Two types of calcium-dependent channels of potassium outward current in the somatic membrane of Helix pomatia neurons

1987 ◽  
Vol 19 (2) ◽  
pp. 143-148
Author(s):  
A. E. Martynyuk
Keyword(s):  
Helix Pomatia ◽  
Outward Current ◽  
Somatic Membrane ◽  
Calcium Dependent

Calcium-dependent current generating the afterhyperpolarization of hippocampal neurons

1986 ◽  
Vol 55 (6) ◽  
pp. 1268-1282 ◽  
Author(s):  
B. Lancaster ◽  
P. R. Adams
Keyword(s):  
Voltage Clamp ◽  
Hippocampal Neurons ◽  
Hippocampal Slices ◽  
Outward Current ◽  
Pyramidal Cells ◽  
Resting Potential ◽  
Tail Current ◽  
Calcium Dependent ◽  
K Current

A single-electrode voltage-clamp technique was employed on in vitro hippocampal slices to examine the membrane current responsible for the slow afterhyperpolarization (AHP) in CA1 pyramidal cells. This was achieved by using conventional procedures to evoke an AHP in current clamp, followed rapidly by a switch into voltage clamp (hybrid clamp). The AHP current showed a dependence on extracellular K+, which was close to that predicted for a K+ current by the Nernst equation. The AHP current could be blocked by Cd2+ or norepinephrine. Although the AHP current showed a requirement for voltage-dependent Ca2+ entry, the current did not show any clear intrinsic voltage dependence. Once activated, AHP current is not turned off by hyperpolarizing the membrane potential. The effects of norepinephrine, Cd2+, and tetraethylammonium (TEA) were used to identify an AHP current component to the outward current evoked by depolarizing voltage commands from holding potentials that approximate to the resting potential for these cells. The AHP current can contribute significantly to the outward current during the depolarizing command. Upon repolarization it is evident as a slow outward tail current. This slow tail current had the same time constant as AHP currents evoked by hybrid clamp. Fast components to the tail currents were also observed. These were sensitive to Cd2+ and TEA. They probably represent a voltage-sensitive gKCa, sometimes termed C-current. The strong sensitivity to voltage and TEA displayed by the conventionally described gKCa (IC) are properties inconsistent with the AHP. It seems likely that the AHP current (IAHP) represents a Ca2+-activated K+ current separate from IC and that these two currents coexist in the same cell.

Voltage-clamp analysis of the ionic conductances in a leech neuron with a purely calcium-dependent action potential

1987 ◽  
Vol 58 (6) ◽  
pp. 1468-1484 ◽  
Author(s):  
J. Johansen ◽  
J. Yang ◽  
A. L. Kleinhaus
Keyword(s):  
Steady State ◽  
Action Potential ◽  
Time Course ◽  
Outward Current ◽  
Time Constants ◽  
Exponential Time ◽  
Calcium Dependent ◽  
Voltage Dependent ◽  
Ca Currents ◽  
Single Exponential

1. The purely calcium-dependent action potential of the anterior lateral giant (ALG) cell in the leech Haementeria was examined under voltage clamp. 2. Analysis with ion substitutions showed that the ALG cell action potential is generated by only two time- and voltage-dependent conductance systems, an inward Ca-dependent current (ICa) and an outward Ca-dependent K current IK(Ca). 3. The kinetic properties of the inward current were examined both in Cs-loaded neurons with Ca as the current carrier as well as in Ba-containing Ringer solutions with Ba as the current carrier, since Ba effectively blocked all time- and voltage-dependent outward current. 4. During a maintained depolarization, Ba and Ca currents activated with a time constant tau m, they then inactivated with the decay following a single exponential time course with a time constant tau h. The time constants for decay of both Ba and Ca currents were comparable, suggesting that the mechanism of inactivation of ICa in the ALG cell is largely voltage dependent. In the range of potentials from 5 to 45 mV, tau m varied from 8 to 2 ms and tau h varied from 250 to 125 ms. 5. The activation of currents carried by Ba, after correction for inactivation, could be described reasonably well by the expression I'Ba = I'Ba(infinity) [1--exp(-t/tau m)]. 6. The steady-state activation of the Ba-conductance mBa(infinity) increased sigmoidally with voltage and was approximated by the equation mBa(infinity) = (1 + exp[(Vh-6)/3])-1. The steady-state inactivation hBa(infinity) varied with holding potential and could be described by the equation hBa(infinity) = [1 + exp(Vh + 10/7)]-1. Recovery from inactivation of IBa was best described by the sum of two exponential time courses with time constants of 300 ms and 1.75 s, respectively. 7. The outward current IK(Ca) developed very slowly (0.5–1 s to half-maximal amplitude) and did not inactivate during a 20-s depolarizing command pulse. Tail current decay of IK(Ca) followed a single exponential time course with voltage-dependent time constants of between 360 and 960 ms. The steady-state activation n infinity of IK(Ca) increased sigmoidally with depolarization as described by the equation n infinity = [1 + exp(Vh-13.5)/-8)]-1. 8. The reversal potentials of IK(Ca) tail currents were close to the expected equilibrium potential for potassium and they varied linearly with log [K]o with a slope of 51 mV. These results suggest a high selectivity of the conductance for K ions.(ABSTRACT TRUNCATED AT 400 WORDS)

Sodium-dependent plateau potentials in cultured Retzius cells of the medicinal leech

1996 ◽  
Vol 76 (3) ◽  
pp. 1491-1502 ◽  
Author(s):  
J. D. Angstadt ◽  
J. J. Choo
Keyword(s):  
Outward Current ◽  
Channel Blockers ◽  
Plateau Potentials ◽  
Calcium Dependent ◽  
Current Pulses ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Prolonged Duration ◽  
Input Conductance ◽  
Retzius Cells

1. Individual leech Retzius (Rz) cells were removed from mid-body ganglia and plated in cell culture on concanavalin A or polylysine. Experiments on the majority of cells were performed after 6-11 days in culture. Isolated Rz cells were superfused with normal leech saline (NS), cobalt saline (Ca2+ replaced with Co2+), or one of a variety of other modified salines. 2. Prolonged plateau potentials (PPs) with durations ranging from several seconds to nearly 2 min were evoked in isolated Rz cells in response to 1-s depolarizing current pulses delivered under discontinuous current clamp. Some PPs terminated spontaneously while others were terminated with hyperpolarizing current pulses. PPs were associated with a dramatic increase in the input conductance of the neuron. The PP decayed slightly over time, and this decay was accompanied by a small decrease in the input conductance. 3. PP duration was enhanced by penetrating cells with electrodes containing tetraethylammonium (TEA) and by bathing cells in Co2+ saline, but PPs were evoked also in NS and using electrodes without TEA. The effects of TEA and Co2+ saline suggest that voltage-dependent and especially calcium-dependent outward currents normally suppress plateau formation. 4. PPs occurred most reliably in neurons with extensive neurite sprouting. Isolated somata with few or no neurites usually failed to express PP, although there were several exceptions to this trend. 5. PPs persisted when Ca2+ was replaced with either of the calcium channel blockers Co2+, Ni2+, or Mn2+, when 200 microM Cd2+ was added to normal saline, or when Na+ was replaced with Li+. In contrast, PPs were eliminated rapidly when Na+ was replaced with N-methyl-D-glucamine. 6. Isolated Rz cells also expressed repetitive PPs either spontaneously or in response to injection of sustained depolarizing current. Spontaneous repetitive PPs were suppressed by hyperpolarizing current. Repetitive PPs in isolated Rz cells are similar in many respects to the bursting electrical activity induced by Co2+ saline in Rz and other neurons in intact ganglia. 7. The ionic dependence and prolonged duration of PPs suggest that these responses are generated by a persistent voltage-dependent Na+ current. A quantitative computer simulation of PPs was achieved using a depolarization-activated Na+ conductance with very slow inactivation. Repetitive PPs were simulated by addition of a slow outward current in the form of an electrogenic pump.

Calcium-dependent outward current in nodose ganglion neurones of the rabbit

1985 ◽  
Vol 1 ◽  
pp. S48
Author(s):  
Kiichiro Morita ◽  
Yoshifumi Katayama ◽  
Hitoshi Tatsumi
Keyword(s):  
Outward Current ◽  
Nodose Ganglion ◽  
Calcium Dependent

Mechanism of action of baclofen in rat dorsal motor nucleus of the vagus

2001 ◽  
Vol 280 (6) ◽  
pp. G1106-G1113 ◽  
Author(s):  
K. N. Browning ◽  
R. A. Travagli
Keyword(s):  
Mechanism Of Action ◽  
Receptor Agonist ◽  
Outward Current ◽  
Calcium Currents ◽  
Motor Nucleus ◽  
Channel Blockers ◽  
Calcium Dependent ◽  
Ion Channel Blockers ◽  
Dorsal Motor Nucleus ◽  
Whole Cell Patch Clamp

Using whole cell patch-clamp recordings, we investigated the effects of the GABAB receptor agonist baclofen in thin slices of rat brain stem containing identified gastric- or intestinal-projecting dorsal motor nucleus of the vagus (DMV) neurons. Perfusion with baclofen (0.1–100 μM) induced a concentration-dependent outward current (EC50, 3 μM) in 54% of DMV neurons with no apparent differences between gastric- and intestinal-projecting neurons. The outward current was attenuated by pretreatment with the selective GABAB antagonists saclofen and 2-hydroxysaclofen, but not by the synaptic blocker TTX, indicating a direct effect at GABAB receptors on DMV neurons. Using the selective ion channel blockers barium, nifedipine, and apamin, we showed that the outward current was due to effects on potassium and calcium currents as well as calcium-dependent potassium currents. The calcium-mediated components of the outward current were more prominent in intestinal-projecting neurons than in gastric-projecting neurons. These data indicate that although baclofen inhibits both intestinal- and gastric-projecting neurons in the rat DMV, its mechanism of action differs among the neuronal subpopulations.

scholarly journals JMV5656, A Novel Derivative of TLQP-21, Triggers the Activation of a Calcium-Dependent Potassium Outward Current in Microglial Cells

2017 ◽  
Vol 11 ◽  
Author(s):  
Ilaria Rivolta ◽  
Anna Binda ◽  
Laura Molteni ◽  
Laura Rizzi ◽  
Elena Bresciani ◽  
...  
Keyword(s):  
Outward Current ◽  
Microglial Cells ◽  
Calcium Dependent

5-HT modulation of hyperpolarization-activated inward current and calcium-dependent outward current in a crustacean motor neuron

1992 ◽  
Vol 68 (2) ◽  
pp. 496-508 ◽  
Author(s):  
O. Kiehn ◽  
R. M. Harris-Warrick
Keyword(s):  
Motor Neuron ◽  
Time Course ◽  
Reversal Potential ◽  
Outward Current ◽  
Resting Membrane Potential ◽  
Inward Current ◽  
Calcium Dependent ◽  
Voltage Dependent ◽  
K Concentration ◽  
Conductance Increase

1. Serotonergic modulation of a hyperpolarization-activated inward current, Ih, and a calcium-dependent outward current, Io(Ca), was examined in the dorsal gastric (DG) motor neuron, with the use of intracellular recording techniques in an isolated preparation of the crab stomatogastric ganglion (STG). 2. Hyperpolarization of the membrane from rest with maintained current pulses resulted in a slow time-dependent relaxation back toward rest and a depolarizing overshoot after termination of the current pulse. In voltage clamp, hyperpolarizing commands negative to approximately -70 mV caused a slowly developing inward current, Ih, which showed no inactivation. Repolarization back to the holding potential of -50 mV revealed a slow inward tail current. 3. The reversal potential for Ih was approximately -35 mV. Raising extracellular K+ concentration ([K+]o) from 11 to 22 mM enhanced, whereas decreasing extracellular Na+ concentration ([Na+]o) reduced the amplitude of Ih. These results indicate that Ih in DG is carried by both K+ and Na+ ions. 4. Bath application of serotonin (5-HT; 10 microM) caused a marked increase in the amplitude of Ih through its active voltage ranges. 5. The time course of activation of Ih was well fitted by a single exponential function and strongly voltage dependent. 5-HT increased the rate of activation of Ih. 5-HT also slowed the rate of deactivation of the Ih tail on repolarization to -50 mV. 6. The activation curve for the conductance (Gh) underlying Ih was obtained by analyzing tail currents. 5-HT shifted the half activation for Gh from approximately -105 mV in control to -95 mV, resulting in an increase in the amplitude of Gh active at rest. 7. Two to 4 mM Cs+ abolished Ih, whereas barium (200 microM to 2 mM) had only weak suppressing effects on Ih. Concomitantly, Cs+ also blocked the 5-HT-induced inward current and conductance increase seen at voltages negative to rest. In current clamp, Cs+ caused DG to hyperpolarize 3-4 mV from rest, suggesting that Ih is partially active at rest and contributes to the resting membrane potential. 8. Depolarizing voltage commands from a holding potential of -50 mV resulted in a total outward current (Io) with an initial transient component and a sustained steady-state component. Application of 5-HT reduced both the transient and sustained components of Io. 9. Io was reduced by 10-20 mM tetraethylammonium (TEA), suggesting that it is primarily a K+ current.(ABSTRACT TRUNCATED AT 400 WORDS)

Investigation of the TEA-resistant outward current in the somatic membrane of perfused nerve cells

1980 ◽  
Vol 11 (5) ◽  
pp. 341-348
Author(s):  
P. A. Doroshenko ◽  
P. G. Kostyuk ◽  
A. Ya. Tsyndrenko
Keyword(s):  
Outward Current ◽  
Nerve Cells ◽  
Somatic Membrane
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