Single-channel current/voltage relationships of two kinds of Na+ channel in vertebrate sensory neurons

1993 ◽  
Vol 423 (5-6) ◽  
pp. 492-496 ◽  
Author(s):  
Donald T. Campbell
Keyword(s):  
Sensory Neurons ◽  
Single Channel ◽  
Na Channel ◽  
Channel Current ◽  
Single Channel Current ◽  
Current Voltage

scholarly journals Endogenous Protease Activation of ENaC

2005 ◽  
Vol 126 (4) ◽  
pp. 339-352 ◽  
Author(s):  
Adedotun Adebamiro ◽  
Yi Cheng ◽  
John P. Johnson ◽  
Robert J. Bridges
Keyword(s):  
Single Channel ◽  
Apical Membrane ◽  
Open Channels ◽  
Na Channel ◽  
Fluctuation Analysis ◽  
Protease Inhibition ◽  
Open Probability ◽  
Channel Current ◽  
Single Channel Current ◽  
Channel Properties

Endogenous serine proteases have been reported to control the reabsorption of Na+ by kidney- and lung-derived epithelial cells via stimulation of electrogenic Na+ transport mediated by the epithelial Na+ channel (ENaC). In this study we investigated the effects of aprotinin on ENaC single channel properties using transepithelial fluctuation analysis in the amphibian kidney epithelium, A6. Aprotinin caused a time- and concentration-dependent inhibition (84 ± 10.5%) in the amiloride-sensitive sodium transport (INa) with a time constant of 18 min and half maximal inhibition constant of 1 μM. Analysis of amiloride analogue blocker–induced fluctuations in INa showed linear rate–concentration plots with identical blocker on and off rates in control and aprotinin-inhibited conditions. Verification of open-block kinetics allowed for the use of a pulse protocol method (Helman, S.I., X. Liu, K. Baldwin, B.L. Blazer-Yost, and W.J. Els. 1998. Am. J. Physiol. 274:C947–C957) to study the same cells under different conditions as well as the reversibility of the aprotinin effect on single channel properties. Aprotinin caused reversible changes in all three single channel properties but only the change in the number of open channels was consistent with the inhibition of INa. A 50% decrease in INa was accompanied by 50% increases in the single channel current and open probability but an 80% decrease in the number of open channels. Washout of aprotinin led to a time-dependent restoration of INa as well as the single channel properties to the control, pre-aprotinin, values. We conclude that protease regulation of INa is mediated by changes in the number of open channels in the apical membrane. The increase in the single channel current caused by protease inhibition can be explained by a hyperpolarization of the apical membrane potential as active Na+ channels are retrieved. The paradoxical increase in channel open probability caused by protease inhibition will require further investigation but does suggest a potential compensatory regulatory mechanism to maintain INa at some minimal threshold value.

scholarly journals AMRP Peptides Modulate a Novel K+ Current in Pleural Sensory Neurons of Aplysia

2002 ◽  
Vol 88 (1) ◽  
pp. 323-332 ◽  
Author(s):  
Jonathan R. McDearmid ◽  
Vladimir Brezina ◽  
Klaudiusz R. Weiss
Keyword(s):  
Sensory Neurons ◽  
Single Channel ◽  
Outward Current ◽  
Negative Slope ◽  
Open Probability ◽  
Channel Current ◽  
Single Channel Current ◽  
Outward Rectification ◽  
Defensive Behaviors ◽  
Mechanosensory Neurons

Modulation of Aplysia mechanosensory neurons is thought to underlie plasticity of defensive behaviors that are mediated by these neurons. In the past, identification of modulators that act on the sensory neurons and characterization of their actions has been instrumental in providing insight into the functional role of the sensory neurons in the defensive behaviors. Motivated by this precedent and a recent report of the presence of Aplysia Mytilusinhibitory peptide-related (AMRP) neuropeptides in the neuropile and neurons of the pleural ganglia, we sought to determine whether and how pleural sensory neurons respond to the AMRPs. In cultured pleural sensory neurons under voltage clamp, AMRPs elicited a relatively rapidly developing, then partially desensitizing, outward current. The current exhibited outward rectification; in normal 10 mM K+, it was outward at membrane potentials more positive than −80 mV but disappeared without reversing at more negative potentials. When external K+ was elevated to 100 mM, the AMRP-elicited current reversed around −25 mV; the shift in reversal potential was as expected for a current carried primarily by K+. In the high-K+ solution, the reversed current began to decrease at potentials more negative than −60 mV, creating a region of negative slope resistance in the I-V relationship. The AMRP-elicited K+ current was blocked by extremely low concentrations of 4-aminopyridine (4-AP; IC50= 1.7 × 10−7 M) but was not very sensitive to TEA. In cell-attached patches, AMRPs applied outside the patch—thus presumably through a diffusible messenger—increased the activity of a K+ channel that very likely underlies the macroscopic current. The single-channel current exhibited outward rectification, and the open probability of the channel decreased with hyperpolarization; together, these two factors accounted for the outward rectification of the macroscopic current. Submicromolar 4-AP included in the patch pipette blocked the channel by reducing its open probability without altering the single-channel current. Based on the characteristics of the AMRP-modulated K+ current, we conclude that it is a novel current that has not been previously described in Aplysia mechanosensory neurons. In addition to this current, two other AMRP-elicited currents, a slow, 4-AP-resistant outward current and a Na+-dependent inward current, were occasionally observed in the cultured sensory neurons. Responses consistent with all three currents were observed in sensory neurons in situ in intact pleural ganglia.

Current-noise analysis of Na absorption in the embryonic coprodeum: stimulation by aldosterone and thyroxine

1993 ◽  
Vol 265 (5) ◽  
pp. R1100-R1108 ◽  
Author(s):  
W. Clauss ◽  
B. Hoffmann ◽  
R. Krattenmacher ◽  
W. Van Driessche
Keyword(s):  
Sodium Transport ◽  
Single Channel ◽  
Short Circuit ◽  
Noise Analysis ◽  
Current Noise ◽  
Na Channel ◽  
Channel Density ◽  
Channel Current ◽  
Single Channel Current

The mechanism and regulation of sodium transport in the embryonic coprodeum of chicken were investigated with isolated epithelia in vitro by electrophysiological techniques. Electrogenic sodium transport (INa) was measured in Ussing chambers by the short-circuit current (Isc) technique and identified by the diuretic amiloride or by removal of sodium from the apical medium. Apical sodium channels and the kinetics of amiloride binding were investigated by current-noise analysis. Isc and INa were measured under control conditions and under the influence of in vitro incubation with aldosterone and thyroxine. At 20 days the embryonic coprodeum has an Isc of 12.6 +/- 1.4 microA/cm2 and a transepithelial resistance of 519 +/- 40 omega.cm2. Amiloride blocks 9.0 +/- 1.3 microA/cm2 of the Isc, which represents electrogenic Na+ absorption and can be inhibited by serosal ouabain. Aldosterone does not stimulate Isc or INa, whereas thyroxine increases Isc and INa about threefold. Aldosterone in combination with thyroxine increases Isc and INa further to about five- to sixfold. In both cases the hormonal stimulation can be totally blocked by spironolactone. Current-noise analysis of the apical Na+ entry step reveals amiloride-sensitive Na+ channels with a single-channel current of approximately 2.3 pA and a channel density of 9-16 million/cm2 under stimulated conditions. Half-maximal amiloride block occurs at 0.8-1 microM. The hormones stimulate Na+ absorption by increasing the Na+ channel density and not the single-channel current.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Internal block of human heart sodium channels by symmetrical tetra-alkylammoniums.

1994 ◽  
Vol 104 (3) ◽  
pp. 507-522 ◽  
Author(s):  
M E O'Leary ◽  
R Horn
Keyword(s):  
Electric Field ◽  
Human Heart ◽  
Voltage Dependence ◽  
Single Channel ◽  
Na Channel ◽  
Channel Current ◽  
Single Channel Current ◽  
Wide Range ◽  
Alkyl Side Chains ◽  
Internal Block

The human heart Na channel (hH1) was expressed by transient transfection in tsA201 cells, and we examined the block of Na current by a series of symmetrical tetra-alkylammonium cations: tetramethylammonium (TMA), tetraethylammonium (TEA), tetrapropylammonium (TPrA), tetrabutylammonium (TBA), and tetrapentylammonium (TPeA). Internal TEA and TBA reduce single-channel current amplitudes while having little effect on single channel open times. The reduction in current amplitude is greater at more depolarized membrane potentials. Analysis of the voltage-dependence of single-channel current block indicates that TEA, TPrA and TBA traverse a fraction of 0.39, 0.52, and 0.46 of the membrane electric field to reach their binding sites. Rank potency determined from single-channel experiments indicates that block increases with the lengths of the alkyl side chains (TBA > TPrA > TEA > TMA). Internal TMA, TEA, TPrA, and TBA also reduce whole-cell Na currents in a voltage-dependent fashion with increasing block at more depolarized voltages, consistent with each compound binding to a site at a fractional distance of 0.43 within the membrane electric field. The correspondence between the voltage dependence of the block of single-channel and macroscopic currents indicates that the blockers do not distinguish open from closed channels. In support of this idea TPrA has no effect on deactivation kinetics, and therefore does not interfere with the closing of the activation gates. At concentrations that substantially reduce Na channel currents, TMA, TEA, and TPrA do not alter the rate of macroscopic current inactivation over a wide range of voltages (-50 to +80 mV). Our data suggest that TMA, TEA, and TPrA bind to a common site deep within the pore and block ion transport by a fast-block mechanism without affecting either activation or inactivation. By contrast, internal TBA and TPeA increase the apparent rate of inactivation of macroscopic currents, suggestive of a block with slower kinetics.

scholarly journals Ca2+ block and flickering both contribute to the negative slope of the IV curve in BK channels

2013 ◽  
Vol 141 (4) ◽  
pp. 499-505 ◽  
Author(s):  
Indra Schroeder ◽  
Gerhard Thiel ◽  
Ulf-Peter Hansen
Keyword(s):  
Open Channel ◽  
Single Channel ◽  
Bk Channels ◽  
Negative Slope ◽  
Channel Noise ◽  
Channel Current ◽  
Single Channel Current ◽  
Current Voltage ◽  
Per Se ◽  
Iv Curves

Single-channel current–voltage (IV) curves of human large-conductance, voltage- and Ca2+-activated K+ (BK) channels are quite linear in 150 mM KCl. In the presence of Ca2+ and/or Mg2+, they show a negative slope conductance at high positive potentials. This is generally explained by a Ca2+/Mg2+ block as by Geng et al. (2013. J. Gen. Physiol. http://dx.doi.org/10.1085/jgp.201210955) in this issue. Here, we basically support this finding but add a refinement: the analysis of the open-channel noise by means of β distributions reveals what would be found if measurements were done with an amplifier of sufficient temporal resolution (10 MHz), namely that the block by 2.5 mM Ca2+ and 2.5 mM Mg2+ per se would only cause a saturating curve up to +160 mV. Further bending down requires the involvement of a second process related to flickering in the microsecond range. This flickering is hardly affected by the presence or absence of Ca2+/Mg2+. In contrast to the experiments reported here, previous experiments in BK channels (Schroeder and Hansen. 2007. J. Gen. Physiol. http://dx.doi.org/10.1085/jgp.200709802) showed saturating IV curves already in the absence of Ca2+/Mg2+. The reason for this discrepancy could not be identified so far. However, the flickering component was very similar in the old and new experiments, regardless of the occurrence of noncanonical IV curves.

Effect of Prozac on whole cell ionic currents in lens and corneal epithelia

1995 ◽  
Vol 269 (1) ◽  
pp. C250-C256 ◽  
Author(s):  
J. L. Rae ◽  
A. Rich ◽  
A. C. Zamudio ◽  
O. A. Candia
Keyword(s):  
Potassium Channels ◽  
Single Channel ◽  
Ionic Currents ◽  
Current Amplitude ◽  
Human Lens ◽  
Delayed Rectifier ◽  
Open Probability ◽  
Channel Current ◽  
Single Channel Current ◽  
Ionic Conductances

Prozac (fluoxetine), a compound used therapeutically in humans to combat depression, has substantial effects on ionic conductances in rabbit corneal epithelial cells and in cultured human lens epithelium. In corneal epithelium, it reduces the current due to the large-conductance potassium channels that dominate this preparation. Its effects seem largely to decrease the open probability while leaving the single-channel current amplitude unaltered. In cultured human epithelium, currents from calcium-activated potassium channels and inward rectifiers are unaffected by Prozac. Delayed-rectifier potassium currents are reduced by Prozac in a complicated way that involves both gating and single-channel current amplitude. Fast tetrodotoxin-blockable sodium currents are also decreased by Prozac in this preparation. For all of these ion conductance effects, Prozac concentrations of 10(-5) to 10(-4) M are required. Whereas these levels are 10- to 100-fold higher than the plasma levels achieved in therapeutic use in humans, they are comparable to or less than levels needed for many other blockers of the ionic conductances studied here.

Properties and distribution of single voltage-gated calcium channels in adult hippocampal neurons

1990 ◽  
Vol 64 (1) ◽  
pp. 91-104 ◽  
Author(s):  
R. E. Fisher ◽  
R. Gray ◽  
D. Johnston
Keyword(s):  
Guinea Pig ◽  
Calcium Channels ◽  
Single Channel ◽  
Cell Types ◽  
Voltage Gated ◽  
Channel Current ◽  
Single Channel Current ◽  
Voltage Gated Calcium Channels ◽  
Large Conductance Channel ◽  
Small Conductance

1. The properties of single voltage-gated calcium channels were investigated in acutely exposed CA3 and CA1 pyramidal neurons and granule cells of area dentata in the adult guinea pig hippocampal formation. 2. Guinea pig hippocampal slices were prepared in a conventional manner, then treated with proteolytic enzymes and gently shaken to expose the somata of the three cell types studied. Standard patch-clamp techniques were used to record current flow through calcium channels in cell-attached membrane patches with isotonic barium as the charge carrier. 3. Single-channel current amplitudes were measured at different membrane potentials. Single-channel current-voltage plots were constructed and single-channel slope conductances were found to fall into three classes. These were (approximately) 8, 14, and 25 pS, and were observed in all three cell types. 4. The three groups of channels differed from each other in voltage dependence of activation: from a holding potential of -80, the small-conductance channel began to activate at about -40 to -30 mV, the medium-conductance channel at about -20 mV, and the large-conductance channel at approximately 0 mV. 5. Ensemble averages of single-channel currents during voltage steps revealed differences in voltage-dependent inactivation. The small-conductance channel inactivated completely within approximately 50 ms during steps from -80 to -10 mV or more positive. Steps to less positive potentials resulted in less inactivation. The medium-conductance channel displayed variable inactivation during steps from -80 to 0 mV. Inactivation of this channel during a 160-ms step ranged from virtually zero to approximately 100%. The large-conductance channel displayed no significant inactivation during steps as long as 400 ms. 6. The large-conductance channel was strikingly affected by the dihydropyridine agonist Bay K8644 (0.5-2.0 microM), resulting in a high probability of channel opening, prolonged openings, and an apparent increase in the number of channels available for activation. The medium and small-conductance channels were not noticeably affected by the drug. 7. The large-conductance channel could be induced to open at very negative membrane potentials by holding the patch for several seconds at 20 or 30 mV and stepping to -30 or -40 mV. This process was enhanced by Bay K8644, resulting in prolonged openings at potentials as negative as -100 mV.(ABSTRACT TRUNCATED AT 400 WORDS)

Time-dependent expression of ryanodine receptors in sea urchin eggs, zygotes and early embryos

Zygote ◽  
2021 ◽  
pp. 1-4
Author(s):  
G. Percivale ◽  
C. Angelini ◽  
C. Falugi ◽  
C. Picco ◽  
G. Prestipino
Keyword(s):  
Single Channel ◽  
Ryanodine Receptors ◽  
Paracentrotus Lividus ◽  
Current Fluctuations ◽  
Calcium Dependent ◽  
Channel Current ◽  
Single Channel Current ◽  
Electrophysiological Recordings ◽  
Early Embryos ◽  
Zygote Stage

Summary In this work, the presence of calcium-dependent calcium channels and their receptors (RyR) has been investigated in Paracentrotus lividus eggs and early embryos, from unfertilized egg to four-blastomere stages. Electrophysiological recordings of RyR single-channel current fluctuations showed that RyRs are functional during the first developmental events with a maximum at zygote stage, c. 40 min after fertilization, corresponding to the first cleavage. The nature of vertebrate-like RyRs active at this stage was established by specific activation/blockade experiments.

A rapidly activating delayed rectifier K+ channel in rabbit sinoatrial node cells

1995 ◽  
Vol 269 (2) ◽  
pp. H443-H452 ◽  
Author(s):  
H. Ito ◽  
K. Ono
Keyword(s):  
Steady State ◽  
Sinoatrial Node ◽  
Single Channel ◽  
Ensemble Average ◽  
Negative Slope ◽  
Delayed Rectifier ◽  
Channel Current ◽  
Single Channel Current ◽  
Sinoatrial Node Cells ◽  
Rabbit Sinoatrial Node

The single-channel current of the delayed rectifier K+ current (IK) was recorded in rabbit sinoatrial node cells. In the cell-attached patch, depolarization from -70 mV to potentials more positive than -50 mV activated the IK channel while repolarization deactivated it. The single-channel conductance was 7.8 pS for the outward current and 10.8 pS for the inward current (n = 6). The steady-state open probability (NPo) was maximum at around -30 mV and markedly decreased at more positive potentials. On repolarization from positive potentials, the channel was initially closed and then rapidly opened. The ensemble average showed an initial rise to a peak followed by the deactivation time course. Because the channel events were completely blocked by E-4031, the drug-sensitive component was examined in the whole cell current. The steady-state current-voltage relation of the drug-sensitive current showed a marked negative slope at potentials more positive than -10 mV. Upon repolarization, the drug-sensitive current initially increased (removal of inactivation) to the peak of the outward tail current, which was in agreement with the ensemble average of the single-channel current. We conclude that IK in the sinoatrial node cells is largely composed of the rapidly activating IK (IK,r) channels and that the inward rectification of IK,r, which is more marked than had been assumed in previous studies, is due to the decrease in NPo.

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