Slow inactivation of a TEA-sensitive K current in acutely isolated rat thalamic relay neurons

1991 ◽  
Vol 66 (4) ◽  
pp. 1316-1328 ◽  
Author(s):  
J. R. Huguenard ◽  
D. A. Prince
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Outward Current ◽  
Resting Potential ◽  
Transient Outward Current ◽  
Voltage Range ◽  
Voltage Dependent ◽  
Kinetics Of ◽  
K Currents ◽  
Relay Neurons

1. Voltage-gated K currents were studied in relay neurons (RNs) acutely isolated from somatosensory (VB) thalamus of 7- to 14-day-old rats. In addition to a rapidly activated, transient outward current, IA, depolarizations activated slower K+ currents, which were isolated through the use of appropriate ionic and pharmacological conditions and measured via whole-cell voltage-clamp. 2. At least two slow components of outward current were observed, both of which were sensitive to changes in [K+]o, as expected for K conductances. The first, IK1, had an amplitude that was insensitive to holding potential and a relatively small conductance of 150 pS/pF. It was blocked by submillimolar levels of tetraethylammonium [TEA, 50%-inhibitory concentration (IC50 = 30 microM)] and 4-aminopyridine (4-AP, 40 microM). In the absence of intracellular Ca2+ buffering, the amplitude of IK1 was both larger and dependent on holding potential, as expected for a Ca(2+)-dependent current. Replacement of [Ca2+]o by Co2+ reduced IK1, although the addition of Cd2+ to Ca(2+)-containing solutions had no effect. 3. The second component, IK2, had a normalized conductance of 2.0 nS/pF and was blocked by millimolar concentrations of TEA (IC50 = 4 mM) but not by 4AP. The kinetics of IK2 were analogous to (but much slower than) those of IA in that both currents displayed voltage-dependent activation and voltage-independent inactivation. IK2 was not reduced by the addition of Cd2+ to Ca(2+)-containing solutions or by replacement of Ca2+ by Co2+. 4. IK2 had a more depolarized activation threshold than IA and attained peak amplitude with a latency of approximately 100 ms at room temperature. IK2 decay was nonexponential and could be described as the sum of two components with time constants (tau) near 1 and 10 s. 5. IK2 was one-half steady-state inactivated at a membrane potential of -63 mV, near the normal resting potential for these cells. The slope factor of the Boltzman function describing steady-state inactivation was 13 mV-1, which indicates that IK2 varies in availability across a broad voltage range between -100 and -20 mV. 6. Activation kinetics of IK2 were voltage dependent, with peak latency shifting from 300 to 50 ms in the voltage range -50 to +30 mV. Deinactivation and deactivation were also voltage dependent, in contrast to inactivation, which showed little dependence on membrane potential. Increase in temperature sped the kinetics of IK2, with temperature coefficient (Q10) values near 3 for activation and inactivation. Heating increased the amplitude of IK2 with a Q10 value near 2.(ABSTRACT TRUNCATED AT 400 WORDS)

Activators of protein kinase C decrease Ca2+ spark frequency in smooth muscle cells from cerebral arteries

1997 ◽  
Vol 273 (6) ◽  
pp. C2090-C2095 ◽  
Author(s):  
Adrian D. Bonev ◽  
Jonathan H. Jaggar ◽  
Michael Rubart ◽  
Mark T. Nelson
Keyword(s):  
Protein Kinase C ◽  
Membrane Potential ◽  
Protein Kinase ◽  
Cerebral Arteries ◽  
Outward Current ◽  
Transient Outward Current ◽  
Open Probability ◽  
Kinase C ◽  
Voltage Dependent ◽  
Channel Currents

Local Ca2+ transients (“Ca2+ sparks”) caused by the opening of one or the coordinated opening of a number of tightly clustered ryanodine-sensitive Ca2+-release (RyR) channels in the sarcoplasmic reticulum (SR) activate nearby Ca2+-dependent K+(KCa) channels to cause an outward current [referred to as a “spontaneous transient outward current” (STOC)]. These KCa currents cause membrane potential hyperpolarization of arterial myocytes, which would lead to vasodilation through decreasing Ca2+ entry through voltage-dependent Ca2+ channels. Therefore, modulation of Ca2+spark frequency should be a means to regulation of KCa channel currents and hence membrane potential. We examined the frequency modulation of Ca2+ sparks and STOCs by activation of protein kinase C (PKC). The PKC activators, phorbol 12-myristate 13-acetate (PMA; 10 nM) and 1,2-dioctanoyl- sn-glycerol (1 μM), decreased Ca2+ spark frequency by 72% and 60%, respectively, and PMA reduced STOC frequency by 83%. PMA also decreased STOC amplitude by 22%, which could be explained by an observed reduction (29%) in KCa channel open probability in the absence of Ca2+ sparks. The reduction in STOC frequency occurred in the presence of an inorganic blocker (Cd2+) of voltage-dependent Ca2+ channels. The reduction in Ca2+ spark frequency did not result from SR Ca2+ depletion, since caffeine-induced Ca2+ transients did not decrease in the presence of PMA. These results suggest that activators of PKC can modulate the frequency of Ca2+ sparks, through an effect on the RyR channel, which would decrease STOC frequency (i.e., KCa channel activity).

scholarly journals Voltage-Activated Potassium Outward Currents in Two Types of Spider Mechanoreceptor Neurons

1999 ◽  
Vol 81 (6) ◽  
pp. 2937-2944 ◽  
Author(s):  
Shin-Ichi Sekizawa ◽  
Andrew S. French ◽  
Ulli Höger ◽  
Päivi H. Torkkeli
Keyword(s):  
Outward Current ◽  
Type A ◽  
Transient Current ◽  
Resting Potential ◽  
Transient Outward Current ◽  
Type B ◽  
Outward Currents ◽  
The Difference ◽  
Major Factors ◽  
Kinetics Of

Voltage-activated potassium outward currents in two types of spider mechanoreceptor neurons. We studied the properties of voltage-activated outward currents in two types of spider cuticular mechanoreceptor neurons to learn if these currents contribute to the differences in their adaptation properties. Both types of neurons adapt rapidly to sustained stimuli, but type A neurons usually only fire one or two action potentials, whereas type B neurons can fire bursts lasting several hundred milliseconds. We found that both neurons had two outward current components, 1) a transient current that activated rapidly when stimulated from resting potential and inactivated with maintained stimuli and 2) a noninactivating outward current. The transient outward current could be blocked by 5 mM tetraethylammonium chloride, 5 mM 4-aminopyridine, or 100 μM quinidine, but these blockers also reduced the amplitude of the noninactivating outward current. Charybdotoxin or apamin did not have any effect on the outward currents, indicating that Ca2+-activated K+ currents were not present or not inhibited by these toxins. The only significant differences between type A and type B neurons were found in the half-maximal activation ( V 50) values of both currents. The transient current had a V 50 value of 9.6 mV in type A neurons and −13.1 mV in type B neurons, whereas the V 50 values of noninactivating outward currents were −48.9 mV for type A neurons and −56.7 mV for type B neurons. We conclude that, although differences in the activation kinetics of the voltage-activated K+ currents could contribute to the difference in the adaptation behavior of type A and type B neurons, they are not major factors.

Four different components contribute to outward current in rat ventricular myocytes

1999 ◽  
Vol 277 (1) ◽  
pp. H107-H118 ◽  
Author(s):  
Herbert M. Himmel ◽  
Erich Wettwer ◽  
Qi Li ◽  
Ursula Ravens
Keyword(s):  
Steady State ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Cell Voltage ◽  
Differential Sensitivity ◽  
Resting Potential ◽  
Residual Fraction ◽  
Voltage Range ◽  
Rat Ventricular Myocytes ◽  
Steady State Current

In rat ventricle, two Ca2+-insensitive components of K+ current have been distinguished kinetically and pharmacologically, the transient, 4-aminopyridine (4-AP)-sensitive I to and the sustained, tetraethylammonium (TEA)-sensitive I K. However, a much greater diversity of depolarization-activated K+ channels has been reported on the level of mRNA and protein. In the search for electrophysiological evidence of further current components, the whole cell voltage-clamp technique was used to analyze steady-state inactivation of outward currents by conditioning potentials in a wide voltage range. Peak ( I peak) and late ( I late) currents during the test pulse were analyzed by Boltzmann curve fitting, producing three fractions each. Fractions a and b had different potentials of half-maximum inactivation ( V 0.5); the third residual fraction, r, did not inactivate. Fractions a for I peak and I late had similar relative amplitudes and V 0.5 values, whereas size and V 0.5 of fractions b differed significantly between I peak and I late. Only b of I peak was transient, suggesting a relation with I to, whereas a, b, and r of I late appeared to be three different sustained currents. Therefore, four individual outward current components were distinguished: I to( b of I peak), I K( a), the steady-state current I ss( r), and the novel current I Kx( b of I late). This was further supported by differential sensitivity to TEA, 4-AP, clofilium, quinidine, dendrotoxin, heteropodatoxin, and hanatoxin. With the exception of I to, none of the currents exhibited a marked transmural gradient. Availability of I K was low at resting potential; nevertheless, I K contributed to action potential shortening in hyperpolarized subendocardial myocytes. In conclusion, on the basis of electrophysiological and pharmacological evidence, at least four components contribute to outward current in rat ventricular myocytes.

scholarly journals Serotonin differentially modulates two K+ currents in the Retzius cell of the leech

1989 ◽  
Vol 145 (1) ◽  
pp. 403-417
Author(s):  
J. Acosta-Urquidi ◽  
C. L. Sahley ◽  
A. L. Kleinhaus
Keyword(s):  
Steady State ◽  
Action Potential ◽  
Voltage Clamp ◽  
Negative Feedback ◽  
Outward Current ◽  
Current Clamp ◽  
Macrobdella Decora ◽  
Voltage Dependent ◽  
Retzius Cell ◽  
K Currents

The effects of 100 mumol l-1 serotonin (5-HT) were investigated on the Na+- and Ca2+-dependent action potential and distinct K+ currents in the Retzius (R) cells of the hirudinid leeches Macrobdella decora and Hirudo medicinalis by conventional current-clamp and two-microelectrode voltage-clamp techniques. 1. In normal Na+-containing Ringer, 5-HT decreased the duration of the action potential prolonged by 5 mmol l-1 tetraethylammonium (TEA+) chloride. 2. In Na+-free saline containing 25 mumol l-1 TEA+ to block IK, 5-HT reduced the amplitude and duration of Ca2+ spikes evoked by intracellular current injection. 3. Under voltage-clamp, 5-HT enhanced the peak amplitude of an early transient 4-aminopyridine (4-AP)-sensitive, voltage-dependent outward current, termed IA. A small but significant increase in the time constant of inactivation (tau off) of IA was also measured after exposure to 5-HT. 4. 5-HT suppressed the peak and steady-state amplitudes of a delayed TEA+-sensitive, voltage-dependent outward current, termed IK. These results demonstrate differential simultaneous modulation of distinct K+ currents in the Retzius cell of the leech by the endogenous transmitter serotonin. These cells contain and release 5-HT, and are believed to be multifunction neurons implicated in feeding and swimming. This modulation may change the excitable properties of the cell, leading to a negative feedback autoregulation of its transmitter output.

A fast transient potassium current in thalamic relay neurons: kinetics of activation and inactivation

1991 ◽  
Vol 66 (4) ◽  
pp. 1304-1315 ◽  
Author(s):  
J. R. Huguenard ◽  
D. A. Coulter ◽  
D. A. Prince
Keyword(s):  
Steady State ◽  
Reversal Potential ◽  
Cell Voltage ◽  
Inactivation Kinetics ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
K Current ◽  
K Currents ◽  
Relay Neurons

1. Whole-cell voltage-clamp techniques were used to record K+ currents in relay neurons (RNs) that had been acutely isolated from rat thalamic ventrobasal complex and maintained at 23 degrees C in vitro. Tetrodoxin (TTX; 0.5 microM) was used to block Na+ currents, and reduced extracellular levels of Ca2+ (1 mM) were used to minimize contributions from Ca2+ current (ICa). 2. In RNs, depolarizing commands activate K+ currents characterized by a substantial rapidly inactivating (time constant approximately 20 ms) component, the features of which correspond to those of the transient K+ current (IA) in other preparations, and by a smaller, more slowly activating K+ current, "IK". IA was reversibly blocked by 4-aminopyridine (4-AP, 5 mM), and the reversal potential varied with [K+]o as predicted by the Nernst equation. 3. IA was relatively insensitive to blockade by tetraethylammonium [TEA; 50%-inhibitory concentration (IC50) much much greater than 20 mM]; however, two components of IK were blocked with IC50S of 30 microM and 3 mM. Because 20 mM TEA blocked 90% of the sustained current while reducing IA by less than 10%, this concentration was routinely used in experiments in which IA was isolated and characterized. To further minimize contamination by other conductances, 4-AP was added to TEA-containing solutions and the 4-AP-sensitive current was obtained by subtraction. 4. Voltage-dependent steady-state inactivation of peak IA was described by a Boltzman function with a slope factor (k) of -6.5 and half-inactivation (V1/2) occurring at -75 mV. Activation of IA was characterized by a Boltzman curve with V1/2 = -35 mV and k = 10.8. 5. IA activation and inactivation kinetics were best fitted by the Hodgkin-Huxley m4h formalism. The rate of activation was voltage dependent, with tau m decreasing from 2.3 ms at -40 mV to 0.5 ms at +50 mV. Inactivation was relatively voltage independent and nonexponential. The rate of inactivation was described by two exponential decay processes with time constants (tau h1 and tau h2) of 20 and 60 ms. Both components were steady-state inactivated with similar voltage dependence. 6. Temperature increases within the range of 23-35 degrees C caused IA activation and inactivation rates to become faster, with temperature coefficient (Q10) values averaging 2.8. IA amplitude also increased as a function of temperature, albeit with a somewhat lower Q10 of 1.6. 7. Several voltage-dependent properties of IA closely resemble those of the transient inward Ca2+ current, IT. (ABSTRACT TRUNCATED AT 400 WORDS)

Rat hippocampal neurons in culture: potassium conductances

1984 ◽  
Vol 51 (6) ◽  
pp. 1409-1433 ◽  
Author(s):  
M. Segal ◽  
J. L. Barker
Keyword(s):  
Time Constant ◽  
Hippocampal Neurons ◽  
Outward Current ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Transient Outward Current ◽  
Current Response ◽  
Normal Medium ◽  
Inward Current ◽  
Voltage Dependent

Two-electrode voltage-clamp methodology was used to analyze voltage-dependent ionic conductances in 81 rat hippocampal neurons grown in culture for 4-6 wk. Pyramidal and multipolar cells with 15- to 20-micron-diameter cell bodies were impaled with two independent KCl electrodes. The cells had resting potentials of -30 to -60 mV and an average input resistance of about 30 M omega. A depolarizing command applied to a cell maintained in normal medium invariably evoked a fast (2-10 ms) inward current that saturated the current-passing capacity of the system. This was blocked in a reversible manner by application of tetrodotoxin (TTX) (0.1-1.0 microM) near the recorded cell. In the presence of TTX, a depolarizing command evoked a rapidly rising (3-5 ms), rapidly decaying (25 ms) transient outward current reminiscent of "IA" reported in molluscan neurons. This was followed by a more slowly activating (approximately 100 ms) outward current response of greater amplitude that decayed with a time constant of about 2-3 s. These properties resemble those associated with the K+ conductance, IK, underlying delayed rectification described in many excitable membranes. IK was blocked by extracellular application of tetraethylammonium (TEA) but was insensitive to 4-aminopyridine (4-AP) at concentrations that effectively eliminated IA. IA, in turn, was only marginally depressed by TEA. Unlike IK, IA was completely inactivated when the membrane was held at potentials positive to -50 mV. Inactivation was completely removed by conditioning hyperpolarization at -90 mV. A brief hyperpolarizing pulse (10 ms) was sufficient to remove 95% of the inactivation. IA activated on commands to potentials more positive than -50 mV. The inversion potential of the ionic conductance underlying IA and IK was in the range of the K+ equilibrium potential, EK, as measured by the inversion of tail currents; and this potential was shifted in a depolarizing direction by elevated [K+]0. Thus, both current species reflect activation of membrane conductance to K+ ions. Hyperpolarizing commands from resting potentials revealed a time- and voltage-dependent slowly developing inward current in the majority of cells studied. This membrane current was observed in cells exhibiting "anomalous rectification" and was therefore labeled IAR. It was activated at potentials negative to -70 mV with a time constant of 100-200 ms and was not inactivated. A return to resting potential revealed a tail current that disappeared at about EK. IAR was blocked by extracellular CS+ and was enhanced by elevating [K+]0. It thus appears to be carried by inward movement of K+ ions.(ABSTRACT TRUNCATED AT 400 WORDS)

Kinetics of slow inactivation of persistent sodium current in layer V neurons of mouse neocortical slices

1996 ◽  
Vol 76 (3) ◽  
pp. 2125-2130 ◽  
Author(s):  
I. A. Fleidervish ◽  
M. J. Gutnick
Keyword(s):  
Time Course ◽  
Sodium Current ◽  
Outward Current ◽  
Slow Inactivation ◽  
Voltage Dependent ◽  
Layer V ◽  
Neuronal Functions ◽  
Kinetics Of ◽  
Whole Cell Recordings ◽  
K Currents

1. In whole cell recordings from layer V neurons in slices of mouse somatosensory neocortex, tetrodotoxin (TTX)-sensitive persistent Na+ current (INaP) was studied by blocking K+ currents with intracellular Cs+ and Ca2+ currents with extracellular Cd2+. During slow voltage ramps, INaP began to activate at around -60 mV, and attained a peak at around -25 mV. The peak amplitude of INaP varied widely from cell to cell (range 60-3,160 pA; median 308 pA, n = 77). At potentials more positive than -35 mV, INaP in all cells was superimposed on a large, TTX-resistant outward current. 2. In hybrid clamp experiments, INaP was significantly reduced by a preceding high-frequency train of spikes. 3. INaP underwent pronounced slow inactivation, which was revealed by systematically varying the ramp speed between 233 and 2.33 mV/s, or varying the duration of a depolarizing prepulse between 0.1 and 10 s. 4. Onset of slow inactivation at +20 mV was monoexponential with tau = 2.06 s (n = 17 cells). Recovery from slow inactivation was voltage dependent. It followed a monoexponential time course with tau = 2.31 s (n = 6) at -70 mV and tau = 1.10 s (n = 4) at -90 mV. These values are not significantly different than values previously reported for slow inactivation of fast-inactivating INa. 5. Slow inactivation of neocortical INaP will influence all neuronal functions in which this current plays a role, including spike threshold determination, synaptic integration, and active propagation in dendrites. The kinetics of slow inactivation suggest that it may be a factor not only during extremely intense spiking, but also during periods of "spontaneous" activity.

Oscillation of Membrane Currents During the Action Potential in Chara corallina: Modification and Significance for Repolarisation of the Membrane Potential and Salt Sensitivity

1996 ◽  
Vol 23 (3) ◽  
pp. 361
Author(s):  
J.I Kourie
Keyword(s):  
Time Course ◽  
Outward Current ◽  
Chara Corallina ◽  
Membrane Currents ◽  
Inactivation Kinetics ◽  
Transient Outward Current ◽  
Voltage Dependent ◽  
Current Activation ◽  
K Current ◽  
Kinetics Of

Depolarising voltage-clamp steps in C. corallina induced membrane currents which differ from those of C. inflata in two aspects: (1) The absence of a 'hump', i.e. a transient outward current,Io(max) which is present in C. inflata, and (2) the presence in C, corallina of a voltage-dependent current oscillation, i.e. a succession of decaying peaks. The peaks of the oscillating transient inward current, Ii(max), were voltage dependent and sensitive to block with 9-anthracenecarboxylic acid (9-AC). The oscillating current is carried by C1- and its time course is determined by the activation and inactivation kinetics of C1- channels. Extracellular NaCl delayed current activation, induced a voltage-dependent increase in Ii(max) and a decrease in the steady-state outward K+ current, Is. NaCl increased the occurrence of oscillation and enhanced the amplitude of the oscillating current. Extracellular sorbitol induced an overall reduction in Ii(max) and had virtually no effect on Is. I suggest that the enhancement of the oscillating transient inward CI- current, Ii(max), by NaCl is due to ionic effects of NaCl rather than to its osmotic effects.

Contributions of a transient outward current to repolarization in human atrium

1989 ◽  
Vol 257 (6) ◽  
pp. H1773-H1781 ◽  
Author(s):  
E. F. Shibata ◽  
T. Drury ◽  
H. Refsum ◽  
V. Aldrete ◽  
W. Giles
Keyword(s):  
Action Potential ◽  
Right Atrium ◽  
Outward Current ◽  
Resting Potential ◽  
Transient Outward Current ◽  
Human Atrium ◽  
Human Right ◽  
Early Repolarization ◽  
Human Right Atrium ◽  
Voltage Dependent

Conventional microelectrode recordings combined with enzymatic cell dispersion methods and a single microelectrode voltage-clamp technique were used to record transmembrane action potentials and ionic currents in isolated single myocytes and in excised segments of human right atrium. Recordings of the outward current(s), which is responsible for the resting potential and early repolarization of the action potential in human right atrium, consistently showed that this tissue has 1) a relatively small inwardly rectifying background potassium current (IK1) which generates the resting potential in mammalian ventricular tissue and Purkinje fibers, and 2) a large time- and voltage-dependent, but Ca2(+)-independent, transient outward current. A somewhat similar K+ current was originally described in neurons and recently has also been identified in a variety of mammalian cardiac tissues. As expected from previous work, this transient outward current in human atrium is blocked by 4-aminopyridine (4-AP; 0.5 mM) and exhibits time- and voltage-dependent inactivation and reactivation. Measurements of action potential shape changes and phasic tension as a function of stimulus frequency, or after 4-AP application, show that in human atrium this current can produce pronounced changes in both the early repolarization of the action potential and force generation.

Patch-clamp study of postnatal development of CA1 neurons in rat hippocampal slices: membrane excitability and K+ currents

1992 ◽  
Vol 68 (1) ◽  
pp. 55-69 ◽  
Author(s):  
I. Spigelman ◽  
L. Zhang ◽  
P. L. Carlen
Keyword(s):  
Membrane Potential ◽  
Patch Clamp ◽  
Action Potentials ◽  
Hippocampal Slices ◽  
Outward Current ◽  
Resting Potential ◽  
Resting Membrane Potential ◽  
Ca1 Neurons ◽  
Outward Currents ◽  
K Currents

1. The postnatal development of membrane properties and outward K+ currents in CA1 neurons in rat hippocampal slices was studied with the use of whole-cell patch-clamp techniques. 2. Neurons at all postnatal ages (2-30 days; P2-30) were capable of generating tetrodotoxin (TTX)-sensitive action potentials in response to intracellular injection of depolarizing current pulses. There was a gradual increase in the amplitude and a decrease in the duration of these action potentials with age. Stable values for spike duration were reached by P15, whereas spike amplitude increased until P20-25. In P2-5 neurons, the duration of action potentials was greatly prolonged by depolarization from the resting membrane potential, indicating a weak spike repolarizing mechanism at depolarized potentials. In contrast, the duration of spikes evoked in P20-30 neurons was not affected by similar changes in the membrane potential. 3. Application of tetraethylammonium (TEA, 10 mM) had no effect on the duration of spikes in P3-5 neurons, whereas application of 4-aminopyridine (4-AP, 2 mM) produced large increases in spike duration. In contrast, the duration of spikes in P26 neurons was greatly increased after TEA application, whereas 4-AP had smaller effects on spike duration in these neurons. 4. The input resistance and membrane time constant decreased with age from P2 to P15. The values for both parameters were considerably greater than those reported with conventional intracellular recording electrodes in the immature hippocampus. The resting membrane potential became more hyperpolarized with age. When the recording pipettes contained KCl (140 mM), the resting potential of P3-4 neurons was 34 mV depolarized compared with resting potentials observed with potassium gluconate-filled pipettes. Only a 13-mV change in resting potential was observed during similar comparisons in P27-28 neurons. 5. Outward currents activated by depolarization were examined with the use of voltage-clamp techniques in P2-30 neurons. In P2-5 cells, a small, slowly inactivating outward current was evoked with depolarizing commands from holding potentials near -50 mV. By preceding the depolarizing commands with a hyperpolarizing prepulse, an additional early transient outward current was evoked. The sustained and transient outward currents were separated by their kinetic properties and their sensitivity to cobalt (Co2+), TEA, and 4-AP.(ABSTRACT TRUNCATED AT 400 WORDS)

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