SEARCH · PubMed Health

Results for “Potassium Channels, Inwardly Rectifying”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources

PubMed2001

Multiple PIP2 binding sites in Kir2.1 inwardly rectifying potassium channels.

Inwardly rectifying potassium channels require binding of phosphatidylinositol-4,5-bisphosphate (PIP2) for channel activity. Three independent sites (aa 175-206, aa 207-246, aa 324-365) were located in the C-terminal domain of Kir2.1 channels by assaying the binding of overlapping fragments to PIP2 containing liposomes. Mutations in the first site, which abolished channel activity, reduced PIP2 binding of this fragment but not of the complete C-terminus. Point mutations in the third site also reduced both, channel activity and PIP2 binding of this segment. The relevance of the third PIP2 binding site provides a basis for the understanding of constitutively active Kir2 channels.

Animals↗

PubMed1996

Regions responsible for the assembly of inwardly rectifying potassium channels.

Inwardly rectifying potassium channels have an important role in determining the resting potential of the cell. They are tetrameric proteins with two transmembrane segments (M1 and M2), a pore-forming loop (H5), a cytoplasmic N-terminal, and longer C-terminal domain. We have used biochemical and electrophysiological methods to identify regions required for homotypic interactions and those responsible for the incompatibility between IRK1 and two other members of the same subfamily (IRK2 and IRK3) and two members from other subfamilies (ROMK1 and 6.1 uK(ATP)). The data indicate that, in contrast to the voltage-gated class of potassium channel, the proximal C-terminus and the transmembrane segment M2 determine homo-and heteromultimerization and that heteromultimerization between members of the same or different subfamilies is case specific.

Animals↗

PubMed1999

Transmembrane structure of an inwardly rectifying potassium channel.

Inwardly rectifying potassium channels (K(ir)), comprising four subunits each with two transmembrane domains, M1 and M2, regulate many important physiological processes. We employed a yeast genetic screen to identify functional channels from libraries of K(ir) 2.1 containing mutagenized M1 or M2 domains. Patterns in the allowed sequences indicate that M1 and M2 are helices. Protein-lipid and protein-water interaction surfaces identified by the patterns were verified by sequence minimization experiments. Second-site suppressor analyses of helix packing indicate that the M2 pore-lining inner helices are surrounded by the M1 lipid-facing outer helices, arranged such that the M1 helices participate in subunit-subunit interactions. This arrangement is distinctly different from the structure of a bacterial potassium channel with the same topology and identifies helix-packing residues as hallmark sequences common to all K(ir) superfamily members.

Amino Acid Sequence↗

PubMed2000

The role of members of the pertussis toxin-sensitive family of G proteins in coupling receptors to the activation of the G protein-gated inwardly rectifying potassium channel.

Inwardly rectifying potassium (K(+)) channels gated by G proteins (Kir3.x family) are widely distributed in neuronal, atrial, and endocrine tissues and play key roles in generating late inhibitory postsynaptic potentials, slowing the heart rate and modulating hormone release. They are directly activated by G(betagamma) subunits released from G protein heterotrimers of the G(i/o) family upon appropriate receptor stimulation. Here we examine the role of isoforms of pertussis toxin (PTx)-sensitive G protein alpha subunits (G(ialpha1-3) and G(oalphaA)) in mediating coupling between various receptor systems (A(1), alpha(2A), D(2S), M(4), GABA(B)1a+2, and GABA(B)1b+2) and the cloned counterpart of the neuronal channel (Kir3.1+3.2A). The expression of mutant PTx-resistant G(i/oalpha) subunits in PTx-treated HEK293 cells stably expressing Kir3.1+3.2A allows us to selectively investigate that coupling. We find that, for those receptors (A(1), alpha(2A)) known to interact with all isoforms, G(ialpha1-3) and G(oalphaA) can all support a significant degree of coupling to Kir3.1+3.2A. The M(4) receptor appears to preferentially couple to G(ialpha2) while another group of receptors (D(2S), GABA(B)1a+2, GABA(B)1b+2) activates the channel predominantly through G(betagamma) liberated from G(oA) heterotrimers. Interestingly, we have also found a distinct difference in G protein coupling between the two splice variants of GABA(B)1. Our data reveal selective pathways of receptor activation through different G(i/oalpha) isoforms for stimulation of the G protein-gated inwardly rectifying K(+) channel.

Cell Line↗

PubMed1999

Inwardly rectifying potassium channels.

Inwardly rectifying potassium (Kir) channels regulate the resting membrane potential of the cell and thereby modulate the electrical activity of cardiac and neuronal cells, insulin secretion and epithelial K(+) transport. Considerable progress in understanding the molecular structure of Kir channels and the way in which they are regulated by extracellular and intracellular modulators has been made during the past year.

Animals↗

PubMed1995

Determination of the subunit stoichiometry of an inwardly rectifying potassium channel.

Inwardly rectifying K+ channels are distantly related to their voltage-gated counterparts and possess a structural motif of only two putative transmembrane segments in each subunit. They are formed by the assembly of an unknown number of subunits. We have examined the subunit stoichiometry of a strongly rectifying K+ channel, IRK1, by linking together the coding sequence of three or four subunits and distinguishing channels with different numbers of subunits carrying a double mutation that alters inward rectification and single-channel properties. We find that IRK1 channels, like voltage-gated K+ channels, are tetrameric channels. Interestingly, the high sensitivity to Mg2+ and polyamines, cations that produce inward rectification by blocking the channel pore from the cytoplasmic side is largely retained in a channel containing only one wild-type subunit and three subunits bearing mutations that abolish high affinity Mg2+ and polyamine block.

Animals↗

PubMed1995

Contributions of the C-terminal domain to gating properties of inward rectifier potassium channels.

Two inward rectifier potassium channels, the G protein-dependent GIRK1 and the G protein-independent BIR10, display large differences in rectification and macroscopic kinetics. A chimeric channel was constructed in which the putative intracellular carboxy-terminal domain of the G protein-dependent channel replaced the corresponding domain of the G protein-independent channel. The chimeric channel conducted potassium ions without the requirement of activated G proteins, yet displayed activation and deactivation kinetics and rectification properties similar to those of the G protein-dependent channel. The results demonstrate that structural elements in the C-terminus can independently control gating but not G protein signal transduction. The voltage dependence, time course, and kinetics of gating suggest a mechanism in which the pore may be occluded by reversible interactions with charged residues in the C-terminus.

Amino Acid Sequence↗

PubMed1995

Identification and molecular localization of a pH-sensing domain for the inward rectifier potassium channel HIR.

Inward rectifier potassium channels are found in the heart and CNS, where they are critical for the modulation and maintenance of cellular excitability. We present evidence that the inward rectifier potassium channel HIR is modulated by extracellular pH in the physiological range. We show that proton-induced changes in HIR single-channel conductance underlie the HIR pH sensitivity seen on the macroscopic level. We used chimeric and mutant channels to localize the molecular determinant of HIR pH sensitivity to a single residue, H117, in the M1-to-H5 linker region. This residue provides a molecular context that allows a titratable group to influence pore properties. We present evidence that this titratable group is one of two cysteines located in the M1-to-H5 and H5-to-M2 linkers.

Amino Acid Sequence↗

PubMed2000

Effects of inhibitors of small- and intermediate-conductance calcium-activated potassium channels, inwardly-rectifying potassium channels and Na(+)/K(+) ATPase on EDHF relaxations in the rat hepatic artery.

1. In the rat hepatic artery, the SK(Ca) inhibitors UCL 1684 (300 nM) completely blocked, and scyllatoxin (1 microM) and d-tubocurarine (100 microM) partially inhibited EDHF relaxations when each of them was combined with charybdotoxin (300 nM). 2. The IK(Ca) inhibitors clotrimazole (3 microM) and 2-chlorophenyl-bisphenyl-methanol (3 microM) strongly depressed EDHF relaxations when each of them was combined with apamin (300 nM). The cytochrome P450 mono-oxygenase inhibitor ketoconazole (10 microM) had no effect in the presence of apamin. 3. Ciclazindol (10 microM), which abolishes EDHF relaxations in the presence of apamin, almost completely prevented the calcium ionophore (A23187) stimulated (86)Rb(+) influx via the Gardos channel (IK(Ca)) in human erythrocytes. 4. The Na(+)/K(+) ATPase inhibitor ouabain (500 microM) and the K(IR) blocker Ba(2+) (30 microM) neither alone nor in combination inhibited EDHF relaxations. Ba(2+) was also without effect in the presence of either apamin or charybdotoxin. 5. In contrast to EDHF, an increase in extracellular [K(+)] from 4.6 mM to 9.6, 14.6 and 19.6 mM inconsistently relaxed arteries. In K(+)-free physiological salt solution, re-admission of K(+) always caused complete and sustained relaxations which were abolished by ouabain but unaffected by Ba(2+). 6. The present study provides pharmacological evidence for the involvement of SK(Ca) and IK(Ca) in the action of EDHF in the rat hepatic artery. Our results are not consistent with the idea that EDHF is K(+) activating Na(+)/K(+) ATPase and K(IR) in this blood vessel.

Acetylcholine↗

PubMed1996

[K+] dependence of open-channel conductance in cloned inward rectifier potassium channels (IRK1, Kir2.1).

Potassium conduction through unblocked inwardly rectifying (IRK1, Kir2.1) potassium channels was measured in inside-out-patches from Xenopus oocytes, after removal of polyamine-induced strong inward rectification. Unblocked IRK1 channel current-voltage (I-V) relations show very mild inward rectification in symmetrical solutions, are linearized in nonsymmetrical solutions that bring the K+ reversal potential to extreme negative values, and follow Goldman-Hodgkin-Katz constant field equation at extreme positive E alpha. When intracellular K+ concentration (KIN) was varied, at constant extracellular K+ concentration (KOUT) the conductance at the reversal potential (GREV) followed closely the predictions of the Goldman-Hodgkin-Katz constant field equation at low concentrations and saturated sharply at concentrations of > 150 mM. Similarly, when KOUT was varied, at constant KIN, GREV saturated at concentrations of > 150 mM. A square-root dependence of conductance on KOUT is a well-known property of inward rectifier potassium channels and is a property of the open channel. A nonsymmetrical two-site three-barrier model can qualitatively explain both the I-V relations and the [K+] dependence of conductance of open IRK1 (Kir2.1) channels.

Animals↗

PubMed1998

Tetrameric subunit structure of the native brain inwardly rectifying potassium channel Kir 2.2.

Strongly inwardly rectifying potassium channels of the Kir 2 subfamily (IRK1, IRK2, and IRK3) are involved in maintenance and modulation of cell excitability in brain and heart. Electrophysiological studies of channels expressed in heterologous systems have suggested that the pore-conducting pathway contains four subunits. However, inferences from electrophysiological studies have not been tested on native channels and do not address the possibility of nonconducting auxiliary subunits. Here, we investigate the subunit stoichiometry of endogenous inwardly rectifying potassium channel Kir 2.2 (IRK2) from rat brain. Using chemical cross-linking, immunoprecipitiation, and velocity sedimentation, we report physical evidence demonstrating the tetrameric organization of the native channel. Kir 2.2 was sequentially cross-linked to produce bands on SDS-polyacrylamide gel electrophoresis corresponding in size to monomer, dimer, trimer, and three forms of tetramer. Fully cross-linked channel was present as a single band of tetrameric size. Immunoprecipitation of biotinylated membranes revealed a single band corresponding to Kir 2.2, suggesting that the channel is composed of a single type of subunit. Hydrodynamic properties of 3-[(3-cholamidopropyl)dimethylammonio]-1-propane sulfonic acid-solubilized channel were used to calculate the molecular mass of the channel. Velocity sedimentation in H2O or D2O gave a sharp peak with a sedimentation coefficient of 17.3 S. Gel filtration yielded a Stokes radius of 5.92 nm. These data indicate a multisubunit protein with a molecular mass of 193 kDa, calculated to contain 3.98 subunits. Together, these results demonstrate that Kir 2.2 channels are formed by the homotetrameric association of Kir 2.2 subunits and do not contain tightly associated auxiliary subunits. These studies suggest that Kir 2.2 channels differ in structure from related heterooctomeric ATP-sensitive K channels and heterotetrameric G-protein-regulated inward rectifier K channels.

Amino Acid Sequence↗

PubMed2001

Coupling Gbetagamma-dependent activation to channel opening via pore elements in inwardly rectifying potassium channels.

G protein-coupled inwardly rectifying potassium channels, GIRK/Kir3.x, are gated by the Gbetagamma subunits of the G protein. The molecular mechanism of gating was investigated by employing a novel yeast-based random mutagenesis approach that selected for channel mutants that are active in the absence of Gbetagamma. Mutations in TM2 were found that mimicked the Gbetagamma-activated state. The activity of these channel mutants was independent of receptor stimulation and of the availability of heterologously expressed Gbetagamma subunits but depended on PtdIns(4,5)P(2). The results suggest that the TM2 region plays a key role in channel gating following Gbetagamma binding in a phospholipid-dependent manner. This mechanism of gating in inwardly rectifying K+ channels may be similar to the involvement of the homologous region in prokaryotic KcsA potassium channel and, thus, suggests evolutionary conservation of the gating structure.

Amino Acid Sequence↗

PubMed2000

Single channel studies of inward rectifier potassium channel regulation by muscarinic acetylcholine receptors.

Negative regulation of the heartbeat rate involves the activation of an inwardly rectifying potassium current (I(KACh)) by G protein-coupled receptors such as the m2 muscarinic acetylcholine receptor. Recent studies have shown that this process involves the direct binding of G(betagamma) subunits to the NH(2)- and COOH-terminal cytoplasmic domains of the proteins termed GIRK1 and GIRK4 (Kir3.1 and Kir3.4/CIR), which mediate I(KACh). Because of the very low basal activity of native I(KACh), it has been difficult to determine the single channel effect of G(betagamma) subunit binding on I(KACh) activity. Through analysis of a novel G protein-activated chimeric inward rectifier channel that displays increased basal activity relative to I(KACh), we find that single channel activation can be explained by a G protein-dependent shift in the equilibrium of open channel transitions in favor of a bursting state of channel activity over a long-lived closed state.

Animals↗

PubMed2002

Characterization of Dir: a putative potassium inward rectifying channel in Drosophila.

Potassium channels vary in their function and regulation, yet they maintain a number of important features - they are involved in the control of potassium flow, cell volume, cell membrane resting potential, cell excitability and hormone release. The potassium (K(+)) inward rectifier (Kir) superfamily of channels are potassium selective channels, that are sensitive to the concentration of K(+) ions. They are termed inward rectifiers since they allow a much greater K(+) influx than efflux. There are at least seven subfamilies of Kir channels, grouped according to sequence and functional similarities (Curr. Opin. Neurobiol. 5 (1995) 268; Annu. Rev. Physiol. 59 (1997) 171). While numerous Kir channels have been discovered in a variety of organisms, Drosophila inward rectifier (Dir) is the first putative inward rectifier to be studied in Drosophila. In fact, there are only three genes (including Dir) encoding putative inward rectifiers in the Drosophila genome. Though there are other known potassium channels in Drosophila such as ether-a-go-go and shaker, most are voltage-gated channels. As an important first step in characterizing Kir channels in Drosophila, we initiated studies on Dir.

Amino Acid Sequence↗

PubMed2000

Functional evidence for inward-rectifier potassium channels in rat cremaster muscle arterioles.

Moderate increases in extracellular K(+) produce vasodilation in fourth order cremasteric arterioles in the anesthetized rat. We studied the contribution of different subtypes of K(+) channels to this response. Cremaster muscle arteriolar diameters were observed during superfusion with buffer containing 5-30 mM K(+) in the absence (control) and presence of barium (Ba(2+), 50 microM), glibenclamide (GLIB, 1 microM), or iberiotoxin (IBTX, 100 nM) to block inward-rectifier, ATP-sensitive, or Ca(2+)-activated K(+) channels, respectively. Under control conditions, vessels dilated in response to 10-25 mM K(+) and constricted at higher concentrations. At 5 mM K(+), vessel diameters were significantly decreased by GLIB and Ba(2+), but not IBTX, suggesting that basal diameter was regulated by inward-rectifier and ATP-sensitive K(+) channels. In contrast, Ba(2+), but not GLIB or IBTX, prevented K(+)-induced dilation. The data indicate that the inward-rectifier K(+) channel (blocked by low concentrations of Ba(2+), but not GLIB or IBTX) was most likely responsible for the K(+)-induced arteriolar dilation.

Adenosine↗

PubMed1999

Expression of adenosine triphosphate-sensitive potassium channel subunits in female rat reproductive tissues: overlapping distribution of messenger ribonucleic acid for weak inwardly rectifying potassium channel subunit 6.1 and sulfonylurea-binding regulatory subunit 2.

OBJECTIVE: Potassium channel activation has been shown to decrease uterine tone and is a target for inhibition of uterine activity in the treatment of preterm labor. In addition, potassium channel activation also appears to be involved in oocyte maturation. The specific potassium channels responsible for these channel currents have not been identified but are known to be responsive to such agents as pinacidil and to be inhibited by glibenclamide. These findings suggest the presence of an adenosine triphosphate-sensitive potassium channel that is a complex of a weak inwardly rectifying potassium channel subunit 6.1 or 6.2 and sulfonylurea-binding regulatory subunit 1 or 2. STUDY DESIGN: The technique of reverse transcriptase-polymerase chain reaction was used to detect the presence of messenger ribonucleic acid for sulfonylurea-binding regulatory subunit 1 and 2 and weak inwardly rectifying potassium channel subunit 6.1 and 6.2 in the ovary and myometrium of the pregnant rat. In situ hybridization histochemical analysis was used to identify the specific cell types expressing each messenger ribonucleic acid. RESULTS: Reverse transcriptase-polymerase chain reaction analysis found expression of messenger ribonucleic acid for sulfonylurea-binding regulatory subunits 1 and 2B and messenger ribonucleic acid for weak inwardly rectifying potassium channel subunit 6.1 in rat myometrium and ovary during gestation. There was no evidence for expression of weak inwardly rectifying potassium channel subunit 6.2 messenger ribonucleic acid in the ovary or the myometrium of the pregnant rat. In situ hybridization histochemical examination localized expression of messenger ribonucleic acid for sulfonylurea-binding regulatory subunit 2B and messenger ribonucleic acid for weak inwardly rectifying potassium channel subunit 6.1 to uterine myocytes and granulosa cells of the corpus luteum. The cells expressing sulfonylurea-binding regulatory subunit 1 messenger ribonucleic acid could not be identified because of the scarcity of this messenger ribonucleic acid. Messenger ribonucleic acid for sulfonylurea-binding regulatory subunit 1, messenger ribonucleic acid for sulfonylurea-binding regulatory subunit 2B, and messenger ribonucleic acid for weak inwardly rectifying potassium channel subunit 6.1 were also observed in the placenta by in situ hybridization histochemical examination. CONCLUSION: The results suggest that the major adenosine triphosphate-sensitive potassium channel expressed in the myometrium and the corpus luteum during pregnancy is a complex of sulfonylurea-binding regulatory subunit 2B and weak inwardly rectifying potassium channel subunit 6.1.

ATP-Binding Cassette Transporters↗

PubMed1998

Expression of two inward rectifier potassium channels is essential for differentiation of primitive human hematopoietic progenitor cells.

A potassium inward rectifier (K(ir)) current was previously shown by us to be induced in primitive hematopoietic progenitor cells, stimulated with the combination of interleukin-3 (IL-3) and stem cell factor (SCF). Biophysical features of whole cell currents implicated the involvement of more than one K(ir) channel type. Employing IL-3 + SCF stimulated human cord blood CD34+38- cells, we isolated and characterized different components of this current. Reverse transcription-polymerase chain reaction (RT-PCR) subcloning identified the expression of a strongly rectifying K(ir) channel (K(ir) 4.3) as well as a weakly rectifying K(ir) channel (K(ir) 1.1) in these cells. Inhibition of the expression of each of the channels suppressed progenitor cell generation by IL-3 and SCF-stimulated CD34+38- cells in 7-day suspension cultures. The variable expression of two essential inward rectifying potassium channels early in the course of hematopoietic progenitor cell differentiation may play a potentially important role in potassium homeostasis in these cells.

ADP-ribosyl Cyclase↗

PubMed1998

P2Y receptor subtypes differentially couple to inwardly-rectifying potassium channels.

Subtypes of P2Y receptors are well characterized with respect to their agonist profile but little is known about differences in their intracellular signalling properties. When expressed in Xenopus oocytes, both P2Y2 and P2Y6 receptors effectively couple to endogenous Ca2+-dependent Cl--channels. However, only P2Y2 receptors increased currents mediated by inward-rectifier K+ channels of the Kir3.0 subfamily. This increase in Kir-current was sensitive to pertussis toxin, while activation of Ca2+-dependent Cl--channels was not. In contrast, suramin, a P2 receptor antagonist, inhibited activation of both channels. These observations suggest that, in contrast to P2Y6, P2Y2 receptors couple to two different classes of G proteins.

Adenosine Triphosphate↗