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Potassium Replacement

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4301. Calcium and potassium currents in muscle fibres of an insect (Carausius morosus). Full Text available with Trip Pro

Calcium and potassium currents in muscle fibres of an insect (Carausius morosus). 1. A three electrode voltage-clamp was used to investigate membrane currents in the skeletal muscle fibres of the stick insect, Carausius morosus. Contraction was blocked by hypertonic solutions. 2. Membrane currents elicited by step depolarizations consisted of an inward current, an early outward current and a delayed outward current. 3. The reversal potential of the delayed outward current did not change when (...) SO4(2-) was substituted for Cl-, but shifted by 14.1 mV when [K]0 was increased from 20 mM to 40 mM in SO4(2-) solution, suggesting that the delayed current is carried by K+. Both early and delayed outward currents were substantially reduced by 120 mM-tetraethylammonium (TEA) ions. 4. The small size of the shift in the reversal potential of the delayed outward current with increased pulse duration suggests that the delayed current measured flows mainly across the surface membrane. 5. Increasing

1982 The Journal of physiology

4302. Effect of potassium depolarization on sodium-dependent calcium efflux from goldfish heart ventricles and guinea-pig atria Full Text available with Trip Pro

Effect of potassium depolarization on sodium-dependent calcium efflux from goldfish heart ventricles and guinea-pig atria 1. (45)Ca fluxes were studied in normal and potassium-depolarized goldfish ventricles as a function of the external Na concentration. Some of the experiments were also performed on guinea-pig auricles.2. When the external K concentration was increased from 5.4 to 142 mM, keeping osmolarity constant by adding 137 mM-Li or choline (hyperosmotically) to the low K solution (...) in guinea-pig atria.4. A similar repolarization and Na-dependent reactivation of (45)Ca efflux was obtained in goldfish ventricles superfused with 10(-6) M-Ca(2+) (4.5 mM-Ca, 5 mM-EGTA, pH 7.1), provided that the (45)Ca washout was started in high K.5. In 10(-6) M-Ca(2+), 137 mM-Na, 5.4 mM-K and 137 mM-choline goldfish ventricles depolarized to about -25 mV within 80 min. If the choline was now replaced by 137 mM-K, the membrane potential moved to ca. -15 mV, and under these conditions the (45)Ca efflux

1982 The Journal of physiology

4303. Slow calcium and potassium currents across frog muscle membrane: measurements with a vaseline-gap technique. Full Text available with Trip Pro

Slow calcium and potassium currents across frog muscle membrane: measurements with a vaseline-gap technique. 1. A vaseline-gap voltage-clamp technique was used to record slow Ca2+ and K+ currents from frog skeletal muscle fibres loaded with the Ca2+ chelator EGTA. 2. K+ currents were increased when Mg2+ replaced external Ca2+, and they were abolished when internal K+ was replaced by tetraethylammonium (TEA+). Ca2+ currents could be studied in isolation in fibres loaded with (TEA)2EGTA. 3. Under

1981 The Journal of physiology

4304. Chloride dependence of frusemide- and phloretin-sensitive passive sodium and potassium fluxes in human red cells. Full Text available with Trip Pro

Chloride dependence of frusemide- and phloretin-sensitive passive sodium and potassium fluxes in human red cells. 1. In outdated human red blood cells, there was a Ko-dependent, ouabain-insensitive efflux of Na that was inhibited by frusemide and phloretin. 2. It was reduced or absent (a) in media containing Ca or Mg, (b) in fresh cells. 3. In media with Cl partly replaced by NO3, Na efflux, and its sensitivity to Ko and frusemide, were reduced. 4. The saturable component of ouabain-insensitive

1981 The Journal of physiology

4305. The effect of external potassium on the removal of sodium inactivation in squid giant axons. Full Text available with Trip Pro

The effect of external potassium on the removal of sodium inactivation in squid giant axons. 1. The effect of external and internal electrolytes on the parameters of the Na conductance, in particular on the time constant of removal of Na inactivation, was studied in intact and perfused squid giant axons under voltage-clamp conditions. 2. Adding 20-40 mM-KCl, -CsCl or -RbCl to K-free sea water reversibly increased the time constant of removal of inactivation by a factor of about 1.3; adding 20 (...) concentration of 0.1 mM in the internal solution had no effect on Na inactivation. 3. The observations are compatible with the idea that external K, Cs or Rb interfere with the binding of Ca to negative fixed charges at the outer side of the membrane, thereby causing a shift in the opposite direction to the shift produced by raising external Ca. 5. Replacing two thirds of the internal K by Na reversibly increased the time constant of removal of sodium inactivation and moved the tau h(V) curve

1981 The Journal of physiology

4306. 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

4307. 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

4308. 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

4309. 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

4310. 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

4311. 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

4312. 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

4313. 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

4314. 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

4315. 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

4316. 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

4317. On the mechanism of a pH-induced rise in membrane potassium conductance in hamster eggs. Full Text available with Trip Pro

On the mechanism of a pH-induced rise in membrane potassium conductance in hamster eggs. 1. The effect of external pH (pHo) on the membrane potential and resistance of unfertilized zona-free hamster eggs was investigated by intracellular recording techniques. 2. A hyperpolarization of the hamster egg membrane was induced by raising the extracellular pH above 8.0. This hyperpolarization was accompanied by a rise in membrane conductance and was reversible by washing the egg. 3. The estimated (...) value of the reversal potential of the hyperpolarizing response to a solution with pHo 9.5 was about -85 mV. The membrane potential changed linearly with log [K+]o with a slope of 43 +/- 2 mV (mean +/- S.D.; n = 4) for a 10-fold change in [K+]o, while it was unaltered by the removal of Cl- from the solution. 4. The amplitude of the pHo-induced hyperpolarization decreased substantially as [Ca2+]o was lowered from 20 to 1 mM. Sr2+ could substitute for Ca2+ in sustaining the response to high pHo

1988 The Journal of physiology

4318. 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

4319. 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

4320. 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

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