Influence of L-type Ca channel alpha 2/delta-subunit on ionic and gating current in transiently transfected HEK 293 cells

We have measured ionic and gating currents in human embryonic kidney (HEK 293) cells transiently transfected with cDNAs encoding subunits of the cardiac voltage-gated L-type Ca2+ channel. Robust recombinant ionic current and associated nonlinear charge movement could be measured over a broad voltage range without contamination by endogenous channel activity. Coexpression of the alpha 2/delta-subunit along with alpha 1- and beta 2-subunits speeded activation and deactivation kinetics and significantly increased the maximal conductance of ionic current. Charge movement was measured at voltages negative to the threshold for activation of ionic current, and gating charge could be immobilized at positive holding potentials that did not inactivate ionic current. The ratio of maximal ionic conductance to maximal charge moved remained the same in the absence or presence of the alpha 2/delta-subunit. However, the maximal amount of charge moved was increased about twofold in the presence of the alpha 2/delta-subunit. These results suggest that coexpression of the alpha 2/delta-subunit enhances the expression of functional L-type channels and, in addition, provide evidence that most of the L-type channel-associated nonlinear charge movement is caused by transitions between nonconducting states of the channel protein that precede the open and inactivated states.

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Intramembrane Charge Movement Associated with Endogenous K+Channel Activity in HEK-293 Cells

Cellular and Molecular Neurobiology ◽

10.1023/b:cemn.0000022765.52109.26 ◽

2004 ◽

Vol 24 (3) ◽

pp. 317-330 ◽

Cited By ~ 48

Author(s):

Guillermo Avila ◽

Alejandro Sandoval ◽

Ricardo Felix

Keyword(s):

K Channel ◽

Charge Movement ◽

Channel Activity ◽

Hek 293 ◽

Hek 293 Cells ◽

293 Cells ◽

Intramembrane Charge Movement

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Voltage-dependent facilitation of cardiac L-type Ca channels expressed in HEK-293 cells requires β-subunit

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.2000.278.1.h126 ◽

2000 ◽

Vol 278 (1) ◽

pp. H126-H136 ◽

Cited By ~ 15

Author(s):

Timothy J. Kamp ◽

Hai Hu ◽

Eduardo Marban

Keyword(s):

G Protein ◽

Somatostatin Receptors ◽

Ca Channel ◽

Β Subunit ◽

Ca Channels ◽

Hek 293 ◽

Hek 293 Cells ◽

Protein Inhibition ◽

293 Cells ◽

Voltage Dependent

The activity of native L-type Ca channels can be facilitated by strong depolarizations. The cardiac Ca channel α1C-subunit was transiently expressed in human embryonic kidney (HEK-293) cells, but these channels did not exhibit voltage-dependent facilitation. Coexpression of the Ca channel β1a- or β2a-subunit with the α1C-subunit enabled voltage-dependent facilitation in 40% of cells tested. The onset of facilitation in α1C + β1a-expressing HEK-293 cells was rapid after a depolarization to +100 mV (τ = 7.0 ms). The kinetic features of the facilitated currents were comparable to those observed for voltage-dependent relief of G protein inhibition demonstrated for many neuronal Ca channels; however, intracellular dialysis with guanosine 5′- O-(2-thiodiphosphate) and guanosine 5′- O-(3-thiotriphosphate) in the patch pipette had no effect on facilitation. Stimulation of G protein-coupled receptors, either endogenous (somatostatin receptors) or coexpressed (adenosine A1receptors), did not affect voltage-dependent facilitation. These results indicate that the cardiac Ca channel α1C-subunit can exhibit voltage-dependent facilitation in HEK-293 cells only when coexpressed with an auxiliary β-subunit and that this facilitation is independent of G protein pathways.

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Isolation of myocardial L-type calcium channel gating currents with the spider toxin omega-Aga-IIIA.

The Journal of General Physiology ◽

10.1085/jgp.103.5.731 ◽

1994 ◽

Vol 103 (5) ◽

pp. 731-753 ◽

Cited By ~ 14

Author(s):

E A Ertel ◽

M M Smith ◽

M D Leibowitz ◽

C J Cohen

Keyword(s):

Guinea Pig ◽

Time Course ◽

Slow Component ◽

Ionic Current ◽

Reversal Potential ◽

Ca Channel ◽

Ca Channels ◽

Gating Currents ◽

Voltage Range ◽

Charge Movements

The peptide omega-agatoxin-IIIA (omega-Aga-IIIA) blocks ionic current through L-type Ca channels in guinea pig atrial cells without affecting the associated gating currents. omega-Aga-IIIA permits the study of L-type Ca channel ionic and gating currents under nearly identical ionic conditions. Under conditions that isolate L-type Ca channel currents, omega-Aga-IIIA blocks all ionic current during a test pulse and after repolarization. This block reveals intramembrane charge movements of equal magnitude and opposite sign at the beginning of the pulse (Q(on)) and after repolarization (Q(off)). Q(on) and Q(off) are suppressed by 1 microM felodipine, saturate with increasing test potential, and are insensitive to Cd. The decay of the transient current associated with Q(on) is composed of fast and slow exponential components. The slow component has a time constant similar to that for activation of L-type Ca channel ionic current, over a broad voltage range. The current associated with Q(off) decays monoexponentially and more slowly than ionic current. Similar charge movements are found in guinea pig tracheal myocytes, which lack Na channels and T-type Ca channels. The kinetic and pharmacological properties of Q(on) and Q(off) indicate that they reflect gating currents associated with L-type Ca channels. omega-Aga-IIIA has no effect on gating currents when ionic current is eliminated by stepping to the reversal potential for Ca or by Cd block. Gating currents constitute a significant component of total current when physiological concentrations of Ca are present and they obscure the activation and deactivation of L-type Ca channels. By using omega-Aga-IIIA, we resolve the entire time course of L-type Ca channel ionic and gating currents. We also show that L- and T-type Ca channel ionic currents can be accurately quantified by tail current analysis once gating currents are taken into account.

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Characteristics and requirements of basal autophagy in HEK 293 cells

Autophagy ◽

10.4161/auto.25455 ◽

2013 ◽

Vol 9 (9) ◽

pp. 1407-1417 ◽

Cited By ~ 41

Author(s):

Patience Musiwaro ◽

Matthew Smith ◽

Maria Manifava ◽

Simon A. Walker ◽

Nicholas T. Ktistakis

Keyword(s):

Hek 293 ◽

Hek 293 Cells ◽

293 Cells

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Correlation between Charge Movement and Ionic Current during Slow Inactivation in Shaker K+ Channels

The Journal of General Physiology ◽

10.1085/jgp.110.5.579 ◽

1997 ◽

Vol 110 (5) ◽

pp. 579-589 ◽

Cited By ~ 146

Author(s):

Riccardo Olcese ◽

Ramón Latorre ◽

Ligia Toro ◽

Francisco Bezanilla ◽

Enrico Stefani

Keyword(s):

Time Course ◽

Voltage Dependence ◽

Ionic Current ◽

K Channel ◽

Charge Movement ◽

Slow Inactivation ◽

Gating Currents ◽

Similar Time ◽

K Channels ◽

Recovery From Inactivation

Prolonged depolarization induces a slow inactivation process in some K+ channels. We have studied ionic and gating currents during long depolarizations in the mutant Shaker H4-Δ(6–46) K+ channel and in the nonconducting mutant (Shaker H4-Δ(6–46)-W434F). These channels lack the amino terminus that confers the fast (N-type) inactivation (Hoshi, T., W.N. Zagotta, and R.W. Aldrich. 1991. Neuron. 7:547–556). Channels were expressed in oocytes and currents were measured with the cut-open-oocyte and patch-clamp techniques. In both clones, the curves describing the voltage dependence of the charge movement were shifted toward more negative potentials when the holding potential was maintained at depolarized potentials. The evidences that this new voltage dependence of the charge movement in the depolarized condition is associated with the process of slow inactivation are the following: (a) the installation of both the slow inactivation of the ionic current and the inactivation of the charge in response to a sustained 1-min depolarization to 0 mV followed the same time course; and (b) the recovery from inactivation of both ionic and gating currents (induced by repolarizations to −90 mV after a 1-min inactivating pulse at 0 mV) also followed a similar time course. Although prolonged depolarizations induce inactivation of the majority of the channels, a small fraction remains non–slow inactivated. The voltage dependence of this fraction of channels remained unaltered, suggesting that their activation pathway was unmodified by prolonged depolarization. The data could be fitted to a sequential model for Shaker K+ channels (Bezanilla, F., E. Perozo, and E. Stefani. 1994. Biophys. J. 66:1011–1021), with the addition of a series of parallel nonconducting (inactivated) states that become populated during prolonged depolarization. The data suggest that prolonged depolarization modifies the conformation of the voltage sensor and that this change can be associated with the process of slow inactivation.

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Halothane Inhibition of Recombinant Cardiac L-type Ca2+ Channels Expressed in HEK-293 Cells

Anesthesiology ◽

10.1097/00000542-200512000-00009 ◽

2005 ◽

Vol 103 (6) ◽

pp. 1156-1166 ◽

Cited By ~ 7

Author(s):

Kevin J. Gingrich ◽

Son Tran ◽

Igor M. Nikonorov ◽

Thomas J. Blanck

Keyword(s):

Charge Transfer ◽

Calcium Channels ◽

Dependent Manner ◽

Current Time ◽

Hek 293 ◽

Hek 293 Cells ◽

293 Cells ◽

Dependent Inactivation ◽

Voltage Dependent

Background Volatile anesthetics depress cardiac contractility, which involves inhibition of cardiac L-type calcium channels. To explore the role of voltage-dependent inactivation, the authors analyzed halothane effects on recombinant cardiac L-type calcium channels (alpha1Cbeta2a and alpha1Cbeta2aalpha2/delta1), which differ by the alpha2/delta1 subunit and consequently voltage-dependent inactivation. Methods HEK-293 cells were transiently cotransfected with complementary DNAs encoding alpha1C tagged with green fluorescent protein and beta2a, with and without alpha2/delta1. Halothane effects on macroscopic barium currents were recorded using patch clamp methodology from cells expressing alpha1Cbeta2a and alpha1Cbeta2aalpha2/delta1 as identified by fluorescence microscopy. Results Halothane inhibited peak current (I(peak)) and enhanced apparent inactivation (reported by end pulse current amplitude of 300-ms depolarizations [I300]) in a concentration-dependent manner in both channel types. alpha2/delta1 coexpression shifted relations leftward as reported by the 50% inhibitory concentration of I(peak) and I300/I(peak)for alpha1Cbeta2a (1.8 and 14.5 mm, respectively) and alpha1Cbeta2aalpha2/delta1 (0.74 and 1.36 mm, respectively). Halothane reduced transmembrane charge transfer primarily through I(peak) depression and not by enhancement of macroscopic inactivation for both channels. Conclusions The results indicate that phenotypic features arising from alpha2/delta1 coexpression play a key role in halothane inhibition of cardiac L-type calcium channels. These features included marked effects on I(peak) inhibition, which is the principal determinant of charge transfer reductions. I(peak) depression arises primarily from transitions to nonactivatable states at resting membrane potentials. The findings point to the importance of halothane interactions with states present at resting membrane potential and discount the role of inactivation apparent in current time courses in determining transmembrane charge transfer.

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