-
Diabetes Dec 2002Sulfonylureas are widely used to treat type 2 diabetes because they stimulate insulin secretion from pancreatic beta-cells. They primarily act by binding to the SUR... (Review)
Review
Sulfonylureas are widely used to treat type 2 diabetes because they stimulate insulin secretion from pancreatic beta-cells. They primarily act by binding to the SUR subunit of the ATP-sensitive potassium (K(ATP)) channel and inducing channel closure. However, the channel is still able to open to a limited extent when the drug is bound, so that high-affinity sulfonylurea inhibition is not complete, even at saturating drug concentrations. K(ATP) channels are also found in cardiac, skeletal, and smooth muscle, but in these tissues are composed of different SUR subunits that confer different drug sensitivities. Thus tolbutamide and gliclazide block channels containing SUR1 (beta-cell type), but not SUR2 (cardiac, smooth muscle types), whereas glibenclamide, glimepiride, repaglinide, and meglitinide block both types of channels. This difference has been exploited to determine residues contributing to the sulfonylurea-binding site. Sulfonylurea block is decreased by mutations or agents (e.g., phosphatidylinositol bisphosphate) that increase K(ATP) channel open probability. We now propose a kinetic model that explains this effect in terms of changes in the channel open probability and in the transduction between the drug-binding site and the channel gate. We also clarify the mechanism by which MgADP produces an apparent increase of sulfonylurea efficacy on channels containing SUR1 (but not SUR2).
Topics: ATP-Binding Cassette Transporters; Adenosine Triphosphate; Animals; Binding Sites; Insulin; Insulin Secretion; Potassium Channel Blockers; Potassium Channels; Potassium Channels, Inwardly Rectifying; Receptors, Drug; Sulfonylurea Compounds; Sulfonylurea Receptors
PubMed: 12475777
DOI: 10.2337/diabetes.51.2007.s368 -
The Journal of Neuroscience : the... Mar 2002M-currents are K+ currents generated by members of the KCNQ family of K+ channels (Wang et al., 1998). However, in some cells, M-like currents may be contaminated by...
M-currents are K+ currents generated by members of the KCNQ family of K+ channels (Wang et al., 1998). However, in some cells, M-like currents may be contaminated by members of other K+ channel gene families, such as the erg family (Meves et al., 1999; Selyanko et al., 1999). In the present experiments, we have used the acute expression of pore-defective mutants of KCNQ3 (DN-KCNQ3) and Merg1a (DN-Merg1a) as dominant negatives to separate the contributions of these two families to M-like currents in NG108-15 neuroblastoma hybrid cells and rat sympathetic neurons. Two kinetically and pharmacologically separable components of M-like current could be recorded from NG108-15 cells that were individually suppressed by DN-Merg1a and DN-KCNQ3, respectively. In contrast, only DN-KCNQ3, and not DN-Merg1a, reduced currents recorded from sympathetic neurons. Pharmacological tests suggested that the residual current in DN-KCNQ3-treated sympathetic neurons was carried by residual KCNQ channels. Ineffectiveness of DN-Merg1a in sympathetic neurons was not caused by lack of expression, as judged by confocal microscopy of Flag-tagged DN-Merg1a. These results accord with previous inferences regarding the roles of erg and KCNQ channels in generating M-like currents. This experimental approach should therefore be useful in delineating the contributions of members of these two gene families to K+ currents in other cells.
Topics: Animals; Cells, Cultured; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels; Gene Expression; Genes, Dominant; Hybrid Cells; KCNQ3 Potassium Channel; Mice; Multigene Family; Neuroblastoma; Neurons; Patch-Clamp Techniques; Potassium; Potassium Channels; Potassium Channels, Voltage-Gated; Protein Subunits; Rats; Rats, Sprague-Dawley; Superior Cervical Ganglion; Transfection
PubMed: 11880533
DOI: 10.1523/JNEUROSCI.22-05-j0001.2002 -
Current Topics in Medicinal Chemistry 2009Potassium ion (K(+)) channels consist of a ubiquitous family of membrane proteins that play critical roles in a wide variety of physiological processes, such as the... (Review)
Review
Potassium ion (K(+)) channels consist of a ubiquitous family of membrane proteins that play critical roles in a wide variety of physiological processes, such as the regulation of neuronal excitability, muscle contraction, cell proliferation, and insulin secretion. Due to their pivotal functions in biological systems, K(+) channels have long been attractive targets for the rational drug design on the basis of their structures and interaction mechanisms. Various small-molecular compounds and toxins have been discovered to act as K(+) channel modulators. In the present review, we will first briefly discuss current knowledge of the structures and functions of K(+) channels, and then review the recent strategies for the discovery of K(+) channel modulators, focusing especially on the virtual screening approaches and chemical synthesis technologies.
Topics: Drug Discovery; Humans; Potassium Channel Blockers; Potassium Channels; Structure-Activity Relationship
PubMed: 19442206
DOI: 10.2174/156802609788317865 -
Circulation Research Jul 2000
Topics: Action Potentials; Animals; Electrocardiography; Heart; Heart Block; Kv1.4 Potassium Channel; Mice; Potassium Channels; Potassium Channels, Voltage-Gated; Tachycardia, Ventricular
PubMed: 10884364
DOI: 10.1161/01.res.87.1.6 -
Science (New York, N.Y.) Aug 1992The functional heterogeneity of potassium channels in eukaryotic cells arises not only from the multiple potassium channel genes and splice variants but also from the...
The functional heterogeneity of potassium channels in eukaryotic cells arises not only from the multiple potassium channel genes and splice variants but also from the combinatorial mixing of different potassium channel polypeptides to form heteromultimeric channels with distinct properties. One structural element that determines the compatibility of different potassium channel polypeptides in subunit assembly has now been localized to the hydrophilic amino-terminal domain. A Drosophila Shaker B (ShB) potassium channel truncated polypeptide that contains only the hydrophilic amino-terminal domain can form a homomultimer; the minimal requirement for the homophilic interaction has been localized to a fragment of 114 amino acids. Substitution of the amino-terminal domain of a distantly related mammalian potassium channel polypeptide (DRK1) with that of ShB permits the chimeric DRK1 polypeptide to coassemble with ShB.
Topics: Amino Acid Sequence; Animals; Aplysia; Baculoviridae; Biological Transport; Drosophila; Electrophoresis, Polyacrylamide Gel; Genes; Models, Biological; Molecular Sequence Data; Peptides; Polymerase Chain Reaction; Potassium; Potassium Channels; Recombinant Fusion Proteins; Sequence Homology, Nucleic Acid; Shaker Superfamily of Potassium Channels
PubMed: 1519059
DOI: 10.1126/science.1519059 -
Circulation Research May 2001
Topics: Animals; CHO Cells; Cricetinae; Gene Expression; Ion Channel Gating; Macromolecular Substances; Microinjections; Oocytes; Potassium Channels; Potassium Channels, Voltage-Gated; Protein Subunits; RNA, Messenger; Shal Potassium Channels; Xenopus
PubMed: 11375265
DOI: 10.1161/hh1001.091869 -
FEBS Letters Jul 2003The scorpion toxin peptide BeKm-1 was synthesised by fluorenylmethoxycarbonyl solid phase chemistry and folded by air oxidation. The peptide's effects on heterologous...
The scorpion toxin peptide BeKm-1 was synthesised by fluorenylmethoxycarbonyl solid phase chemistry and folded by air oxidation. The peptide's effects on heterologous human ether-a-go-go-related gene potassium current (I(HERG)) in HEK293 cells were assessed using 'whole-cell' patch clamp. Blockade of I(HERG) by BeKm-1 was concentration-dependent, temperature-dependent, and rapid in onset and reversibility. Blockade also exhibited inverse voltage dependence, inverse dependence on duration of depolarisation, and reverse use- and frequency-dependence. Blockade by BeKm-1 and recombinant ergtoxin, another scorpion toxin known to block HERG, differed in their recovery from HERG current inactivation elicited by strong depolarisation and in their ability to block HERG when the channels were already activated. We conclude that synthetic BeKm-1 toxin blocks HERG preferentially through a closed (resting) state channel blockade mechanism, although some open channel blockade also occurs.
Topics: Cation Transport Proteins; Cell Line; DNA-Binding Proteins; ERG1 Potassium Channel; Ether-A-Go-Go Potassium Channels; Humans; Kinetics; Patch-Clamp Techniques; Potassium Channel Blockers; Potassium Channels; Potassium Channels, Voltage-Gated; Protein Folding; Recombinant Proteins; Scorpion Venoms; Thermodynamics; Trans-Activators; Transcriptional Regulator ERG; Transfection
PubMed: 12860380
DOI: 10.1016/s0014-5793(03)00662-8 -
Science (New York, N.Y.) Apr 1995In voltage-dependent potassium channels, the molecular determinants of ion selectivity are found in the P (pore) region, a stretch of 21 contiguous residues. Cysteine...
In voltage-dependent potassium channels, the molecular determinants of ion selectivity are found in the P (pore) region, a stretch of 21 contiguous residues. Cysteine was introduced at each P region position in a Shaker potassium channel. Residues projecting side chains into the pore were identified by means of channel inhibition by a sulfhydryl-reactive potassium ion analog, silver ion. The pattern of silver ion reactivity contradicts a beta barrel architecture of potassium channel pores.
Topics: Animals; Cysteine; Mutation; Oocytes; Patch-Clamp Techniques; Potassium Channels; Shaker Superfamily of Potassium Channels; Silver; Xenopus laevis
PubMed: 7716526
DOI: 10.1126/science.7716526 -
Neuropharmacology Jan 2003Background or leak conductances are a major determinant of membrane resting potential and input resistance, two key components of neuronal excitability. The primary... (Review)
Review
Background or leak conductances are a major determinant of membrane resting potential and input resistance, two key components of neuronal excitability. The primary structure of the background K(+) channels has been elucidated. They form a family of channels that are molecularly and functionally divergent from the voltage-gated K(+) channels and inward rectifier K(+) channels. In the nervous system, the main representatives of this family are the TASK and TREK channels. They are relatively insensitive to the broad-spectrum K(+) channel blockers tetraethylammonium (TEA), 4-aminopyridine (4-AP), Cs(+), and Ba(2+). They display very little time- or voltage-dependence. Open at rest, they are involved in the maintenance of the resting membrane potential in somatic motoneurones, brainstem respiratory and chemoreceptor neurones, and cerebellar granule cells. TASK and TREK channels are also the targets of many physiological stimuli, including intracellular and extracellular pH and temperature variations, hypoxia, bioactive lipids, and neurotransmitter modulation. Integration of these different signals has major effects on neuronal excitability. Activation of some of these channels by volatile anaesthetics and by other neuroprotective agents, such as riluzole and unsaturated fatty acids, illustrates how the neuronal background K(+) conductances are attractive targets for the development of new drugs.
Topics: Animals; Humans; Hydrogen-Ion Concentration; Lipid Metabolism; Membrane Potentials; Nerve Tissue Proteins; Neurons; Neurotransmitter Agents; Potassium Channel Blockers; Potassium Channels; Potassium Channels, Tandem Pore Domain; Temperature
PubMed: 12559116
DOI: 10.1016/s0028-3908(02)00339-8 -
The Journal of Biological Chemistry Oct 2001The slowly activating cardiac potassium current (I(Ks)) is generated by a heteromultimeric potassium channel complex consisting of pore-forming (KvLQT1) and accessory...
The slowly activating cardiac potassium current (I(Ks)) is generated by a heteromultimeric potassium channel complex consisting of pore-forming (KvLQT1) and accessory (minK) subunits belonging to the KCNQ and KCNE gene families, respectively. Evidence indicating that minK residues line the I(Ks) pore originates from the observation that two minK cysteine mutants (G55C and F54C) render I(Ks) Cd2+-sensitive. We have identified a single cysteine residue in the KvLQT1 S6 segment (Cys-331) that contributes to Cd2+ coordination in conjunction with cysteine residues engineered into the minK transmembrane domain. This observation indicates that minK resides in close proximity to S6 in the I(Ks) channel complex. On the basis of homology modeling that compares the KvLQT1 S6 segment with the structure of the bacterial potassium channel KcsA, we predict that the sulfhydryl side chain of Cys-331 projects away from the central axis of the KvLQT1 pore and suggest that minK resides outside of the permeation pathway. A preliminary model illustrating the orientation of minK with S6 was validated by successful prediction of a novel Cd2+ binding site created within the I(Ks) channel complex by engineering additional cysteine residues into both subunits. Our results indicate the location and orientation of minK within the I(Ks) channel complex and further suggest that Cd2+ exerts its effect on I(Ks) through an allosteric mechanism rather than direct pore blockade.
Topics: Animals; Binding Sites; Cadmium; Cysteine; Humans; KCNQ Potassium Channels; KCNQ1 Potassium Channel; Long QT Syndrome; Mutagenesis; Potassium Channels; Potassium Channels, Voltage-Gated; Protein Binding; Xenopus
PubMed: 11479291
DOI: 10.1074/jbc.M103956200