Effects of Pb2+ on the transient outward potassium current in acutely dissociated rat hippocampal neurons

2003 ◽  
Vol 81 (8) ◽  
pp. 825-833 ◽  
Author(s):  
Kuai Yu ◽  
Shao-Yu Ge ◽  
Xiao-Qing Dai ◽  
Di-Yun Ruan
Keyword(s):  
Steady State ◽  
Patch Clamp ◽  
Potassium Current ◽  
Patch Clamp Technique ◽  
Transient Outward Potassium Current ◽  
Boltzmann Function ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
Outward Potassium Current ◽  
Initial Delay

Modulation of the voltage-dependent transient outward potassium current (IA) by Pb2+ was studied in acutely dissociated rat hippocampal pyramidal cells from the CA1 region at postnatal ages 7–14 days using the conventional whole-cell patch-clamp technique. In the presence of different concentrations of external Pb2+, the initial delay and activation time of IA were concentration-dependently lengthened. In particular, the initial delay was evenlonger in 1 mM Pb2+, showing no signs of saturation. Pb2+ also slowed the inactivation of IA, for decay time constants in the presence of Pb2+ were increased under the same experimental protocols. The activation curves, which were reasonably fitted by a single Boltzmann function, illustrated that Pb2+ increased the voltage threshold of IA and shifted the normalized activation current–voltage curves to more depolarizing voltage commands. Moreover, Pb2+ significantly affected the steady-state inactivation of IA. The application of Pb2+ made the curves of the steady-state inactivation of IA shift to more depolarizing voltages with little change in the slopes factors. In brief, the results demonstrated that Pb2+ is a dose- and voltage-dependent, reversible blocker of IA currents of hippocampal CA1 neurons. The observations were fitted by the revised "Kuo and Chen type model", which postulates a Pb2+-selective site near the pore of the IA channel and that modulation of the IA channel by Pb2+ is the result of the competitive influences of Pb2+ on opening and inactivating different pathways.Key words: patch clamp, IA, Pb2+, hippocampal neuron, rat.

scholarly journals Effect of acidosis on transient outward potassium current in isolated rat ventricular myocytes

2000 ◽  
Vol 278 (1) ◽  
pp. H50-H59 ◽  
Author(s):  
J. T. Hulme ◽  
C. H. Orchard
Keyword(s):  
Potassium Current ◽  
Voltage Dependence ◽  
Ventricular Myocytes ◽  
Solution Ph ◽  
Patch Clamp Technique ◽  
Inactivation Curve ◽  
Rat Ventricular Myocytes ◽  
Steady State Inactivation ◽  
Perforated Patch Clamp ◽  
Outward Potassium Current

The effect of acidosis on the transient outward K+ current ( Ito ) of rat ventricular myocytes has been investigated using the perforated patch-clamp technique. When the holding potential was −80 mV, depolarizing pulses to potentials positive to −20 mV activated Ito in subepicardial cells but activated little Ito in subendocardial cells. Exposure to an acid solution (pH 6.5) had no significant effect on Ito activated from this holding potential in either subepicardial or subendocardial cells. When the holding potential was −40 mV, acidosis significantly increased Ito at potentials positive to −20 mV in subepicardial cells but had little effect on Ito in subendocardial cells. The increase in Ito in subepicardial cells was inhibited by 10 mM 4-aminopyridine. In subepicardial cells, acidosis caused a +8.57-mV shift in the steady-state inactivation curve. It is concluded that in subepicardial rat ventricular myocytes acidosis increases the amplitude of Ito as a consequence of a depolarizing shift in the voltage dependence of inactivation.

scholarly journals The calcium-independent transient outward potassium current in isolated ferret right ventricular myocytes. I. Basic characterization and kinetic analysis.

1993 ◽  
Vol 101 (4) ◽  
pp. 571-601 ◽  
Author(s):  
D L Campbell ◽  
R L Rasmusson ◽  
Y Qu ◽  
H C Strauss
Keyword(s):  
Steady State ◽  
Ventricular Myocytes ◽  
Nonlinear Least Squares ◽  
Patch Clamp Technique ◽  
Time Constants ◽  
Whole Cell Patch Clamp ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
K Current ◽  
Necessary And Sufficient

Enzymatically isolated myocytes from ferret right ventricles (12-16 wk, male) were studied using the whole cell patch clamp technique. The macroscopic properties of a transient outward K+ current I(to) were quantified. I(to) is selective for K+, with a PNa/PK of 0.082. Activation of I(to) is a voltage-dependent process, with both activation and inactivation being independent of Na+ or Ca2+ influx. Steady-state inactivation is well described by a single Boltzmann relationship (V1/2 = -13.5 mV; k = 5.6 mV). Substantial inactivation can occur during a subthreshold depolarization without any measurable macroscopic current. Both development of and recovery from inactivation are well described by single exponential processes. Ensemble averages of single I(to) channel currents recorded in cell-attached patches reproduce macroscopic I(to) and indicate that inactivation is complete at depolarized potentials. The overall inactivation/recovery time constant curve has a bell-shaped potential dependence that peaks between -10 and -20 mV, with time constants (22 degrees C) ranging from 23 ms (-90 mV) to 304 ms (-10 mV). Steady-state activation displays a sigmoidal dependence on membrane potential, with a net aggregate half-activation potential of +22.5 mV. Activation kinetics (0 to +70 mV, 22 degrees C) are rapid, with I(to) peaking in approximately 5-15 ms at +50 mV. Experiments conducted at reduced temperatures (12 degrees C) demonstrate that activation occurs with a time delay. A nonlinear least-squares analysis indicates that three closed kinetic states are necessary and sufficient to model activation. Derived time constants of activation (22 degrees C) ranged from 10 ms (+10 mV) to 2 ms (+70 mV). Within the framework of Hodgkin-Huxley formalism, Ito gating can be described using an a3i formulation.

Voltage-dependent inactivation of the potassium current of embryonic chick hepatocytes

1991 ◽  
Vol 69 (6) ◽  
pp. 739-745 ◽  
Author(s):  
Ceredwyn E. Hill ◽  
Alvin Shrier
Keyword(s):  
Steady State ◽  
Potassium Current ◽  
Time Course ◽  
Resting Potential ◽  
Embryonic Chick ◽  
Dependent Inactivation ◽  
Voltage Dependent ◽  
Open Development ◽  
Steady State Inactivation ◽  
Time Courses

The whole-cell patch electrode voltage clamp technique was used to study the inactivation properties of the delayed rectifying potassium current of single cultured embryonic chick hepatocytes at 20 °C. The potassium current activates maximally within 250–500 ms of membrane depolarization, after which it decays with a monoexponential time course. Both steady-state activation and inactivation are voltage dependent. Steady-state inactivation declines from 100% at −5 mV to 0 near −70 mV, with half inactivation at −41 mV. At the resting potential (EM) of these cells (−21.5 ± 6.0 mV, n = 36) 6–18% of the IK channels are not inactivated and less than 5% are open. Development and removal of inactivation follow single exponential time courses. The inactivation time constant attains a maximum of around 30 s at −35 mV and is sharply voltage dependent at the EM of these cells. Measurement of EM under current clamp shows random oscillations of 5–10 mV amplitude. We suggest that the voltage- and time-dependent properties of IK, in tandem with a time- and voltage-independent, nonselective current also seen here, would provide the mechanism for a fluctuating EM.Key words: hepatocyte, embryonic, potassium current.

Effects of anandamide on potassium channels in rat ventricular myocytes: a suppression of Ito and augmentation of KATP channels

2012 ◽  
Vol 302 (6) ◽  
pp. C924-C930 ◽  
Author(s):  
Qian Li ◽  
Hui-Jie Ma ◽  
Sheng-Li Song ◽  
Min Shi ◽  
Hui-Juan Ma ◽  
...  
Keyword(s):  
Steady State ◽  
Receptor Antagonist ◽  
Potassium Current ◽  
Ventricular Myocytes ◽  
Dependent Manner ◽  
Patch Clamp Technique ◽  
Concentration Dependent Manner ◽  
Inactivation Curve ◽  
Rat Ventricular Myocytes ◽  
Outward Potassium Current

Anandamide is an endocannabinoid that has antiarrhythmic effects through inhibition of L-type Ca2+ channels in cardiomyocytes. In this study, we investigated the electrophysiological effects of anandamide on K+ channels in rat ventricular myocytes. Whole cell patch-clamp technique was used to record K+ currents, including transient outward potassium current ( Ito), steady-state outward potassium current ( Iss), inward rectifier potassium current ( IK1), and ATP-sensitive potassium current ( IKATP) in isolated rat cardiac ventricular myocytes. Anandamide decreased Ito while increasing IKATP in a concentration-dependent manner but had no effect on Iss and IK1 in isolated ventricular myocytes. Furthermore, anandamide shifted steady-state inactivation curve of Ito to the left and shifted the recovery curve of Ito to the right. However, neither cannabinoid 1 (CB1) receptor antagonist AM251 nor CB2 receptor antagonist AM630 eliminated the inhibitory effect of anandamide on Ito. In addition, blockade of CB2 receptors, but not CB1 receptors, eliminated the augmentation effect of anandamide on IKATP. These data suggest that anandamide suppresses Ito through a non-CB1 and non-CB2 receptor-mediated pathway while augmenting IKATP through CB2 receptors in ventricular myocytes.

scholarly journals Prostaglandins Suppress an Outward Potassium Current in Embryonic Rat Sensory Neurons

1997 ◽  
Vol 77 (1) ◽  
pp. 167-176 ◽  
Author(s):  
G. D. Nicol ◽  
M. R. Vasko ◽  
A. R. Evans
Keyword(s):  
Steady State ◽  
Sensory Neurons ◽  
Potassium Current ◽  
Current Treatment ◽  
Resting Membrane Potential ◽  
Prostaglandin E ◽  
Patch Clamp Recording ◽  
Cellular Mechanisms ◽  
Steady State Inactivation ◽  
Outward Potassium Current

Nicol, G. D., M. R. Vasko, and A. R. Evans. Prostaglandins suppress an outward potassium current in embryonic rat sensory neurons. J. Neurophysiol. 77: 167–176, 1997. The cellular mechanisms giving rise to the enhanced excitability induced by prostaglandin E2 (PGE2) and carba prostacyclin (CPGI2) in embryonic rat sensory neurons were investigated using the whole cell patch-clamp recording technique. Exposing sensory neurons to 1 μM PGE2 produced a twofold increase in the number of action potentials elicited by a ramp of depolarizing current, but this eicosanoid had no effect on the resting membrane potential or the amplitude of the slow afterhyperpolarization. Characterization of the outward potassium currents in the embryonic sensory neurons indicated that the composition of the total current was variable among these neurons. A steady-state inactivation protocol was used to determine the extent of residual noninactivating current. A conditioning prepulse to +20 mV demonstrated that some of these neurons exhibited only a sustained potassium current with little steady-state inactivation whereas others exhibited some combination of a sustained as well as a rapidly inactivating I A-type current. Treatment with 1 μM PGE2 or 1 μM CPGI2, but not 1 μM prostaglandin F2α (PGF2α) produced a time-dependent suppression of the total potassium current. After a 20-min exposure, PGE2 and CPGI2 inhibited the maximal current obtained at +60 mV by 48 and 40%, respectively. The prostaglandin-induced suppression of the potassium current was not associated with a shift in the voltage dependence for activation. Subtraction of the currents remaining after PGE2 or CPGI2 treatment from their respective control recordings revealed that the prostaglandin-sensitive current had characteristics that were consistent with a sustained-type of potassium current. This idea is supported by the following observation. The steady-state inactivation protocol revealed that for prepulse voltages activating both rapidly inactivating and sustained currents, the relaxation of the current was accelerated after treatment with PGE2 or CPGI2 suggesting the removal of a slower component. This effect was not observed in neurons exhibiting only the sustained type current. These results suggest that pro-inflammatory prostaglandins enhance the excitability of rat sensory neurons, in part, through the suppression of an outward potassium current that may modulate the firing threshold for generation of the action potential.

Calcineurin-independent inhibition of KV1.3 by FK-506 (tacrolimus): a novel pharmacological property

2007 ◽  
Vol 292 (5) ◽  
pp. C1714-C1722 ◽  
Author(s):  
Hye Sook Ahn ◽  
Sung Eun Kim ◽  
Bok Hee Choi ◽  
Jin-Sung Choi ◽  
Myung-Jun Kim ◽  
...  
Keyword(s):  
Steady State ◽  
Chinese Hamster Ovary Cells ◽  
Dependent Manner ◽  
Patch Clamp Technique ◽  
Concentration Dependent Manner ◽  
Fk 506 ◽  
Inactivation Curve ◽  
Voltage Dependent ◽  
Dependent Inhibition ◽  
Steady State Inactivation

The interaction of FK-506 with KV1.3, stably expressed in Chinese hamster ovary cells, was investigated with the whole cell patch-clamp technique. FK-506 inhibited KV1.3 in a reversible, concentration-dependent manner with an IC50 of 5.6 μM. Rapamycin, another immunosuppressant, produced effects that were similar to those of FK-506 (IC50 = 6.7 μM). Other calcineurin inhibitors (cypermethrin or calcineurin autoinhibitory peptide) alone had no effect on the amplitude or kinetics of KV1.3. In addition, the inhibitory action of FK-506 continued, even after the inhibition of calcineurin activity. The inhibition produced by FK-506 was voltage dependent, increasing in the voltage range for channel activation. At potentials positive to 0 mV (where maximal conductance is reached), however, no voltage-dependent inhibition was found. FK-506 exhibited a strong use-dependent inhibition of KV1.3. FK-506 shifted the steady-state inactivation curves of KV1.3 in the hyperpolarizing direction in a concentration-dependent manner. The apparent dissociation constant for FK-506 to inhibit KV1.3 in the inactivated state was estimated from the concentration-dependent shift in the steady-state inactivation curve and was calculated to be 0.37 μM. Moreover, the rate of recovery from inactivation of KV1.3 was decreased. In inside-out patches, FK-506 not only reduced the current amplitude but also accelerated the rate of inactivation during depolarization. FK-506 also inhibited KV1.5 and KV4.3 in a concentration-dependent manner with IC50 of 4.6 and 53.9 μM, respectively. The present results indicate that FK-506 inhibits KV1.3 directly and that this effect is not mediated via the inhibition of the phosphatase activity of calcineurin.

Inhibition of metabolism abolishes transient outward current in rabbit atrial myocytes

1994 ◽  
Vol 266 (1) ◽  
pp. H182-H190 ◽  
Author(s):  
A. Ogbaghebriel ◽  
A. Shrier
Keyword(s):  
Steady State ◽  
Patch Clamp ◽  
Potassium Current ◽  
Outward Current ◽  
Transient Outward Current ◽  
Atrial Myocytes ◽  
Patch Clamp Technique ◽  
Outward Currents ◽  
Inward Currents ◽  
Inhibition Of Metabolism

Outward currents were measured in single rabbit atrial myocytes using the whole cell configuration of the patch-clamp technique in the presence of tetrodotoxin (5–10 microM) and MnCl2 (2 mM) to block inward currents. Depolarizing voltage-clamp steps from a holding potential of -80 mV elicited a predominant 4-aminopyridine (4-AP)-sensitive transient outward current (Ito). Inhibitors of oxidative metabolism, 2,4-dinitrophenol (DNP; 100 microM) and cyanide (3 mM) abolished Ito and caused a large increase in the steady-state outward current. This steady-state outward current was inhibited by glibenclamide (5 microM), a blocker of the ATP-regulated potassium current (IKATP). In the presence of DNP, glibenclamide (5 microM) not only inhibited IKATP but also partially restored Ito. Absence of ATP from the pipette produced effects on outward currents similar to those induced by DNP or cyanide. We conclude that metabolic inhibition abolishes Ito in rabbit atrial myocytes and suggest that ATP may be required for the activation of the channel.

scholarly journals Depressed transient outward potassium current density in catecholamine-depleted rat ventricular myocytes

2002 ◽  
Vol 282 (4) ◽  
pp. H1237-H1247 ◽  
Author(s):  
Gilles Bru-Mercier ◽  
Edith Deroubaix ◽  
Delphine Rousseau ◽  
Alain Coulombe ◽  
Jean-François Renaud
Keyword(s):  
Potassium Current ◽  
Ventricular Myocytes ◽  
Cell Voltage ◽  
Wistar Rat ◽  
Perfused Heart ◽  
Transient Outward Potassium Current ◽  
Rat Ventricular Myocytes ◽  
Control Value ◽  
Steady State Inactivation ◽  
Outward Potassium Current

The effect of catecholamine depletion (induced by prior treatment with reserpine) was studied in Wistar rat ventricular myocytes using whole cell voltage-clamp methods. Two calcium-independent outward currents, the transient outward potassium current ( I to) and the sustained outward potassium current ( I sus), were measured. Reserpine treatment decreased tissue norepinephrine content by 97%. Action potential duration in the isolated perfused heart was significantly increased in reserpine-treated hearts. In isolated ventricular myocytes, I to density was decreased by 49% in reserpine-treated rats. This treatment had no effect on I sus. The I tosteady-state inactivation-voltage relationship and recovery from inactivation remained unchanged, whereas the conductance-voltage activation curve for reserpine-treated rats was significantly shifted (6.7 mV) toward negative potentials. The incubation of myocytes with 10 μM norepinephrine for 7–10 h restored I to, an effect that was abolished by the presence of actinomycin D. Norepinephrine (0.5 μM) had no effect on I to. However, in the presence of both 0.5 μM norepinephrine and neuropeptide Y (0.1 μM), I to density was restored to its control value. These results suggest that the sympathetic nervous system is involved in I to regulation. Sympathetic norepinephrine depletion decreased the number of functional channels via an effect on the α-adrenergic cascade and norepinephrine is able to restore expression of I to channels.

Ionic currents in hair cells dissociated from frog semicircular canals after preconditioning under microgravity conditions

2009 ◽  
Vol 296 (5) ◽  
pp. R1585-R1597 ◽  
Author(s):  
Marta Martini ◽  
Rita Canella ◽  
Alessandro Leparulo ◽  
Ivo Prigioni ◽  
Riccardo Fesce ◽  
...  
Keyword(s):  
Steady State ◽  
Hair Cells ◽  
Potassium Current ◽  
Time Course ◽  
Calcium Influx ◽  
Current System ◽  
Patch Clamp Technique ◽  
Inactivation Curve ◽  
Steady State Inactivation ◽  
Microgravity Conditions

The effects of microgravity on the biophysical properties of frog labyrinthine hair cells have been examined by analyzing calcium and potassium currents in isolated cells by the patch-clamp technique. The entire, anesthetized frog was exposed to vector-free gravity in a random positioning machine (RPM) and the functional modification induced on single hair cells, dissected from the crista ampullaris, were subsequently studied in vitro. The major targets of microgravity exposure were the calcium/potassium current system and the kinetic mechanism of the fast transient potassium current, IA. The amplitude of ICa was significantly reduced in microgravity-conditioned cells. The delayed current, IKD (a complex of IKV and IKCa), was drastically reduced, mostly in its IKCa component. Microgravity also affected IKD kinetics by shifting the steady-state inactivation curve toward negative potentials and increasing the sensitivity of inactivation removal to voltage. As concerns the IA, the I- V and steady-state inactivation curves were indistinguishable under normogravity or microgravity conditions; conversely, IA decay systematically displayed a two-exponential time course and longer time constants in microgravity, thus potentially providing a larger K+ charge; furthermore, IA inactivation removal at −70 mV was slowed down. Stimulation in the RPM machine under normogravity conditions resulted in minor effects on IKD and, occasionally, incomplete IA inactivation at −40 mV. Reduced calcium influx and increased K+ repolarizing charge, to variable extents depending on the history of membrane potential, constitute a likely cause for the failure in the afferent mEPSP discharge at the cytoneural junction observed in the intact labyrinth after microgravity conditioning.

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