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Nihon Ika Daigaku Zasshi Feb 1998
Review
Topics: Animals; Base Sequence; Cloning, Molecular; Electrophysiology; Humans; Molecular Sequence Data; Myocardium; Potassium Channels
PubMed: 9513373
DOI: 10.1272/jnms1923.65.73 -
Receptors & Channels 1995A concatenated cDNA was made that comprised four contiguous copies of the rat brain potassium channel subunit Kv1.1. Currents were measured in oocytes that had been...
A concatenated cDNA was made that comprised four contiguous copies of the rat brain potassium channel subunit Kv1.1. Currents were measured in oocytes that had been injected with in vitro transcribed RNA. A Pro residue was introduced by site-directed mutagenesis into the S4 transmembrane region of one of the four domains, at a position corresponding to that in which a Pro is found in voltage-dependent sodium and calcium channels. This substitution (L305P in any one domain) led to currents having a shallow activation curve, and an additional fast component of deactivation from strongly positive potentials. cDNAs with L305P substitution in two domains formed functional channels only if the domains were non-adjacent; the properties of the currents were similar to the wild-type concatemer. In both cases, 100-1000 x more RNA was injected to obtain maximal currents similar to those seen with the wild-type concantemer. The point mutation Y379V is known to reduce the blocking potency of extracellular tetraethylammonium; this residue from each of the four domains is exposed at the outer mouth of the pore because the progressive introduction of 1, 2, 3 and 4 such mutations causes progressive reductions in tetraethylammonium sensitivity. The Y379V mutation was introduced into concatenated cDNAs with two non-adjacent Pro-containing domains; the sensitivity to TEA of the resulting currents showed that the Pro-containing subunits did not contribute to the pore-forming part of the channel. The results suggest that channels can form with a Pro substitution in a single S4 domain, but they require strong depolarization to open and deactivate rapidly upon repolarization. With Pro substitutions in two domains, channels appear to be formed as a multimerized concatemer, in which the Pro-containing domains are excluded from pore formation.
Topics: Amino Acid Sequence; Animals; DNA, Complementary; Kv1.1 Potassium Channel; Molecular Sequence Data; Mutagenesis, Site-Directed; Oocytes; Potassium Channels; Potassium Channels, Voltage-Gated; Proline; Sequence Homology, Amino Acid; Xenopus
PubMed: 8833999
DOI: No ID Found -
Progress in Drug Research. Fortschritte... 2002Existing drugs that modulate ion channels represent a key class of pharmaceutical agents across many therapeutic areas and there is considerable further potential for... (Review)
Review
Existing drugs that modulate ion channels represent a key class of pharmaceutical agents across many therapeutic areas and there is considerable further potential for potassium channel drug discovery. Potassium channels represent the largest and most diverse sub-group of ion channels and they play a central role in regulating the membrane potential of cells. Recent advances in genomics have greatly added to the number of these potential drug targets, but selecting a suitable potassium channel for drug discovery research is a key step. In particular, the potential therapeutic relevance of a potassium channel should be taken into account when selecting a target for screening. Potassium channel drug discovery is being driven by a need to identify lead compounds that can provide tractable starting points for medicinal chemistry. Furthermore, advances in laboratory automation have brought significant opportunities to increase screening throughput for potassium channel assays, but careful assay configuration to model drug-target interactions in a physiological manner is an essential consideration. Several potassium channel screening platforms are described in this review in order to provide some insight into the variety of formats available for screening, together with some of their inherent advantages and limitations. Particular emphasis is placed on the mechanistic basis of drug-target interaction and those aspects of structure/function that are of prime importance in potassium channel drug discovery.
Topics: Animals; Drug Design; Drug Evaluation, Preclinical; Humans; Pharmacology, Clinical; Potassium Channels
PubMed: 12079199
DOI: 10.1007/978-3-0348-8183-8_4 -
Nature Feb 1998Ion channels form transmembrane water-filled pores that allow ions to cross membranes in a rapid and selective fashion. The amino acid residues that line these pores...
Ion channels form transmembrane water-filled pores that allow ions to cross membranes in a rapid and selective fashion. The amino acid residues that line these pores have been sought to reveal the mechanisms of ion conduction and selectivity. The pore (P) loop is a stretch of residues that influences single-channel-current amplitude, selectivity among ions and open-channel blockade and is conserved in potassium-channel subunits previously recognized to contribute to pore formation. To date, potassium-channel pores have been shown to form by symmetrical alignment of four P loops around a central conduction pathway. Here we show that the selectivity-determining pore region of the voltage-gated potassium channel of human heart through which the I(Ks) current passes includes the transmembrane segment of the non-P-loop protein minK. Two adjacent residues in this segment of minK are exposed in the pore on either side of a short barrier that restricts the movement of sodium, cadmium and zinc ions across the membrane. Thus, potassium-selective pores are not restricted to P loops or a strict P-loop geometry.
Topics: Animals; Cadmium; Electrophysiology; Humans; KCNQ Potassium Channels; KCNQ1 Potassium Channel; Mutation; Myocardium; Potassium Channel Blockers; Potassium Channels; Potassium Channels, Voltage-Gated; Rats; Tetraethylammonium; Xenopus
PubMed: 9468141
DOI: 10.1038/35416 -
Advances in Pharmacology (San Diego,... 2010Cardiac K(+) channels are cardiomyocyte membrane proteins that regulate K(+) ion flow across the cell membrane on the electrochemical gradient and determine the resting... (Review)
Review
Cardiac K(+) channels are cardiomyocyte membrane proteins that regulate K(+) ion flow across the cell membrane on the electrochemical gradient and determine the resting membrane potential and the cardiac action potential morphology and duration. Several K(+) channels have been well studied in the human heart. They include the transient outward K(+) current I(to1), the ultra-rapidly activating delayed rectifier current I(Kur), the rapidly and slowly activating delayed rectifier currents I(Kr) and I(Ks), the inward rectifier K(+) current I(K1), and ligand-gated K(+) channels, including adenosine-5'-triphosphate (ATP)-sensitive K(+) current (I(KATP)) and acetylcholine-activated current (I(KACh)). Regional differences of K(+) channel expression contribute to the variable morphologies and durations of cardiac action potentials from sinus node and atrial to ventricular myocytes, and different ventricular layers from endocardium and midmyocardium to epicardium. They also show different responses to endogenous regulators and/or pharmacological agents. K(+) channels are well-known targets for developing novel anti-arrhythmic drugs that can effectively prevent/inhibit cardiac arrhythmias. Especially, atrial-specific K(+) channel currents (I(Kur) and I(KACh)) are the targets for developing atrial-selective anti-atrial fibrillation drugs, which has been greatly progressed in recent years. This chapter concentrates on recent advances in intracellular signaling regulation and pharmacology of cardiac K(+) channels under physiological and pathophysiological conditions.
Topics: Action Potentials; Animals; Anti-Arrhythmia Agents; Arrhythmias, Cardiac; Delayed Rectifier Potassium Channels; Drug Discovery; Heart Atria; Heart Ventricles; Humans; Ion Channel Gating; KATP Channels; Organ Specificity; Potassium Channel Blockers; Potassium Channels; Potassium Channels, Inwardly Rectifying; Potassium Channels, Tandem Pore Domain; Potassium Channels, Voltage-Gated
PubMed: 20933200
DOI: 10.1016/S1054-3589(10)59004-5 -
Sheng Li Ke Xue Jin Zhan [Progress in... Oct 2005
Review
Topics: Animals; Humans; KCNQ Potassium Channels; KCNQ2 Potassium Channel; KCNQ3 Potassium Channel; Mutation; Potassium Channels; Recombinant Proteins
PubMed: 16408781
DOI: No ID Found -
British Journal of Pharmacology Jan 2006The development of our knowledge of the function, structure and pharmacology of K(+) channels is briefly outlined. This is the most diverse of all the ion channel... (Review)
Review
The development of our knowledge of the function, structure and pharmacology of K(+) channels is briefly outlined. This is the most diverse of all the ion channel families with at least 75 coding genes in mammals. Alternative splicing as well as variations in the channel subunits and accessory proteins that co-assemble to form the functional channel add to the multiplicity. Whereas diversity of this order suggests that it may be possible to develop new classes of drug, for example, for immunomodulation and some diseases of the central nervous system, the ubiquity of K(+) channels imposes stringent requirements for selectivity. Animal toxins from the snake, bee and scorpion provide useful leads, though only in a few instances (e.g. with apamin) it has been possible to produce non-peptidic analogues of high potency. The scale of the resources needed to identify, and characterize fully, specific K(+) channel as targets and then develop modulators with the required selectivity presents a challenge to both academic and applied pharmacologists.
Topics: Animals; Anticonvulsants; Cardiovascular Diseases; History, 20th Century; History, 21st Century; Humans; Immunosuppressive Agents; Ion Channel Gating; Potassium Channel Blockers; Potassium Channels; Protein Conformation
PubMed: 16402122
DOI: 10.1038/sj.bjp.0706447 -
Nature Jan 2000Mutations in all four known KCNQ potassium channel alpha-subunit genes lead to human diseases. KCNQ1 (KvLQT1) interacts with the beta-subunit KCNE1 (IsK, minK) to form...
Mutations in all four known KCNQ potassium channel alpha-subunit genes lead to human diseases. KCNQ1 (KvLQT1) interacts with the beta-subunit KCNE1 (IsK, minK) to form the slow, depolarization-activated potassium current I(Ks) that is affected in some forms of cardiac arrhythmia. Here we show that the novel beta-subunit KCNE3 markedly changes KCNQ1 properties to yield currents that are nearly instantaneous and depend linearly on voltage. It also suppresses the currents of KCNQ4 and HERG potassium channels. In the intestine, KCNQ1 and KCNE3 messenger RNAs colocalized in crypt cells. This localization and the pharmacology, voltage-dependence and stimulation by cyclic AMP of KCNQ1/KCNE3 currents indicate that these proteins may assemble to form the potassium channel that is important for cyclic AMP-stimulated intestinal chloride secretion and that is involved in secretory diarrhoea and cystic fibrosis.
Topics: Amino Acid Sequence; Animals; Cloning, Molecular; Colon; Cyclic AMP; Electrochemistry; Humans; Intestine, Small; KCNQ Potassium Channels; KCNQ1 Potassium Channel; Mice; Molecular Sequence Data; Potassium Channels; Potassium Channels, Voltage-Gated; Rats; Xenopus
PubMed: 10646604
DOI: 10.1038/35003200 -
Toxicon : Official Journal of the... Jun 2004Potassium channel inhibitor peptides from scorpion venom, alpha-KTx, have greatly advanced our understanding of potassium channel structure and function, Because of... (Review)
Review
Potassium channel inhibitor peptides from scorpion venom, alpha-KTx, have greatly advanced our understanding of potassium channel structure and function, Because of their high affinity interaction with the outer pore, alpha-KTx's have aided, in identification of amino acids lining the pore and of proteins constituting functional channels. The alpha-KTx's display a large range of affinities for different potassium channels with differences in binding free energy exceeding approximately 8 kcal/mol. These differences in affinities are the foundation of alpha-KTx specificity and have aided in revealing the physiological and patho-physiological roles of potassium channels. The alpha-KTx subfamilies 1-3, display gross differences in specificity for maxi-K vs. KV channels. However, many potassium channels are largely untouched by alpha-KTx's. Differences in toxin binding free energy provide a quantitative framework for defining specificity. As a practical criterion for specificity a minimum binding free energy difference of 2.72 kcal/mol is proposed. Binding free energy differences for wild-type and mutant toxins and channels can point to amino acids underlying specificity and to unique features of potassium channel outer pores. Known 3D structures of potassium channels in combination with CLUSTALW sequence alignment of over 60 potassium channels reveal significant variation in alpha-KTx binding domains. Structure-based homology models of potassium channels complexed with alpha-KTxs, in combination with measurements of toxin binding free energy, will further our understanding of the molecular basis of alpha-KTx specificity.
Topics: Amino Acid Sequence; Animals; Molecular Sequence Data; Potassium Channel Blockers; Potassium Channels; Protein Binding; Protein Structure, Tertiary; Scorpion Venoms; Scorpions; Sequence Alignment; Substrate Specificity
PubMed: 15208020
DOI: 10.1016/j.toxicon.2003.11.029 -
Current Opinion in Structural Biology Aug 2001More than three years have passed since the first structure of a potassium channel protein revealed fundamental molecular details of a platform for ion-selective... (Review)
Review
More than three years have passed since the first structure of a potassium channel protein revealed fundamental molecular details of a platform for ion-selective conduction. Recent efforts have turned to understanding what this structure tells us about potassium channel structure and function in general and, most importantly, which questions remain unanswered. Successes in solving membrane protein structures are still hard won and slow. High-resolution studies of cytoplasmic channel domains and channel-associated proteins, the most tractable entry points for dissecting large, complex eukaryotic channels, are revealing a modularity of function commonly seen in many other biological systems. Studies of these domains bring into sharp focus issues of channel regulation, how these domains and associated proteins are coupled to the transmembrane domains to influence channel function, and how ion channels are integrated into cellular signaling pathways.
Topics: Amino Acid Sequence; Bacteria; Biological Transport; Conserved Sequence; Ion Channel Gating; Models, Molecular; Mutation; Potassium Channels; Protein Conformation; Sequence Alignment
PubMed: 11495731
DOI: 10.1016/s0959-440x(00)00225-6