Member of the Ampakine class of memory enhancers prolongs the single channel open time of reconstituted AMPA receptors

Synapse ◽  
2001 ◽  
Vol 40 (2) ◽  
pp. 154-158 ◽  
Author(s):  
Vishnu Suppiramaniam ◽  
Ben A. Bahr ◽  
Srikumar Sinnarajah ◽  
Kittra Owens ◽  
Gary Rogers ◽  
...  
Keyword(s):  
Ampa Receptors ◽  
Single Channel ◽  
Open Time ◽  
Channel Open Time

Internal and external TEA block in single cloned K+ channels

1991 ◽  
Vol 261 (4) ◽  
pp. C583-C590 ◽  
Author(s):  
G. E. Kirsch ◽  
M. Taglialatela ◽  
A. M. Brown
Keyword(s):  
Single Channel ◽  
Channel Structure ◽  
K Channel ◽  
Cdna Clones ◽  
K Channels ◽  
Open Time ◽  
Voltage Dependent ◽  
Internal Site ◽  
Channel Open Time ◽  
Single Channel Currents

Tetraethylammonium (TEA) has been used recently to probe natural and mutational variants of voltage-dependent K+ channels encoded by cDNA clones. Its usefulness as a probe of channel structure prompted us to examine the molecular mechanism by which TEA blocks single-channel currents in Xenopus oocytes expressing the rat brain K+ channel, RCK2. TEA at the intracellular surface of membrane patches decreased channel open time and increased the duration of closed intervals. Tetrapentylammonium had similar but more potent effects. Extracellular application of TEA caused an apparent reduction of single-channel amplitude. Block was slower at the high-affinity internal site than at the low-affinity external site. Internal TEA selectively blocks open K+ channels, and the voltage dependence of the block indicates that the binding site lies within the membrane electric field at a point 25% of the distance from the cytoplasmic margin. External TEA also interacts with the open channel but is less sensitive to membrane potential. The results indicate that the internal and external TEA binding sites define the inner and outer margins of the aqueous pore.

Effects of extracellular sodium concentration on null potential, conductance and open time of endplate channels

1982 ◽  
Vol 216 (1203) ◽  
pp. 225-251 ◽  
Keyword(s):  
Binding Sites ◽  
Single Channel ◽  
Sodium Concentration ◽  
Potassium Ions ◽  
Channel Conductance ◽  
Channel Characteristics ◽  
Open Time ◽  
Na Ions ◽  
Channel Open Time ◽  
Extracellular Sodium

(i) Effects of extracellular sodium concentration, [Na] o , on endplate channel characteristics were investigated in voltage-clamped, glycerol- treated toad sartorius fibres. (ii) The relation between [Na] o (and [K] o ) and acetylcholine null potential could be reasonably well fitted by the Goldman-Hodgkin-Katz type of equation, except when [Na] o was higher than normal. Anions had no significant effect on the null potential. (iii) Endplate channel open time (ז), whether measured from miniature endplate currents or from current fluctuations induced by iontophoresis of acetylcholine, varied inversely with [Na] o . The relation between ז -1 (=α) and [Na] o could be fitted by α = αmax [Na] o / ( K m +|[Na] o ) with a K m of 92 mM. (iv) Endplate conductance, measured at the peak of endplate currents or at the peak of spontaneous miniature endplate currents, increased nonlinearly with [Na] o . (v) Single channel conductance, γ, also increased nonlinearly with [Na] o . Experimental observations at -90 mV could be fitted by the relation γ = γ max [Na] o / ( K m + [Na] o ), giving values for γ max and K m of 47 pS and 146 mM respectively. Correcting channel conductance for the contribution from potassium ions gave values of γmax and K m of 78 pS and 423 mM respectively. (vi) The results are consistent with the hypothesis that binding sites for Na ions can modulate both channel lifetime and conductance and that these sites become saturated at higher sodium concentrations.

scholarly journals Comparison of excitatory currents activated by different transmitters on crustacean muscle. I. Acetylcholine-activated channels.

1983 ◽  
Vol 81 (4) ◽  
pp. 547-569 ◽  
Author(s):  
C Lingle ◽  
A Auerbach
Keyword(s):  
Membrane Potential ◽  
Time Course ◽  
Voltage Dependence ◽  
Single Channel ◽  
Noise Analysis ◽  
Synaptic Currents ◽  
Cancer Borealis ◽  
Open Time ◽  
Conductance Increase ◽  
Channel Open Time

The properties of acetylcholine-activated excitatory currents on the gm1 muscle of three marine decapod crustaceans, the spiny lobsters Panulirus argus and interruptus, and the crab Cancer borealis, were examined using either noise analysis, analysis of synaptic current decays, or analysis of the voltage dependence of ionophoretically activated cholinergic conductance increases. The apparent mean channel open time (tau n) obtained from noise analysis at -80 mV and 12 degrees C was approximately 13 ms; tau n was prolonged e-fold for about every 100-mV hyperpolarization in membrane potential; tau n was prolonged e-fold for every 10 degrees C decrease in temperature. Gamma, the single-channel conductance, at 12 degrees C was approximately 18 pS and was not affected by voltage; gamma was increased approximately 2.5-fold for every 10 degrees C increase in temperature. Synaptic currents decayed with a single exponential time course, and at -80 mV and 12 degrees C, the time constant of decay of synaptic currents, tau ejc, was approximately 14-15 ms and was prolonged e-fold about every 140-mV hyperpolarization; tau ejc was prolonged about e-fold for every 10 degrees C decrease in temperature. The voltage dependence of the amplitude of steady-state cholinergic currents suggests that the total conductance increase produced by cholinergic agonists is increased with hyperpolarization. Compared with glutamate channels found on similar decapod muscles (see the following article), the acetylcholine channels stay open longer, conduct ions more slowly, and are more sensitive to changes in the membrane potential.

Serine protease activation of near-silent epithelial Na+ channels

2004 ◽  
Vol 286 (1) ◽  
pp. C190-C194 ◽  
Author(s):  
Ray A. Caldwell ◽  
Richard C. Boucher ◽  
M. Jackson Stutts
Keyword(s):  
Plasma Membrane ◽  
Serine Protease ◽  
Serine Proteases ◽  
Single Channel ◽  
Open Probability ◽  
Open Time ◽  
Protease Activation ◽  
Salt And Water Balance ◽  
Channel Open Time ◽  
Nih 3T3

The regulation of epithelial Na+ channel (ENaC) function is critical for normal salt and water balance. This regulation is achieved through cell surface insertion/retrieval of channels, by changes in channel open probability ( Po), or through a combination of these processes. Epithelium-derived serine proteases, including channel activating protease (CAP) and prostasin, regulate epithelial Na+ transport, but the molecular mechanism is unknown. We tested the hypothesis that extracellular serine proteases activate a near-silent ENaC population resident in the plasma membrane. Single-channel events were recorded in outside-out patches from fibroblasts (NIH/3T3) stably expressing rat α-, β-, and γ-subunits (rENaC), before and during exposure to trypsin, a serine protease homologous to CAP and prostasin. Under baseline conditions, near-silent patches were defined as having rENaC activity ( NPo) < 0.03, where N is the number of channels. Within 1–5 min of 3 μg/ml bath trypsin superfusion, NPo increased ∼66-fold ( n = 7). In patches observed to contain a single functional channel, trypsin increased Po from 0.02 ± 0.01 to 0.57 ± 0.03 ( n = 3, mean ± SE), resulting from the combination of an increased channel open time and decreased channel closed time. Catalytic activity was required for activation of near-silent ENaC. Channel conductance and the Na+/Li+ current ratio with trypsin were similar to control values. Modulation of ENaC Po by endogenous epithelial serine proteases is a potentially important regulator of epithelial Na+ transport, distinct from the regulation achieved by hormone-induced plasma membrane insertion of channels.

scholarly journals Pathophysiology of and therapeutic options for a GABRA1 variant linked to epileptic encephalopathy

2019 ◽  
Vol 12 (1) ◽  
Author(s):  
Yun-Fei Bai ◽  
Michelle Chiu ◽  
Elizabeth S. Chan ◽  
Peter Axerio-Cilies ◽  
Jie Lu ◽  
...  
Keyword(s):  
Single Channel ◽  
Epileptic Encephalopathy ◽  
Functional Restoration ◽  
Receptor Expression ◽  
Therapeutic Options ◽  
Whole Cell ◽  
Expression Levels ◽  
Open Time ◽  
Channel Open Time ◽  
Mutant Receptors

Abstract We report the identification of a de novo GABRA1 (R214C) variant in a child with epileptic encephalopathy (EE), describe its functional characterization and pathophysiology, and evaluate its potential therapeutic options. The GABRA1 (R214C) variant was identified using whole exome sequencing, and the pathogenic effect of this mutation was investigated by comparing wild-type (WT) α1 and R214C α1 GABAA receptor-expressing HEK cells. GABA-evoked currents in these cells were recorded using whole-cell, outside-out macro-patch and cell-attached single-channel patch-clamp recordings. Changes to surface and total protein expression levels of WT α1 and R214C α1 were quantified using surface biotinylation assay and western blotting, respectively. Finally, potential therapeutic options were explored by determining the effects of modulators, including diazepam, insulin, and verapamil, on channel gating and receptor trafficking of WT and R214C GABAA receptors. We found that the GABRA1 (R214C) variant decreased whole-cell GABA-evoked currents by reducing single channel open time and both surface and total GABAA receptor expression levels. The GABA-evoked currents in R214C GABAA receptors could only be partially restored with benzodiazepine (diazepam) and insulin. However, verapamil treatment for 24 h fully restored the function of R214C mutant receptors, primarily by increasing channel open time. We conclude that the GABRA1 (R214C) variant reduces channel activity and surface expression of mutant receptors, thereby contributing to the pathogenesis of genetic EE. The functional restoration by verapamil suggests that it is a potentially new therapeutic option for patients with the R214C variant and highlights the value of precision medicine in the treatment of genetic EEs.

Blockade of lysophosphatidylcholine-modified cardiac Na channels by a lidocaine derivative QX-222

1996 ◽  
Vol 271 (2) ◽  
pp. H790-H797
Author(s):  
A. I. Undrovinas ◽  
J. C. Makielski
Keyword(s):  
Single Channel ◽  
Cardiac Cells ◽  
Na Channels ◽  
Patch Clamp Technique ◽  
Ventricular Cells ◽  
Open Time ◽  
Channel Open Time ◽  
Open States ◽  
Inside Out ◽  
Cytoplasmic Side

Single Na channels from rat and rabbit ventricular cells were studied with use of the excised inside-out patch-clamp technique. To investigate local anesthetic interactions with Na channels modified by the ischemic metabolite lysophosphatidylcholine (LPC), the quaternary ammonium lidocaine derivative QX-222 [2-(trimethylamino)-N-(2,6-dimethylphenyl)acetamide] was applied to the cytoplasmic side of patches from untreated cells and from those treated with LPC for approximately 1 h. Single-channel amplitudes and kinetics for unmodified channels were similar to those reported previously for cardiac cells with a single-component, mean-channel open time. LPC-modified channels showed prolonged open channel bursting with a two-component, mean open time, suggesting two open states. Conductance sublevels to the 60-70% level of the main conductance were found in both unmodified and LPC-modified channels and also with and without QX-222 present. QX-222 reversibly shortened the open time of the unmodified channel and for both open times of the LPC-modified channel without decreasing single-channel amplitude. Calculated association rates for QX-222 with the channel were found to be greater for the open states of the modified channel than those for the unmodified channel. Thus the lidocaine analogue QX-222 interacts with and blocks the open state of both unmodified and LPC-modified, cardiac Na channels. The blocking effect on LPC-modified channels would be predicted to be greater both because of the longer dwell time in the high-affinity open states for modified channels and also because of an intrinsically greater association rate in the modified channels.

Single channel recordings of Nt- and L-type Ca2+ currents in rat neurohypophysial terminals

1993 ◽  
Vol 70 (4) ◽  
pp. 1617-1628 ◽  
Author(s):  
X. Wang ◽  
S. N. Treistman ◽  
J. R. Lemos
Keyword(s):  
Time Constant ◽  
Voltage Pulse ◽  
Single Channel ◽  
Single Channels ◽  
Open Probability ◽  
Time Constants ◽  
Channel Current ◽  
Open Time ◽  
The Mean ◽  
Channel Open Time

1. Ca2+ currents through single channels in acutely dissociated nerve terminals from rat neurohypophyses were recorded using cell-attached patch recordings with 110 mM Ba2+ as the charge carrier. 2. One type (Nt, where the t denotes terminal) of single Ca2+ channel current was evoked only by depolarizing steps from holding potentials less negative than -50 mV. Because this channel opened primarily at the beginning of a 180-ms-long voltage pulse, the averaged ensemble current decayed rapidly (approximately 30 ms). Infrequently, the channel opened throughout such a long pulse, resulting in a long-lasting averaged ensemble current. The averaged channel open time constant (tau) was 0.34 ms and the two averaged closed time constants were 1.78 (tau 1) and 86.57 (tau 2) ms. The mean unitary slope conductance for this channel was 11 pS and its threshold for activation was approximately -10 mV. 3. The other type (L) of single Ca2+ channel current could be evoked in isolation by depolarizations from holding potentials more positive than or equal to -50 mV. This channel opened throughout an entire 180-ms-long voltage pulse. The averaged ensemble current, therefore, showed little inactivation. The averaged channel open-time constant was 0.49 ms and the two average closed time constants were 2.02 (tau 1) and 79.91 (tau 2) ms. The mean unitary slope conductance for this channel was 25 pS. 4. Bay K 8644 (5 microM), a dihydropyridine (DHP) Ca2+ channel agonist, increased the open probability of the larger-conductance L-type Ca2+ channel by prolonging the average duration (to 2.79 ms) of channel openings, but did not alter the single channel slope conductance. In contrast, the same concentration of Bay K 8644 did not affect the smaller-conductance Nt-type Ca2+ channel. The DHP Ca2+ channel antagonist nicardipine (5 microM), but not nifedipine (5 microM), reduced the open probability of the large-conductance L-type Ca2+ channel by shortening the duration (to 0.36 ms) of channel openings. 5. The voltage- and time-dependent properties of these two types of single Ca2+ channel currents are in close agreement with those of the two components of macroscopic Ca2+ currents previously reported using the "whole-terminal" recording method. Therefore these two types of single channels appear to underlie the macroscopic current. 6. Our studies suggest that the terminal Nt-type Ca2+ channel differs from the conventional somatic N- and T-type Ca2+ channels in some respects, and that the terminal L-type Ca2+ channel is similar to the conventional somatic L-type Ca2+ channel.(ABSTRACT TRUNCATED AT 400 WORDS)

Two Types of ACh Receptors Contribute to Fast Channel Gating on Mouse Skeletal Muscle

1997 ◽  
Vol 78 (6) ◽  
pp. 2966-2974 ◽  
Author(s):  
Dawn Shepherd ◽  
Paul Brehm
Keyword(s):  
Skeletal Muscle ◽  
Single Channel ◽  
Channel Gating ◽  
Receptor Type ◽  
Open Probability ◽  
Mouse Skeletal Muscle ◽  
Single Channel Recordings ◽  
Open Time ◽  
Channel Open Time ◽  
Ach Receptors

Shepherd, Dawn and Paul Brehm. Two types of ACh receptors contribute to fast channel gating on mouse skeletal muscle. J. Neurophysiol. 78: 2966–2974, 1997. Single-channel recordings from mouse C2 myotubes indicate that maturation of skeletal muscle is accompanied by the appearance of two types of fast acetylcholine (ACh) receptor channels that are each functionally distinct from the embryonic receptor type present at early stages of differentiation. The embryonic receptor type has a low conductance (45 pS) and long channel open time, rendering slowly decaying synaptic currents. One fast channel type that appears during muscle maturation is distinguished from the embryonic receptor type on the basis of both higher conductance (65 pS) and shorter open time. However, single-channel recordings from differentiated mouse skeletal muscle cell line (C2) point to the existence of a second fast receptor type, which has a conductance similar to the embryonic receptor type (45 pS), yet significantly reduced mean channel open time. Analyses of individual channel function at high ACh concentrations directly demonstrate the coexistence of two kinetically distinct types of 45 pS ACh receptors. Openings by fast type and slow embryonic type of 45 pS receptors occurred in bursts, allowing distinction on the basis of both mean open time and open probability for individual receptors. The embryonic type of 45 pS receptor has an open time approximately twofold longer than the fast-receptor counterpart. Additional differences were reflected in the open probability distributions for fast and slow 45 pS receptor types. Both types of 45 pS receptor were kinetically distinguishable from the 65 pS receptor. We found no support for the idea that the slow and fast 45 pS receptor types result from the interconversion of dual gating modes involving the same receptor protein. Our results are consistent with the idea that the acquisition of fast synaptic current decay, required at mature neuromuscular synapses, is the result of the up-regulation of two distinct fast types of nicotinic ACh receptors during skeletal muscle development.

scholarly journals Mechanisms of GABAB receptor enhancement of extrasynaptic GABAA receptor currents in cerebellar granule cells

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Shailesh N. Khatri ◽  
Wan-Chen Wu ◽  
Ying Yang ◽  
Jason R. Pugh
Keyword(s):  
Granule Cells ◽  
Single Channel ◽  
Cerebellar Granule Cells ◽  
Gabab Receptor ◽  
Open Probability ◽  
Cerebellar Granule ◽  
Channel Current ◽  
Open Time ◽  
Patch Clamp Electrophysiology ◽  
Channel Open Time

Abstract Many neurons, including cerebellar granule cells, exhibit a tonic GABA current mediated by extrasynaptic GABAA receptors. This current is a critical regulator of firing and the target of many clinically relevant compounds. Using a combination of patch clamp electrophysiology and photolytic uncaging of RuBi-GABA we show that GABAB receptors are tonically active and enhance extrasynaptic GABAA receptor currents in cerebellar granule cells. This enhancement is not associated with meaningful changes in GABAA receptor potency, mean channel open-time, open probability, or single-channel current. However, there was a significant (~40%) decrease in the number of channels participating in the GABA uncaging current and an increase in receptor desensitization. Furthermore, we find that adenylate cyclase, PKA, CaMKII, and release of Ca2+ from intracellular stores are necessary for modulation of GABAA receptors. Overall, this work reveals crosstalk between postsynaptic GABAA and GABAB receptors and identifies the signaling pathways and mechanisms involved.

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