Voltage-gated potassium channel Kv1.3 regulates GLUT4 trafficking to the plasma membrane via a Ca2+-dependent mechanism

2006 ◽  
Vol 290 (2) ◽  
pp. C345-C351 ◽  
Author(s):  
Yanyan Li ◽  
Peili Wang ◽  
Jianchao Xu ◽  
Gary V. Desir
Keyword(s):  
Plasma Membrane ◽  
Insulin Sensitivity ◽  
Protein Translocation ◽  
Channel Activity ◽  
Voltage Gated ◽  
White Adipocytes ◽  
Kv1.3 Channel ◽  
Channel Inhibition ◽  
Intracellular Ca ◽  
Insulin Dependent

Kv1.3 is a voltage-gated K+ channel expressed in insulin-sensitive tissues. We previously showed that gene inactivation or pharmacological inhibition of Kv1.3 channel activity increased peripheral insulin sensitivity independently of body weight by augmenting the amount of GLUT4 at the plasma membrane. In the present study, we further examined the effect Kv1.3 on GLUT4 trafficking and tested whether it occurred via an insulin-dependent pathway. We found that Kv1.3 inhibition by margatoxin (MgTX) stimulated glucose uptake in adipose tissue and skeletal muscle and that the effect of MgTX on glucose transport was additive to that of insulin. Furthermore, whereas the increase in uptake was wortmannin insensitive, it was completely inhibited by dantrolene, a blocker of Ca2+ release from intracellular Ca2+ stores. In white adipocytes in primary culture, channel inhibition by Psora-4 increased GLUT4 translocation to the plasma membrane. In these cells, GLUT4 protein translocation was unaffected by the addition of wortmannin but was significantly inhibited by dantrolene. Channel inhibition depolarized the membrane voltage and led to sustained, dantrolene-sensitive oscillations in intracellular Ca2+ concentration. These results indicate that the apparent increase in insulin sensitivity observed in association with inhibition of Kv1.3 channel activity is mediated by an increase in GLUT4 protein at the plasma membrane, which occurs largely through a Ca2+-dependent process.

scholarly journals CaV1.2 and CaV1.3 voltage-gated L-type Ca2+ channels in rat white fat adipocytes

2020 ◽  
Vol 244 (2) ◽  
pp. 369-381 ◽  
Author(s):  
Olena A Fedorenko ◽  
Pawitra Pulbutr ◽  
Elin Banke ◽  
Nneoma E Akaniro-Ejim ◽  
Donna C Bentley ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Confocal Microscopy ◽  
Therapeutic Benefit ◽  
Voltage Gated ◽  
Adult Rat ◽  
White Adipocytes ◽  
Intracellular Ca ◽  
Treatment Of Obesity ◽  
White Fat ◽  
Constitutively Active

L-type channel antagonists are of therapeutic benefit in the treatment of hyperlipidaemia and insulin resistance. Our aim was to identify L-type voltage-gated Ca2+ channels in white fat adipocytes, and determine if they affect intracellular Ca2+, lipolysis and lipogenesis. We used a multidisciplinary approach of molecular biology, confocal microscopy, Ca2+ imaging and metabolic assays to explore this problem using adipocytes isolated from adult rat epididymal fat pads. CaV1.2, CaV1.3 and CaV1.1 alpha1, beta and alpha2delta subunits were detected at the gene expression level. The CaV1.2 and CaV1.3 alpha1 subunits were identified in the plasma membrane at the protein level. Confocal microscopy with fluorescent antibodies labelled CaV1.2 in the plasma membrane. Ca2+ imaging revealed that the intracellular Ca2+ concentration, [Ca2 +]i was reversibly decreased by removal of extracellular Ca2+, an effect mimicked by verapamil, nifedipine and Co2+, all blockers of L-type channels, whereas the Ca2+ channel agonist BAY-K8644 increased [Ca2+]i. The finding that the magnitude of these effects correlated with basal [Ca2+]i suggests that adipocyte [Ca2+]i is controlled by L-type Ca2+ channels that are constitutively active at the adipocyte depolarized membrane potential. Pharmacological manipulation of L-type channel activity modulated both basal and catecholamine-stimulated lipolysis but not insulin-induced glucose uptake or lipogenesis. We conclude that white adipocytes have constitutively active L-type Ca2+ channels which explains their sensitivity of lipolysis to Ca2+ channel modulators. Our data suggest CaV1.2 as a potential novel therapeutic target in the treatment of obesity.

Cerebral artery KATP- and KCa-channel activity and contractility: changes with development

2000 ◽  
Vol 279 (6) ◽  
pp. R2004-R2014 ◽  
Author(s):  
Wen Long ◽  
Lubo Zhang ◽  
Lawrence D. Longo
Keyword(s):  
Channel Blocker ◽  
Cerebral Arteries ◽  
Dependent Manner ◽  
Channel Activity ◽  
Channel Opener ◽  
Channel Inhibition ◽  
Middle Cerebral Arteries ◽  
Intracellular Ca ◽  
Near Term ◽  
Nonpregnant Adult

The present study was designed to test the hypothesis that in cerebral arteries of the fetus, ATP-sensitive (KATP) and Ca2+-activated K+channels (KCa) play an important role in the regulation of intracellular Ca2+ concentration ([Ca2+]i) and that this differs significantly from that of the adult. In main branch middle cerebral arteries (MCA) from near-term fetal (∼140 days) and nonpregnant adult sheep, simultaneously we measured norepinephrine (NE)-induced responses of vascular tension and [Ca2+]i in the absence and presence of selective K+-channel openers/blockers. In fetal MCA, in a dose-dependent manner, both the KATP-channel opener pinacidil and the KCa-channel opener NS 1619 significantly inhibited NE-induced tension [negative logarithm of the half-maximal inhibitory concentration (pIC50) = 5.0 ± 0.1 and 8.2 ± 0.1, respectively], with a modest decrease of [Ca2+]i. In the adult MCA, in contrast, both pinacidil and NS 1619 produced a significant tension decrease (pIC50 = 5.1 ± 0.1 and 7.6 ± 0.1, respectively) with no change in [Ca2+]i. In addition, the KCa-channel blocker iberiotoxin (10−7 to 10−6 M) resulted in increased tension and [Ca2+]i in both adult and fetal MCA, although the KATP-channel blocker glibenclamide (10−7 to 3 × 10−5 M) failed to do so. Of interest, administration of 10−7 M iberiotoxin totally eliminated vascular contraction and increase in [Ca2+]i seen in response to 10−5M ryanodine. In precontracted fetal cerebral arteries, activation of the KATP and KCa channels significantly decreased both tension and [Ca2+]i, suggesting that both K+ channels play an important role in regulating L-type channel Ca2+ flux and therefore vascular tone in these vessels. In the adult, KATP and the KCa channels also appear to play an important role in this regard; however, in the adult vessel, activation of these channels with resultant vasorelaxation can occur with no significant change in [Ca2+]i. These channels show differing responses to inhibition, e.g., KCa-channel inhibition, resulting in increased tension and [Ca2+]i, whereas KATP-channel inhibition showed no such effect. In addition, the KCa channel appears to be coupled to the sarcoplasmic reticulum ryanodine receptor. Thus differences in plasma membrane K+-channel activity may account, in part, for the differences in the regulation of contractility of fetal and adult cerebral arteries.

Inhibition of voltage-gated K+ channels in dendritic cells by rapamycin

2010 ◽  
Vol 299 (6) ◽  
pp. C1379-C1385 ◽  
Author(s):  
Leonid Tyan ◽  
Mentor Sopjani ◽  
Miribane Dërmaku-Sopjani ◽  
Evi Schmid ◽  
Wenting Yang ◽  
...  
Keyword(s):  
Dendritic Cells ◽  
Xenopus Oocytes ◽  
Statistical Significance ◽  
Immunosuppressive Drug ◽  
Channel Activity ◽  
Voltage Gated ◽  
Kv Channel ◽  
Kv Channels ◽  
Channel Inactivation ◽  
Kv1.3 Channel

Rapamycin, an inhibitor of the serine/threonine kinase mammalian target of rapamycin (mTOR), is a widely used immunosuppressive drug. Rapamycin affects the function of dendritic cells (DCs), antigen-presenting cells participating in the initiation of primary immune responses and the establishment of immunological memory. Voltage-gated K+ (Kv) channels are expressed in and impact on the function of DCs. The present study explored whether rapamycin influences Kv channels in DCs. To this end, DCs were isolated from murine bone marrow and ion channel activity was determined by whole cell patch clamp. To more directly analyze an effect of mTOR on Kv channel activity, Kv1.3 and Kv1.5 were expressed in Xenopus oocytes with or without the additional expression of mTOR and voltage-gated currents were determined by dual-electrode voltage clamp. As a result, preincubation with rapamycin (0–50 nM) led to a gradual decline of Kv currents in DCs, reaching statistical significance within 6 h and 50 nM of rapamycin. Rapamycin accelerated Kv channel inactivation. Coexpression of mTOR upregulated Kv1.3 and Kv1.5 currents in Xenopus oocytes. Furthermore, mTOR accelerated Kv1.3 channel activation and slowed down Kv1.3 channel inactivation. In conclusion, mTOR stimulates Kv channels, an effect contributing to the immunomodulating properties of rapamycin in DCs.

Somatostatin peptides inhibit basolateral potassium channels in human colonic crypts

1999 ◽  
Vol 277 (5) ◽  
pp. G967-G975 ◽  
Author(s):  
Geoffrey I. Sandle ◽  
Geoffrey Warhurst ◽  
Ian Butterfield ◽  
Norman B. Higgs ◽  
Richard B. Lomax
Keyword(s):  
G Protein ◽  
Basolateral Membrane ◽  
Secretory Process ◽  
Synthetic Analog ◽  
Channel Activity ◽  
Patch Clamp Recording ◽  
Channel Inhibition ◽  
Colonic Crypts ◽  
Intracellular Ca ◽  
Dependent Mechanism

Somatostatin is a powerful inhibitor of intestinal Cl− secretion. We used patch-clamp recording techniques to investigate the effects of somatostatin on low-conductance (23-pS) K+ channels in the basolateral membrane of human colonic crypts, which are an important component of the Cl− secretory process. Somatostatin (2 μM) elicited a >80% decrease in “spontaneous” K+ channel activity in cell-attached patches in nonstimulated crypts (50% inhibition =∼8 min), which was voltage-independent and was prevented by pretreating crypts for 18 h with pertussis toxin (200 ng/ml), implicating a G protein-dependent mechanism. In crypts stimulated with 100–200 μM dibutyryl cAMP, 2 μM somatostatin and its synthetic analog octreotide (2 μM) both produced similar degrees of K+ channel inhibition to that seen in nonstimulated crypts, which was also present under low-Cl− (5 mM) conditions. In addition, 2 μM somatostatin abolished the increase in K+ channel activity stimulated by 2 μM thapsigargin but had no effect on the thapsigargin-stimulated rise in intracellular Ca2+. These results indicate that somatostatin peptides inhibit 23-pS basolateral K+ channels in human colonic crypt cells via a G protein-dependent mechanism, which may result in loss of the channel's inherent Ca2+sensitivity.

scholarly journals Disease-Linked Super-Trafficking of a Mutant Potassium Channel

2020 ◽  
Author(s):  
Hui Huang ◽  
Laura M. Chamness ◽  
Carlos G. Vanoye ◽  
Georg Kuenze ◽  
Jens Meiler ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Cell Surface ◽  
Potassium Channel ◽  
Single Channel ◽  
Channel Activity ◽  
Wild Type ◽  
Channel Activation ◽  
Voltage Gated ◽  
Disease Mutations ◽  
Single Channel Activity

ABSTRACTGain-of-function (GOF) mutations in the KCNQ1 voltage-gated potassium channel can induce cardiac arrhythmia. We tested whether any of the known GOF disease mutations in KCNQ1 act by increasing the amount of KCNQ1 that reaches the cell surface—“super-trafficking”. We found that levels of R231C KCNQ1 in the plasma membrane are 5-fold higher than wild type KCNQ1. This arises from both enhanced translocon-mediated membrane integration of the S4 voltage-sensor helix and an energetic linkage of C231 with the V129 and F166 side chains. Whole-cell electrophysiology recordings confirmed that R231C KCNQ1 in complex with KCNE1 is constitutively active, but also revealed the single channel activity of this mutant to be only 20% that of WT. The GOF phenotype associated with R231C therefore reflects the net effects of super-trafficking, reduced single channel activity, and constitutive channel activation. These investigations document membrane protein super-trafficking as a contributing mechanism to human disease.

Propofol and thiopental attenuate adenosine triphosphate-sensitive potassium channel relaxation in pulmonary veins

2006 ◽  
Vol 291 (4) ◽  
pp. L636-L643 ◽  
Author(s):  
Woon-Seok Roh ◽  
Xueqin Ding ◽  
Paul A. Murray
Keyword(s):  
Nitric Oxide ◽  
Adenosine Triphosphate ◽  
Pulmonary Veins ◽  
Inhibitory Effect ◽  
Cellular Mechanisms ◽  
Voltage Gated ◽  
Channel Inhibition ◽  
Dependent Component ◽  
Intracellular Ca ◽  
Oxide Synthase

Pulmonary veins (PV) make a significant contribution to total pulmonary vascular resistance. We investigated the cellular mechanisms by which the intravenous anesthetics propofol and thiopental alter adenosine triphosphate-sensitive potassium (KATP+) channel relaxation in canine PV. The effects of KATP+ channel inhibition (glybenclamide), cyclooxygenase inhibition (indomethacin), nitric oxide synthase inhibition (l-NAME), and L-type voltage-gated Ca2+ channel inhibition (nifedipine) on vasorelaxation responses to levcromakalim (KATP+ channel activator) alone and in combination with the anesthetics were assessed. The maximal relaxation response to levcromakalim was attenuated by removing the endothelium and by l-NAME, but not by indomethacin. Propofol (10−5, 3 × 10−5, and 10−4 M) and thiopental (10−4 and 3 × 10−4 M) each attenuated levcromakalim relaxation in endothelium-intact (E+) rings, whereas propofol (3 × 10−5 and 10−4 M) and thiopental (3 × 10−4 M) attenuated levcromakalim relaxation in endothelium-denuded (E−) rings. In E+ rings, the anesthesia-induced attenuation of levcromakalim relaxation was decreased after pretreatment with l-NAME but not with indomethacin. In E-strips, propofol (10−4 M) and thiopental (3 × 10−4 M) inhibited decreases in tension and intracellular Ca2+ concentration ([Ca2+]i) in response to levcromakalim, and these changes were abolished by nifedipine. These findings indicate that propofol and thiopental attenuate the endothelium-dependent component of KATP+ channel-induced PV vasorelaxation via an inhibitory effect on the nitric oxide pathway. Both anesthetics also attenuate the PV smooth muscle component of KATP+ channel-induced relaxation by reducing the levcromakalim-induced decrease in [Ca2+]i via an inhibitory effect on L-type voltage-gated Ca2+ channels.

scholarly journals Phosphatidylinositol 4,5-bisphosphate and loss of PLCγ activity inhibit TRPM channels required for oscillatory Ca2+ signaling

2010 ◽  
Vol 298 (2) ◽  
pp. C274-C282 ◽  
Author(s):  
Juan Xing ◽  
Kevin Strange
Keyword(s):  
Transient Receptor Potential ◽  
Single Channel ◽  
Receptor Activity ◽  
Intestinal Cell ◽  
Channel Activity ◽  
Open Probability ◽  
Channel Inhibition ◽  
Intracellular Ca ◽  
Hydrolysis Of ◽  
Trpm Channels

The Caenorhabditis elegans intestinal epithelium generates rhythmic inositol 1,4,5-trisphosphate (IP3)-dependent Ca2+ oscillations that control muscle contractions required for defecation. Two highly Ca2+-selective transient receptor potential (TRP) melastatin (TRPM) channels, GON-2 and GTL-1, function with PLCγ in a common signaling pathway that regulates IP3-dependent intracellular Ca2+ release. A second PLC, PLCβ, is also required for IP3-dependent Ca2+ oscillations, but functions in an independent signaling mechanism. PLCγ generates IP3 that regulates IP3 receptor activity. We demonstrate here that PLCγ via hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) also regulates GON-2/GTL-1 function. Knockdown of PLCγ but not PLCβ activity by RNA interference (RNAi) inhibits channel activity ∼80%. Inhibition is fully reversed by agents that deplete PIP2 levels. PIP2 added to the patch pipette has no effect on channel activity in PLCγ RNAi cells. However, in control cells, 10 μM PIP2 inhibits whole cell current ∼80%. Channel inhibition by phospholipids is selective for PIP2 with an IC50 value of 2.6 μM. Elevated PIP2 levels have no effect on channel voltage and Ca2+ sensitivity and likely inhibit by reducing channel open probability, single-channel conductance, and/or trafficking. We conclude that hydrolysis of PIP2 by PLCγ functions in the activation of both the IP3 receptor and GON-2/GTL-1 channels. GON-2/GTL-1 functions as the major intestinal cell Ca2+ influx pathway. Calcium influx through the channel feedback regulates its activity and likely functions to modulate IP3 receptor function. PIP2-dependent regulation of GON-2/GTL-1 may provide a mechanism to coordinate plasma membrane Ca2+ influx with PLCγ and IP3 receptor activity as well as intracellular Ca2+ store depletion.

scholarly journals The HOOK region of voltage-gated Ca2+ channel β subunits senses and transmits PIP2 signals to the gate

2017 ◽  
Vol 149 (2) ◽  
pp. 261-276 ◽  
Author(s):  
Cheon-Gyu Park ◽  
Yongsoo Park ◽  
Byung-Chang Suh
Keyword(s):  
Amino Acids ◽  
Plasma Membrane ◽  
Binding Assay ◽  
Channel Gating ◽  
Inactivation Kinetics ◽  
Β Subunit ◽  
Voltage Gated ◽  
Anionic Phospholipids ◽  
Channel Inhibition ◽  
Important Regulator

The β subunit of voltage-gated Ca2+ (CaV) channels plays an important role in regulating gating of the α1 pore-forming subunit and its regulation by phosphatidylinositol 4,5-bisphosphate (PIP2). Subcellular localization of the CaV β subunit is critical for this effect; N-terminal–dependent membrane targeting of the β subunit slows inactivation and decreases PIP2 sensitivity. Here, we provide evidence that the HOOK region of the β subunit plays an important role in the regulation of CaV biophysics. Based on amino acid composition, we broadly divide the HOOK region into three domains: S (polyserine), A (polyacidic), and B (polybasic). We show that a β subunit containing only its A domain in the HOOK region increases inactivation kinetics and channel inhibition by PIP2 depletion, whereas a β subunit with only a B domain decreases these responses. When both the A and B domains are deleted, or when the entire HOOK region is deleted, the responses are elevated. Using a peptide-to-liposome binding assay and confocal microscopy, we find that the B domain of the HOOK region directly interacts with anionic phospholipids via polybasic and two hydrophobic Phe residues. The β2c-short subunit, which lacks an A domain and contains fewer basic amino acids and no Phe residues in the B domain, neither associates with phospholipids nor affects channel gating dynamically. Together, our data suggest that the flexible HOOK region of the β subunit acts as an important regulator of CaV channel gating via dynamic electrostatic and hydrophobic interaction with the plasma membrane.

The assembly of lipid droplets and its relation to cellular insulin sensitivity

2009 ◽  
Vol 37 (5) ◽  
pp. 981-985 ◽  
Author(s):  
Pontus Boström ◽  
Linda Andersson ◽  
Lu Li ◽  
Rosie Perkins ◽  
Kurt Højlund ◽  
...  
Keyword(s):  
Insulin Resistance ◽  
Plasma Membrane ◽  
Insulin Sensitivity ◽  
Lipid Droplets ◽  
Glucose Transporter ◽  
Protein Receptor ◽  
Phospholipase D1 ◽  
Insulin Dependent ◽  
Glucose Transporter Glut4

The assembly of lipid droplets is dependent on PtdIns(4,5)P2 that activates PLD1 (phospholipase D1), which is important for the assembly process. ERK2 (extracellular-signal-regulated kinase 2) phosphorylates the motor protein dynein and sorts it to lipid droplets, allowing them to be transported on microtubules. Lipid droplets grow in size by fusion, which is dependent on dynein and the transfer on microtubules, and is catalysed by the SNARE (soluble N-ethylmaleimide-sensitive fusion protein-attachment protein receptor) proteins SNAP-23 (23 kDa synaptosome-associated protein), syntaxin-5 and VAMP-4 (vesicle-associated protein 4). SNAP-23 is also involved in the insulin-dependent translocation of the glucose transporter GLUT4 to the plasma membrane. Fatty acids induce a missorting of SNAP-23, from the plasma membrane to the interior of the cell, resulting in cellular insulin resistance that can be overcome by increasing the levels of SNAP-23. The same missorting of SNAP-23 occurs in vivo in skeletal-muscle biopsies from patients with T2D (Type 2 diabetes). Moreover, there was a linear relation between the amount of SNAP-23 in the plasma membrane from human skeletal-muscles biopsies and the systemic insulin-sensitivity. Syntaxin-5 is low in T2D patients, which leads to a decrease in the insulin-dependent phosphorylation of Akt (also known as protein kinase B). Thus both SNAP-23 and syntaxin-5 are highly involved in the development of insulin resistance.

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