scholarly journals Actions of dendrotoxin on K+ channels and neuromuscular transmission in Drosophila melanogaster, and its effects in synergy with K+ channel-specific drugs and mutations

1989 ◽  
Vol 147 (1) ◽  
pp. 21-41 ◽  
Author(s):  
C. F. Wu ◽  
M. C. Tsai ◽  
M. L. Chen ◽  
Y. Zhong ◽  
S. Singh ◽  
...  
Keyword(s):  
Neuromuscular Junction ◽  
Neuromuscular Transmission ◽  
Synergistic Effects ◽  
Facilitatory Effect ◽  
Muscle Membrane ◽  
K Channel ◽  
Delayed Rectifier ◽  
K Channels ◽  
Channel Blocking ◽  
K Current

The blockade of K+ channels and enhancement of neuromuscular transmission by dendrotoxin (DTX), a convulsant peptide from mamba snake venom, were examined in normal and mutant larval preparations of Drosophila. Two-microelectrode voltage-clamp experiments showed that DTX reduced the transient K+ current, IA, in muscle membrane. This effect was suppressed by raising the Mg2+ concentration or by lowering the temperature. The interaction of DTX with Mg2+ was further analyzed at a low cation concentration, at which DTX reduced both IA and the delayed rectifier IK. These results were correlated with the action of DTX on the neuromuscular junction. Its facilitatory effect on excitatory junctional potentials (EJPs) was relatively mild but the effect was drastically enhanced when combined with certain mutations and K+ channel blocking drugs, leading to repetitive or prolonged giant EJPs. Only the mutations or drugs that reduced IK or the Ca2(+)-dependent K+ current, ICF, could yield these synergistic effects with DTX. In contrast, the abnormal EJPs caused by the mutation or drug that blocked IA were not further enhanced by DTX, indicating that DTX also affects IA at the neuromuscular junction. Thus, the A-type K+ channels in muscle and nerve terminals appeared very similar in their sensitivity to the specific toxin, drugs and mutations examined here.

scholarly journals Actions of FTY720 (Fingolimod), a Sphingosine-1-Phosphate Receptor Modulator, on Delayed-Rectifier K+ Current and Intermediate-Conductance Ca2+-Activated K+ Channel in Jurkat T-Lymphocytes

Molecules ◽  
2020 ◽  
Vol 25 (19) ◽  
pp. 4525
Author(s):  
Wei-Ting Chang ◽  
Ping-Yen Liu ◽  
Sheng-Nan Wu
Keyword(s):  
T Lymphocytes ◽  
Immune Cells ◽  
K Channel ◽  
Delayed Rectifier ◽  
Inactivation Kinetics ◽  
Dependent Manner ◽  
Inactivation Curve ◽  
K Channels ◽  
Sphingosine 1 Phosphate ◽  
K Current

FTY720 (fingolimod), a modulator of sphingosine-1-phosphate receptors, is known to produce the immunomodulatory actions and to be beneficial for treating the relapsing multiple sclerosis. However, whether it exerts any effects on membrane ion currents in immune cells remains largely unknown. Herein, the effects of FTY720 on ionic currents in Jurkat T-lymphocytes were investigated. Cell exposure to FTY720 suppressed the amplitude of delayed-rectifier K+ current (IK(DR)) in a time- and concentration-dependent manner with an IC50 value of 1.51 μM. Increasing the FTY720 concentration not only decreased the IK(DR) amplitude but also accelerated the inactivation time course of the current. By using the minimal reaction scheme, the effect of FTY720 on IK(DR) inactivation was estimated with a dissociation constant of 3.14 μM. FTY720 also shifted the inactivation curve of IK(DR) to a hyperpolarized potential with no change in the slope factor, and recovery from IK(DR) became slow during the exposure to this compound. Cumulative inactivation for IK(DR) in response to repetitive depolarizations was enhanced in the presence of FTY720. In SEW2871-treated cells, FTY720-induced inhibition of IK(DR) was attenuated. This compound also exerted a stimulatory action on the activity of intermediate-conductance Ca2+-activated K+ channels in Jurkat T-lymphocytes. However, in NSC-34 neuronal cells, FTY720 did not modify the inactivation kinetics of KV3.1-encoded IK(DR), although it suppressed IK(DR) amplitude in these cells. Collectively, the perturbations by FTY720 on different types of K+ channels may contribute to the functional activities of immune cells, if similar findings appear in vivo.

Complexity of the outward K+ current of the rat megakaryocyte

1997 ◽  
Vol 272 (5) ◽  
pp. C1525-C1531 ◽  
Author(s):  
E. Romero ◽  
R. Sullivan
Keyword(s):  
K Channel ◽  
Delayed Rectifier ◽  
Channel Blockers ◽  
Excitable Cells ◽  
Electrophysiological Properties ◽  
Relative Contribution ◽  
Delayed Rectifier Current ◽  
Dependent Inactivation ◽  
Voltage Dependent ◽  
K Current

Megakaryocytes isolated from rat bone marrow express a voltage-dependent, outward K+ current with complex kinetics of activation and inactivation. We found that this current could be separated into at least two components based on differential responses to K+ channel blockers. One component, which exhibited features of the "transient" or "A-type" K+ current of excitable cells, was more strongly blocked by 4-aminopyridine (4-AP) than by tetrabutylammonium (TBA). This current, which we designated as "4-AP-sensitive" current, activated rapidly at potentials more positive than -40 mV and subsequently underwent rapid voltage-dependent inactivation. A separate current that activated slowly was blocked much more effectively by TBA than by 4-AP. This "TBA-sensitive" component, which resembled a typical delayed rectifier current, was much more resistant to voltage-dependent inactivation. The relative contribution of each of these components varied from cell to cell. The effect of charybdotoxin was similar to that of 4-AP. Our data indicate that the voltage-dependent K+ current of resting megakaryocytes is more complex than heretofore believed and support the emerging concept that megakaryocytes possess intricate electrophysiological properties.

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.

Different properties of the atrial G protein-gated K+ channels activated by extracellular ATP and adenosine

1995 ◽  
Vol 269 (4) ◽  
pp. H1349-H1358 ◽  
Author(s):  
C. Fu ◽  
A. Pleumsamran ◽  
U. Oh ◽  
D. Kim
Keyword(s):  
G Protein ◽  
Single Channel ◽  
Extracellular Atp ◽  
K Channel ◽  
Affinity Constant ◽  
Channel Activity ◽  
K Channels ◽  
Atrial Cells ◽  
K Current ◽  
Inside Out

Extracellular ATP (ATPo) and adenosine activate G protein-gated inwardly rectifying K+ currents in atrial cells. Earlier studies have suggested that the two agonists may use separate pathways to activate the K+ current. Therefore, we examined whether the K+ channels activated by the two agonists have different properties under identical ionic conditions. In cell-attached patches, K+ channels activated by 100 microM ATP in the pipette had a single-channel conductance and mean open time of 32.0 +/- 0.2 pS and 0.5 +/- 0.1 ms, respectively, compared with 31.3 +/- 0.3 pS and 0.9 +/- 0.1 ms for the K+ channels activated by adenosine (140 mM KCl). With ATPo as the agonist, the K+ channel activity in cell-attached patches was approximately threefold lower than that in inside-out patches with 100 microM GTP in the bath. Applying ATP to the cytoplasmic side of the membrane (ATPi) produced a biphasic concentration-dependent effect on channel activity: an increase at low [mean affinity constant (K0.5) = 190 microM] and a decrease at high (K0.5 = 1.3 mM) concentrations. In contrast, with adenosine as the agonist, K+ channel activity in cell-attached patches was approximately fourfold greater than that in inside-out patches with 100 microM GTP in the bath. In inside-out patches, ATPi only augmented the K+ channel activity (K0.5 = 32 microM). These results show that although both ATPo and adenosine activate kinetically similar K+ channels in atrial cells, the channels are regulated differently by intracellular nucleotides.

scholarly journals Changes in the expression of potassium channels during mouse T cell development.

1986 ◽  
Vol 164 (6) ◽  
pp. 1846-1861 ◽  
Author(s):  
D McKinnon ◽  
R Ceredig
Keyword(s):  
T Cell ◽  
T Lymphocytes ◽  
Cell Lineage ◽  
Electrophysiological Recording ◽  
K Channel ◽  
Delayed Rectifier ◽  
Developmentally Regulated ◽  
K Channels ◽  
Channel Expression ◽  
Low Levels

In this report we have combined the whole-cell electrophysiological recording technique with flow microfluorometry to isolate phenotypically defined thymocytes and T lymphocytes. Results obtained showed that J11d-/Lyt-2-/L3T4- cells express none or very few delayed rectifier K+ channels, whereas most other Lyt-2-/L3T4- cells, as well as typical cortical thymocytes (Lyt-2+/L3T4+), do express K+ channels. Mature (Lyt-2+/L3T4- or Lyt-2-/L3T4+) thymocytes, which are heterogeneous for J11d expression, were also found to be heterogeneous for K+ channel expression. Consistent with this finding was the observation that the cortisone-resistant subpopulation of thymocytes, which express low levels of J11d, were enriched for cells expressing low levels of K+ channels. Mature phenotype peripheral T lymphocytes expressed very low levels of K+ channels, but upon activation with Con A were found to express high levels of K+ channels. The results suggest that K+ channel expression in T cells is developmentally regulated. Increased expression of the channel is induced in response to mitogenic signals throughout the T cell lineage. Expression of the channel, therefore, serves as a useful marker in defining steps in the T cell differentiation pathway.

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.

scholarly journals A novel structural class of K+-channel blocking toxin from the scorpion Pandinus imperator

1996 ◽  
Vol 315 (3) ◽  
pp. 977-981 ◽  
Author(s):  
Timoteo OLAMENDI-PORTUGAL ◽  
Froylan GÓMEZ-LAGUNAS ◽  
Georgina B. GURROLA ◽  
Lourival D. POSSANI
Keyword(s):  
Channel Blocker ◽  
General Structure ◽  
Three Dimensional ◽  
The Other ◽  
K Channel ◽  
Synaptosomal Membranes ◽  
Enzymic Hydrolysis ◽  
Structural Class ◽  
K Channels ◽  
Channel Blocking

A novel peptide was purified and characterized from the venom of the scorpion Pandinus imperator. Analysis of its primary structure reveals that it belongs to a new structural class of K+-channel blocking peptide, composed of only 35 amino acids, but cross-linked by four disulphide bridges. It is 40, 43 and 46% identical to noxiustoxin, margatoxin and toxin 1 of Centruroides limpidus respectively. However, it is less similar (26 to 37% identity) to toxins from scorpions of the geni Leiurus, Androctonus and Buthus. The disulphide pairing was determined by sequencing heterodimers produced by mild enzymic hydrolysis. They are formed between Cys-4–Cys-25, Cys-10–Cys-30, Cys-14–Cys-32 and Cys-20–Cys-35. Three-dimensional modelling, using the parameters determined for charybdotoxin, showed that is it possible to accommodate the four disulphide bridges in the same general structure of the other K+-channel blocking peptides. The new peptide (Pi1) blocks Shaker B K+ channels reversibly. It also displaces the binding of a known K+-channel blocker, [125I]noxiustoxin, from rat brain synaptosomal membranes with an IC50 of about 10 nM.

scholarly journals Prolactin stimulates cell proliferation through a long form of prolactin receptor and K+ channel activation

2004 ◽  
Vol 377 (3) ◽  
pp. 569-578 ◽  
Author(s):  
Fabien VAN COPPENOLLE ◽  
Roman SKRYMA ◽  
Halima OUADID-AHIDOUCH ◽  
Christian SLOMIANNY ◽  
Morad ROUDBARAKI ◽  
...  
Keyword(s):  
Signal Transduction ◽  
Cell Proliferation ◽  
Tyrosine Kinase ◽  
Current Amplitude ◽  
K Channel ◽  
Lncap Cells ◽  
Activity Increase ◽  
K Channels ◽  
Long Form ◽  
K Current

PRL (prolactin) has been implicated in the proliferation and differentiation of numerous tissues, including the prostate gland. However, the PRL-R (PRL receptor) signal transduction pathway, leading to the stimulation of cell proliferation, remains unclear and has yet to be mapped. The present study was undertaken to develop a clear understanding of the mechanisms involved in this pathway and, in particular, to determine the role of K+ channels. We used androgen-sensitive prostate cancer (LNCaP) cells whose proliferation is known to be stimulated by PRL. Reverse transcriptase PCR analysis showed that LNCaP cells express a long form of PRL-R, but do not produce its intermediate isoform. Patch-clamp techniques showed that the application of 5 nM PRL increased both the macroscopic K+ current amplitude and the single K+-channel open probability. This single-channel activity increase was reduced by the tyrosine kinase inhibitors genistein, herbimycin A and lavandustine A, thereby indicating that tyrosine kinase phosphorylation is required in PRL-induced K+ channel stimulation. PRL enhances p59fyn phosphorylation by a factor of 2 after a 10 min application in culture. In addition, where an antip59fyn antibody is present in the patch pipette, PRL no longer increases K+ current amplitude. Furthermore, the PRL-stimulated proliferation is inhibited by the K+ channel inhibitors α-dendrotoxin and tetraethylammonium. Thus, as K+ channels are known to be involved in LNCaP cell proliferation, we suggest that K+ channel modulation by PRL, via p59fyn pathway, is the primary ionic event in PRL signal transduction, triggering cell proliferation.

scholarly journals Cation permeation through the voltage-dependent potassium channel in the squid axon. Characteristics and mechanisms.

1987 ◽  
Vol 90 (2) ◽  
pp. 261-290 ◽  
Author(s):  
P K Wagoner ◽  
G S Oxford
Keyword(s):  
Binding Energies ◽  
Ion Concentration ◽  
K Channel ◽  
Delayed Rectifier ◽  
Dependent Manner ◽  
K Channels ◽  
Energy Profiles ◽  
Current Voltage ◽  
Voltage Dependent ◽  
Ion Binding Sites

Characteristics of cation permeation through voltage-dependent delayed rectifier K channels in squid giant axons were examined. Axial wire voltage-clamp measurements and internal perfusion were used to determine conductance and permeability properties. These K channels exhibit conductance saturation and decline with increases in symmetrical K+ concentrations to 3 M. They also produce ion- and concentration-dependent current-voltage shapes. K channel permeability ratios obtained with substitutions of internal Rb+ or NH+4 for K+ are higher than for external substitution of these ions. Furthermore, conductance and permeability ratios of NH+4 or Rb+ to K+ are functions of ion concentration. Conductance measurements also reveal the presence of an anomalous mole fraction effect for NH+4, Rb+, or Tl+ to K+. Finally, internal Cs+ blocks these K channels in a voltage-dependent manner, with relief of block by elevations in external K+ but not external NH+4 or Cs+. Energy profiles for K+, NH+4, Rb+, Tl+, and Cs+ incorporating three barriers and two ion-binding sites are fitted to the data. The profiles are asymmetric with respect to the center of the electric field, have different binding energies and electrical positions for each ion, and (for K+) exhibit concentration-dependent barrier positions.

scholarly journals Mechanism of K+ channel block by verapamil and related compounds in rat alveolar epithelial cells.

1995 ◽  
Vol 106 (4) ◽  
pp. 745-779 ◽  
Author(s):  
T E DeCoursey
Keyword(s):  
Epithelial Cells ◽  
Alveolar Epithelial Cells ◽  
K Channel ◽  
Delayed Rectifier ◽  
Neutral Form ◽  
Pipette Solution ◽  
K Channels ◽  
Alveolar Epithelial ◽  
State Dependent ◽  
Related Compounds

The mechanism by which the phenylalkylamines, verapamil and D600, and related compounds, block inactivating delayed rectifier K+ currents in rat alveolar epithelial cells, was investigated using whole-cell tight-seal recording. Block by phenylalkylamines added to the bath resembles state-dependent block of squid K+ channels by internally applied quarternary ammonium ions (Armstrong, C.M. 1971. Journal of General Physiology. 58:413-437): open channels are blocked preferentially, increased [K+]o accelerates recovery from block, and recovery occurs mainly through the open state. Slow recovery from block is attributed to the existence of a blocked-inactivated state, because recovery was faster in three situations where recovery from inactivation is faster: (a) at high [K+]o, (b) at more negative potentials, and (c) in cells with type l K+ channels, which recover rapidly from inactivation. The block rate was used as a bioassay to reveal the effective concentration of drug at the block site. When external pH, pHo, was varied, block was much faster at pHo 10 than pHo 7.4, and very slow at pHo 4.5. The block rate was directly proportional to the concentration of neutral drug in the bath, suggesting that externally applied drug must enter the membrane in neutral form to reach the block site. High internal pH (pHi 10) reduced the apparent potency of externally applied phenylalkylamines, suggesting that the cationic form of these drugs blocks K+ channels at an internal site. The permanently charged analogue D890 blocked more potently when added to the pipette than to the bath. However, lowering pHi to 5.5 did not enhance block by external drug, and tertiary phenylalkylamines added to the pipette solution blocked weakly. This result can be explained if drug diffuses out of the cell faster than it is delivered from the pipette, the block site is reached preferentially via hydrophobic pathways, or both. Together, the data indicate the neutral membrane-bound drug blocks K+ channels more potently than intracellular cationic drug. Neutral drug has rapid access to the receptor, where block is stabilized by protonation of the drug from the internal solution. In summary, externally applied phenylalkylamines block open or inactivated K+ channels by partitioning into the cell membrane in neutral form and are stabilized at the block site by protonation.

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