scholarly journals A Potassium-Selective Current Affected by Micromolar Concentrations of Anion Transport Inhibitors

2018 ◽  
Vol 45 (3) ◽  
pp. 867-882
Author(s):  
Roberta Costa ◽  
Davide Antonio Civello ◽  
Emanuele Bernardinelli ◽  
Simone Vanoni ◽  
Michaela Zopf ◽  
...  
Keyword(s):  
Niflumic Acid ◽  
Disulfonic Acid ◽  
Hek 293 ◽  
K Channels ◽  
Inflammatory Drug ◽  
Physiological Phenomenon ◽  
Voltage Dependent ◽  
Cl Channels ◽  
K Current ◽  
Anti Inflammatory

Background/Aims: In the human genome, more than 400 genes encode ion channels, which are ubiquitously expressed and often coexist and participate in almost all physiological processes. Therefore, ion channel blockers represent fundamental tools in discriminating the contribution of individual channel types to a physiological phenomenon. However, unspecific effects of these compounds may represent a confounding factor. Three commonly used chloride channel inhibitors, i.e. 4,4′-diisothiocyano-2,2′-stilbene-disulfonic acid (DIDS), 5-nitro-2-[(3-phenylpropyl) amino]benzoic acid (NPPB) and the anti-inflammatory drug niflumic acid were tested to identify the lowest concentration effective on Cl- channels and ineffective on K+ channels. Methods: The activity of the above mentioned compounds was tested by whole cell patch-clamp on the swelling-activated Cl- current ICl,swell and on the endogenous voltage-dependent, outwardly rectifying K+ selective current in human kidney cell lines (HEK 293/HEK 293 Phoenix). Results: Micromolar (1-10 µM) concentrations of DIDS and NPPB could not discriminate between the Cl- and K+ selective currents. Specifically, 1 µM DIDS only affected the K+ current and 10 µM NPPB equally affected the Cl- and K+ currents. Only relatively high (0.1-1 mM) concentrations of DIDS and prolonged (5 minutes) exposure to 0.1-1 mM NPPB preferentially suppressed the Cl- current. Niflumic acid preferentially inhibited the Cl- current, but also significantly affected the K+ current. The endogenous voltage-dependent, outwardly rectifying K+ selective current in HEK 293/HEK 293 Phoenix cells was shown to arise from the Kv 3.1 channel, which is extensively expressed in brain and is involved in neurological diseases. Conclusion: The results of the present study underscore that sensitivity of a given physiological phenomenon to the Cl- channel inhibitors NPPB, DIDS and niflumic acid may actually arise from an inhibition of Cl- channels but can also result from an inhibition of voltage-dependent K+ channels, including the Kv 3.1 channel. The use of niflumic acid as anti-inflammatory drug in patients with concomitant Kv 3.1 dysfunction may result contraindicated.

scholarly journals Potassium channel types in arterial chemoreceptor cells and their selective modulation by oxygen.

1992 ◽  
Vol 100 (3) ◽  
pp. 401-426 ◽  
Author(s):  
M D Ganfornina ◽  
J López-Barneo
Keyword(s):  
Time Course ◽  
Single Channel ◽  
K Channel ◽  
Open Probability ◽  
K Channels ◽  
Glomus Cells ◽  
Control Value ◽  
Voltage Dependent ◽  
K Current ◽  
Chemoreceptor Cells

Single K+ channel currents were recorded in excised membrane patches from dispersed chemoreceptor cells of the rabbit carotid body under conditions that abolish current flow through Na+ and Ca2+ channels. We have found three classes of voltage-gated K+ channels that differ in their single-channel conductance (gamma), dependence on internal Ca2+ (Ca2+i), and sensitivity to changes in O2 tension (PO2). Ca(2+)-activated K+ channels (KCa channels) with gamma approximately 210 pS in symmetrical K+ solutions were observed when [Ca2+]i was greater than 0.1 microM. Small conductance channels with gamma = 16 pS were not affected by [Ca2+]i and they exhibited slow activation and inactivation time courses. In these two channel types open probability (P(open)) was unaffected when exposed to normoxic (PO2 = 140 mmHg) or hypoxic (PO2 approximately 5-10 mmHg) external solutions. A third channel type (referred to as KO2 channel), having an intermediate gamma(approximately 40 pS), was the most frequently recorded. KO2 channels are steeply voltage dependent and not affected by [Ca2+]i, they inactivate almost completely in less than 500 ms, and their P(open) reversibly decreases upon exposure to low PO2. The effect of low PO2 is voltage dependent, being more pronounced at moderately depolarized voltages. At 0 mV, for example, P(open) diminishes to approximately 40% of the control value. The time course of ensemble current averages of KO2 channels is remarkably similar to that of the O2-sensitive K+ current. In addition, ensemble average and macroscopic K+ currents are affected similarly by low PO2. These observations strongly suggest that KO2 channels are the main contributors to the macroscopic K+ current of glomus cells. The reversible inhibition of KO2 channel activity by low PO2 does not desensitize and is not related to the presence of F-, ATP, and GTP-gamma-S at the internal face of the membrane. These results indicate that KO2 channels confer upon glomus cells their unique chemoreceptor properties and that the O2-K+ channel interaction occurs either directly or through an O2 sensor intrinsic to the plasma membrane closely associated with the channel molecule.

scholarly journals A chloride channel from lobster walking leg nerves. Characterization of single-channel properties in planar bilayers.

1990 ◽  
Vol 96 (4) ◽  
pp. 707-733 ◽  
Author(s):  
G L Lukács ◽  
E Moczydlowski
Keyword(s):  
Single Channel ◽  
Disulfonic Acid ◽  
Ph Change ◽  
Planar Bilayers ◽  
Voltage Range ◽  
Cl Channel ◽  
Voltage Dependent ◽  
Cl Channels ◽  
Transport Inhibitors ◽  
Small Conductance

A novel, small conductance of Cl- channel was characterized by incorporation into planar bilayers from a plasma membrane preparation of lobster walking leg nerves. Under conditions of symmetrical 100 mM NaCl, 10 mM Tris-HCl, pH 7.4, single Cl- channels exhibit rectifying current-voltage (I-V) behavior with a conductance of 19.2 +/- 0.8 pS at positive voltages and 15.1 +/- 1.6 pS in the voltage range of -40 to 0 mV. The channel exhibits a negligible permeability for Na+ compared with Cl- and displays the following sequence of anion permeability relative to Cl- as measured under near bi-ionic conditions: I- (2.7) greater than NO3- (1.8) greater than Br- (1.5) greater than Cl- (1.0) greater than CH3CO2- (0.18) greater than HCO3- (0.10) greater than gluconate (0.06) greater than F- (0.05). The unitary conductance saturates with increasing Cl- concentration in a Michaelis-Menten fashion with a Km of 100 mM and gamma max = 33 pS at positive voltage. The I-V curve is similar in 10 mM Tris or 10 mM HEPES buffer, but substitution of 100 mM NaCl with 100 mM tetraethylammonium chloride on the cis side results in increased rectification with a 40% reduction in current at negative voltages. The gating of the channel is weakly voltage dependent with an open-state probability of 0.23 at -75 mV and 0.64 at +75 mV. Channel gating is sensitive to cis pH with an increased opening probability observed for a pH change of 7.4 to 11 and nearly complete inhibition for a pH change of 7.4 to 6.0. The lobster Cl- channel is reversibly blocked by the anion transport inhibitors, SITS (4-acetamido, 4'-isothiocyanostilbene-2,2'-disulfonic acid) and NPPB (5-nitro-2-(3-phenylpropylamino)benzoic acid). Many of these characteristics are similar to those previously described for small conductance Cl- channels in various vertebrate cells, including epithelia. These functional comparisons suggest that this invertebrate Cl- channel is an evolutionary prototype of a widely distributed class of small conductance anion channels.

scholarly journals Charybdotoxin selectively blocks small Ca-activated K channels in Aplysia neurons.

1987 ◽  
Vol 90 (1) ◽  
pp. 27-47 ◽  
Author(s):  
A Hermann ◽  
C Erxleben
Keyword(s):  
Single Channel ◽  
Delayed Rectifier ◽  
Pacemaker Activity ◽  
Dependent Manner ◽  
Open Probability ◽  
Apparent Dissociation Constant ◽  
External Application ◽  
K Channels ◽  
Voltage Dependent ◽  
K Current

The action of charybdotoxin (ChTX), a peptide component isolated from the venom of the scorpion Leiurus quinquestriatus, was investigated on membrane currents of identified neurons from the marine mollusk, Aplysia californica. Macroscopic current recordings showed that the external application of ChTX blocks the Ca-activated K current in a dose- and voltage-dependent manner. The apparent dissociation constant is 30 nM at V = -30 mV and increases e-fold for a +50- to +70-mV change in membrane potential, which indicates that the toxin molecule is sensitive to approximately 35% of the transmembrane electric field. The toxin is bound to the receptor with a 1:1 stoichiometry and its effect is reversible after washout. The toxin also suppresses the membrane leakage conductance and a resting K conductance activated by internal Ca ions. The toxin has no significant effect on the inward Na or Ca currents, the transient K current, or the delayed rectifier K current. Records from Ca-activated K channels revealed a single channel conductance of 35 +/- 5 pS at V = 0 mV in asymmetrical K solution. The channel open probability increased with the internal Ca concentration and with membrane voltage. The K channels were blocked by submillimolar concentrations of tetraethylammonium ions and by nanomolar concentrations of ChTX, but were not blocked by 4-aminopyridine if applied externally on outside-out patches. From the effects of ChTX on K current and on bursting pacemaker activity, it is concluded that the termination of bursts is in part controlled by a Ca-activated K conductance.

Interaction of zinc(II) with the non-steroidal anti-inflammatory drug niflumic acid

2017 ◽  
Vol 176 ◽  
pp. 100-112 ◽  
Author(s):  
Alketa Tarushi ◽  
Catherine P. Raptopoulou ◽  
Vassilis Psycharis ◽  
Dimitris P. Kessissoglou ◽  
Athanasios N. Papadopoulos ◽  
...  
Keyword(s):  
Niflumic Acid ◽  
Inflammatory Drug ◽  
Anti Inflammatory

scholarly journals Dynamics of aminopyridine block of potassium channels in squid axon membrane.

1976 ◽  
Vol 68 (5) ◽  
pp. 519-535 ◽  
Author(s):  
J Z Yeh ◽  
G S Oxford ◽  
C H Wu ◽  
T Narahashi
Keyword(s):  
Time Course ◽  
Membrane Surface ◽  
K Channel ◽  
Dependent Manner ◽  
Squid Axon ◽  
Axon Membrane ◽  
K Channels ◽  
Voltage Dependent ◽  
K Current ◽  
Kinetics Of

Aminopyridines (2-AP, 3-AP, and 4-AP) selectively block K channels of squid axon membranes in a manner dependent upon the membrane potential and the duration and frequency of voltage clamp pulses. They are effective when applied to either the internal or the external membrane surface. The steady-state block of K channels by aminopyridines is more complete for low depolarizations, and is gradually relieved at higher depolarizations. The K current in the presence of aminopyridines rises more slowly than in control, the change being more conspicuous in 3-AP and 4-AP than in 2-AP. Repetitive pulsing relieves the block in a manner dependent upon the duration and interval of pulses. The recovery from block during a given test pulse is enhanced by increasing the duration of a conditioning depolarizing prepulse. The time constant for this recovery is in the range of 10-20 ms in 3-AP and 4-AP, and shorter in 2-AP. Twin pulse experiments with variable pulse intervals have revealed that the time course for re-establishment of block is much slower in 3-AP and 4-AP than in 2-AP. These results suggest that 2-AP interacts with the K channel more rapidly than 3-AP and 4-AP. The more rapid interaction of 2-AP with K channels is reflected in the kinetics of K current which is faster than that observed in 3-AP or 4-AP, and in the pattern of frequency-dependent block which is different from that in 3-AP or 4-AP. The experimental observations are not satisfactorily described by alterations of Hodgkin-Huxley n-type gating units. Rather, the data are consistent with a simple binding scheme incorporating no changes in gating kinetics which conceives of aminopyridine molecules binding to closed K channels and being released from open channels in a voltage-dependent manner.

Diverse modulations of chloride channels in renal proximal tubules

1994 ◽  
Vol 267 (5) ◽  
pp. F716-F724 ◽  
Author(s):  
N. Darvish ◽  
J. Winaver ◽  
D. Dagan
Keyword(s):  
Chloride Channels ◽  
Disulfonic Acid ◽  
Channel Activity ◽  
Cation Permeability ◽  
Voltage Dependent ◽  
Selective Channel ◽  
Cl Channels ◽  
The Rich ◽  
Apical Membranes ◽  
Inside Out

Cl- selective channels were detected and characterized in apical membranes of cultured rat renal proximal convoluted tubule cells (PCT) using patch-clamping methods. Subpopulations of Cl- channels modulated by cyclic nucleotides, Ca2+, or voltage were identified. Two different 30-pS, voltage-independent, Cl- channels modulated by adenosine 3',5'-cyclic monophosphate (cAMP) or Ca2+ were seen most frequently. The cAMP-dependent channel was activated by membrane-permeable analogues of cAMP, dibutyryl-cAMP or 8-bromo-cAMP. Catalytic subunit of protein kinase A (PKA) applied to detached inside-out patches, activated the channel as well, suggesting activation via phosphorylation. Channel activity was blocked by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, by 4,4-dinitrostilbene-2,2-disulfonic acid, and by SCN-. Permeability sequence for different halides was Cl- > I > F with a Cl(-)-to-cation permeability ratio (PCl/Pcation) of 7:1. The Ca(2+)-sensitive channel was not activated by cAMP nor by PKA. A third anionic selective channel encountered infrequently is voltage dependent and has a unitary conductance of 145 pS, with a PCl/Pcation value of 9:1. This diversity of Cl- channels may underlie the rich repertoire of physiological functions attributed to Cl- channels.

Muscarinic suppression of Ca2+-dependent K current in colonic smooth muscle

1989 ◽  
Vol 257 (3) ◽  
pp. C481-C487 ◽  
Author(s):  
W. C. Cole ◽  
A. Carl ◽  
K. M. Sanders
Keyword(s):  
Smooth Muscle ◽  
Single Channel ◽  
Circular Muscle ◽  
Outward Current ◽  
Cell Voltage ◽  
Proximal Colon ◽  
K Channels ◽  
Positive Shift ◽  
Voltage Dependent ◽  
K Current

Acetylcholine (ACh) increases the amplitude and duration of colonic electrical slow waves. This suggests that ACh either increases an inward current or suppresses an outward current. The latter hypothesis was tested in whole cell voltage-clamp experiments performed on freshly dispersed smooth muscle cells from canine proximal colon. Addition of ACh (10(-5) M) to solutions bathing cells reduced time-dependent outward currents elicited by depolarizing test pulses in the range of -45 to +30 mV. Analysis of tail currents showed that ACh caused a 10- to 15-mV positive shift in voltage-dependent activation. When cells were pretreated with 10(-6) M nifedipine to abolish the Ca2+-dependent component of the outward current, the reduction of outward current by ACh was blocked. Single-channel experiments were performed to determine whether ACh had a direct effect on Ca2+-activated K channels. ACh, 10(-5) M, added to bath and pipette solutions caused a positive shift in voltage-dependent activation in on-cell experiments. This effect of ACh on Ca2+-activated K channels provides a mechanism for the effects of muscarinic, excitatory stimulation of circular muscle of the colon.

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