Functional consequences of lidocaine binding to slow-inactivated sodium channels.

Na channels open upon depolarization but then enter inactivated states from which they cannot readily reopen. After brief depolarizations, native channels enter a fast-inactivated state from which recovery at hyperpolarized potentials is rapid (< 20 ms). Prolonged depolarization induces a slow-inactivated state that requires much longer periods for recovery (> 1 s). The slow-inactivated state therefore assumes particular importance in pathological conditions, such as ischemia, in which tissues are depolarized for prolonged periods. While use-dependent block of Na channels by local anesthetics has been explained on the basis of delayed recovery of fast-inactivated Na channels, the potential contribution of slow-inactivated channels has been ignored. The principal (alpha) subunits from skeletal muscle or brain Na channels display anomalous gating behavior when expressed in Xenopus oocytes, with a high percentage entering slow-inactivated states after brief depolarizations. This enhanced slow inactivation is eliminated by coexpressing the alpha subunit with the subsidiary beta 1 subunit. We compared the lidocaine sensitivity of alpha subunits expressed in the presence and absence of the beta 1 subunit to determine the relative contributions of fast-inactivated and slow-inactivated channel block. Coexpression of beta 1 inhibited the use-dependent accumulation of lidocaine block during repetitive (1-Hz) depolarizations from -100 to -20 mV. Therefore, the time required for recovery from inactivated channel block was measured at -100 mV. Fast-inactivated (alpha + beta 1) channels were mostly unblocked within 1 s of repolarization; however, slow-inactivated (alpha alone) channels remained blocked for much longer repriming intervals (> 5 s). The affinity of the slow-inactivated state for lidocaine was estimated to be 15-25 microM, versus 24 microM for the fast-inactivated state. We conclude that slow-inactivated Na channels are blocked by lidocaine with an affinity comparable to that of fast-inactivated channels. A prominent functional consequence is potentiation of use-dependent block through a delay in repriming of lidocaine-bound slow-inactivated channels.

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Open-channel block of Na+ channels by intracellular Mg2+

European Biophysics Journal ◽

10.1007/bf00196922 ◽

1990 ◽

Vol 18 (6) ◽

Cited By ~ 9

Author(s):

M. Pusch

Keyword(s):

Open Channel ◽

Channel Block ◽

Na Channels ◽

Open Channel Block ◽

Block Of Na Channels

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Functional association of the beta 1 subunit with human cardiac (hH1) and rat skeletal muscle (mu 1) sodium channel alpha subunits expressed in Xenopus oocytes.

The Journal of General Physiology ◽

10.1085/jgp.106.6.1171 ◽

1995 ◽

Vol 106 (6) ◽

pp. 1171-1191 ◽

Cited By ~ 82

Author(s):

H B Nuss ◽

N Chiamvimonvat ◽

M T Pérez-García ◽

G F Tomaselli ◽

E Marbán

Keyword(s):

Skeletal Muscle ◽

Xenopus Oocytes ◽

Normal Function ◽

Alpha Subunit ◽

Na Channels ◽

Rat Skeletal Muscle ◽

Time Constants ◽

Alpha Subunits ◽

Na Currents ◽

Steady State Inactivation

Native cardiac and skeletal muscle Na channels are complexes of alpha and beta 1 subunits. While structural correlates for activation, inactivation, and permeation have been identified in the alpha subunit and the expression of alpha alone produces functional channels, beta 1-deficient rat skeletal muscle (mu 1) and brain Na channels expressed in Xenopus oocytes do not gate normally. In contrast, the requirement of a beta 1 subunit for normal function of Na channels cloned from rat heart or human heart (hH1) has been disputed. Coinjection of rat brain beta 1 subunit cRNA with hH1 (or mu 1) alpha subunit cRNA into oocytes increased peak Na currents recorded 2 d after injection by 240% (225%) without altering the voltage dependence of activation. In mu 1 channels, steady state inactivation was shifted to more negative potentials (by 6 mV, p < 0.01), but the shift of 2 mV was not significant for hH1 channels. Nevertheless, coexpression with beta 1 subunit speeded the decay of macroscopic current of both isoforms. Ensemble average hH1 currents from cell-attached patches revealed that coexpression of beta 1 increases the rate of inactivation (quantified by time to 75% decay of current; p < 0.01 at -30, -40, and -50 mV). Use-dependent decay of hH1 Na current during repeated pulsing to -20 mV (1 s, 0.5 Hz) after a long rest was reduced to 16 +/- 2% of the first pulse current in oocytes coexpressing alpha and beta 1 subunits compared to 35 +/- 8% use-dependent decay for oocytes expressing the alpha subunit alone. Recovery from inactivation of mu 1 and hH1 Na currents after 1-s pulses to -20 mV is multiexponential with three time constants; coexpression of beta 1 subunit decreased all three recovery time constants. We conclude that the beta 1 subunit importantly influences the function of Na channels produced by coexpression with either the hH1 or mu 1 alpha subunits.

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Negative Pressure Therapy in Wounds Surgical Treatment

Revista de Chimie ◽

10.37358/rc.17.11.5955 ◽

2017 ◽

Vol 68 (11) ◽

pp. 2687-2690 ◽

Cited By ~ 1

Author(s):

Bogdan Mihnea Ciuntu ◽

Stefan Octavian Georgescu ◽

Ciprian Cirdeiu ◽

Daniel Timofte ◽

Doina Azoicai ◽

...

Keyword(s):

Negative Pressure ◽

Healing Time ◽

Negative Pressure Therapy ◽

Simultaneous Application ◽

Average Hospital ◽

Pressure Therapy ◽

Days Of Therapy ◽

Functional Consequences ◽

Time Required ◽

A Prospective Study

The study aims to assess the significance of negative pressure therapy in the treatment of 1 January 2014 - 31 June 2017. The objectives intend to evaluate the healing time required after applying the method and the functional consequences for the patient. A prospective study was conducted on a sample of 31 patients with various tipe of wounds which were monitored their clinical course between September 2014 - February 2017, following negative pressure therapy. There were used vacuum assisted closure devices (VAC � -Hartman) in order to apply negative pressure to the wound, while complying with specified settings in accordance with patients� outcome. Healing was obtained in all cases, to an average hospital stay of 30 days and 12 days of therapy application.The negative result of microbial cultures was obtained after an average of 7.55 days by simultaneous application of negative pressure and antibiotic treatment according to the antibiogram. After basic treatment of the wound, auxiliary methods such as negative pressure contribute to the healing. Evolution was favorable with wound granulation in 95% cases, which allowed surgery under local anesthesia, and defect was covered with skin graft. VAC therapy falls into the last group of treatments by eliminating healing inhibitors. This regenerates the wound in a damp environment and essentially turns an open wound into a closed system.

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Interactions among DIV voltage-sensor movement, fast inactivation, and resurgent Na current induced by the NaVβ4 open-channel blocking peptide

The Journal of General Physiology ◽

10.1085/jgp.201310984 ◽

2013 ◽

Vol 142 (3) ◽

pp. 191-206 ◽

Cited By ~ 16

Author(s):

Amanda H. Lewis ◽

Indira M. Raman

Keyword(s):

Open Channel ◽

Voltage Sensor ◽

Channel Block ◽

Na Channels ◽

Fast Inactivation ◽

Na Current ◽

Open Channel Block ◽

Channel Blocking ◽

Open States ◽

Resurgent Currents

Resurgent Na current flows as voltage-gated Na channels recover through open states from block by an endogenous open-channel blocking protein, such as the NaVβ4 subunit. The open-channel blocker and fast-inactivation gate apparently compete directly, as slowing the onset of fast inactivation increases resurgent currents by favoring binding of the blocker. Here, we tested whether open-channel block is also sensitive to deployment of the DIV voltage sensor, which facilitates fast inactivation. We expressed NaV1.4 channels in HEK293t cells and assessed block by a free peptide replicating the cytoplasmic tail of NaVβ4 (the “β4 peptide”). Macroscopic fast inactivation was disrupted by mutations of DIS6 (L443C/A444W; “CW” channels), which reduce fast-inactivation gate binding, and/or by the site-3 toxin ATX-II, which interferes with DIV movement. In wild-type channels, the β4 peptide competed poorly with fast inactivation, but block was enhanced by ATX. With the CW mutation, large peptide-induced resurgent currents were present even without ATX, consistent with increased open-channel block upon depolarization and slower deactivation after blocker unbinding upon repolarization. The addition of ATX greatly increased transient current amplitudes and further enlarged resurgent currents, suggesting that pore access by the blocker is actually decreased by full deployment of the DIV voltage sensor. ATX accelerated recovery from block at hyperpolarized potentials, however, suggesting that the peptide unbinds more readily when DIV voltage-sensor deployment is disrupted. These results are consistent with two open states in Na channels, dependent on the DIV voltage-sensor position, which differ in affinity for the blocking protein.

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Sequences in the human c-myc P2 promoter affect the elongation and premature termination of transcripts initiated from the upstream P1 promoter.

Molecular and Cellular Biology ◽

10.1128/mcb.12.10.4590 ◽

1992 ◽

Vol 12 (10) ◽

pp. 4590-4600 ◽

Cited By ~ 19

Author(s):

T Meulia ◽

A Krumm ◽

C Spencer ◽

M Groudine

Keyword(s):

Mammalian Cells ◽

Xenopus Oocyte ◽

Xenopus Oocytes ◽

Premature Termination ◽

Deletion Mutants ◽

Potential Contribution ◽

Germinal Vesicles ◽

Exon 1 ◽

P2 Promoter ◽

Steady State Levels

A conditional block to transcription elongation provides one mechanism for controlling the steady-state levels of c-myc RNA in mammalian cells. Although prematurely terminated c-myc RNAs are not detectable in mammalian cells, truncated c-myc RNAs with 3' ends that map near the end of the first exon are transcribed from human c-myc templates injected into Xenopus oocytes germinal vesicles. A series of linker scanner and deletion mutants within the c-myc P2 promoter was tested in the Xenopus oocyte injection assay to determine the potential contribution of promoter elements to the elongation or premature termination of c-myc transcription. Although this analysis failed to identify sequences in the P2 promoter that significantly affect the elongation or termination of P2-initiated transcripts, our results suggest that sequences within the P2 promoter contribute to the premature termination of transcripts initiated at the upstream P1 promoter. A subset of these sequences is essential for the efficient elongation of P1-initiated transcripts through intrinsic sites of termination at the end of exon 1. These sequences affect P1 elongation when they are downstream of the site of initiation, and we hypothesize that they may be analogous to a class of prokaryotic elements required for antitermination.

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State-Dependent Mibefradil Block of Na+ Channels

Molecular Pharmacology ◽

10.1124/mol.66.6.1652 ◽

2004 ◽

Vol 66 (6) ◽

pp. 1652-1661 ◽

Cited By ~ 32

Author(s):

Megan M. McNulty ◽

Dorothy A. Hanck

Keyword(s):

Na Channels ◽

State Dependent ◽

Block Of Na Channels

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Characteristics of membrane currents evoked by photoreleased inositol trisphosphate in Xenopus oocytes

AJP Cell Physiology ◽

10.1152/ajpcell.1992.263.1.c154 ◽

1992 ◽

Vol 263 (1) ◽

pp. C154-C165 ◽

Cited By ~ 31

Author(s):

I. Parker ◽

I. Ivorra

Keyword(s):

Xenopus Oocytes ◽

Threshold Level ◽

Dose Dependence ◽

Evoked Responses ◽

Flash Duration ◽

Competitive Antagonist ◽

Study Characteristics ◽

Time Required ◽

Threshold Duration ◽

Interflash Interval

Photorelease of inositol 1,4,5-trisphosphate (InsP3) from a caged precursor was used to study characteristics of Ca(2+)-activated Cl- currents activated in Xenopus oocytes by the InsP3-Ca2+ signaling pathway. Photolysis flashes shorter than a threshold duration evoked no response, but the current amplitude then grew about linearly as the flash duration was further lengthened. Currents directly evoked by photorelease of Ca2+ from a caged precursor grew linearly with increasing flash duration and showed a small threshold before they were activated. However, the major part of the threshold of InsP3-evoked responses appears to arise because a certain concentration of InsP3 (estimated to be approximately 60 nM) is required to evoke Ca2+ liberation. Subthreshold conditioning flashes potentiated responses to subsequent flashes, and the potentiation increased linearly with increasing conditioning flash duration before abruptly declining. The potentiation decayed exponentially with a time constant of approximately 17 s with increasing interflash interval. Currents evoked by photoreleased InsP3 began after a latency that shortened from 10 s or longer to 100 ms as the photolysis intensity was increased. This dose dependence of the latency could be quantitatively explained by the time required for the InsP3 concentration to rise above threshold. Intracellular injection of heparin (a competitive antagonist at the InsP3 receptor) increased the threshold for InsP3 action, as did increased temperature. We conclude that several characteristics of InsP3-evoked responses, including their dose dependence, latency, and facilitation with paired stimuli, arise because a distinct threshold level of InsP3 is required to evoke release of Ca2+ from intracellular stores.

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