scholarly journals Slc7a5 alters Kvβ-mediated regulation of Kv1.2

2020 ◽  
Vol 152 (7) ◽  
Author(s):  
Shawn M. Lamothe ◽  
Harley T. Kurata
Keyword(s):  
Neuronal Excitability ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Extrinsic Factors ◽  
Neutral Amino Acid Transporter ◽  
Recovery From Inactivation ◽  
Steady State Inactivation ◽  
Accessory Subunit ◽  
Delayed Recovery ◽  
Hyperpolarizing Shift

The voltage-gated potassium channel Kv1.2 plays a pivotal role in neuronal excitability and is regulated by a variety of known and unknown extrinsic factors. The canonical accessory subunit of Kv1.2, Kvβ, promotes N-type inactivation and cell surface expression of the channel. We recently reported that a neutral amino acid transporter, Slc7a5, alters the function and expression of Kv1.2. In the current study, we investigated the effects of Slc7a5 on Kv1.2 in the presence of Kvβ1.2 subunits. We observed that Slc7a5-induced suppression of Kv1.2 current and protein expression was attenuated with cotransfection of Kvβ1.2. However, gating effects mediated by Slc7a5, including disinhibition and a hyperpolarizing shift in channel activation, were observed together with Kvβ-mediated inactivation, indicating convergent regulation of Kv1.2 by both regulatory proteins. Slc7a5 influenced several properties of Kvβ-induced inactivation of Kv1.2, including accelerated inactivation, a hyperpolarizing shift and greater extent of steady-state inactivation, and delayed recovery from inactivation. These modified inactivation properties were also apparent in altered deactivation of the Kv1.2/Kvβ/Slc7a5 channel complex. Taken together, these findings illustrate a functional interaction arising from simultaneous regulation of Kv1.2 by Kvβ and Slc7a5, leading to powerful effects on Kv1.2 expression, gating, and overall channel function.

scholarly journals Decreased neuronal excitability in hippocampal neurons of mice exposed to cyclic hypoxia

2001 ◽  
Vol 91 (3) ◽  
pp. 1245-1250 ◽  
Author(s):  
Xiang Q. Gu ◽  
Gabriel G. Haddad
Keyword(s):  
Membrane Potential ◽  
Hippocampal Neurons ◽  
Neuronal Excitability ◽  
Resting Membrane Potential ◽  
Ca1 Neurons ◽  
Recovery From Inactivation ◽  
Channel Expression ◽  
Steady State Inactivation ◽  
And Function

To study the physiological effects of chronic intermittent hypoxia on neuronal excitability and function in mice, we exposed animals to cyclic hypoxia for 8 h daily (12 cycles/h) for ∼4 wk, starting at 2–3 days of age, and examined the properties of freshly dissociated hippocampal neurons in vitro. Compared with control (Con) hippocampal CA1 neurons, exposed (Cyc) neurons showed action potentials (AP) with a smaller amplitude and a longer duration and a more depolarized resting membrane potential. They also have a lower rate of spontaneous firing of AP and a higher rheobase. Furthermore, there was downregulation of the Na+ current density in Cyc compared with Con neurons (356.09 ± 54.03 pA/pF in Cyc neurons vs. 508.48 ± 67.30 pA/pF in Con, P < 0.04). Na+ channel characteristics, including activation, steady-state inactivation, and recovery from inactivation, were similar in both groups. The deactivation rate, however, was much larger in Cyc than in Con (at −100 mV, time constant for deactivation = 0.37 ± 0.04 ms in Cyc neurons and 0.18 ± 0.01 ms in Con neurons). We conclude that the decreased neuronal excitability in mice neurons treated with cyclic hypoxia is due, at least in part, to differences in passive properties (e.g., resting membrane potential) and in Na+ channel expression and/or regulation. We hypothesize that this decreased excitability is an adaptive response that attempts to decrease the energy expenditure that is used for adjusting disturbances in ionic homeostasis in low-O2conditions.

scholarly journals Calmodulin Regulation of NaV1.4 Current: Role of Binding to the Carboxyl Terminus

2008 ◽  
Vol 131 (3) ◽  
pp. 197-209 ◽  
Author(s):  
Subrata Biswas ◽  
Isabelle Deschênes ◽  
Deborah DiSilvestre ◽  
Yanli Tian ◽  
Victoria L. Halperin ◽  
...  
Keyword(s):  
Mammalian Cells ◽  
Surface Membrane ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Na Channel ◽  
Na Current ◽  
Iq Motif ◽  
C Terminus ◽  
Steady State Inactivation ◽  
And Function

Calmodulin (CaM) regulates steady-state inactivation of sodium currents (NaV1.4) in skeletal muscle. Defects in Na current inactivation are associated with pathological muscle conditions such as myotonia and paralysis. The mechanisms of CaM modulation of expression and function of the Na channel are incompletely understood. A physical association between CaM and the intact C terminus of NaV1.4 has not previously been demonstrated. FRET reveals channel conformation-independent association of CaM with the C terminus of NaV1.4 (CT-NaV1.4) in mammalian cells. Mutation of the NaV1.4 CaM-binding IQ motif (NaV1.4IQ/AA) reduces cell surface expression of NaV1.4 channels and eliminates CaM modulation of gating. Truncations of the CT that include the IQ region abolish Na current. NaV1.4 channels with one CaM fused to the CT by variable length glycine linkers exhibit CaM modulation of gating only with linker lengths that allowed CaM to reach IQ region. Thus one CaM is sufficient to modulate Na current, and CaM acts as an ancillary subunit of NaV1.4 channels that binds to the CT in a conformation-independent fashion, modulating the voltage dependence of inactivation and facilitating trafficking to the surface membrane.

Chronic High-Inspired CO2 Decreases Excitability of Mouse Hippocampal Neurons

2007 ◽  
Vol 97 (2) ◽  
pp. 1833-1838 ◽  
Author(s):  
Xiang Q. Gu ◽  
Amjad Kanaan ◽  
Hang Yao ◽  
Gabriel G. Haddad
Keyword(s):  
Hippocampal Neurons ◽  
Neuronal Excitability ◽  
Input Resistance ◽  
Resting Membrane Potential ◽  
Channel Current ◽  
Conductance Curve ◽  
Recovery From Inactivation ◽  
Channel Expression ◽  
Steady State Inactivation ◽  
And Function

To examine the effect of chronically elevated CO2 on excitability and function of neurons, we exposed mice to 8 and 12% CO2 for 4 wk (starting at 2 days of age), and examined the properties of freshly dissociated hippocampal neurons obtained from slices. Chronic CO2-treated neurons (CC) had a similar input resistance ( Rm) and resting membrane potential ( Vm) as control (CON). Although treatment with 8% CO2 did not change the rheobase (64 ± 11 pA, n = 9 vs. 47 ± 12 pA, n = 8 for CC 8% vs. CON; means ± SE), 12% CO2 treatment increased it significantly (73 ± 8 pA, n = 9, P = 0.05). Furthermore, the 12% CO2 but not the 8% CO2 treatment decreased the Na+ channel current density (244 ± 36 pA/pF, n = 17, vs. 436 ± 56 pA/pF, n = 18, for CC vs. CON, P = 0.005). Recovery from inactivation was also lowered by 12% but not 8% CO2. Other gating properties of Na+ current, such as voltage-conductance curve, steady-state inactivation, and time constant for deactivation, were not modified by either treatment. Western blot analysis showed that the expression of Na+ channel types I–III was not changed by 8% CO2 treatment, but their expression was significantly decreased by 20–30% ( P = 0.03) by the 12% treatment. We conclude from these data and others that neuronal excitability and Na+ channel expression depend on the duration and level of CO2 exposure and maturational changes occur in early life regarding neuronal responsiveness to CO2.

scholarly journals Secretory carrier-associated membrane protein 2 (SCAMP2) regulates cell surface expression of T-type calcium channels

2022 ◽  
Vol 15 (1) ◽  
Author(s):  
Leos Cmarko ◽  
Robin N. Stringer ◽  
Bohumila Jurkovicova-Tarabova ◽  
Tomas Vacik ◽  
Lubica Lacinova ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Cell Surface ◽  
Mammalian Cells ◽  
Neuronal Excitability ◽  
Low Voltage ◽  
Activity Patterns ◽  
Surface Expression ◽  
Single Amino Acid ◽  
Cell Surface Expression ◽  
Charge Movement

AbstractLow-voltage-activated T-type Ca2+ channels are key regulators of neuronal excitability both in the central and peripheral nervous systems. Therefore, their recruitment at the plasma membrane is critical in determining firing activity patterns of nerve cells. In this study, we report the importance of secretory carrier-associated membrane proteins (SCAMPs) in the trafficking regulation of T-type channels. We identified SCAMP2 as a novel Cav3.2-interacting protein. In addition, we show that co-expression of SCAMP2 in mammalian cells expressing recombinant Cav3.2 channels caused an almost complete drop of the whole cell T-type current, an effect partly reversed by single amino acid mutations within the conserved cytoplasmic E peptide of SCAMP2. SCAMP2-induced downregulation of T-type currents was also observed in cells expressing Cav3.1 and Cav3.3 channel isoforms. Finally, we show that SCAMP2-mediated knockdown of the T-type conductance is caused by the lack of Cav3.2 expression at the cell surface as evidenced by the concomitant loss of intramembrane charge movement without decrease of total Cav3.2 protein level. Taken together, our results indicate that SCAMP2 plays an important role in the trafficking of Cav3.2 channels at the plasma membrane.

scholarly journals Independent Versus Coupled Inactivation in Sodium Channels

1998 ◽  
Vol 111 (3) ◽  
pp. 451-462 ◽  
Author(s):  
Nenad Mitrovic ◽  
Alfred L. George ◽  
Richard Horn
Keyword(s):  
Steady State ◽  
Peak Current ◽  
Recovery From Inactivation ◽  
Current Voltage ◽  
Steady State Inactivation ◽  
Kinetics Of ◽  
Current Voltage Relationship ◽  
Hyperpolarizing Shift ◽  
S4 Segment ◽  
Positively Charged

The voltage sensor of the sodium channel is mainly comprised of four positively charged S4 segments. Depolarization causes an outward movement of S4 segments, and this movement is coupled with opening of the channel. A mutation that substitutes a cysteine for the outermost arginine in the S4 segment of the second domain (D2:R1C) results in a channel with biophysical properties similar to those of wild-type channels. Chemical modification of this cysteine with methanethiosulfonate-ethyltrimethylammonium (MTSET) causes a hyperpolarizing shift of both the peak current–voltage relationship and the kinetics of activation, whereas the time constant of inactivation is not changed substantially. A conventional steady state inactivation protocol surprisingly produces an increase of the peak current at −20 mV when the 300-ms prepulse is depolarized from −190 to −110 mV. Further depolarization reduces the current, as expected for steady state inactivation. Recovery from inactivation in modified channels is also nonmonotonic at voltages more hyperpolarized than −100 mV. At −180 mV, for example, the amplitude of the recovering current is briefly almost twice as large as it was before the channels inactivated. These data can be explained readily if MTSET modification not only shifts the movement of D2/S4 to more hyperpolarized potentials, but also makes the movement sluggish. This behavior allows inactivation to have faster kinetics than activation, as in the HERG potassium channel. Because of the unique properties of the modified mutant, we were able to estimate the voltage dependence and kinetics of the movement of this single S4 segment. The data suggest that movement of modified D2/S4 is a first-order process and that rate constants for outward and inward movement are each exponential functions of membrane potential. Our results show that D2/S4 is intimately involved with activation but plays little role in either inactivation or recovery from inactivation.

scholarly journals Increased neuronal excitability and seizures in the Na+/H+ exchanger null mutant mouse

2001 ◽  
Vol 281 (2) ◽  
pp. C496-C503 ◽  
Author(s):  
Xiang Q. Gu ◽  
Hang Yao ◽  
Gabriel G. Haddad
Keyword(s):  
Neuronal Excitability ◽  
Neurological Diseases ◽  
Seizure Disorder ◽  
Motor Deficits ◽  
Wild Type ◽  
Ca1 Neurons ◽  
Recovery From Inactivation ◽  
Hippocampal Ca1 ◽  
Channel Expression ◽  
Steady State Inactivation

Mice lacking the Na+/H+ exchanger isoform 1 (NHE1) manifest neurological diseases that include ataxia, motor deficits, and a seizure disorder. The molecular basis for the phenotype has not been clear, and it has not been determined how the lack of NHE1 leads, in particular, to the seizure disorder. We have shown in this work that hippocampal CA1 neurons in mutant mice have a much higher excitability than in wild-type mice. This higher excitability is partly based on an upregulation of the Na+ current density (608.2 ± 123.2 pA/pF in NHE1 mutant vs. 334.7 ± 63.7 pA/pF in wild type in HCO[Formula: see text]/CO2). Alterations in Na+channel characteristics, including steady-state inactivation (shift of 18 mV in the depolarization direction in the mutant), recovery from inactivation (τh = 5.22 ± 0.49 ms in wild-type neurons and 2.20 ± 0.20 ms in mutant neurons), and deactivation (at −100 mV, τd = 1.75 ± 0.53 ms in mutant and 0.21 ± 0.05 ms in wild-type neurons) further enhance the differences in excitability between mutant and wild-type mice. Our investigation demonstrates the existence of an important functional interaction between the NHE1 protein and the voltage-sensitive Na+ channel. We hypothesize that the increased neuronal excitability and possibly the seizure disorder in mice lacking the NHE1 is due, at least in part, to changes in Na+ channel expression and/or regulation.

Increased Expression of u-PA and u-PAR on Monocytes by LDL and Lp(a) Lipoproteins – Consequences for Plasmin Generation and Monocyte Adhesion

1999 ◽  
Vol 81 (04) ◽  
pp. 594-560 ◽  
Author(s):  
Florence Ganné ◽  
Marc Vasse ◽  
Jean-Louis Beaudeu ◽  
Jacqueline Peynet ◽  
Arnaud François ◽  
...  
Keyword(s):  
Fold Increase ◽  
Surface Expression ◽  
Cell Surface Expression ◽  
Atheromatous Plaque ◽  
Monocyte Adhesion ◽  
Blood Monocytes ◽  
Proteolytic Cascade ◽  
Ecm Degradation ◽  
Dose Dependent Increase ◽  
Dose Dependent

SummaryMonocyte-derived foam cells figure prominently in rupture-prone regions of atherosclerotic plaque. As urokinase/urokinase-receptor (u-PA/u-PAR) is the trigger of a proteolytic cascade responsible for ECM degradation, we have examined the effect of atherogenic lipoproteins on monocyte surface expression of u-PAR and u-PA. Peripheral blood monocytes, isolated from 10 healthy volunteers, were incubated with 10 to 200 µg/ml of native or oxidised (ox-) atherogenous lipoproteins for 18 h and cell surface expression of u-PA and u-PAR was analysed by flow cytometry. Both LDL and Lp(a) induced a dose-dependent increase in u-PA (1.6-fold increase with 200 μg/ml of ox-LDL) and u-PAR [1.7-fold increase with 200 μg/ml of ox-Lp(a)]. There is a great variability of the response among the donors, some of them remaining non-responders (absence of increase of u-PA or u-PAR) even at 200 μg/ml of lipoproteins. In positive responders, enhanced u-PA/u-PAR is associated with a significant increase of plasmin generation (1.9-fold increase with 200 μg/ml of ox-LDL), as determined by an amidolytic assay. Furthermore, monocyte adhesion to vitronectin and fibrinogen was significantly enhanced by the lipoproteins [respectively 2-fold and 1.7-fold increase with 200 μg/ml of ox-Lp(a)], due to the increase of u-PAR and ICAM-1, which are receptors for vitronectin and fibrinogen. These data suggest that atherogenous lipoproteins could contribute to the development of atheromatous plaque by increasing monocyte adhesion and trigger plaque weakening by inducing ECM degradation.

Sign in / Sign up

Export Citation Format

Share Document