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Potassium Replacement

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4381. Potassium-resistant triple helix formation and improved intracellular gene targeting by oligodeoxyribonucleotides containing 7-deazaxanthine. Full Text available with Trip Pro

Potassium-resistant triple helix formation and improved intracellular gene targeting by oligodeoxyribonucleotides containing 7-deazaxanthine. Triple helix formation by purine-rich oligonucleotides in the anti-parallel motif is inhibited by physiological concentrations of potassium. Substitution with 7-deazaxanthine (c7X) has been suggested as a strategy to overcome this effect. We have tested this by examining triple helix formation both in vitro and in vivo by a series of triple helix-forming (...) in a shuttle vector-based mutagenesis assay designed to detect mutations induced by third strand-directed psoralen adducts. When the phosphodiester backbone was replaced by a phosphorothioate one, the in vitro binding of the c7X-TFOs was not affected, but the efficiency of in vivo triple helix formation was reduced. These results indicate the utility of the c7X substitution for in vivo gene targeting experiments, and they show that the feasibility of the triplex anti-gene strategy can be significantly

1997 Nucleic acids research

4382. Heteromerization of Kir2.x potassium channels contributes to the phenotype of Andersen's syndrome Full Text available with Trip Pro

Heteromerization of Kir2.x potassium channels contributes to the phenotype of Andersen's syndrome Andersen's syndrome, an autosomal dominant disorder related to mutations of the potassium channel Kir2.1, is characterized by cardiac arrhythmias, periodic paralysis, and dysmorphic bone structure. The aim of our study was to find out whether heteromerization of Kir2.1 channels with wild-type Kir2.2 and Kir2.3 channels contributes to the phenotype of Andersen's syndrome. The following results show (...) expression of homomeric channels. (iv) Coexpression of nonfunctional Kir2.x constructs, in which the GYG region of the pore region was replaced by AAA, with wild-type Kir2.x channels produced both homomeric and heteromeric dominant-negative effects. (v) Kir2.1 and Kir2.3 channels could be coimmunoprecipitated in membrane extracts from isolated guinea pig cardiomyocytes. (vi) Yeast two-hybrid analysis showed interaction between the N- and C-terminal intracellular domains of different Kir2.x subunits

2002 Proceedings of the National Academy of Sciences of the United States of America

4383. Calcium currents in GH3 cultured pituitary cells under whole-cell voltage-clamp: inhibition by voltage-dependent potassium currents. Full Text available with Trip Pro

Calcium currents in GH3 cultured pituitary cells under whole-cell voltage-clamp: inhibition by voltage-dependent potassium currents. To isolate inward Ca2+ currents in GH3 rat pituitary cells, an inward Na+ current as well as two outward K+ currents, a transient voltage-dependent current (IKV) and a slowly rising Ca2+-activated current (IKCa), must be suppressed. Blockage of these outward currents, usually achieved by replacement of intracellular K+ with Cs+, reveals sustained inward currents (...) Vm to 0 mV. Furthermore, substitution of Ba2+ for Ca2+ causes blockage of IKV and inhibition of this current results in inward Ba2+ currents with square wave kinetics. These data indicate that the Ca2+ current is completely inhibited at peak outward IKV and that Ca2+ conductance is progressively disinhibited as the transient K+ current declines due to channel inactivation. This suggests that in GH3 cells Ca2+ channels are regulated by IKV.

1985 Proceedings of the National Academy of Sciences of the United States of America

4384. Acetylcholine-evoked potassium release in the mouse pancreas. Full Text available with Trip Pro

- was replaced by bromide (Br-) the response to ACh was virtually unaffected. When sodium (Na+) was replaced by lithium (Li+) ACh did not evoke K+ release but instead K+ uptake was observed. However, when Tris+ was substituted for Na+ ACh evoked a very small K+ release. Pre-treatment of pancreatic segments with 10(-3) M-ouabain resulted in a marked sustained K+ release. In the continuing presence of ouabain ACh induced a further increase in K+ outflow. Pre-treatment of the preparation with 10 mM-tetraethyl (...) Acetylcholine-evoked potassium release in the mouse pancreas. Mouse pancreatic segments were superfused with physiological saline solutions and the K+ concentration in the effluent was measured by flame photometry. Acetylcholine (ACh) evoked a dose-dependent and transient increase in the K+ concentration in the effluent (K+ release). The removal of calcium (Ca2+) from the superfusing solution and addition of 10(-4) M-EGTA (ethyleneglycol-bis-(beta-amino-ethylether)N,N'-tetraacetic acid) caused

1985 The Journal of physiology

4385. Effects of external calcium on potassium contractures in tonic muscle fibers of the frog (Rana pipiens). Full Text available with Trip Pro

Effects of external calcium on potassium contractures in tonic muscle fibers of the frog (Rana pipiens). K+ contractures of tonic bundles from cruralis muscle of the frog were studied with different K+ concentrations (10-120 mM). K+ contractures had an initial transient phase followed by a sustained tension. The amplitude of the sustained tension diminished with high K+ concentration (80-120 mM). However, in all cases, tension was maintained for several minutes. External Ca2+ reduction (...) + substitution for Ca2+ before or during K+ contractures. These results indicate that external Ca2+ had to be continuously present to maintain the tension during K+ contractures and that Ni2+ was not able to restore the normal temporal course of K+ contracture. The sustained phase was diminished by blocking agents of Ca2+ channels, such as nifedipine (1 microM) and diltiazem (1-10 microM). The present results can be explained by a direct control of the Ca2+ currents on K+ contracture or by specific

1986 The Journal of physiology

4386. Modulation of potassium conductances by an endogenous neuropeptide in neurones of Aplysia californica. Full Text available with Trip Pro

Modulation of potassium conductances by an endogenous neuropeptide in neurones of Aplysia californica. 1. Macroscopic and single-channel currents were recorded from voltage-clamped neurones in the abdominal and pleural ganglia of Aplysia californica in order to investigate conductance changes elicited by application of the endogenous peptide FMRFamide (Phe-Met-Arg-Phe-NH2) and related neuropeptides to the cell surface. 2. The Ca-dependent K current, IK(Ca), when elicited at a constant voltage (...) by intracellular injection of Ca2+, was insensitive to FMRFamide or its derivative YGG-FMRFamide (Tyr-Gly-Gly-Phe-Met-Arg-Phe-NH2). 3. Under steady voltage clamp, certain cells responded to a brief puff of FMRFamide or YGG-FMRFamide with a transient outward current lasting about 1 min. Unclamped cells responded with a corresponding hyperpolarization. These responses reversed at about -75 mV. Ion substitution indicated that the current is carried by K+. 4. FMRFamide and YGG-FMRFamide were equally effective

1987 The Journal of physiology

4387. Potassium uptake in the mouse submandibular gland is dependent on chloride and sodium and abolished by piretanide. Full Text available with Trip Pro

+ uptake was, however, unaffected when Br- replaced Cl- in the superfusate. Similar effects were observed in the unstimulated glandular tissues. The introduction of Cl-(-)free media containing either NO3- or SO4(2-) resulted in a loss of K+ from the tissue which was followed, upon reintroduction of Cl-, by a pronounced uptake of K+. When Br- was substituted for Cl- there was very little change in [K+] upon removal or reintroduction of Cl-. The uptake of K+ induced by reintroduction of Cl- after (...) Potassium uptake in the mouse submandibular gland is dependent on chloride and sodium and abolished by piretanide. Nervous or hormonal stimulation of salivary secretion in vivo is associated with a pronounced efflux of K+ from the secretory, acinar cells into the blood. This K+ efflux is followed in the post-stimulus period by a reuptake of K+ into the glandular tissue. In the present study we monitor the changes in [K+] of physiological solutions perfusing a flow chamber containing isolated

1986 The Journal of physiology

4388. The effects of rubidium ions on components of the potassium conductance in the frog node of Ranvier. Full Text available with Trip Pro

The effects of rubidium ions on components of the potassium conductance in the frog node of Ranvier. The effects of replacement of external and internal K+ ions by Rb+ ions on the two fast components (gf1 and gf2) and slow component (gs) of the K+ conductance (gK) in frog nodes of Ranvier were investigated under voltage- and current-clamp conditions. Fast and slow components of gK were separated by double exponential fits to tail currents following long depolarizing pre-pulses, or by the use (...) component of the tail current. Regenerative responses, which occur in high [K+] (+300 nM-tetrodotoxin) solutions in current clamp did not repolarize in Rb+. Voltage-clamp experiments showed that inactivation of inward currents is slowed when Rb+ is the charge carrier. Replacement of internal K+, by application of Rb+ to the cut ends of the fibre, shifted the reversal potential to more positive potentials but had no effect on the conductance or kinetics. External Rb+ has a large number of effects

1986 The Journal of physiology

4389. Effects of glucose removal and readmission on potassium contracture in the guinea-pig taenia coli. Full Text available with Trip Pro

Effects of glucose removal and readmission on potassium contracture in the guinea-pig taenia coli. The effects of removal and readmission of substrates on the K contracture were investigated in the guinea-pig taenia coli. When, after exposure to excess K in Ca-free and glucose-free medium, the readmission and removal of 2.4 mM-Ca were repeated at regular intervals, the Ca-induced contractions decreased progressively. The decrease was more marked in the late than in the early part of the tension (...) response. The rate of O2 consumption decreased when the normal medium was replaced by glucose-free, Ca-free, excess-K solution, but substantially recovered following Ca readmission. ATP and creatine phosphate contents decreased during the Ca-induced contraction, but recovered partially during the subsequent relaxation in Ca-free solution. The effects of glucose removal were rapidly reversed when glucose or beta-hydroxybutyrate (beta-HB) were readmitted to the bathing solution. In the absence of Ca

1984 The Journal of physiology

4390. Calcium and potassium currents in spermatogenic cells dissociated from rat seminiferous tubules. Full Text available with Trip Pro

Calcium and potassium currents in spermatogenic cells dissociated from rat seminiferous tubules. The electrophysiological properties of the cell membrane of rat spermatogenic cells were studied using the whole-cell variation of the patch-electrode voltage-clamp technique. In late primary spermatocytes and early spermatids isolated from adult testis, a transient inward current followed by a slowly developing outward current was produced when the membrane potential was made more positive than -60 (...) mV. Early spermatogenic cells which consist of spermatogonia and early spermatocytes were isolated either from new-born rats (12-14 days old) of from adult cryptorchid rats 15-21 days after the operation. In early spermatogenic cells, some showed a slowly developing outward current with negligible initial inward current, while others showed a recognizable inward current followed by the slowly developing outward current. The inward currents are identified as Ca2+-carried current, since replacement

1984 The Journal of physiology

4391. Inhibition of the sodium pump in guinea-pig ventricular muscle by dihydro-ouabain: effects of external potassium and sodium. Full Text available with Trip Pro

Inhibition of the sodium pump in guinea-pig ventricular muscle by dihydro-ouabain: effects of external potassium and sodium. The inhibition of the electrogenic pump current in quiescent guinea-pig ventricular muscle by dihydro-ouabain (DHO) was studied with the three-micro-electrode voltage-clamp technique described previously (Daut, 1982c). From dose-response curves of the drug-induced current change (ID) the equilibrium dissociation constant of the binding of DHO to the Na-K pump (KD (...) ) and the electrogenic pump current flowing in the steady state (Ip) were inferred (Daut & Rüdel, 1982b). The external K concentration ([K]o) was varied between 2 and 4.5 mM (substituted by Na). KD was found to increase with increasing [K]o. A plot of log KD versus log [K]o gave a straight line with a slope of about 1.5. The time constants of the onset (tau on) and decay (tau off) of ID are supposed to represent the chemical kinetics of binding and unbinding of the drug (Daut & Rüdel, 1981, 1982b). Tau on was found

1983 The Journal of physiology

4392. Identification of delayed potassium and calcium currents in the rat sympathetic neurone under voltage clamp. Full Text available with Trip Pro

Identification of delayed potassium and calcium currents in the rat sympathetic neurone under voltage clamp. Post-ganglionic neurones of the isolated rat superior cervical ganglion were studied at 37 degrees C under two-electrode voltage-clamp conditions. Membrane depolarization beyond -40 mV from holding levels between -50 and -100 mV produced a delayed outward current which exhibited no inactivation within this voltage range. The current is carried primarily by K+ ions and its instantaneous I (...) -V relation is linear. The total outward current could be separated into two distinct components on the basis of ion-substitution experiments. A voltage-dependent component of the delayed current, termed IK(V), is activated by membrane depolarization beyond -40 mV when Ca2+ fluxes are selectively blocked by Cd2+ or in Ca2+-free solution. IK(V) develops following first-order kinetics and rises to a peak with a voltage-dependent delay (239 ms at -30 mV and 23 ms at +10 mV). GK(V) attains

1985 The Journal of physiology

4393. A voltage-gated potassium channel in human T lymphocytes. Full Text available with Trip Pro

A voltage-gated potassium channel in human T lymphocytes. Human peripheral T lymphocytes were studied at 20-24 degrees C using the gigaohm seal recording technique in whole-cell or outside-out patch conformations. The predominant ion channel present under the conditions employed was a voltage-gated K+ channel closely resembling delayed rectifier K+ channels of nerve and muscle. The maximum K+ conductance in ninety T lymphocytes ranged from 0.7 to 8.9 nS, with a mean of 4.2 nS. The estimated (...) permeability. Tail current kinetics were slowed about 2-fold by raising the external K+ concentration from 4.5 to 160 mM, and were 5 times slower in Rb+ Ringer solution than in K+ Ringer solution. Single K+ channel currents had two amplitudes corresponding to about 9 and 16 pS in Ringer solution. Replacing Ringer solution with isotonic K+ Ringer solution increased the unitary conductance and resulted in inward rectification of the unitary current-voltage relation. Comparable effects of external K+ were

1985 The Journal of physiology

4394. Apical membrane potassium and chloride permeabilities in surface cells of rabbit descending colon epithelium. Full Text available with Trip Pro

Apical membrane potassium and chloride permeabilities in surface cells of rabbit descending colon epithelium. The apical membranes of surface cells in the rabbit descending colon possess a significant ionic conductance in parallel to amiloride-blockable Na+ channels. The identity of the ion(s) responsible for the amiloride-insensitive conductance is unknown. The purpose of the present paper was to assess the permeability and net driving forces for K+ and Cl- across this membrane using (...) conventional and ion-sensitive micro-electrode techniques. Intracellular Cl- activity (aiCl) averaged 23 +/- 2 mM with an equilibrium potential (ECl) of -38 +/- 2 mV. This value is less than previous estimates of the electromotive force (e.m.f.) of the amiloride-insensitive pathway (ca. -50 mV). Consequently, Cl- alone cannot account for the amiloride-insensitive conductance. Replacement of Cl- by gluconate in the serosal solution decreased aiCl to 17 +/- 2.8 mM. aiCl was lowered to approximately 1 mM

1985 The Journal of physiology

4395. Calcium- and voltage-activated potassium channels in human macrophages. Full Text available with Trip Pro

Calcium- and voltage-activated potassium channels in human macrophages. Single calcium-activated potassium channel currents were recorded in intact and excised membrane patches from cultured human macrophages. Channel conductance was 240 pS in symmetrical 145 mM K+ and 130 pS in 5 mM external K+. Lower conductance current fluctuations (40% of the larger channels) with the same reversal potential as the higher conductance channels were noted in some patches. Ion substitution experiments (...) indicated that the channel is permeable to potassium and relatively impermeable to sodium. The frequency of channel opening increased with depolarization and intracellular calcium concentration. At 10(-7) M (Ca++)i, channel activity was evident only at potentials of +40 mV or more depolarized, while at 10(-5) M, channels were open at all voltages tested (-40 to +60 mV). In intact patches, channels were seen at depolarized patch potentials of +50 mV or greater, indicating that the ionized calcium

1984 Biophysical journal

4396. Potassium Transport in Corn Roots : IV. Characterization of the Linear Component Full Text available with Trip Pro

Potassium Transport in Corn Roots : IV. Characterization of the Linear Component A detailed examination was conducted on the linear, or first-order kinetic component for K(+)((86)Rb(+)) influx into root segments of both low- and high-salt grown corn seedlings (Zea mays [A632 x Oh 43]). In tissue from both low- and high-salt grown roots, replacement of Cl(-) in the uptake solution by either SO(4) (2-), H(2)PO(4) (-), or NO(3) (-) caused a significant (50-60%) and specific inhibition (...) of the linear component of K(+) influx. The anion transport inhibitor, 4,4'-diisothiocyano-2,2'-disulfonic acid, was found to abolish saturable Cl(-) influx in corn roots while causing a significant (50-60%) and specific inhibition of the linear K(+) uptake system; this inhibition was identical to that observed when Cl(-) was replaced by other anions in the K(+) uptake solution. Additionally, the quaternary ammonium cation, tetraethylammonium, which has been shown to block K(+) channels in nerve axons, also

1985 Plant physiology

4397. Slow components of potassium tail currents in rat skeletal muscle Full Text available with Trip Pro

for the latter did not allow significant outward current. Substitution of Rb for extracellular K abolished current through the anomalous (inward-going) rectifier and at the same time eliminated the slow inward tail, which suggests that the slow inward tail current flows through anomalous rectifier channels. The amplitude of the slow inward tail was increased and VK was shifted in the depolarizing direction by longer conditioning pulses. The shift in VK implies that during outward currents potassium (...) Slow components of potassium tail currents in rat skeletal muscle The kinetics of potassium tail currents have been studied in the omohyoid muscle of the rat using the three-microelectrode voltage-clamp technique. The currents were elicited by a two-pulse protocol in which a conditioning pulse to open channels was followed by a test step to varying levels. The tail currents reversed at a single well-defined potential (VK). At hyperpolarized test potentials (-100 mV and below), tail currents

1983 The Journal of general physiology

4398. Na+-K+ pump activities of high- and low-potassium sheep red cells with internal magnesium and calcium altered by A23187. Full Text available with Trip Pro

Na+-K+ pump activities of high- and low-potassium sheep red cells with internal magnesium and calcium altered by A23187. 1. Sheep erythrocytes were treated with the divalent metal ionophore A23187 to alter the cellular magnesium (Mgi) and calcium (Cai) composition. Ouabain-sensitive Na+-K+ pump fluxes were measured using rubidium as a potassium congener in media where Cl- was replaced by NO3-. 2. A23187, per se, had no effect on ouabain-sensitive rubidium influx. However, lowering (...) the concentration of cellular magnesium [( Mg]i) and increasing that of calcium [( Ca]i) decreased Na+-K+ pump flux. 3. Ouabain-sensitive rubidium influx was found to be a saturating function of [Mg]i in high-potassium (HK) red cells with a Hill coefficient of about 1.8 and an apparent half-activation constant (K0.5) of 0.46 mmol/(l original cells). In low-potassium (LK) cells, in the absence and presence of the Na+-K+ pump stimulatory L-antibody, ouabain-sensitive rubidium influx was also saturated with Mgi

1988 The Journal of physiology

4399. Potassium (86Rb+) efflux from the rat submandibular gland under sodium-free conditions in vitro. Full Text available with Trip Pro

Potassium (86Rb+) efflux from the rat submandibular gland under sodium-free conditions in vitro. 1. Fragments of rat submandibular gland were pre-loaded with 86Rb+, an isotopic marker of potassium transport, and rate constants for 86Rb+ efflux were determined during superfusion with a physiological salt solution. 2. In sodium-containing solutions acetylcholine evoked a rapid and immediate increase in efflux rate. After reaching a peak value, the efflux rate initially declined rapidly (...) , but a second, slowly declining phase to the response was also evident. The response could be resolved into Ca2(+)-independent and Ca2(+)-dependent phases. 3. The basal efflux rate was elevated during superfusion with solutions in which sodium had been replaced with either lithium or N-methyl-D-glucammonium (NMDG+). Although lithium had a greater effect, which was absent under calcium-free conditions, addition of calcium to initially calcium-free, lithium-containing solutions did not affect the rate

1989 The Journal of physiology

4400. Rubidium ions and the gating of delayed rectifier potassium channels of frog skeletal muscle. Full Text available with Trip Pro

Rubidium ions and the gating of delayed rectifier potassium channels of frog skeletal muscle. 1. Unitary currents were measured through delayed rectifier potassium channels of frog skeletal muscle, under conditions where either potassium or rubidium ions carried current. 2. Unitary currents were reduced in amplitude when Rb+ was the charge carrier, indicating that Rb+ permeated the channel less readily than did K+. On the other hand permeability ratios (PRb/PK) measured from the change (...) in reversal potential upon ionic substitution were 0.92 for the external and 0.67 for the internal mouth of the channel. 3. Ensemble-averaged currents activated under depolarization along a similarly S-shaped time course whether K+ or Rb+ carried current, though slightly more slowly in Rb+. However, under repolarization to a negative level, tail currents were prolonged about tenfold in Rb+. 4. The duration of channel opening was substantially prolonged in Rb+. The distribution of open times was fitted

1989 The Journal of physiology

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