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.

Single-channel basis for conductance increase induced by isoflurane in Shaker H4 IR K+ channels

2001 ◽  
Vol 280 (5) ◽  
pp. C1130-C1139 ◽  
Author(s):  
Jichang Li ◽  
Ana M. Correa
Keyword(s):  
Time Course ◽  
Xenopus Oocytes ◽  
Single Channel ◽  
Noise Analysis ◽  
Single Channels ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Open Probability ◽  
Slowing Down ◽  
Conductance Increase

Volatile anesthetics modulate the function of various K+ channels. We previously reported that isoflurane induces an increase in macroscopic currents and a slowing down of current deactivation of Shaker H4 IR K+ channels. To understand the single-channel basis of these effects, we performed nonstationary noise analysis of macroscopic currents and analysis of single channels in patches from Xenopus oocytes expressing Shaker H4 IR. Isoflurane (1.2% and 2.5%) induced concentration-dependent, partially reversible increases in macroscopic currents and in the time course of tail currents. Noise analysis of currents (70 mV) revealed an increase in unitary current (∼17%) and maximum open probability (∼20%). Single-channel conductance was larger (∼20%), and opening events were more stable, in isoflurane. Tail-current slow time constants increased by 41% and 136% in 1.2% and 2.5% isoflurane, respectively. Our results show that, in a manner consistent with stabilization of the open state, isoflurane increased the macroscopic conductance of Shaker H4 IR K+ channels by increasing the single-channel conductance and the open probability.

scholarly journals Comparison of excitatory currents activated by different transmitters on crustacean muscle. II. Glutamate-activated currents and comparison with acetylcholine currents present on the same muscle.

1983 ◽  
Vol 81 (4) ◽  
pp. 571-588 ◽  
Author(s):  
C Lingle ◽  
A Auerbach
Keyword(s):  
Steady State ◽  
Time Constant ◽  
Voltage Dependence ◽  
Noise Analysis ◽  
Power Spectra ◽  
Synaptic Current ◽  
Cancer Borealis ◽  
Current Decay ◽  
Marine Crustacean ◽  
Conductance Increase

The properties of glutamate-activated excitatory currents on the gm6 muscle from the foregut of the spiny lobsters Panulirus argus and interruptus and the crab Cancer borealis were examined using either noise analysis, analysis of synaptic current decays, or slow iontophoretic currents. The properties of acetylcholine currents activated in nonjunctional regions of the gm6 muscle were also examined. At 12 degrees C and -80 mV, the predominant time constant of power spectra from glutamate-activated current noise was approximately 7 ms and the elementary conductance was approximately 34 pS. At 12 degrees C and -80 mV, the predominant time constant of acetylcholine-activated channels was approximately 11 ms with a conductance of approximately 12 pS. Focally recorded glutamatergic extracellular synaptic currents on the gm6 muscle decayed with time constants of approximately 7-8 ms at 12 degrees C and -80 mV. The decay time constant was prolonged e-fold about every 225-mV hyperpolarization in membrane potential. The Q10 of the time constant of the synaptic current decay was approximately 2.6. The voltage dependence of the steady-state conductance increase activated by iontophoretic application of glutamate has the opposite direction of the steady-state conductance activated by cholinergic agonists when compared on the gm6 muscles. The glutamate-activated conductance increase is diminished with hyperpolarization. The properties of the marine crustacean glutamate channels are discussed in relation to glutamate channels in other organisms and to the acetylcholine channels found on the gm6 muscle and the gm1 muscle of the decapod foregut (Lingle and Auerbach, 1983).

scholarly journals Inactivation viewed through single sodium channels.

1984 ◽  
Vol 84 (4) ◽  
pp. 535-564 ◽  
Author(s):  
C A Vandenberg ◽  
R Horn
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Time Course ◽  
Voltage Dependence ◽  
Single Channel ◽  
Gh3 Cells ◽  
Activation Process ◽  
Whole Cell ◽  
Open Time ◽  
Voltage Dependent

Recordings of the sodium current in tissue-cultured GH3 cells show that the rate of inactivation in whole cell and averaged single channel records is voltage dependent: tau h varied e-fold/approximately 26 mV. The source of this voltage dependence was investigated by examining the voltage dependence of individual rate constants, estimated by maximum likelihood analysis of single channel records, in a five-state kinetic model. The rate constant for inactivating from the open state, rather than closing, increased with depolarization, as did the probability that an open channel inactivates. The rate constant for closing from the open state had the opposite voltage dependence. Both rate constants contributed to the mean open time, which was not very voltage dependent. Both open time and burst duration were less than tau h for voltages up to -20 mV. The slowest time constant of activation, tau m, was measured from whole cell records, by fitting a single exponential either to tail currents or to activating currents in trypsin-treated cells, in which the inactivation was abolished. tau m was a bell-shaped function of voltage and had a voltage dependence similar to tau h at voltages more positive than -35 mV, but was smaller than tau h. At potentials more negative than about -10 mV, individual channels may open and close several times before inactivating. Therefore, averaged single channel records, which correspond with macroscopic current elicited by a depolarization, are best described by a convolution of the first latency density with the autocorrelation function rather than with 1 - (channel open time distribution). The voltage dependence of inactivation from the open state, in addition to that of the activation process, is a significant factor in determining the voltage dependence of macroscopic inactivation. Although the rates of activation and inactivation overlapped greatly, independent and coupled inactivation could not be statistically distinguished for two models examined. Although rates of activation affect the observed rate of inactivation at intermediate voltages, extrapolation of our estimates of rate constants suggests that at very depolarized voltages the activation process is so fast that it is an insignificant factor in the time course of inactivation. Prediction of gating currents shows that an inherently voltage-dependent inactivation process need not produce a conspicuous component in the gating current.

scholarly journals Gating of Na channels in the rat cortical collecting tubule: effects of voltage and membrane stretch.

1996 ◽  
Vol 107 (1) ◽  
pp. 35-45 ◽  
Author(s):  
L G Palmer ◽  
G Frindt
Keyword(s):  
Voltage Dependence ◽  
Single Channel ◽  
Apical Membrane ◽  
Na Channels ◽  
Patch Clamp Technique ◽  
Open Time ◽  
Collecting Tubule ◽  
Excised Patches ◽  
The Mean ◽  
Cortical Collecting Tubule

The gating kinetics of apical membrane Na channels in the rat cortical collecting tubule were assessed in cell-attached and inside-out excised patches from split-open tubules using the patch-clamp technique. In patches containing a single channel the open probability (Po) was variable, ranging from 0.05 to 0.9. The average Po was 0.5. However, the individual values were not distributed normally, but were mainly < or = 0.25 or > or = 0.75. Mean open times and mean closed times were correlated directly and inversely, respectively, with Po. In patches where a sufficient number of events could be recorded, two time constants were required to describe the open-time and closed-time distributions. In most patches in which basal Po was < 0.3 the channels could be activated by hyperpolarization of the apical membrane. In five such patches containing a single channel hyperpolarization by 40 mV increased Po by 10-fold, from 0.055 +/- 0.023 to 0.58 +/- 0.07. This change reflected an increase in the mean open time of the channels from 52 +/- 17 to 494 +/- 175 ms and a decrease in the mean closed time from 1,940 +/- 350 to 336 +/- 100 ms. These responses, however, could not be described by a simple voltage dependence of the opening and closing rates. In many cases significant delays in both the activation by hyperpolarization and deactivation by depolarization were observed. These delays ranged from several seconds to several tens of seconds. Similar effects of voltage were seen in cell-attached and excised patches, arguing against a voltage-dependent chemical modification of the channel, such as a phosphorylation. Rather, the channels appeared to switch between gating modes. These switches could be spontaneous but were strongly influenced by changes in membrane voltage. Voltage dependence of channel gating was also observed under whole-cell clamp conditions. To see if mechanical perturbations could also influence channel kinetics or gating mode, negative pressures of 10-60 mm Hg were applied to the patch pipette. In most cases (15 out of 22), this maneuver had no significant effect on channel behavior. In 6 out of 22 patches, however, there was a rapid and reversible increase in Po when the pressure was applied. In one patch, there was a reversible decrease. While no consistent effects of pressure could be documented, membrane deformation could contribute to the variation in Po under some conditions.

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

Gating currents in the node of Ranvier: voltage and time dependence

1975 ◽  
Vol 270 (908) ◽  
pp. 483-492 ◽  
Keyword(s):  
Membrane Potential ◽  
Time Constant ◽  
Time Course ◽  
Voltage Dependence ◽  
Sudden Change ◽  
Node Of Ranvier ◽  
Ionic Currents ◽  
Gating Currents ◽  
Myelinated Nerve ◽  
Sodium Conductance

Like the axolemma of the giant nerve fibre of the squid, the nodal membrane of frog myelinated nerve fibres after blocking transmembrane ionic currents exhibits asymmetrical displacement currents during and after hyperpolarizing and depolarizing voltage clamp pulses of equal size. The steady-state distribution of charges as a function of membrane potential is consistent with Boltzmann’s law (midpoint potential —33.7 mV; saturation value 17200 charges/(μm 2 ). The time course of the asymmetry current and the voltage dependence of its time constant are consistent with the notion that due to a sudden change in membrane potential the charges undergo a first order transition between two configurations. Size and voltage dependence of the time constant are similar to those of the activation of the sodium conductance assuming m 2 h kinetics, The results suggest the presence of ten times more sodium channels (5000/μm2) in the node of Ranvier than in the squid giant axon with similar sodium conductance per channel (2-3 pS),

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 Shaker potassium channel gating. II: Transitions in the activation pathway.

1994 ◽  
Vol 103 (2) ◽  
pp. 279-319 ◽  
Author(s):  
W N Zagotta ◽  
T Hoshi ◽  
J Dittman ◽  
R W Aldrich
Keyword(s):  
Conformational Changes ◽  
Time Course ◽  
Voltage Dependence ◽  
Single Channel ◽  
Ionic Current ◽  
Activation Process ◽  
Charge Movement ◽  
Open Probability ◽  
Current Time ◽  
Gating Charge

Voltage-dependent gating behavior of Shaker potassium channels without N-type inactivation (ShB delta 6-46) expressed in Xenopus oocytes was studied. The voltage dependence of the steady-state open probability indicated that the activation process involves the movement of the equivalent of 12-16 electronic charges across the membrane. The sigmoidal kinetics of the activation process, which is maintained at depolarized voltages up to at least +100 mV indicate the presence of at least five sequential conformational changes before opening. The voltage dependence of the gating charge movement suggested that each elementary transition involves 3.5 electronic charges. The voltage dependence of the forward opening rate, as estimated by the single-channel first latency distribution, the final phase of the macroscopic ionic current activation, the ionic current reactivation and the ON gating current time course, showed movement of the equivalent of 0.3 to 0.5 electronic charges were associated with a large number of the activation transitions. The equivalent charge movement of 1.1 electronic charges was associated with the closing conformational change. The results were generally consistent with models involving a number of independent and identical transitions with a major exception that the first closing transition is slower than expected as indicated by tail current and OFF gating charge measurements.

Properties of single Na+ channels in cut-open Myxicola giant axons

1987 ◽  
Vol 65 (4) ◽  
pp. 568-573 ◽  
Author(s):  
C. L. Schauf
Keyword(s):  
Patch Clamp ◽  
Time Dependence ◽  
Voltage Dependence ◽  
Single Channel ◽  
Single Channels ◽  
Channel Conductance ◽  
Dependent Behavior ◽  
Open Time ◽  
Voltage Dependent ◽  
Steady State Inactivation

Time- and voltage-dependent behavior of the Na+ conductance in dialyzed intact Myxicola axons was compared with cut-open axons subjected to loose-patch clamp of the interior and to axons where Gigaseals were formed after brief enzyme digestion. Voltage and time dependence of activation, inactivation, and reactivation were identical in whole-axons and loose-patch preparations. Single channels observed in patch-clamp axons had a conductance of 18.3 ± 2.3 pS and a mean open time of 0.84 ± 0.12 ms. The time-dependence of Na+ currents found by averaging patch-clamp records was similar to intact axons, as was the voltage dependence of activation. Steady-state inactivation in patch-clamped axons was shifted by an average of 15 mV from that seen in loose-patch or intact axons. Substitution of D2O for H2O decreased single channel conductance by 24 ± 6% in patch-clamped axons compared with 28 ± 4% in intact axons, slowed inactivation by 58 ± 8% compared with 49 ± 6%, and increased mean open time by 52 ± 7%. The results confirm observations on macroscopic channel behavior in Myxicola and resemble that seen in other excitable tissues.

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