they utilize. Then, we again regroup these studies based on different traffic scheduling and multimedia content adaptation mechanisms. The traffic scheduling category contains those solutions that optimize the wireless receiving energy without changing the actual multimedia content. The second category on the other hand, specifically modifies the content, in order to reduce the energy consumed by the wireless receiver and to decode and view the content. We compare them and provide evidence of the fact that some of these tactics already exist in modern smaprtphones and provide energy savings with real measurements. In addition, we discuss some relevant literature on the complementary problem of energy-aware multimedia delivery from mobile devices and contrast with our target approaches for multimedia transmission to mobile devices.

The device characteristics of Ti–InSnO thin film transistors (TFTs) with modulated channels were investigated. The field effect mobility was enhanced to 14.9 cm2/V s in the channel-modulated TFT. The electrical performance of the TFT device was improved by the insertion of a high carrier concentration layer at the channel/gate insulator and channel/electrode interfaces. It was due to the enhancement of carrier accumulation and the reduction of parasitic resistance via channel modulation. The threshold voltage was controlled at moderate value. These results indicate that the device characteristic of TFTs can be enhanced by the modulated channel structure.

Signaling pathways involving phospholipase C (PLC) are involved in various neural functions. Understanding how these pathways are regulated will lead to a better understanding of their roles in neural functions. Previous studies demonstrated that receptor-driven PLCβ activation depends on intracellular Ca 2+ concentration ([Ca 2+ ] i ), suggesting the possibility that PLCβ-dependent cellular responses are basically Ca 2+ dependent. To test this possibility, we examined whether modulations of ion channels driven by PLC-coupled metabotropic receptors are sensitive to [Ca 2+ ] i using cultured hippocampal neurons. Muscarinic activation triggered an inward current at −100 mV (the equilibrium potential for K + ) in a subpopulation of neurons. This current response was suppressed by pirenzepine (an M 1 -preferring antagonist), PLC inhibitor, non-selective cation channel blocker, and lowering [Ca 2+ ] i . Using the neurons showing no response at −100 mV, effects of muscarinic activation on K + channels were examined at −40 mV. Muscarinic activation induced a transient decrease of the holding outward current. This current response was mimicked and occluded by XE991, an M-current K + channel blocker, suppressed by pirenzepine, PLC inhibitor and lowering [Ca 2+ ] i , and enhanced by elevating [Ca 2+ ] i . Similar results were obtained when group I metabotropic glutamate receptors were activated instead of muscarinic receptors. These results clearly show that ion channel modulations driven by PLC-coupled metabotropic receptors are dependent on [Ca 2+ ] i , supporting the hypothesis that cellular responses induced by receptor-driven PLCβ activation are basically Ca 2+ dependent.

This paper discusses the design and implementation of a pseudo-differential high-speed and highly linear novel Source-Follower Buffer in 0.35 μm CMOS. The high linearity of Source Follower is achieved by means of a cascode transistor and an auxiliary structure to mitigate impact of channel modulation and parasitic capacitances. The new architecture consumes 10 mW from a 3.3-V supply and it achieves a total harmonic distortion of -74.5 dB at 100 MHz, yielding 12-b resolution. Design methodology, simulation and experimental results are presented.

The large-conductance, Ca(2+)- and voltage-activated K(+) (BK) channel is ubiquitously expressed in mammalian tissues and displays diverse biophysical or pharmacological characteristics. This diversity is in part conferred by channel modulation with different regulatory auxiliary subunits. To date, two distinct classes of BK channel auxiliary subunits have been identified: β subunits and γ subunits. Modulation of BK channels by the four auxiliary β (β1-β4) subunits has been well established and intensively investigated over the past two decades. The auxiliary γ subunits, however, were identified only very recently, which adds a new dimension to BK channel regulation and improves our understanding of the physiological functions of BK channels in various tissues and cell types. This chapter will review the current understanding of BK channel modulation by auxiliary β and γ subunits, especially the latest findings.

In recent years, it has become evident that cholesterol plays a direct role in the modulation of a variety of ion channels. In most cases, cholesterol downregulates channel activity. In contrast, our earlier studies have demonstrated that atrial G protein inwardly rectifying potassium (GIRK) channels are upregulated by cholesterol. Recently, we have shown that hippocampal GIRK currents are also upregulated by cholesterol. A combined computational-experimental approach pointed to putative cholesterol-binding sites in the transmembrane domain of the GIRK2 channel, the primary subunit in hippocampal GIRK channels. In particular, the principal cholesterol-binding site was located in the center of the transmembrane domain in between the inner and outer α-helices of 2 adjacent subunits. Further studies pointed to a similar cholesterol-binding site in GIRK4, a major subunit in atrial GIRK channels. However, a close look at a sequence alignment of the transmembrane helices of the 2 channels reveals surprising differences among the residues that interact with the cholesterol molecule in these 2 channels. Here, we compare the residues that form putative cholesterol-binding sites in GIRK2 and GIRK4 and discuss the similarities and differences among them.

One of the aims of the SatNEx (Satellite Network of Excellence, http://www.satnex.de) European project is to provide the scientific community that operates on satellite communications with measurement campaign results and evaluation tools, in order to support research activities that investigate problems in satellite communications at different levels of the OSI stack. In fact, the research activities developed in SatNEx address the most relevant aspects of satellite communications, such as channel modulation and coding schemes, access strategies, advanced networking, end-to-end quality of service, transport performance, delay tolerant networks, and new applications. Even if SatNEx is mainly devoted to satellite communications, integration of satellite and terrestrial wireless segments has also been taken into account. This paper presents the results obtained in the specific research activity devoted to trials and testbeds developed during the SatNEx project. The high number of authors of this paper is an indication of the strong collaborative work sustained, the numerous measurement campaigns, and the complexity in developing integrated testbeds. Copyright © 2008 John Wiley & Sons, Ltd.

Ca2+/calmodulin-dependent regulation of voltage-gated CaV1-2 Ca2+ channels shows extraordinary modes of spatial Ca2+ decoding and channel modulation, vital for many biological functions. A single calmodulin (CaM) molecule associates constitutively with the channel's carboxy-terminal tail, and Ca2+ binding to the C-terminal and N-terminal lobes of CaM can each induce distinct channel regulations. As expected from close channel proximity, the C-lobe responds to the roughly 100-microM Ca2+ pulses driven by the associated channel, a behaviour defined as 'local Ca2+ selectivity'. Conversely, all previous observations have indicated that the N-lobe somehow senses the far weaker signals from distant Ca2+ sources. This 'global Ca2+ selectivity' satisfies a general signalling requirement, enabling a resident molecule to remotely sense cellular Ca2+ activity, which would otherwise be overshadowed by Ca2+ entry through the host channel. Here we show that the spatial Ca2+ selectivity of N-lobe CaM regulation is not invariably global but can be switched by a novel Ca2+/CaM-binding site within the amino terminus of channels (NSCaTE, for N-terminal spatial Ca2+ transforming element). Native CaV2.2 channels lack this element and show N-lobe regulation with a global selectivity. On the introduction of NSCaTE into these channels, spatial Ca2+ selectivity transforms from a global to local profile. Given this effect, we examined CaV1.2/CaV1.3 channels, which naturally contain NSCaTE, and found that their N-lobe selectivity is indeed local. Disruption of this element produces a global selectivity, confirming the native function of NSCaTE. Thus, differences in spatial selectivity between advanced CaV1 and CaV2 channel isoforms are explained by the presence or absence of NSCaTE. Beyond functional effects, the position of NSCaTE on the channel's amino terminus indicates that CaM can bridge the amino terminus and carboxy terminus of channels. Finally, the modularity of NSCaTE offers practical means for understanding the basis of global Ca2+ selectivity.

This paper analyzes the standard of TETRA which is the existing digital trunking system evolution in our country and introduces the new requirements and characteristic of the channel technology for a new generation of broadband wireless trunking system of our country in detail. On this basis, this paper analyzes and simulates the new generation of PDT standard in the view of channel technology such as synchronization technology, channel modulation, and channel coding, respectively, and compares the performance of two plans. Analysis results show that China’s independent development and customization of a new generation of police digital trunking standard PDT is more in line with the national conditions and has showed great advantages. It will gradually replace the TETRA and become the mainstream of public security digital trunking system.

Neuronal Ca2+ channels are key transducers coupling excitability to cellular function. As such, they are tightly regulated by multiple G protein-signaling pathways that finely tune their activity. In addition to fast, direct G(beta)gamma modulation of Ca2+ channels, a slower Galpha(q/11)-mediated mechanism has remained enigmatic despite intensive study. Recent work suggests that membrane phosphoinositides are crucial determinants of Ca2+ channel activity. Here, we discuss their role in Ca2+ channel modulation and the leading theories that seek to elucidate the underlying molecular details of the so-called "mysterious" G(q/11)-mediated signal.

Delta-palutoxins from the spider Paracoelotes luctuosus (Araneae: Amaurobiidae) are 36-37 residue long peptides that show preference for insect sodium channels (NaChs) and modulate their function. Although they slow NaCh inactivation in a fashion similar to that of receptor site 3 modifiers, such as scorpion alpha-toxins, they actually bind with high affinity to the topologically distinct receptor site 4 of scorpion beta-toxins. To resolve this riddle, we scanned by Ala mutagenesis the surface of delta-PaluIT2, a delta-palutoxin variant with the highest affinity for insect NaChs, and compared it to the bioactive surface of a scorpion beta-toxin. We found three regions on the surface of delta-PaluIT2 important for activity: the first consists of Tyr-22 and Tyr-30 (aromatic), Ser-24 and Met-28 (polar), and Arg-8, Arg-26, Arg-32, and Arg-34 (basic) residues; the second is made of Trp-12; and the third is made of Asp-19, whose substitution by Ala uncoupled the binding from toxicity to lepidopteran larvae. Although spider delta-palutoxins and scorpion beta-toxins have developed from different ancestors, they show some commonality in their bioactive surfaces, which may explain their ability to compete for an identical receptor (site 4) on voltage-gated NaChs. Yet, their different mode of channel modulation provides a novel perspective about the structural relatedness of receptor sites 3 and 4, which until now have been considered topologically distinct.

Key elements of tumor development include proliferation, migration, invasiveness, and angiogenesis. Activation of the volume-sensitive organic osmolyte/anion channel (VSOAC) has been suggested to play a role in all of these processes. VSOACs may therefore represent an important therapeutic target in the etiology of cancer. However, pharmacological inhibitors of VSOAC are nonselective and of low potency, highlighting the importance of identifying novel regulators of the channel. The use of electrophysiological methods coupled with techniques such as pull-down assays, yeast 2-hybrid, and functional protein arrays have already proved valuable in studying protein-protein interactions in a variety of systems. Some of these methods have been used to identify small molecules that modulate the function of other types of ion channels. Given that several proteins have already been identified as putative modulators of VSOACs, proteomics technologies may prove useful in elucidating the molecular identity of VSOACs and helpful in identifying novel modulators of channel function. In this paper, we review the involvement of VSOACs in tumor development processes and its regulation by pharmacological agents and cellular proteins. Proteomic approaches to study protein-protein interactions and how such approaches may be used to study VSOACs are also discussed. We speculate on how modulation of protein-protein interactions may result in the identification of a novel class of compounds for modulating VSOACs.

In skeletal muscle, the waveform of Ca(2+) release under clamp depolarization exhibits an early peak. Its decay reflects an inactivation, which locally corresponds to the termination of Ca(2+) sparks, and is crucial for rapid control. In cardiac muscle, both the frequency of spontaneous sparks (i.e., their activation) and their termination appear to be strongly dependent on the Ca(2+) content in the sarcoplasmic reticulum (SR). In skeletal muscle, no such role is established. Seeking a robust measurement of Ca(2+) release and a way to reliably modify the SR content, we combined in the same cells the "EGTA/phenol red" method (Pape et al., 1995) to evaluate Ca(2+) release, with the "removal" method (Melzer et al., 1987) to evaluate release flux. The cytosol of voltage-clamped frog fibers was equilibrated with EGTA (36 mM), antipyrylazo III, and phenol red, and absorbance changes were monitored simultaneously at three wavelengths, affording largely independent evaluations of Delta[H(+)] and Delta[Ca(2+)] from which the amount of released Ca(2+) and the release flux were independently derived. Both methods yielded mutually consistent evaluations of flux. While the removal method gave a better kinetic picture of the release waveform, EGTA/phenol red provided continuous reproducible measures of calcium in the SR (Ca(SR)). Steady release permeability (P), reached at the end of a 120-ms pulse, increased as Ca(SR) was progressively reduced by a prior conditioning pulse, reaching 2.34-fold at 25% of resting Ca(SR) (four cells). Peak P, reached early during a pulse, increased proportionally much less with SR depletion, decreasing at very low Ca(SR). The increase in steady P upon depletion was associated with a slowing of the rate of decay of P after the peak (i.e., a slower inactivation of Ca(2+) release). These results are consistent with a major inhibitory effect of cytosolic (rather than intra-SR) Ca(2+) on the activity of Ca(2+) release channels.

Inhibition of N- (Cav2.2) and P/Q-type (Cav2.1) calcium channels by G-proteins contribute importantly to presynaptic inhibition as well as to the effects of opiates and cannabinoids. Accordingly, elucidating the molecular mechanisms underlying G-protein inhibition of voltage-gated calcium channels has been a major research focus. So far, inhibition is thought to result from the interaction of multiple proposed sites with the Gbetagamma complex (Gbetagamma). Far less is known about the important interaction sites on Gbetagamma itself. Here, we developed a novel electrophysiological paradigm, "compound-state willing-reluctant analysis," to describe Gbetagamma interaction with N- and P/Q-type channels, and to provide a sensitive and efficient screen for changes in modulatory behavior over a broad range of potentials. The analysis confirmed that the apparent (un)binding kinetics of Gbetagamma with N-type are twofold slower than with P/Q-type at the voltage extremes, and emphasized that the kinetic discrepancy increases up to ten-fold in the mid-voltage range. To further investigate apparent differences in modulatory behavior, we screened both channels for the effects of single point alanine mutations within four regions of Gbeta1, at residues known to interact with Galpha. These residues might thereby be expected to interact with channel effectors. Of eight mutations studied, six affected G-protein modulation of both N- and P/Q-type channels to varying degrees, and one had no appreciable effect on either channel. The remaining mutation was remarkable for selective attenuation of effects on P/Q-, but not N-type channels. Surprisingly, this mutation decreased the (un)binding rates without affecting its overall affinity. The latter mutation suggests that the binding surface on Gbetagamma for N- and P/Q-type channels are different. Also, the manner in which this last mutation affected P/Q-type channels suggests that some residues may be important for "steering" or guiding the protein into the binding pocket, whereas others are important for simply binding to the channel.

Hyaluronan (sodium hyaluronate, HA) is a very long, anionic linear polymer ubiquitously present in the extracellular matrix (ECM) of mammals, where it forms loose and elastic matrices. Due to its p...

A-type channels, encoded by the pore-forming alpha-subunits of the Kv4.x family, are particularly important in regulating membrane excitability in the CNS and the heart. Given the key role of modulation of A currents by kinases, we sought to investigate the protein structure-function relationships underlying the regulation of these currents by PKA. We have previously shown the existence of two PKA phosphorylation sites in the Kv4.2 sequence; therefore, we focused this study on the Kv4.2 primary subunit. In the present studies we made the surprising finding that PKA phosphorylation of the Kv4.2 alpha-subunit is necessary but not sufficient for channel modulation; channel modulation by PKA required the presence of an ancillary subunit, the K+ channel interacting protein (KChIP3). Therefore, these findings indicate a surprising complexity to kinase regulation of A currents, in that an interaction of two separate molecular events, alpha-subunit phosphorylation and the association of an ancillary subunit (KChIP3), are necessary for phosphorylation-dependent regulation of Kv4.2-encoded A channels by PKA. Overall, our studies indicate that PKA must of necessity act on a supramolecular complex of pore-forming alpha-subunits plus ancillary subunits to alter channel properties.

Protonated aminosulfonates (AS), notably taurine, directly and reversibly inhibit homomeric and heteromeric channels that contain Cx26, a widely distributed connexin, but not homomeric Cx32 channels. Our previous biophysical studies identify the carboxyl-terminal domain of Cx26 (Cx26CT) as a key component of the channel modulation, suggesting a mechanism by which AS disrupts a pH-dependent association between the CT and cytoplasmic loop of Cx26 (Cx26CL), leading to occlusion of the pore [1,2]. Using recombinantly expressed Cx26CL and a Cx26CT peptide, NMR showed that taurine binds to the CL and not the CT, and that the CT and CL directly interact [3]. Our next goal to further characterize this mechanism is to identify the Cx26CL residues that directly interact with the Cx26CT and taurine. The Cx26CL construct used in the prior study (residues 98-139) contained a number of hydrophobic residues on the C-terminus, likely membrane associated, which decreased solubility below levels needed for detailed structural studies. Therefore, we created a shorter Cx26CL construct (residues 98-134) and were able to achieve millimolar soluble concentrations. Using this construct, we demonstrated by NMR a substantial interaction between the Cx26CT and the Cx26CL, which was blocked by taurine. Ongoing studies will determine (i) the binding affinities between the molecular partners, (ii) identify the Cx26CL residues involved in these regulatory interactions, and (iii) explore the potential effects of the Cx32CL and CT domains on these interactions, as may occur in Cx26-Cx32 heteromeric channels. Support: GM072631 & GM101950.References1. Bevans, C.G. & Harris, A.L. (1999) J. Biol. Chem. 274:3711.2. Tao, L. & Harris, A.L. (2004) J. Biol. Chem. 279:38544.3. Locke, D. et al. (2011) J. Gen. Physiol. 138:321.

We studied the thermal stability of Ge channel modulation doped structures fabricated by solid source molecular beam epitaxy utilizing low-temperature buffer technique. Drastic decrease of mobility and increase of carrier density was observed after annealing at temperature above 600°C. SIMS measurements indicated that this was not due to the B diffusion into Ge channel layers but the Si–Ge interdiffusion at the Ge/SiGe interface. In addition, it was found that the strain relaxation of Ge channel layers could occur after annealing at temperatures even below 500°C and cause the decreased mobility when the channel layers thickness were beyond equilibrium critical one.

Voltage-dependent inhibition of N- and P/Q-type calcium channels by G proteins is crucial for presynaptic inhibition of neurotransmitter release, and may contribute importantly to short-term synaptic plasticity. Such calcium-channel modulation could thereby impact significantly the neuro-computational repertoire of neural networks. The differential modulation of N and P/Q channels could even further enrich their impact upon synaptic tuning. Here, we performed in-depth comparison of the G-protein inhibition of recombinant N and P/Q channels, expressed in HEK 293 cells with the m2 muscarinic receptor. While both channel types display classic features of G-protein modulation (kinetic slowing of activation, prepulse facilitation, and voltage dependence of inhibition), we confirmed previously reported quantitative differences, with N channels displaying stronger inhibition and greater relief of inhibition by prepulses. A more fundamental, qualitative difference in the modulation of these two channels was revealed by a modified tail-activation paradigm, as well as by a novel “slope” analysis method comparing time courses of slow activation and prepulse facilitation. The stark contrast in modulatory behavior can be understood within the context of the “willing–reluctant” model, in which binding of G-protein βγ subunits to channels induces a reluctant mode of gating, where stronger depolarization is required for opening. Our experiments suggest that only N channels could be opened in the reluctant mode, at voltages normally spanned by neuronal action potentials. By contrast, P/Q channels appear to remain closed, especially over these physiological voltages. Further, the differential occurrence of reluctant openings is not explained by differences in the rate of G-protein unbinding from the two channels. These two scenarios predict very different effects of G-protein inhibition on the waveform of Ca2+ entry during action potentials, with potentially important consequences for the timing and efficacy of synaptic transmission.

Cyclic nucleotide–gated (CNG) channels are critical components in the visual and olfactory signal transduction pathways, and they primarily gate in response to changes in the cytoplasmic concentration of cyclic nucleotides. We previously found that the ability of the native rod CNG channel to be opened by cGMP was markedly inhibited by analogues of diacylglycerol (DAG) without a phosphorylation reaction (Gordon, S.E., J. Downing-Park, B. Tam, and A.L. Zimmerman. 1995. Biophys. J. 69:409–417). Here, we have studied cloned bovine rod and rat olfactory CNG channels expressed in Xenopus oocytes, and have determined that they are differentially inhibited by DAG. At saturating [cGMP], DAG inhibition of homomultimeric (α subunit only) rod channels was similar to that of the native rod CNG channel, but DAG was much less effective at inhibiting the homomultimeric olfactory channel, producing only partial inhibition even at high [DAG]. However, at low open probability (Po), both channels were more sensitive to DAG, suggesting that DAG is a closed state inhibitor. The Hill coefficients for DAG inhibition were often greater than one, suggesting that more than one DAG molecule is required for effective inhibition of a channel. In single-channel recordings, DAG decreased the Po but not the single-channel conductance. Results with chimeras of rod and olfactory channels suggest that the differences in DAG inhibition correlate more with differences in the transmembrane segments and their attached loops than with differences in the amino and carboxyl termini. Our results are consistent with a model in which multiple DAG molecules stabilize the closed state(s) of a CNG channel by binding directly to the channel and/or by altering bilayer–channel interactions. We speculate that if DAG interacts directly with the channel, it may insert into a putative hydrophobic crevice among the transmembrane domains of each subunit or at the hydrophobic interface between the channel and the bilayer.

The enhancement of force of contraction (FOC) following increasing frequencies of stimulation is an important mechanism of positive inotropy in human myocardium. The present study aimed to investigate the influence of alterations in Na+ influx on FFR in human myocardium. Isometric FOC of electrically stimulated right auricular trabeculae (AUT, n = 12) from human non-failing hearts (n = 8) was measured at different stimulation rates (0.5-3 Hz) under control conditions, after increasing Na+ influx by the addition of (+/-)BDF 9148 (BDF, 3 mumol l-1) and after decreasing Na+ influx by the addition of lidocaine (LIDO, 10 mumol l-1). Additionally, the rate dependent changes in diastolic tension (DT) were measured in all experiments. Under control conditions FOC increased with increasing frequencies of stimulation. The rate at which maximal FOC was observed (SFmax) was 2.0 +/- 0.2 Hz and maximal increase in FOC (PIEmax) by increasing frequency of stimulation was +1.5 +/- 0.5 mN. After increase of Na+ influx by BDF (3 mumol l-1) SFmax was decreased to 0.8 +/- 0.1 Hz (p0.05 versus control) and PIEmax was +0.1 +/- 0.3 mN (p0.05). When Na+ influx was diminished by LIDO (10 mumol l-1) SFmax and PIEmax were increased compared to control (2.4 +/- 0.1 Hz and +4.1 +/- 0.9 mN, p0.05 versus control). The diastolic tension (DT) of AUT at 3 Hz was not changed at higher rates in the control group and after application of LIDO (10 mumol l-1), whereas after enhancement of Na+ influx by BDF there was an increase in DT of +0.7 +/- 0.2 at 3 Hz (p0.05 versus control and LIDO). An enhanced Na+ influx leads to a decrease in the optimal frequency and to a smaller force potentiation by higher stimulation rates which could be at least partly due to incomplete relaxation at higher frequencies, whereas a reduced Na+ influx is followed by opposite alterations. It is concluded that besides Ca2+ handling also Na+ influx and Na+ homeostasis might determine the frequency-induced force potentiation in human myocardium. Thus, the negative FFR in diseased human myocardium might result from changes in cellular Ca2+ or Na+ regulatory sites.

Dendritic arbors are critical for the information processing capability of central neurons, but quantitative analysis of their membrane properties has been hampered by their geometrical complexity. Here, we have focused on an important source of Ca 2+ entry in dendrites, the voltage-gated Ca 2+ channels, by applying the whole-cell voltage-clamp technique to isolated dendritic segments ("dendrosomes") from rat hippocampal neurons. We found that low voltage-activated T-type Ca 2+ channels provide a significantly larger fraction of the Ca 2+ influx in dendrites than their counterparts in cell bodies. Surprisingly, 60%–70% of the high voltage-activated Ca 2+ current in dendrosomes was N and P/Q type, and these channels were susceptible to neurotransmitter inhibition, suggesting a novel physiological role for G protein–regulated Ca 2+ channel modulation in controlling dendritic excitability and Ca 2+ signaling.

Zhou, Jiuying, Mark S. Shapiro, and Bertil Hille. Speed of Ca2+channel modulation by neurotransmitters in rat sympathetic neurons. J. Neurophysiol. 77: 2040–2048, 1997. We have measured the onset and recovery speed of inhibition of N-type Ca2+channels in adult rat superior cervical ganglion neurons by somatostatin (SS), norepinephrine (NE), and oxotremorine-M (oxo-M, a muscarinic agonist), using the whole cell configuration of the patch-clamp method with 5 mM external Ca2+. With a local perfusion pipette system that changed the solution surrounding the cell within 50 ms, we applied agonists at various times before a brief depolarization from −80 mV that elicited ICa. At concentrations that produced maximal inhibition, the onset time constants for membrane-delimited inhibition by SS (0.5 μM), NE (10 μM), and oxo-M (20 μM) were 2.1, 0.7, and 1.0 s, respectively. The time constants for NE inhibition depended only weakly on the concentration, ranging from 1.2 to 0.4 s in the concentration range from 0.5 to 100 μM. Inhibition by oxo-M (20 μM) through a different G-protein pathway that uses a diffusible cytoplasmic messenger had a time constant near 9 s. The recovery rate constant from membrane-delimited inhibition was between 0.09 and 0.18 s−1, significantly higher than the intrinsic GTPase rate of purified G protein Go, suggesting that Ca2+channels or other proteins in the plasma membrane act as GTPase activating proteins. We also measured the rate of channel reinhibition after relief by strong depolarizing prepulses, which should reflect the kinetics of final steps in the inhibition process. In the presence of different concentrations of NE, reinhibition was four to seven times faster than the onset of inhibition, indicating that the slowest step of inhibition must precede the binding of G protein to the channel. We propose a kinetic model for the membrane-delimited NE inhibition of Ca2+channels. It postulates two populations of receptors with different affinities for NE, a single population of G proteins, and a single population of Ca2+channels. This model closely simulated the time courses of onset and recovery of inhibition and reinhibition, as well as the dose-response curve for inhibition of Ca2+channels by NE.

Because of their remarkable roles in electrical cell signaling, voltage-gated cation channels (VGCCs) have been the subject of intense investigations and debate for more than 50 years. Ultimately, the prospective implications of such studies have an impact on our understanding of the molecular properties of VGCCs involved in consciousness, anesthesia, and diseases, to mention a few. The following review aims to summarize our current knowledge of activation of VGCCs by highlighting major methodological innovations in the field and the breakthroughs they allowed. Focusing mainly on insights gained through computer simulations, while acknowledging important experimental findings, we hope to inspire experimentalists to benefit from these approaches in the generation of hypotheses and design of experiments. Also, we outline major future challenges for the field, such as channel modulation, lesser-known receptors, and molecular origins of channel dysfunctions.

Spectro-temporal variations are a consequence of dynamic structural variations of a sounding body. The human auditory system is highly optimized for the detection, segregation and analysis of one class of such variations—speech. Here, we will examine some consequences of this optimisation in the context of complex listening involving multiple concurrent talkers. In such conversational settings, listeners rapidly shift their attention from one to another talker so foreground and background are defined dynamically by listener intent. Up-regulation of the attended-to talker is generally thought to result from endogenous, top-down attention. Here, we review a recent report indicating that substantial informational masking between concurrent talkers may result from bottom-up interactions between sources within frequency modulation channels. This indicates that temporally dynamic aspects of within-frequency channel processing plays a very important role in speech masking by the sort of “noise” most commonly enc...

Analytical models of threshold voltage and inversion charge for the graded SiGe-channel modulation-doped p-MOSFETs have been derived and verified by SEDAN-3 simulation. The effect of threshold voltage adjustment on hole confinement, and the increase of SiGe channel hole density under the threshold voltage specified by application circuits are then studied.

Calmodulin (CaM) regulation of mammalian CaV channels is both biologically critical and mechanistically rich, rendering this system a central prototype for the decoding of Ca2+ signals and the modulation of channels. This system showcases the remarkable ability of the N- and C-terminal lobes of CaM to function as semiautonomous Ca2+ sensors and effectors, a theme initially recognized in Paramecium (Cell 62:165). In mammalian CaV channels, Ca2+-free CaM (apoCaM) starts off already preassociated with a host channel, and then the C-lobe turns out to respond preferentially to the strong Ca2+ influx through the host channel to induce one form of channel modulation (local selectivity), whereas the N-lobe frequently prefers the far weaker Ca2+ signal emanating from Ca2+ sources at a distance (global selectivity). These striking contrasts in spatial Ca2+ selectivity, crucial to biological Ca2+ signaling, can be simply explained by mechanisms involving the translocation of CaM among an apoCaM preassociation locus and multiple Ca2+/CaM effector sites (Cell 133:1228). However, beyond apoCaM preassociation at an IQ domain on the carboxy-terminus of channels, little has been definitively established regarding the structural identity of Ca2+/CaM effector sites, outside of an NSCaTE element in the channel amino terminus (Nature 451:830). Here, we outline new evidence identifying dominant Ca2+/CaM effector sites outside of the IQ and NSCaTE regions (Ben Johnny et al, Bazzazi et al, this meeting), thereby bolstering a modulatory mechanism wherein CaM departs from an initial IQ preassociation locus, then interacts with structurally distinct effector sites. This intricate translocating dance of CaM complexed with a target molecule may be a general scheme enabling high-order Ca2+ decoding in many signaling complexes throughout biology; indeed, an analogous hypothesis of migratory CaM has been proposed for NaV channels (J. Biol. Chem. 284:6436).

Vertebrate photoreceptors are thought to adapt to light by a change in Ca2+, which is postulated to mediate modulation of (1) excited rhodopsin (Rh*) by Ca2+-dependent binding of recoverin, (2) guanylyl cyclase activity via Ca2+-dependent GCAP proteins, and (3) cyclic nucleotide-gated channels by binding of Ca2+-calmodulin. Previous experiments genetically deleted recoverin and the GCAPs and showed that significant regulation of sensitivity survives removal of (1) and (2). We genetically deleted the channel Ca2+-calmodulin binding site in the mouseMus musculusand found that removal of (3) alters response waveform, but removal of (3) or of (2) and (3) together still leaves much of adaptation intact. These experiments demonstrate that an important additional mechanism is required, which other experiments indicate may be regulation of phosphodiesterase 6 (PDE6). We therefore constructed a kinetic model in which light produces a Ca2+-mediated decrease in PDE6 decay rate, with the novel feature that both spontaneously activated and light-activated PDE6 are modulated. This model, together with Ca2+-dependent acceleration of guanylyl cyclase, can successfully account for changes in sensitivity and response waveform in background light.

The study of channel modulation by regulatory subunits has attracted considerable attention. Evidence indicates a pivotal role for accessory proteins in the channelosome. For instance, these regulatory subunits are necessary to recapitulate in vivo ion currents and to further understand the physiological role of ion channels. KCNEs are a family of regulatory subunits that interact with a wide range of channels. We have described for the first time a molecular interaction between KCNE4 and the voltage-dependent potassium channel K(V)1.3. The association of KCNE4, which alters the biophysical properties, trafficking and membrane localization of K(V)1.3, functions as an endogenous dominantnegative mechanism. Since both proteins are expressed in the immune system, K(V)1.3/KCNE4 channels may contribute to the fine-tuning of the immune response. Therefore, our results point to KCNE4 as a novel target for immunomodulation. KCNE4 is not the only KCNE which is expressed in leukocytes. All KCNEs (KCNE1-5) are present, and some members demonstrate modulation during proliferation and cancer. In summary, regulatory KCNE subunits are expressed in the immune system. In addition, several voltage-dependent K(+) channels, which could interact with KCNEs, are also detected. Therefore, KCNE subunits may play a yet undiscovered role in the physiology of the immune system.

EF-hand Ca2+-binding proteins such as calmodulin and CaBP1 have emerged as important regulatory subunits of voltage-gated Ca2+ channels. Here, we show that caldendrin, a variant of CaBP1 enriched in the brain, interacts with and distinctly modulates Cav1.2 (L-type) voltage-gated Ca2+ channels relative to other Ca2+-binding proteins. Caldendrin binds to the C-terminal IQ-domain of the pore-forming alpha1-subunit of Cav1.2 (alpha(1)1.2) and competitively displaces calmodulin and CaBP1 from this site. Compared with CaBP1, caldendrin causes a more modest suppression of Ca2+-dependent inactivation of Cav1.2 through a different subset of molecular determinants. Caldendrin does not bind to the N-terminal domain of alpha11.2, a site that is critical for functional interactions of the channel with CaBP1. Deletion of the N-terminal domain inhibits CaBP1, but spares caldendrin modulation of Cav1.2 inactivation. In contrast, mutations of the IQ-domain abolish physical and functional interactions of caldendrin and Cav1.2, but do not prevent channel modulation by CaBP1. Using antibodies specific for caldendrin and Cav1.2, we show that caldendrin coimmunoprecipitates with Cav1.2 from the brain and colocalizes with Cav1.2 in somatodendritic puncta of cortical neurons in culture. Our findings reveal functional diversity within related Ca2+-binding proteins, which may enhance the specificity of Ca2+ signaling by Cav1.2 channels in different cellular contexts.

Ca2+ and other divalent cations exert multiple effects on voltage-gated Na channels. Although virtually i yyermeant, both extracellular and intracellular Ca ions block Na+ m vement by binding to sites within the channel. Ca*+ also competes with tetrodotoxin and saxitoxin for a blocking site near the external mouth of the pore. Both internal and external divalent cations also affect voltagedependent Na channel gating by interacting with negatively charged membrane lipids and binding sites on the channel itself. Thus, divalent cations are effective modulators of Na channels and valuable probes of channel structure and function.

The Drosophila Slowpoke calcium-dependent potassium channel (dSlo) binding protein Slob was discovered by a yeast two-hybrid screen using the carboxy-terminal tail region of dSlo as bait. Slob binds to and modulates the dSlo channel. We have found that there are several Slob proteins, resulting from multiple translational start sites and alternative splicing, and have named them based on their molecular weights (in kD). The larger variants, which are initiated at the first translational start site and are called Slob71 and Slob65, shift the voltage dependence of dSlo activation, measured by the whole cell conductance–voltage relationship, to the left (less depolarized voltages). Slob53 and Slob47, initiated at the third translational start site, also shift the dSlo voltage dependence to the left. In contrast, Slob57 and Slob51, initiated at the second translational start site, shift the conductance–voltage relationship of dSlo substantially to more depolarized voltages, cause an apparent dSlo channel inactivation, and increase the deactivation rate of the channel. These results indicate that the amino-terminal region of Slob plays a critical role in its modulation of dSlo.

We study the problem of jointly optimizing source/channel/modulation coding to achieve a given quality of service while minimizing the total power consumption of mobiles. This paper emphasizes the design of a robust transmission framework in the context of a total power minimization scheme. We design a simple but efficient transmission scheme which is called multistage coded modulation that combines source/channel (S/C) coding and multirate modulation (MM). We then integrate into this scheme a complexity-scalable video coder to achieve the best trade-offs in multimedia wireless communications between total power, quality of service, and capacity. Preliminary results show superior video frame quality (around 3 dB better than the simple S/C coding scheme) of the proposed system in the severe channel condition, with total power consumption kept to a minimum.

In this chapter, the properties of the single channel, and summation of single channel currents to produce macroscopic currents are discussed. Macroscopic currents produce changes in the membrane potential. This enhances the basic concepts for a more detailed discussion of the properties of specific ion channels. This chapter provides a basic introduction to ion channel properties rather than a comprehensive review. Detailed properties of single-channel currents, permeation, and electrochemical gradient are covered. The current-voltage relation, permeability and selectivity, gating, Ligand-gated channels, voltage-gated channels, channel modulation, kinetic analysis of single-channel currents, macroscopic current, the membrane current, are also highlighted. From whole-cell currents to changes in the membrane potential, action potential, and synaptic potential are all covered in this topic.

This unit provides an overview of the electrophysiological techniques used to determine the physiological and/or pharmacological properties of membrane ion channels at the single-cell level. Only those techniques that measure potential changes at the transmembrane and membrane levels are discussed. The basics of current-clamp recording, voltage-clamp recording, and patch-clamp procedures are presented along with their advantages and disadvantages. Additional topics are discussed with regard to their relation to electrophysiological measurements, such as membrane properties, ion selectivity, time resolution, ligand-gated ion channels (LGICs), voltage-dependent channels, and channel modulation and interactions. Also included is a discussion the electrophysiological properties of seven-transmembrane-domain receptors. This unit provides an overview of the electrophysiological techniques used to determine the physiological and/or pharmacologic of ion channels.

Photorelease of bioactive molecules from inactive precursors is a very powerful tool for the study of the molecular mechanisms underlying physiological processes as diverse as ionic channel modulation, exocytosis, phototransduction, ligand-receptor interaction, and cross-bridge activity. A brief account of the methodology, available compounds, and fields of application is presented here.

A new class of charge-coupled devices called junction virtual phase (JVP) CCD's is described. JVP CCDs have very high photosensitivity because their pixels are designed without any metal or polysilicon gates. A new principle of buried channel modulation through a narrow depleted layer is used. This principle is realized in a few JVP structures. Two dimensional simulation of these structures are presented.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.