Long non-coding RNA KCNQ1OT1 promotes hydrogen peroxide-induced lens epithelial cell apoptosis and oxidative stress by regulating miR-223-3p/BCL2L2 axis

Many long non-coding RNAs (lncRNAs) can exert crucial roles in the pathogenesis of cataract, including lncRNA KCNQ1 opposite strand/antisense transcript 1 (KCNQ1OT1). We aimed to further elucidate the biological role and regulatory molecular mechanism of KCNQ1OT1 in cataract. The expression of KCNQ1OT1 and miR-223-3p and BCL2 like 2 (BCL2L2) was examined by qRT-PCR. Cataract cell model was constructed by treatment with hydrogen peroxide (H₂O₂) in lens epithelial cells (SRA01/04). SRA01/04 cell viability and cell apoptosis were tested using CCK-8 assay and flow cytometry, respectively. Western blot (WB) was performed to measure the levels of apoptosis-related proteins and BCL2L2 protein. The oxidative stress factors were analyzed by corresponding kits. The interaction between miR-223-3p and KCNQ1OT1 or BCL2L2 was validated by dual-luciferase reporter and RNA Immunoprecipitation (RIP) assays. We found that KCNQ1OT1 was upregulated in cataract anterior lens capsule samples and H₂O₂-induced SRA01/04 cells. Knockdown of KCNQ1OT1 suppressed H₂O₂-induced SRA01/04 cell apoptosis and oxidative stress. KCNQ1OT1 acted as a sponge of miR-223-3p. Inhibition of miR-223-3p could abate the function of KCNQ1OT1 silence in H₂O₂-treated SRA01/04 cells. Additionally, BCL2L2 was a direct target of miR-223-3p, and miR-223-3p weakened H₂O₂-induced SRA01/04 cell apoptosis and oxidative stress by targeting BCL2L2. Collectively, the data suggest a role for the KCNQ1OT1/miR-223-3p/BCL2L2 axis in cataract formation but the data was generated using an epithelial cell line.

KCNQ and KCNE potassium channel subunit expression in bovine retinal pigment epithelium

Human, monkey, and bovine retinal pigment epithelial (RPE) cells exhibit an M-type K+ current, which in many other cell types is mediated by channels composed of KCNQ α-subunits and KCNE auxiliary subunits. Recently, we demonstrated the expression of KCNQ1, KCNQ4, and KCNQ5 in the monkey RPE. Here, we investigated the expression of KCNQ and KCNE subunits in native bovine RPE. RT-PCR analysis revealed the expression of KCNQ1, KCNQ4, and KCNQ5 transcripts in the RPE, but, in Western blot analysis of RPE plasma membranes, only KCNQ5 was detected. Among the five members of the KCNE gene family, transcripts for KCNE1, KCNE2, KCNE3, and KCNE4 were detected in bovine RPE, but only KCNE1 and KCNE2 proteins were detected. Immunohistochemistry of frozen bovine retinal sections revealed KCNE1 expression near the apical and basal membranes of the RPE, in cone outer segments, in the outer nuclear layer, and throughout the inner retina. The localization of KCNE1 in the RPE basal membrane, where KCNQ5 was previously found to be present, suggests that this β-subunit may contribute to M-type K(+) channels in this membrane.

Differential expression of voltage-gated K+ currents in medial septum/diagonal band complex neurons exhibiting distinct firing phenotypes

The medial septum/diagonal band complex (MSDB) controls hippocampal excitability, rhythms and plastic processes. Medial septal neuronal populations display heterogeneous firing patterns. In addition, some of these populations degenerate during age-related disorders (e.g. cholinergic neurons). Thus, it is particularly important to examine the intrinsic properties of theses neurons in order to create new agents that effectively modulate hippocampal excitability and enhance memory processes. Here, we have examined the properties of voltage-gated, K(+) currents in electrophysiologically-identified neurons. These neurons were taken from young rat brain slices containing the MS/DB complex. Whole-cell, patch recordings of outward currents were obtained from slow firing, fast-spiking, regular-firing and burst-firing neurons. Slow firing neurons showed depolarization-activated K(+) current peaks and densities larger than in other neuronal subtypes. Slow firing total current exhibited an inactivating A-type current component that activates at subthreshold depolarization and was reliably blocked by high concentrations of 4-AP. In addition, slow firing neurons expressed a low-threshold delayed rectifier K(+) current component with slow inactivation and intermediate sensitivity to tetraethylammonium. Fast-spiking neurons exhibited the smaller I(K) and I(A) current densities. Burst and regular firing neurons displayed an intermediate firing phenotype with I(K) and I(A) current densities that were larger than the ones observed in fast-spiking neurons but smaller than the ones observed in slow-firing neurons. In addition, the prevalence of each current differed among electrophysiological groups with slow firing and regular firing neurons expressing mostly I(A) and fast spiking and bursting neurons exhibiting mostly delayer rectifier K(+) currents with only minimal contributions of the I(A). The pharmacological or genetic modulations of these currents constitute an important target for the treatment of age-related disorders.

Electrophysiological, pharmacological and molecular profile of the transient outward rectifying conductance in rat sympathetic preganglionic neurons in vitro

Transient outward rectifying conductances or A-like conductances in sympathetic preganglionic neurons (SPN) are prolonged, lasting for hundreds of milliseconds to seconds and are thought to play a key role in the regulation of SPN firing frequency. Here, a multidisciplinary electrophysiological, pharmacological and molecular single-cell rt-PCR approach was used to investigate the kinetics, pharmacological profile and putative K+ channel subunits underlying the transient outward rectifying conductance expressed in SPN. SPN expressed a 4-aminopyridine (4-AP) sensitive transient outward rectification with significantly longer decay kinetics than reported for many other central neurons. The conductance and corresponding current in voltage-clamp conditions was also sensitive to the Kv4.2 and Kv4.3 blocker phrixotoxin-2 (1-10 μM) and the blocker of rapidly inactivating Kv channels, pandinotoxin-Kα (50 nM). The conductance and corresponding current was only weakly sensitive to the Kv1 channel blocker tityustoxin-Kα and insensitive to dendrotoxin I (200 nM) and the Kv3.4 channel blocker BDS-II (1 μM). Single-cell RT-PCR revealed mRNA expression for the α-subunits Kv4.1 and Kv4.3 in the majority and Kv1.5 in less than half of SPN. mRNA for accessory β-subunits was detected for Kvβ2 in all SPN with differential expression of mRNA for KChIP1, Kvβ1 and Kvβ3 and the peptidase homologue DPP6. These data together suggest that the transient outwardly rectifying conductance in SPN is mediated by members of the Kv4 subfamily (Kv4.1 and Kv4.3) in association with the β-subunit Kvβ2. Differential expression of the accessory β subunits, which may act to modulate channel density and kinetics in SPN, may underlie the prolonged and variable time-course of this conductance in these neurons.

Co-expression of KCNE2 and KChIP2c modulates the electrophysiological properties of Kv4.2 current in COS-7 cells

AIM

Several beta-subunits have been suggested to modulate the electrophysiological properties of the transient outward current (I(to)) in cardiac myocytes, including the obligatory beta-subunit K+-channel interacting protein (KChIP2) and KCNE2. However, neither KChIP2 nor KCNE2 modulation of Kv4.x (x=2 and/or 3) can fully recapitulate the electrophysiological properties of native I(to). The present study is to investigate how I(to) current is modulated when both KChIP2 and KCNE2 are coexpressed.

METHODS

Kv4.2, KChIP2c, and KCNE2 cDNA were simultaneously transfected into COS-7 cells at a molar ratio of 3:1:1. Whole-cell currents were recorded by the patch-clamp method.

RESULTS

In comparison with the current regulated by KChIP2c alone, the co-expression of KCNE2 further slowed Kv4.2 current inactivation kinetics, but diminished KChIP2c-induced positive shift of the voltage-dependent activation of Kv4.2 current. Importantly, co-expression of KCNE2 accelerated the current recovery from inactivation, and caused an povershootq of peak current amplitude during Kv4.2 current recovery, a phenomenon which has been uniquely described for human I(to). However, co-expression of KCNE2 exerted no further effect on Kv4.2 current amplitude, the rate of Kv4.2 current activation and voltage-dependent inactivation.

CONCLUSION

Co-expression of Kv4.2 with KChIP2c and KCNE2, but not with KChIP2c or KCNE2 alone, yields a current profile similar to native I(to). Both KChIP2c and KCNE2 simultaneously participate in recapitulation of the electrophysiological properties of I(to) in cardiac myocytes.

[Preparation of mouse KCTD10 antibody and expression analysis of KCTD10 in neuroepithelium of neural tube and dorsal root ganglion]

KCTD10 is a TNF-alpha inducible protein that can interact with the small subunit of DNA polymerase a and PCNA. In order to study the function of KCTD10, we prepared the rabbit anti-mouse KCTD10 polyclonal antibody by using the His-tagged recombinant mouse KCTD10 protein to immune New Zealand white rabbit. Mouse KCTD10 shares significant similarity with PDIP1 (polymerase delta-interacting protein 1) and TNFAIP1 (tumor necrosis factor alpha-induced protein 1) protein,and then KCTD10 polyclonal antiserum possesses cross-reactivity with PDIP1 protein and TNFAIP1 protein. The partially digested fragments of homogeneous proteins PDIP1 and TNFAIP1 were mixed and incubated with anti-KCTD10 antiserum at 4 degrees C for 3 h to deplete unspecific antibodies. Through this method, we removed successfully the cross-reactivity of anti-KCTD10 antibody with PDIP1 and TNFAIP1 and obtained specific anti-KCTD10 antibody. Then, the anti-KCTD10 antibody was used in immunohistochemistry experiments of mouse. The results of immunohistochemistry on whole-mount embryo and paraffin section demonstrated that KCTD10 is highly expressed in neuroepithelium of neural tube and dorsal root ganglion of 12.5 d embryos. These results suggest that KCTD10 may play roles in the development of neuroepithelium of neural tube and dorsal root ganglion.

Expression of voltage-gated potassium channels in human and mouse colonic carcinoma

PURPOSE

Voltage-gated Kv potassium channels, like ether a go-go (EAG) channels, have been recognized for their oncogenic potential in breast cancer and other malignant tumors.

EXPERIMENTAL DESIGN

We examined the molecular and functional expression of Kv channels in human colonic cancers and colon of mice treated with the chemical carcinogens dimethylhydrazine and N-methyl-N-nitrosourea. The data were compared with results from control mice and animals with chemically induced DSS colitis.

RESULTS

Electrogenic salt transport by amiloride-sensitive Na+ channels and cyclic AMP-activated cystic fibrosis transmembrane conductance regulator Cl- channels were attenuated during tumor development and colitis, whereas Ca2+-dependent transport remained unchanged. Kv channels, in particular Eag-1, were enhanced during carcinogenesis. Multiplex reverse transcription-PCR showed increased mRNA expression for Kv1.3, Kv1.5, Kv3.1, and members of the Eag channel family, after dimethylhydrazine and N-methyl-N-nitrosourea treatment. Eag-1 protein was detected in the malignant mouse colon and human colonic cancers. Genomic amplification of Eag-1 was found in 3.4% of all human colorectal adenocarcinoma and was an independent marker of adverse prognosis.

CONCLUSIONS

The study predicts an oncogenic role of Kv and Eag channels for the development of colonic cancer. These channels may represent an important target for a novel pharmacotherapy of colonic cancer.

KCNE1 subunits require co-assembly with K+ channels for efficient trafficking and cell surface expression

KCNE peptides are a class of type I transmembrane beta subunits that assemble with and modulate the gating and ion conducting properties of a variety of voltage-gated K(+) channels. Accordingly, mutations that disrupt the assembly and trafficking of KCNE-K(+) channel complexes give rise to disease. The cellular mechanisms responsible for ensuring that KCNE peptides assemble with voltage-gated K(+) channels have yet to be elucidated. Using enzymatic deglycosylation, immunofluorescence, and quantitative cell surface labeling experiments, we show that KCNE1 peptides are retained in the early stages of the secretory pathway until they co-assemble with specific K(+) channel subunits; co-assembly mediates KCNE1 progression through the secretory pathway and results in cell surface expression. We also address an apparent discrepancy between our results and a previous study in human embryonic kidney cells, which showed wild type KCNE1 peptides can reach the plasma membrane without exogenously expressed K(+) channel subunits. By comparing KCNE1 trafficking in three cell lines, our data suggest that the errant KCNE1 trafficking observed in human embryonic kidney cells may be due, in part, to the presence of endogenous voltage-gated K(+) channels in these cells.

[mRNA expression of voltage-dependent potassium channels in the brain of rats after middle cerebral artery occlusion]

AIM

To study the mRNA expression changes in the brain of rats after middle cerebral artery occlusion.

METHODS

Middle cerebral artery occlusion was used to induce ischemia in rat brain. The mRNA expression of voltage-dependent potassium channel subtypes, including Kv1.4, Kv1.5, Kv2.1 and Kv4.2, were detected in rat hippocampus and cortex by RT-PCR.

RESULTS

Middle cerebral artery occlusion induced a significant neurological injury in rats. After ischemia 2 h, the mRNA of Kv1.4, Kv2.1 and Kv4.2 in hippocampus increased by 50%, 67% and 90% , respectively. And the mRNA of Kv1.4 and Kv4.2 maintained at a high level in hippocampus after ischemia 24 h. In cortex, the mRNA level of all the four subtypes were not changed significantly after ischemia 2 h, but the mRNA of Kv2.1 and Kv4.2 increased by 70% and 62% after ischemia 24 h, respectively.

CONCLUSION

The mRNA expression levels of voltage-dependent potassium channels were up-regulated in rat hippocampus and cortex after middle cerebral artery occlusion.

Expression and transcriptional control of human KCNE genes

Potassium channels are essential for a variety of cellular processes ranging from membrane excitability to cellular proliferation. The KCNE genes (KCNE1-5) encode a family of single-transmembrane-domain proteins that modulate the properties of several potassium channels, suggesting a physiologic role for these accessory subunits in many human tissues. To investigate the expression and transcriptional control of KCNE genes we mapped transcription start sites, delineated 5' genomic structure, and characterized functional promoter elements for each gene. We identified alternatively spliced transcripts for both KCNE1 and KCNE3, including a cardiac-specific KCNE1 transcript. Analysis of relative expression levels of KCNE1-5 in a panel of human tissues revealed distinct, but overlapping, expression patterns. The coexpression of multiple functionally distinct KCNE genes in some tissues infers complex accessory subunit modification of potassium channels. Identification of the core promoter elements necessary for transcriptional control of the KCNE genes facilitates future work investigating factors responsible for tissue-specific expression as well as the discovery of promoter variants associated with disease.

Expression and characterization of delayed rectifying K+channels in anterior rat taste buds

Delayed rectifying K+(DRK) channels in taste cells have been implicated in the regulation of cell excitability and as potential targets for direct and indirect modulation by taste stimuli. In the present study, we have used patch-clamp recording to determine the biophysical properties and pharmacological sensitivity of DRK channels in isolated rat fungiform taste buds. Molecular biological assays at the taste bud and single-cell levels are consistent with the interpretation that taste cells express a variety of DRK channels, including members from each of the three major subfamilies: KCNA, KCNB, and KCNC. Real-time PCR assays were used to quantify expression of the nine DRK channel subtypes. While taste cells express a number of DRK channels, the electrophysiological and molecular biological assays indicate that the Shaker Kv1.5 channel (KCNA5) is the major functional DRK channel expressed in the anterior rat tongue.

Cibenzoline attenuates upregulation of Kv1.5 channel gene expression by experimental paroxysmal atrial fibrillation

Antiarrhythmic drugs exert their effects by inhibiting the ion channels of cardiomyocytes. However, these effects could also modify the ionic environment around them, and thereby affect the expression of ion channels, leading to biochemical enhancement or attenuation of the antiarrhythmic effects. To test this hypothesis, the physiological and biochemical effects of cibenzoline were evaluated in a rapid atrial pacing model in rats. In rats with rapid atrial pacing, pretreatment with cibenzoline significantly inhibited the increases in Kv1.5 mRNA at 2 hours and immunoreactive protein at 4 hours by 35 +/- 15% and 30 +/- 10%, respectively. These effects were observed only in the rapid atrial pacing group, not in the sham-operated group. With cibenzoline pretreatment, 4-hour rapid atrial pacing resulted in significant prolongation of the atrial refractory period compared to the untreated group even after removal of cibenzoline. In contrast, the sham and rapid atrial pacing model with and without cibenzoline pretreatment showed similar acute physiological responses to cibenzoline. In conclusion, in addition to the acute physiological effects, pretreatment with cibenzoline exerted pleiotropic effects of inhibition of Kv1.5 channel upregulation by rapid pacing, implying differences in the cibenzoline effects when administered before and after onset of paroxysmal atrial fibrillation.

Pentamidine reduces hERG expression to prolong the QT interval

Pentamidine, an antiprotozoal agent, has been traditionally known to cause QT prolongation and arrhythmias; however, its ionic mechanism has not been illustrated. In a stable HEK-293 cell line, we observed a concentration-dependent inhibition of the hERG current with an IC50 of 252 microM. In freshly isolated guinea-pig ventricular myocytes, pentamidine showed no effect on the L-type calcium current at concentrations up to 300 microM, with a slight prolongation of the action potential duration at this concentration. Since the effective concentrations of pentamidine on the hERG channel and APD were much higher than clinically relevant exposures (approximately 1 microM free or lower), we speculated that this drug might not prolong the QT interval through direct inhibition of I(Kr) channel. We therefore incubated hERG-HEK cells in 1 and 10 microM pentamidine-containing media (supplemented with 10% serum) for 48 h, and examined the hERG current densities in the vehicle control and pentamidine-treated cells. In all, 36 and 85% reductions of the current densities were caused by 1- and 10-microM pentamidine treatment (P<0.001 vs control), respectively. A similar level of reduction of the hERG polypeptides and a reduced intensity of the hERG protein on the surface membrane in treated cells were observed by Western blot analysis and laser-scanning confocal microscopy, respectively. Taken together, our data imply that chronic administration of pentamidine at clinically relevant exposure reduces the membrane expression of the hERG channel, which may most likely be the major mechanism of QT prolongation and torsade de pointes reported in man.

Open form of syntaxin-1A is a more potent inhibitor than wild-type syntaxin-1A of Kv2.1 channels

We have shown that SNARE (soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor) proteins not only participate directly in exocytosis, but also regulate the dominant membrane-repolarizing Kv channels (voltage-gated K+ channels), such as Kv2.1, in pancreatic beta-cells. In a recent report, we demonstrated that WT (wild-type) Syn-1A (syntaxin-1A) inhibits Kv2.1 channel trafficking and gating through binding to the cytoplasmic C-terminus of Kv2.1. During beta-cell exocytosis, Syn-1A converts from a closed form into an open form which reveals its active H3 domain to bind its SNARE partners SNAP-25 (synaptosome-associated protein of 25 kDa) and synaptobrevin. In the present study, we compared the effects of the WT Syn-1A and a mutant open form Syn-1A (L165A, E166A) on Kv2.1 channel trafficking and gating. When co-expressed in HEK-293 cells (human embryonic kidney-293 cells), the open form Syn-1A decreased Kv2.1 current density more than (P<0.05) the WT Syn-1A (166+/-35 and 371+/-93 pA/pF respectively; control=911+/-91 pA/pF). Confocal microscopy and biotinylation experiments showed that both the WT and open form Syn-1A inhibited Kv2.1 expression at the plasma membrane to a similar extent, suggesting that the stronger reduction of Kv2.1 current density by the open form compared with the WT Syn-1A is probably due to a stronger direct inhibition of channel activity. Consistently, dialysis of the recombinant open form Syn-1A protein into Kv2.1-expressing HEK-293 cells caused stronger inhibition of Kv2.1 current amplitude (P<0.05) than the WT Syn-1A protein (73+/-2 and 82+/-3% of the control respectively). We found that the H3 but not H(ABC) domain is the putative active domain of Syn-1A, which bound to and inhibited the Kv2.1 channel. When co-expressed in HEK-293 cells, the open-form Syn-1A slowed down Kv2.1 channel activation (tau=12.3+/-0.8 ms) much more than (P<0.05) WT Syn-1A (tau=7.9+/-0.8 ms; control tau=5.5+/-0.6 ms). In addition, only the open form Syn-1A, but not the WT Syn-1A, caused a significant (P<0.05) left-shift in the steady-state inactivation curve (V(1/2)=33.1+/-1.3 and -29.4+/-1.1 mV respectively; control V(1/2)=-24.8+/-2 mV). The present study therefore indicates that the open form of Syn-1A is more potent than the WT Syn-1A in inhibiting the Kv2.1 channel. Such stronger inhibition by the open form of Syn-1A may limit K+ efflux and thus decelerate membrane repolarization during exocytosis, leading to optimization of insulin release.

Light and electron microscopic analysis of KChIP and Kv4 localization in rat cerebellar granule cells

Potassium channels are key determinants of neuronal excitability. We recently identified KChIPs as a family of calcium binding proteins that coassociate and colocalize with Kv4 family potassium channels in mammalian brain (An et al. [2000] Nature 403:553). Here, we used light microscopic immunohistochemistry and multilabel immunofluorescence labeling, together with transmission electron microscopic immunohistochemistry, to examine the subcellular distribution of KChIPs and Kv4 channels in adult rat cerebellum. Light microscopic immunohistochemistry was performed on 40-microm free-floating sections using a diaminobenzidine labeling procedure. Multilabel immunofluorescence staining was performed on free-floating sections and on 1-microm ultrathin cryosections. Electron microscopic immunohistochemistry was performed using an immunoperoxidase pre-embedding labeling procedure. By light microscopy, immunoperoxidase labeling showed that Kv4.2, Kv4.3, and KChIPs 1, 3, and 4 (but not KChIP2) were expressed at high levels in cerebellar granule cells (GCs). Kv4.2 and KChIP1 were highly expressed in GCs in rostral cerebellum, whereas Kv4.3 was more highly expressed in GCs in caudal cerebellum. Immunofluorescence labeling revealed that KChIP1 and Kv4.2 are concentrated in somata of cerebellar granule cells and in synaptic glomeruli that surround synaptophysin-positive mossy fiber axon terminals. Electron microscopic analysis revealed that KChIP1 and Kv4.2 immunoreactivity is concentrated along the plasma membrane of cerebellar granule cell somata and dendrites. In synaptic glomeruli, KChIP1 and Kv4.2 immunoreactivity is concentrated along the granule cell dendritic membrane, but is not concentrated at postsynaptic densities. Taken together, these data suggest that A-type potassium channels containing Kv4.2 and KChIP1, and perhaps also KChIP3 and 4, play a critical role in regulating postsynaptic excitability at the cerebellar mossy-fiber/granule cell synapse.

Variants of the Drosophila melanogaster Ih-channel are generated by different splicing

We isolated splice variants of the DMIH cDNA encoding members of the I(h)-channel family from Drosophila melanogaster by means of polymerase chain reaction and homology screening. Splicing at four different sites generates a great variety of different channel transcripts. The variants so obtained code for ion channel proteins with long or short N-termini and variations in the length of the interloop regions between the membrane-spanning domains S3-S4 and S4-S5. The multiple variants of DMIH coded by a single gene thus might form the molecular basis for a variety of I(h)-channels. Functional expression of one of the DMIH variants with a long N-terminus in HEK293 cells produced unitary currents that were preferentially selective for potassium over sodium ions and were activated by hyperpolarizing voltage steps. Cyclic nucleotides shifted the voltage activation curve to more positive membrane potentials. The current kinetics and modulatory influence of cyclic nucleotides resemble closely those of other invertebrate I(h)-channels, but activation by hyperpolarizing voltage steps had a V(1/2) of 123 mV, a more negative value than those of other recombinantly expressed insect I(h)-channels with a short N-terminus.

HERG K+ channel expression-related chemosensitivity in cancer cells and its modulation by erythromycin

PURPOSE

Previous studies have found that the HERG K+ channel is highly expressed in some cancers. In the study reported here, we investigated HERG expression in various cancer cell lines, its correlation with chemosensitivity to vincristine, paclitaxel, and hydroxy-camptothecin, and its biochemical modulation.

METHODS

The MTT assay and clonogenic assay were used to detect the cytotoxicity of anticancer drugs in vitro. HERG expression was analyzed by Western blotting or immunocytochemistry. Gene transfection was used to examine the changes in HERG-related chemosensitivity. Cell cycle phase distribution was detected by flow cytometry and drug combinations were evaluated by the MTT assay.

RESULTS

HERG expression levels differed widely between various human cancer cell lines and HT-29 cells expressing high levels of HERG were more sensitive than A549 cells expressing low levels of HERG to vincristine, paclitaxel, and hydroxy-camptothecin. In terms of IC50, the chemosensitivities of herg-transfected A549 cells to vincristine, paclitaxel and hydroxy-camptothecin were significantly increased. However, for cisplatin and 5-fluorouracil, no significant difference between herg-transfected A549 cells and parent A549 cells was detected. Erythromycin, a HERG K+ channel blocker, suppressed the growth of various cancer cells and the potency was correlated with HERG expression levels. Combinations of erythromycin and vincristine, paclitaxel or hydroxy-camptothecin showed synergy in cytotoxicity to HT-29 cells. Erythromycin also enhanced the G2/M arrest induced by vincristine in HT-29 cells. There were synergistic effects between erythromycin and vincristine, paclitaxel, and hydroxy-camptothecin, and chemosensitivity was correlated with HERG expression level.

CONCLUSIONS

HERG expression levels and chemosensitivity were positively correlated for vincristine, paclitaxel, and hydroxy-camptothecin. Erythromycin was active as a modulator. These results suggest that HERG may serve as a molecular marker and modulating target for individualized cancer therapy.

Stichodactyla helianthus peptide, a pharmacological tool for studying Kv3.2 channels

Voltage-gated potassium (Kv) channels regulate many physiological functions and represent important therapeutic targets in the treatment of several clinical disorders. Although some of these channels have been well-characterized, the study of others, such as Kv3 channels, has been hindered because of limited pharmacological tools. The current study was initiated to identify potent blockers of the Kv3.2 channel. Chinese hamster ovary (CHO)-K1 cells stably expressing human Kv3.2b (CHO-K1.hKv3.2b) were established and characterized. Stichodactyla helianthus peptide (ShK), isolated from S. helianthus venom and a known high-affinity blocker of Kv1.1 and Kv1.3 channels, was found to potently inhibit 86Rb+ efflux from CHO-K1.hKv3.2b (IC50 approximately 0.6 nM). In electrophysiological recordings of Kv3.2b channels expressed in Xenopus laevis oocytes or in planar patch-clamp studies, ShK inhibited hKv3.2b channels with IC50 values of approximately 0.3 and 6 nM, respectively. Despite the presence of Kv3.2 protein in human pancreatic beta cells, ShK has no effect on the Kv current of these cells, suggesting that it is unlikely that homotetrameric Kv3.2 channels contribute significantly to the delayed rectifier current of insulin-secreting cells. In mouse cortical GABAergic fast-spiking interneurons, however, application of ShK produced effects consistent with the blockade of Kv3 channels (i.e., an increase in action potential half-width, a decrease in the amplitude of the action potential after hyperpolarization, and a decrease in maximal firing frequency in response to depolarizing current injections). Taken together, these results indicate that ShK is a potent inhibitor of Kv3.2 channels and may serve as a useful pharmacological probe for studying these channels in native preparations.

Expression of the IKr components KCNH2 (rERG) and KCNE2 (rMiRP1) during late rat heart development

To understand molecular mechanisms that regulate formation and maintenance of cardiac IKr (rapidly activating component of the delayed rectifier K+ current), we have investigated the spatiotemporal expression pattern of two rat potassium voltage-gated channels, namely subfamily H (eag-related), member2 (KCNH2) (alias name: rERG) and Isk-related family, member2 (KCNE2) (alias name: rMiRP1) during late embryonic development by means of the in situ hybridization technique. KCNE2 is transcribed predominantly in atrial und ventricular myocardium at stages E14.5-E18.5dpc and only a minor signal emerged in the tongue at E16.5dpc. In contrast, KCNH2 transcripts appeared in a less confined pattern with intense signals in atrial and ventricular myocardium, somites, spinal cord, bowel system, central nervous system and thymus at stages E14.5-E18.5dpc. Non-cardiac expression even exceeds the intensity of the cardiac signal, indicating that KCNH2 contributes to K+ currents in non-cardiac tissue as well. Transcription of the rat b-subunit KCNE2 is present in all regions of the fetal myocardium and co-distributes perfectly with transcription of the pore forming a-subunit KCNH2. It seems likely that KCNH2 and KCNE2 are linked to form cardiac IKr channels, associated to cardiogenesis and cardiomyocyte excitability.

Expression of ether à go-go potassium channels in human gliomas

Ether à go-go (EAG) K(+) channels have been shown to be involved in tumor generation and malignant growth. Gliomas have not been investigated thus far. Using RT-PCR we investigated healthy human brain and human gliomas of different subtypes and malignancy grades for the expression of human EAG1 and eag-related gene (ERG) 1 channels. mRNA of both channels was detected in all tissues. Expression was strong in normal brain, moderate in high-grade and high in low-grade gliomas. Our findings suggest a differential expression of hEAG1 and hERG1 in gliomas depending on the malignancy grade and nature of the tumor cells. However, the hypothesis that EAG channels are related to the oncogenic process itself is only partly supported by this study.

Tonotopic gradients of membrane and synaptic properties for neurons of the chicken nucleus magnocellularis

Nucleus magnocellularis (NM) is a division of the avian cochlear nucleus that extracts the timing of auditory signals. We compared the membrane excitability and synaptic transmission along the tonotopic axis of NM. Neurons expressed a Kv1.1 potassium channel mRNA and protein predominantly in the high characteristic frequency (CF) region of NM. In contrast, the expression of Kv1.2 mRNA did not change tonotopically. Neurons also showed tonotopic gradients in resting potential, spike threshold, amplitude, and membrane rectification. All neurons were sensitive to 100 nm dendrotoxin, but the effects were most significant in the high CF neurons. The EPSC recorded by minimal stimulation of auditory nerve fibers (ANFs) was 13 times larger in high CF neurons than in low CF neurons. Moreover, EPSCs were generated in an all-or-none manner in the high CF neurons when stimulus intensity was increased, whereas EPSCs were graded in the low CF neurons, indicating multiple axonal inputs. ANF synaptic terminals were visualized by DiI. ANF formed enfolding end-bulbs of Held around the cell body in the high and middle CF region but not in the low CF region. These observations indicate coordinated gradients of neuronal properties both presynaptically and postsynaptically along the tonotopic axis. Such specializations may be suitable for extracting and preserving the timing information of auditory signals over a wide range of acoustic frequencies.

Accessory Kvbeta1 subunits differentially modulate the functional expression of voltage-gated K+ channels in mouse ventricular myocytes

Voltage-gated K+ (Kv) channel accessory (beta) subunits associate with pore-forming Kv alpha subunits and modify the properties and/or cell surface expression of Kv channels in heterologous expression systems. There is very little presently known, however, about the functional role(s) of Kv beta subunits in the generation of native cardiac Kv channels. Exploiting mice with a targeted disruption of the Kvbeta1 gene (Kvbeta1-/-), the studies here were undertaken to explore directly the role of Kvbeta1 in the generation of ventricular Kv currents. Action potential waveforms and peak Kv current densities are indistinguishable in myocytes isolated from the left ventricular apex (LVA) of Kvbeta1-/- and wild-type (WT) animals. Analysis of Kv current waveforms, however, revealed that mean+/-SEM I(to,f) density is significantly (P< or =0.01) lower in Kvbeta1-/- (21.0+/-0.9 pA/pF; n=68), than in WT (25.3+/-1.4 pA/pF; n=42), LVA myocytes, and that mean+/-SEM I(K,slow) density is significantly (P< or =0.01) higher in Kvbeta1-/- (19.1+/-0.9 pA/pF; n=68), compared with WT (15.9+/-0.7 pA/pF; n=42), LVA cells. Pharmacological studies demonstrated that the TEA-sensitive component of I(K,slow), I(K,slow2,) is selectively increased in Kvbeta1-/- LVA myocytes. In parallel with the alterations in I(to,f) and I(K,slow2) densities, Kv4.3 expression is decreased and Kv2.1 expression is increased in Kvbeta1-/- ventricles. Taken together, these results demonstrate that Kvbeta1 differentially regulates the functional cell surface expression of myocardial I(to,f) and I(K,slow2) channels.

Coupled Tertiary Folding and Oligomerization of the T1 Domain of Kv Channels

Acquisition of secondary, tertiary, and quaternary structure is critical to the fabrication, assembly, and function of ion channels, yet the relationship between these biogenic events remains unclear. We now address this issue in voltage-gated K(+) channels (Kv) for the T1 domain, an N-terminal Kv recognition domain that is responsible for subfamily-specific, efficient assembly of Kv subunits. This domain forms a 4-fold symmetric tetramer. We have identified residues along the axial T1-T1 interface that are critical for tertiary and quaternary structure, shown that mutations at one end of the axial T1 interface can perturb the crosslinking of an intersubunit cysteine pair at the other end, and demonstrated that tertiary folding and tetramerization of this Kv domain are coupled. A threshold level of tertiary folding is required for monomers to oligomerize. Coupling between tertiary and quaternary structure formation may be a common feature in the biogenesis of multimeric proteins.

Heteromultimeric Kv1 channels contribute to myogenic control of arterial diameter

Inhibition of vascular smooth muscle (VSM) delayed rectifier K+ channels (K(DR)) by 4-aminopyridine (4-AP; 200 micromol/L) or correolide (1 micromol/L), a selective inhibitor of Kv1 channels, enhanced myogenic contraction of rat mesenteric arteries (RMAs) in response to increases in intraluminal pressure. The molecular identity of K(DR) of RMA myocytes was characterized using RT-PCR, real-time PCR, and immunocytochemistry. Transcripts encoding the pore-forming Kvalpha subunits, Kv1.2, Kv1.4, Kv1.5, and Kv1.6, were identified and confirmed at the protein level with subunit-specific antibodies. Kvbeta transcript (beta1.1, beta1.2, beta1.3, and beta2.1) expression was also identified. Kv1.5 message was approximately 2-fold more abundant than that for Kv1.2 and Kv1.6. Transcripts encoding these three Kv1alpha subunits were approximately 2-fold more abundant in 1st/2nd order conduit compared with 4th order resistance RMAs, and Kvbeta1 was 8-fold higher than Kvbeta2 message. RMA K(DR) activated positive to -50 mV, exhibited incomplete inactivation, and were inhibited by 4-AP and correolide. However, neither alpha-dendrotoxin or kappa-dendrotoxin affected RMA K(DR), implicating the presence of Kv1.5 in all channels and the absence of Kv1.1, respectively. Currents mediated by channels because of coexpression of Kv1.2, Kv1.5, Kv1.6, and Kvbeta1.2 in human embryonic kidney 293 cells had biophysical and pharmacological properties similar to those of RMA K(DR). It is concluded that K(DR) channels composed of heteromultimers of Kv1 subunits play a critical role in myogenic control of arterial diameter.

Identification of the K efflux channel coupled to the gastric H-K-ATPase during acid secretion

Genomic microarray analysis of genes specifically expressed in a pure cell isolate from a heterocellular organ identified the likely K efflux channel associated with the gastric H-K-ATPase. The function of this channel is to supply K to the luminal surface of the pump to allow H for K exchange. KCNQ1-KCNE2 was the most highly expressed and significantly enriched member of the large variety of K channels expressed in the gastric epithelium. The function of this K channel in acid secretion was then shown by inhibition of secretion in isolated gastric glands with specific KCNQ inhibitors and by colocalization of the channel with the H-K-ATPase in the secretory canaliculus of the parietal cell. KCNQ1-KCNE2 appears to be the K efflux channel that is essential for gastric acid secretion.

In vivo cardiac gene transfer of Kv4.3 abrogates the hypertrophic response in rats after aortic stenosis

BACKGROUND

Prolongation of the action potential duration (APD) and decreased transient outward K+ current (I(to)) have been consistently observed in cardiac hypertrophy. The relation between electrical remodeling and cardiac hypertrophy in vivo is unknown.

METHODS AND RESULTS

We studied rat hearts subjected to pressure overload by surgical ascending aortic stenosis (AS) and simultaneously infected these hearts with an adenovirus carrying either the Kv4.3 gene (Ad.Kv4.3) or the beta-galactosidase gene (Ad.beta-gal). I(to) density was reduced and APD50 was prolonged (P<0.05) in AS rats compared with sham rats. Kv4.2 and Kv4.3 expressions were decreased by 58% and 51%, respectively (P<0.05). AS rats infected with Ad.beta-gal developed cardiac hypertrophy compared with sham rats, as assessed by cellular capacitance and heart weight-body weight ratio. Associated with the development of cardiac hypertrophy, the expression of calcineurin and its downstream transcription factor nuclear factor of activated T cells (NFAT) c1 was persistently increased by 47% and 36%, respectively (P<0.05) in AS myocytes infected with Ad.beta-gal compared with sham myocytes. In vivo gene transfer of Kv4.3 in AS rats was shown to increase Kv4.3 expression, increase I(to) density, and shorten APD50 by 1.6-fold, 5.3-fold, and 3.6-fold, respectively (P<0.05). Furthermore, AS rats infected with Ad.Kv4.3 showed significant reductions in calcineurin and NFAT expression. (P<0.05).

CONCLUSIONS

Downregulation of I(to), APD prolongation, and cardiac hypertrophy occur early after AS, and in vivo gene transfer of Kv4.3 can restore these electrical parameters and abrogate the hypertrophic response via the calcineurin pathway.

NFATc3 Regulates Kv2.1 Expression in Arterial Smooth Muscle

Voltage-gated K+ (Kv) channels control the excitability of arterial smooth muscle. However, the molecular mechanisms regulating Kv channel function in smooth muscle remain unclear. We examined the hypothesis that the vasoactive peptide angiotensin II (Ang II) regulates arterial smooth muscle Kv channel function via calcineurin-dependent activation of the transcription factor NFAT. We found that sustained administration of Ang II decreased Kv currents (IKv) by reducing the expression of Kv2.1 K+ channel subunits. This effect of Ang II was independent of pressure but required Ca2+ influx through L-type Ca2+ channels. Consistent with our hypothesis, we found that calcineurin and NFATc3 are obligatory components of the signaling cascade mediating reduced IKv by Ang II. We conclude that sustained Ang II exposure increases smooth muscle Ca2+, which leads to activation of calcineurin and NFATc3, culminating in decreased Kv2.1 expression and reduced IKv function. These results support the novel concept that NFATc3 controls the excitability of arterial smooth muscle by regulating Kv2.1 expression.

Effect of chronic cigarette smoking on large-conductance calcium-activated potassium channel and Kv1.5 expression in bronchial smooth muscle cells of rats

To investigate the role of potassium channels in the pathogenesis of airway hyperresponsiveness induced by cigarette smoking, the alteration in expression of large-conductance calcium-activated potassium channel (BKca) and voltage-dependent delayed rectifier potassium channel (Kv1.5) in bronchial smooth muscle cells were investigated in chronic cigarette smoking rats. Airway responsiveness was determined, hematoxylin and eosin staining, immuno-histochemistry, in-situ hybridization and western blot techniques were used. The results showed: (1) Chronic cigarette smoking down-regulated the protein synthesis and mRNA expression of BKca and Kv1.5 in bronchial and bronchiolar smooth muscles. (2) BKca decreased more markedly than Kv1.5 in bronchi, but there was no difference between them in bronchioli. (3) No changes in the expression of these two potassium channel proteins were found in extracted cell membrane protein from lung tissue. The results suggest that chronic cigarette smoking can down-regulate the levels of BKca and Kv1.5 in rat bronchial smooth muscle cells in vivo, which might contribute to the mechanism of airway hyperresponsiveness induced by cigarette smoking.

Transmural expression of transient outward potassium current subunits in normal and failing canine and human hearts

The transient outward current (I(to)), an important contributor to transmural electrophysiological heterogeneity, is significantly remodelled in congestive heart failure (CHF). The molecular bases of transmural I(to) gradients and CHF-dependent ionic remodelling are incompletely understood. To elucidate these issues, we studied mRNA and protein expression of Kv4.3 and KChIP2, the principal alpha and beta subunits believed to form I(to), in epicardial and endocardial tissues and in isolated cardiomyocytes from control dogs and dogs with CHF induced by 240 beats min(-1) ventricular tachypacing. CHF decreased I(to) density in both epicardium and endocardium (by 73 and 55% at +60 mV, respectively), without a significant change in relative current density (endocardium/epicardium 0.11 control, 0.17 CHF). There were transmural gradients in mRNA expression of both Kv4.3 (endocardium/epicardium ratio 0.3 under control conditions) and KChIP2 (endocardium/epicardium ratio 0.2 control), which remained in the presence of CHF (Kv4.3 endocardium/epicardium ratio 0.4; KChIP2 0.4). There were qualitatively similar protein expression gradients in human and canine cardiac tissues and isolated canine cardiomyocytes; however, the KChIP2 gradient was only detectable with a highly selective monoclonal antibody and closely approximated the I(to) density gradient. Kv4.3 mRNA expression was reduced by CHF, but KChIP2 mRNA was not significantly changed. CHF decreased Kv4.3 protein expression in canine cardiac tissues and cardiomyocytes, as well as in terminally failing human heart tissue samples, but KChIP2 protein was not down-regulated in any of the corresponding sample sets. We conclude that both Kv4.3 and KChIP2 may contribute to epicardial-endocardial gradients in I(to), and that I(to) down-regulation in human and canine CHF appears due primarily to changes in Kv4.3.

Heteromeric KCNE2/KCNQ1 potassium channels in the luminal membrane of gastric parietal cells

Recently, we and others have shown that luminal K+ recycling via KCNQ1 K+ channels is required for gastric H+ secretion. Inhibition of KCNQ1 by the chromanol 293B strongly diminished H+ secretion. The present study aims at clarifying KCNQ1 subunit composition, subcellular localization, regulation and pharmacology in parietal cells. Using in situ hybridization and immunofluorescence techniques, we identified KCNE2 as the beta subunit of KCNQ1 in the luminal membrane compartment of parietal cells. Expressed in COS cells, hKCNE2/hKCNQ1 channels were activated by acidic pH, PIP2, cAMP and purinergic receptor stimulation. Qualitatively similar results were obtained in mouse parietal cells. Confocal microscopy revealed stimulation-induced translocation of H+,K+-ATPase from tubulovesicles towards the luminal pole of parietal cells, whereas distribution of KCNQ1 K+ channels did not change to the same extent. In COS cells the 293B-related substance IKs124 blocked hKCNE2/hKCNQ1 with an IC50 of 8 nM. Inhibition of hKCNE1- and hKCNE3-containing channels was weaker with IC50 values of 370 and 440 nM, respectively. In conclusion, KCNQ1 coassembles with KCNE2 to form acid-activated luminal K+ channels of parietal cells. KCNQ1/KCNE2 is activated during acid secretion via several pathways but probably not by targeting of the channel to the membrane. IKs124 could serve as a leading compound in the development of subunit-specific KCNE2/KCNQ1 blockers to treat peptic ulcers.

Cardiac Memory Evolves With Age in Association With Development of the Transient Outward Current

BACKGROUND

Calcium-insensitive transient outward current (I(to)) is important to the development of cardiac memory (CM), which itself reflects the capacity of the heart to remodel electrophysiologically. We used cardiac pacing to test the hypothesis that CM evolution can be explained by developmental maturation of I(to).

METHODS AND RESULTS

Acutely anesthetized dogs from 1 day old to adult were paced from the left ventricle (VP, n=29) or left atrial appendage (AP, n=12) to induce CM. T-wave vector displacement (TVD) obtained during VP was greater than with AP (adults, 0.39+/-0.06 mV; neonates, 0.04+/-0.01 mV; P<0.05). TVD began to increase at approximately 40 days of age, reaching adult levels by approximately 200 days. Microelectrode studies performed in 18 dogs (ages 3 to 94 days) after completing the CM protocol and 20 additional dogs (1 day old to adult) revealed that the epicardial action potential notch was absent in neonates, became apparent in the young, and was deepest in adults. The relationship between TVD and epicardial notch was such that as notch magnitude increased, TVD increased (r=-0.65, P<0.05). KChIP2 and Kv4.3 mRNA (measured via reverse transcription-polymerase chain reaction) also increased with age.

CONCLUSIONS

The inducibility of CM gradually increases with age in association with evolution of the epicardial action potential notch and mRNA expression for KChIP2 and Kv4.3. This suggests that the capacity of the heart to remodel electrophysiologically and to manifest memory during development depends in part on evolution of the determinants of I(to).

Potentially reversible autoimmune limbic encephalitis with neuronal potassium channel antibody

OBJECTIVES

To describe the clinical features and coexisting serum autoantibodies in seven patients with encephalitis associated with autoantibodies to alpha-dendrotoxin-sensitive voltage-gated potassium channels (VGKCs), and to compare this disorder with other autoimmune encephalopathies.

METHODS

Clinical information was obtained from a retrospective review of medical records and telephone interviews. All autoantibody testing was performed in a single laboratory.

RESULTS

The seven patients were examined for subacute cognitive and behavioral changes. Seizures, usually temporal-onset complex partial type, were documented in six patients, and all seven patients had EEG abnormalities. None had symptoms or signs of neuromuscular hyperexcitability. One described hypersalivation. Four patients had additional autoantibody markers of neurologic autoimmunity (muscle acetylcholine receptor, striational, P/Q-type calcium channel, or GAD65), and two had thyroperoxidase antibodies. Two patients had a history of cancer: one had active prostate adenocarcinoma, and the second had a remote history of tongue carcinoma. Cranial MRI demonstrated mesial temporal lobe abnormalities in all patients. One patient improved spontaneously, and six were treated with IV methylprednisolone. Three improved remarkably with treatment. At follow-up evaluation, one had no cognitive deficits, four had mild persistent short-term memory dysfunction, and two had persistent disabling behavioral deficits.

CONCLUSIONS

Voltage-gated potassium channel antibodies are a valuable serologic marker of a potentially reversible autoimmune encephalopathy. The neurologic manifestations of this disorder are indistinguishable from paraneoplastic limbic encephalitis but are distinct from Morvan syndrome and Hashimoto encephalopathy.

Inhibition of cardiac HERG potassium channels by the atypical antidepressant trazodone

Trazodone is an atypical antidepressant that is commonly used in the treatment of affective disorders. There have repeatedly been reports of cardiac arrhythmia associated with this drug and concerns have been raised regarding the cardiac safety of trazodone. However, interaction with HERG channels as a main factor of cardiac side effects has not been studied to date. Therefore, we investigated the effect of trazodone on HERG potassium channels expressed in human embryonic kidney (HEK) cells and in Xenopus oocytes. Trazodone inhibited HERG currents in a dose-dependent manner with an IC50 of 2.9 microM in HEK cells and 13.2 microM in Xenopus oocytes. The electrophysiological properties of HERG blockade were analysed in detail. In HERG channel mutants Y652A and F656A lacking aromatic residues in the S6 domain, the affinity of trazodone was reduced profoundly. Trazodone accelerated inactivation of HERG currents without markedly affecting activation. Blockade was voltage dependent with a small reduction of block at positive membrane potentials. Frequency dependence of block was not observed. Trazodone block of HERG channels was state dependent. Channels were affected in the activated and inactivated states, but not in the closed states. In summary, the atypical antidepressant trazodone blocks cardiac HERG channels at concentrations that are probably relevant in vivo, particularly in overdosage.

Reduced low-voltage activated K+ conductances and enhanced central excitability in a congenitally deaf (dn/dn) mouse

We have investigated changes in the neuronal excitability of the auditory brainstem in a congenitally deaf mouse (deafness dn/dn). Whole cell patch recordings from principal neurones of the medial nucleus of the trapezoid body (MNTB) showed strikingly enhanced excitability in the deaf mice when compared to control CBA mice at 12-14 days postnatal. MNTB neurones in normal CBA mice showed the phenotypic single action potential response on depolarization in current clamp; however, recordings from CBA mice carrying the homozygous deafness mutation fired trains of action potentials on depolarization. We show here that these changes are associated with reduced functional expression of dendrotoxin-sensitive Kv1 potassium channels. In contrast, no differences were found in voltage-gated calcium currents between control and deaf mice. These results reveal that loss of hair cell function in the cochlea leads to changes in ion channel expression in the central nervous system and suggests that this deafness model will be an important tool in understanding central changes occurring in human congenital deafness and in exploring activity-dependent regulation of ion channel expression.

Preferential expression and function of voltage-gated, O2-sensitive K+ channels in resistance pulmonary arteries explains regional heterogeneity in hypoxic pulmonary vasoconstriction: ionic diversity in smooth muscle cells

Hypoxic pulmonary vasoconstriction (HPV) is initiated by inhibition of O2-sensitive, voltage-gated (Kv) channels in pulmonary arterial smooth muscle cells (PASMCs). Kv inhibition depolarizes membrane potential (E(M)), thereby activating Ca2+ influx via voltage-gated Ca2+ channels. HPV is weak in extrapulmonary, conduit pulmonary arteries (PA) and strong in precapillary resistance arteries. We hypothesized that regional heterogeneity in HPV reflects a longitudinal gradient in the function/expression of PASMC O2-sensitive Kv channels. In adult male Sprague Dawley rats, constrictions to hypoxia, the Kv blocker 4-aminopyridine (4-AP), and correolide, a Kv1.x channel inhibitor, were endothelium-independent and greater in resistance versus conduit PAs. Moreover, HPV was dependent on Kv-inhibition, being completely inhibited by pretreatment with 4-AP. Kv1.2, 1.5, Kv2.1, Kv3.1b, Kv4.3, and Kv9.3. mRNA increased as arterial caliber decreased; however, only Kv1.5 protein expression was greater in resistance PAs. Resistance PASMCs had greater K+ current (I(K)) and a more hyperpolarized E(M) and were uniquely O2- and correolide-sensitive. The O2-sensitive current (active at -65 mV) was resistant to iberiotoxin, with minimal tityustoxin sensitivity. In resistance PASMCs, 4-AP and hypoxia inhibited I(K) 57% and 49%, respectively, versus 34% for correolide. Intracellular administration of anti-Kv1.5 antibodies inhibited correolide's effects. The hypoxia-sensitive, correolide-insensitive I(K) (15%) was conducted by Kv2.1. Anti-Kv1.5 and anti-Kv2.1 caused additive depolarization in resistance PASMCs (Kv1.5>Kv2.1) and inhibited hypoxic depolarization. Heterologously expressed human PASMC Kv1.5 generated an O2- and correolide-sensitive I(K) like that in resistance PASMCs. In conclusion, Kv1.5 and Kv2.1 account for virtually all the O2-sensitive current. HPV occurs in a Kv-enriched resistance zone because resistance PASMCs preferentially express O2-sensitive Kv-channels.

Heterogeneous expression of repolarizing, voltage-gated K+ currents in adult mouse ventricles

Previous studies have documented the expression of four kinetically distinct voltage-gated K(+) (Kv) currents, I(to,f), I(to,s), I(K,slow) and I(ss), in mouse ventricular myocytes and demonstrated that I(to,f) and I(to,s) are differentially expressed in the left ventricular apex and the interventricular septum. The experiments here were undertaken to test the hypothesis that there are further regional differences in the expression of Kv currents or the Kv subunits (Kv4.2, Kv4.3, KChIP2, Kv1.5, Kv2.1) encoding these currents in adult male and female (C57BL6) mouse ventricles. Whole-cell voltage-clamp recordings revealed that mean (+/-s.e.m.) peak outward K(+) current and I(to,f) densities are significantly (P < 0.001) higher in cells isolated from the right (RV) than the left (LV) ventricles. Within the LV, peak outward K(+) current and I(to,f) densities are significantly (P < 0.05) higher in cells from the apex than the base. In addition, I(to,f) and I(K,slow) densities are lower in cells isolated from the endocardial (Endo) than the epicardial (Epi) surface of the LV wall. Importantly, similar to LV apex cells, I(to,s) is not detected in RV, LV base, LV Epi or LV Endo myocytes. No measurable differences in K(+) current densities or properties are evident in RV or LV cells from adult male and female mice, although I(to,f), I(to,s), I(K,slow) and I(ss) densities are significantly (P < 0.01) higher, and action potential durations at 50% (APD(50)) are significantly (P < 0.05) shorter in male septum cells. Western blot analysis revealed that the expression levels of Kv4.2, Kv4.3, KChIP2, Kv1.5 and Kv2.1 are similar in male and female ventricles. In addition, consistent with the similarities in repolarizing Kv current densities, no measurable differences in ECG parameters, including corrected QT (QT(c)) intervals, are detected in telemetric recordings from adult male and female (C57BL6) mice.

Methylamine, but not ammonia, is hypophagic in mouse by interaction with brain Kv1.6 channel subtype

Ammonia and methylamine (MET) are endogenous compounds increased during liver and renal failure, Alzheimer's disease, vascular dementia and diabetes, where they alter some neurobehavioural functions probably acting as potassium channel blockers. We have already described that potassium channel blockers including tetraethylammonium (TEA), ammonia and MET are hypophagic in mice. Antisense oligonucleotides (aODNs) against Shaker-like Kv1.1 gene abolished the effect of TEA but not of ammonia and MET. The central effects elicited in fasted mice by ammonia and MET were further studied. For MET, an ED(50) value 71.4+/-1.8 nmol mouse(-1) was calculated. The slope of the dose-response curves for these two compounds and the partial hypophagic effect elicited by ammonia indicated a different action mechanism for these amines. The aODNs pretreatments capable of temporarily reducing the expression of all seven known subtypes of Shaker-like gene or to inactivate specifically the Kv1.6 subtype abolished the hypophagic effect of MET but not that of ammonia. Reverse transcription-polymerase chain reaction, Western blot and immunohistochemical results indicate that a full expression in the brain of Kv1.6 is required only for the activity of MET, and confirms the different action mechanism of ammonia and MET.

Homeostatic plasticity in hippocampal slice cultures involves changes in voltage-gated Na+ channel expression

Neurons preserve stable electrophysiological properties despite ongoing changes in morphology and connectivity throughout their lifetime. This dynamic compensatory adjustment, termed 'homeostatic plasticity', may be a fundamental means by which the brain normalizes its excitability, and is possibly altered in disease states such as epilepsy. Despite this significance, the cellular mechanisms of homeostatic plasticity are incompletely understood. Using field potential analyses, we observed a compensatory enhancement of neural excitability after 48 h of activity deprivation via tetrodotoxin (TTX) in hippocampal slice cultures. Because activity deprivation can enhance voltage-gated sodium channel (VGSC) currents, we used Western blot analyses to probe for these channels in control and activity-deprived slice cultures. A significant upregulation of VGSCs expression was evident after activity deprivation. Furthermore, immunohistochemistry revealed this upregulation to occur along primarily pyramidal cell dendrites. Western blot analyses of cultures after 1 day of recovery from activity deprivation showed that VGSC levels returned to control levels, indicating that multiple molecular mechanisms contribute to enhanced excitability. Because of their longevity and in vivo-like cytoarchitecture, we conclude that slice cultures may be highly useful for investigating homeostatic plasticity. Furthermore, we demonstrate that enhanced excitability involves changes in channel expression with a targeted localization likely profound transform the integrative capacities of hippocampal pyramidal cells and their dendrites.

Characterization of the Kv channels of mouse carotid body chemoreceptor cells and their role in oxygen sensing

As there are wide interspecies variations in the molecular nature of the O(2)-sensitive Kv channels in arterial chemoreceptors, we have characterized the expression of these channels and their hypoxic sensitivity in the mouse carotid body (CB). CB chemoreceptor cells were obtained from a transgenic mouse expressing green fluorescent protein (GFP) under the control of tyrosine hydroxylase (TH) promoter. Immunocytochemical identification of TH in CB cell cultures reveals a good match with GFP-positive cells. Furthermore, these cells show an increase in [Ca(2+)](i) in response to low P(O(2)), demonstrating their ability to engender a physiological response. Whole-cell experiments demonstrated slow-inactivating K(+) currents with activation threshold around -30 mV and a bi-exponential kinetic of deactivation (tau of 6.24 +/- 0.52 and 32.85 +/- 4.14 ms). TEA sensitivity of the currents identified also two different components (IC(50) of 17.8 +/- 2.8 and 940.0 +/- 14.7 microm). Current amplitude decreased reversibly in response to hypoxia, which selectively affected the fast deactivating component. Hypoxic inhibition was also abolished in the presence of low (10-50 microm) concentrations of TEA, suggesting that O(2) interacts with the component of the current most sensitive to TEA. The kinetic and pharmacological profile of the currents suggested the presence of Kv2 and Kv3 channels as their molecular correlates, and we have identified several members of these two subfamilies by single-cell PCR and immunocytochemistry. This report represents the first functional and molecular characterization of Kv channels in mouse CB chemoreceptor cells, and strongly suggests that O(2)-sensitive Kv channels in this preparation belong to the Kv3 subfamily.

Changes underlying arrhythmia in the transgenic heart overexpressing Refsum disease gene-associated protein

Previously, we identified a novel neuron-specific protein (PAHX-AP1) that binds to Refsum disease gene product (PAHX), and we developed transgenic (TG) mice that overexpress heart-targeted PAHX-AP1. These mice have atrial tachycardia and increased susceptibility to aconitine-induced arrhythmia. This study was undertaken to elucidate the possible changes in ion channels underlying the susceptibility to arrhythmia in these mice. RT-PCR analyses revealed that the cardiac expression of adrenergic beta(1)-receptor (ADRB1) was markedly lower, whereas voltage-gated potassium channel expression (Kv2.1) was higher in PAHX-AP1 TG mice compared with non-TG mice. However, the expression of voltage-sensitive sodium and calcium channels, and muscarinic receptor was not significantly different. Propranolol pretreatment, a non-specific beta-adrenoceptor antagonist, blocked aconitine-induced arrhythmia in non-TG mice, but not in PAHX-AP1 TG mice. Our results indicate that, in the PAHX-AP1 TG heart, the modulation of voltage-gated potassium channel and ADRB1 expression seem to be important in the electrophysiological changes associated with altered ion channel functions, but ADRB1 is not involved in the greater susceptibility to aconitine-induced arrhythmia.

Differential voltage-dependent K+ channel responses during proliferation and activation in macrophages

Voltage-dependent K+ channels (VDPC) are expressed in most mammalian cells and involved in the proliferation and activation of lymphocytes. However, the role of VDPC in macrophage responses is not well established. This study was undertaken to characterize VDPC in macrophages and determine their physiological role during proliferation and activation. Macrophages proliferate until an endotoxic shock halts cell growth and they become activated. By inducing a schedule that is similar to the physiological pattern, we have identified the VDPC in non-transformed bone marrow-derived macrophages and studied their regulation. Patch clamp studies demonstrated that cells expressed outward delayed and inwardly rectifying K+ currents. Pharmacological data, mRNA, and protein analysis suggest that these currents were mainly mediated by Kv1.3 and Kir2.1 channels. Macrophage colony-stimulating factor-dependent proliferation induced both channels. Lipopolysaccharide (LPS)-induced activation differentially regulated VDPC expression. While Kv1.3 was further induced, Kir2.1 was down-regulated. TNF-alpha mimicked LPS effects, and studies with TNF-alpha receptor I/II double knockout mice demonstrated that LPS regulation mediates such expression by TNF-alpha-dependent and -independent mechanisms. This modulation was dependent on mRNA and protein synthesis. In addition, bone marrow-derived macrophages expressed Kv1.5 mRNA with no apparent regulation. VDPC activities seem to play a critical role during proliferation and activation because not only cell growth, but also inducible nitric-oxide synthase expression were inhibited by blocking their activities. Taken together, our results demonstrate that the differential regulation of VDPC is crucial in intracellular signals determining the specific macrophage response.

Control of ion channel expression for patch clamp recordings using an inducible expression system in mammalian cell lines

BACKGROUND

Many molecular studies of ion channel function rely on the ability to obtain high quality voltage clamp recordings using the patch clamp technique. For a variety of channel types studied in mammalian cell heterologous expression systems, the lack of experimenter control over expression levels severely hinders the ability to obtain a high percentage of cells with an expression level suitable for high quality recordings. Moreover, it has been nearly impossible to obtain expression levels in mammalian cells well suited for single channel recordings. We describe here the use of an inducible promoter system in a stably transfected mammalian cell line that produces nearly 100% success in obtaining ion channel expression levels suitable for either whole cell or single ion channel studies.

RESULTS

We used a tetracycline-regulated expression system to control K+ channel expression in a CHO (Chinese hamster ovary) cell line. Current magnitudes within a reasonably narrow range could be easily and reliably obtained for either macroscopic or single channel recordings. Macroscopic currents of 1-2 nA could be obtained in nearly 100% of cells tested. The desired expression level could be obtained within just 2 to 3 hours, and remained stable at room temperature. Very low expression levels of transfected channels could also be obtained, which resulted in a >70% success rate in the ability to record single channel currents from a patch. Moreover, at these low expression levels, it appeared that endogenous channels produced little or no contamination.

CONCLUSION

This approach to controlling ion channel expression is relatively simple, greatly enhances the speed and efficiency with which high quality macroscopic current data can be collected, and makes it possible to easily and reliably record single channel currents in a mammalian cell heterologous expression system. Whereas we demonstrate the ability of this system to control expression levels of voltage-gated K+ channels, it should be applicable to all other channel types that express well in mammalian expression systems.

Microarray analysis reveals complex remodeling of cardiac ion channel expression with altered thyroid status: relation to cellular and integrated electrophysiology

Although electrophysiological remodeling occurs in various myocardial diseases, the underlying molecular mechanisms are poorly understood. cDNA microarrays containing probes for a large population of mouse genes encoding ion channel subunits ("IonChips") were developed and exploited to investigate remodeling of ion channel transcripts associated with altered thyroid status in adult mouse ventricle. Functional consequences of hypo- and hyperthyroidism were evaluated with patch-clamp and ECG recordings. Hypothyroidism decreased heart rate and prolonged QTc duration. Opposite changes were observed in hyperthyroidism. Microarray analysis revealed that hypothyroidism induces significant reductions in KCNA5, KCNB1, KCND2, and KCNK2 transcripts, whereas KCNQ1 and KCNE1 expression is increased. In hyperthyroidism, in contrast, KCNA5 and KCNB1 expression is increased and KCNQ1 and KCNE1 expression is decreased. Real-time RT-PCR validated these results. Consistent with microarray analysis, Western blot experiments confirmed those modifications at the protein level. Patch-clamp recordings revealed significant reductions in I(to,f) and I(K,slow) densities, and increased I(Ks) density in hypothyroid myocytes. In addition to effects on K+ channel transcripts, transcripts for the pacemaker channel HCN2 were decreased and those encoding the alpha1C Ca2+ channel (CaCNA1C) were increased in hypothyroid animals. The expression of Na+, Cl-, and inwardly rectifying K+ channel subunits, in contrast, were unaffected by thyroid hormone status. Taken together, these data demonstrate that thyroid hormone levels selectively and differentially regulate transcript expression for at least nine ion channel alpha- and beta-subunits. Our results also document the potential of cDNA microarray analysis for the simultaneous examination of ion channel transcript expression levels in the diseased/remodeled myocardium.

Expression of voltage-dependent potassium channels in the developing visual system of Xenopus laevis

Accumulating evidence suggests that voltage-dependent potassium (Kv) channels have important and varied roles in the development of neuronal and non-neuronal cell types. They have been implicated in processes such as proliferation, cell adhesion, migration, neurite outgrowth, and axon guidance. In this study, we used antibodies against several electrically active Kv channel alpha-subunits (Kv1-4) to describe the spatial and temporal expression patterns of Kv channel subunits in Xenopus laevis retinal ganglion cell (RGC) somata, axons, and growth cones. We found that RGCs express Kv1.3-, Kv1.5-, Kv3.4-, and Kv4.2-like subunits. Each subunit displayed unique cellular and subcellular distributions. Moreover, the expression patterns changed considerably over the major period of Xenopus retinal cell genesis and differentiation. Weak or no immunoreactivity was observed with antibodies against Kv1.1, Kv1.2, Kv1.4, Kv1.6, and Kv3.2 subunits in RGCs or other retinal cell types. In support of our previous pharmacologic evidence implicating Kv channels in RGC axon outgrowth, we found that Kv1.5-, Kv3.4-, and Kv4.2-like proteins, but not Kv1.3-like subunits, are abundantly expressed in RGC growth cones.

Kv channel subunit expression in rat pulmonary arteries

Hypoxic pulmonary vasoconstriction (HPV) is a mechanism whereby capillary perfusion is modulated to match alveolar ventilation by diverting blood flow away from poorly ventilated regions of the lung. K+ channels, sensitive to changes in oxygen tension, are thought to play a pivotal role in initiating contraction of pulmonary arterial smooth muscle cells. However, the specific channel subtypes involved have not yet been identified. Using RT-PCR, we have investigated the expression of delayed rectifying (Kv) channel mRNA in rat main and small pulmonary arteries and, for comparison, the systemic mesenteric artery. We have identified and fully sequenced a rat Kv9.2 cDNA and also demonstrated the presence of Kv1.7 and Kv4.1. The presence and relative distribution of Kv1.2, Kv1.5, Kv2.1, and Kv9 mRNA is consistent with the proposed contribution of these subunits to oxygen sensing by K channels, previously described in pulmonary arteries. Our data addresses the controversy relating to the likely distribution of Kv channels involved in oxygen sensing without necessarily implying that such subunits are directly responsible for this process. The differential expression of other subunits, particularly Kv4, indicates that these too may have a role in HPV, revealing the need for further biophysical evaluation of these channel subtypes.

[mRNA expressions of voltage-dependent potassium channels in the brain of scopolamine-induced memory impaired rats]

AIM

To study mRNA expression difference of voltage-dependent potassium channels in the brain of scopolamine-induced memory impaired rats.

METHODS

Memory impairments induced in rats by scopolamine (1 mg.kg-1) were assessed in the Morris water maze test. After rats were injected intraperitoneally with scopolamine for 6 days, the mRNA expression level of five voltage-dependent potassium channels, Kv1.4, Kv1.5, Kv2.1, Kv4.2 and Kv4.3 were detected in the rat cortex and hippocampus by RT-PCR.

RESULTS

Scopolamine (1 mg.kg-1) was shown to significantly induce memory impairment in rats. The mRNA levels of Kv4.2 were decreased by 28.8% and 33.9% in the cortex and hippocampus, respectively. The mRNA levels of Kv1.4 and Kv2.1 were increased in the hippocampus by 111.7% and 64.3%, respectively. There were no differences in the brain mRNA levels of other voltage-dependent potassium channels in scopolamine-induced memory impaired rat.

CONCLUSION

The mRNA expression levels of voltage-dependent potassium channels changed significantly in the brain of scopolamine-induced memory impaired rats.

Dichloroacetate, a metabolic modulator, prevents and reverses chronic hypoxic pulmonary hypertension in rats: role of increased expression and activity of voltage-gated potassium channels

BACKGROUND

Chronic hypoxic pulmonary hypertension (CH-PHT) is associated with suppressed expression and function of voltage-gated K(+) channels (Kv) in pulmonary artery (PA) smooth muscle cells (SMCs) and a shift in cellular redox balance toward a reduced state. We hypothesized that dichloroacetate (DCA), a metabolic modulator that can shift redox balance toward an oxidized state and increase Kv current in myocardial cells, would reverse CH-PHT.

METHODS AND RESULTS

We studied 4 groups of rats: normoxic, normoxic+DCA (DCA 70 mg. kg(-1). d(-1) PO), chronically hypoxic (CH), and CH+DCA. CH and CH+DCA rats were kept in a hypoxic chamber (10% FiO(2)) for 2 to 3 weeks. DCA was given either at day 1 to prevent or at day 10 to reverse CH-PHT. We used micromanometer-tipped catheters and measured hemodynamics in closed-chest rats on days 14 to 18. CH+DCA rats had significantly reduced pulmonary vascular resistance, right ventricular hypertrophy, and PA remodeling compared with the CH rats. CH inhibited I(K), eliminated the acute hypoxia-sensitive I(K), and decreased Kv2.1 channel expression. In the short term, low-dose DCA (1 micromol/L) increased I(K) in CH-PASMCs. In a mammalian expression system, DCA activated Kv2.1 by a tyrosine kinase-dependent mechanism. When given long-term, DCA partially restored I(K) and Kv2.1 expression in PASMCs without altering right ventricular pyruvate dehydrogenase activity, suggesting that the beneficial effects of DCA occur by nonmetabolic mechanisms.

CONCLUSIONS

DCA both prevents and reverses CH-PHT by a mechanism involving restoration of expression and function of Kv channels. DCA has previously been used in humans and may potentially be a therapeutic agent for pulmonary hypertension.

Changes in the expression and function of arterial potassium channels during hypertension

Altered function of K+ channels associated with hypertension has been inferred from the effects of K+ channel blockers on contraction of arterial smooth muscle cells (SMCs) and from K+ efflux measurements. Of the classes of K+ channels known to exist in the smooth muscle, the contribution of voltage-gated (KV) and high-conductance, Ca2+ gated K+ (BKCa) channels to the regulation of arterial SMC contractile function has been the most studied in hypertension. The effects of selective and nonselective K+ channel blockers on tonic contraction suggest that these two K+ channel gene families contribute differently to total K+ conductance in arterial SMCs from normal and hypertensive subjects. Direct measurements of K+ channel properties by electrophysiological methods generally support this conclusion. Studies have demonstrated larger BKCa currents in SMCs from several arteries of hypertensive rats, which have been reported to result from a greater Ca2+ sensitivity of BKCa channels and/or from greater protein expression. Some, but not all, studies have shown decreased KV currents in arterial SMCs from hypertensive animals measured under Ca(2+)-replete conditions. However, when external Ca2+ is removed or when Ca2+ influx is inhibited, KV currents are larger in SMCs exposed to chronic hypertension. Gene expression studies of Shaker KV1 transcripts have shown that of the dominant species present in arterial SMCs, KV1.2 expression is higher, whereas KV1.5 is the same in SMCs from hypertensive compared to normal animals. This finding is consistent with the larger KV currents in vascular SMCs from hypertensive animals under low Ca2+ conditions and suggests that Ca2+ influx and/or intracellular Ca2+ per se exerts a greater inhibitory effect on KV currents in the myocytes from these animals. The pathways by which these K+ channel differences are produced during hypertension remain to be elucidated, as does the potential for these channel proteins to be targeted by novel antihypertensive therapies.

Differential expression of K(V) channel alpha- and beta-subunits in the bovine pulmonary arterial circulation

Resistance pulmonary arteries constrict in response to hypoxia, whereas conduit pulmonary arteries typically do not respond or dilate slightly. One proposed mechanism for this differential response is the variable expression of pulmonary arterial smooth muscle cell voltage-gated K(+) (K(V)) channel subunits (Kv1.2, Kv2.1, Kv1.5, and Kv3.1b) shown to be O(2) sensitive in heterologous expression systems. In this study, immunoblotting and immunohistochemistry were used to examine the expression of K(V) channel alpha- and beta-subunits in the bovine pulmonary arterial circulation to determine whether differential K(V) channel subunit distribution is responsible for the distinct sensitivities of pulmonary arteries to hypoxia. Surprisingly, there was little difference in the expression levels of Kv1.2, Kv1.5, and Kv2.1 between conduit and resistance pulmonary arteries. In contrast, expression of the Kv3.1b alpha-subunit and Kv beta.1, Kv beta 1.2, and Kv beta 1.3 accessory subunits dramatically increased along the pulmonary arterial tree. The differential expression of all the beta-subunits but of only one of the putative O(2)-sensitive alpha-subunits suggests that the alpha-subunits alone are not the O(2) sensors but further implicates the auxiliary beta-subunits in pulmonary arterial O(2) sensing.