scholarly journals Novel K+-channel-blocking toxins from the venom of the scorpion Centruroides limpidus limpidus Karsch

1994 ◽  
Vol 304 (1) ◽  
pp. 51-56 ◽  
Author(s):  
B M Martin ◽  
A N Ramirez ◽  
G B Gurrola ◽  
M Nobile ◽  
G Prestipino ◽  
...  
Keyword(s):  
Primary Structure ◽  
Granule Cells ◽  
Cerebellar Granule Cells ◽  
K Channel ◽  
Amino Acid Residues ◽  
Channel Blocking ◽  
Voltage Dependent ◽  
K Current ◽  
Current Reduction ◽  
K Currents

Two novel toxins were purified from the venom of the Mexican scorpion Centruroides limpidus limpidus, using an immunoassay based on antibodies raised against noxiustoxin (NTX), a known K(+)-channel-blocker-peptide. The primary structure of C. l. limpidus toxin 1 was obtained by Edman degradation and was shown to be composed of 38 amino acid residues, containing six half-cystines. The first 36 residues of C. l. limpidus toxin 2 were also determined. Both toxins are capable of displacing the binding of radio-labelled NTX to rat brain synaptosomes with high affinity (about 100 pM). These toxins are capable of inhibiting transient K(+)-currents (resembling IA-type currents), in cultured rat cerebellar granule cells. About 50% of the peak currents are reduced by application of a 1.5 microM solution of toxins 1 and 2 The K+ current reduction is partially reversible, under washing but not voltage-dependent. Comparison of the primary structure of C. l. limpidus toxin 1 with other known toxins shows 74% identity with margatoxin, 64% with NTX, 51% with kaliotoxin, 39% with iberiotoxin, 37% with charybdotoxin and Lq2, and 29% with leirutoxin 1. The only invariant amino acids in all these toxins are the six cysteines, a glycine in position 26 and two lysines at positions 28 and 33, respectively. The relevance of these differences in terms of possible structure-function relationships is discussed.

Appearance of a fast inactivating voltage-dependent K+ currents in developing cerebellar granule cells in vitro

1997 ◽  
Vol 29 (4) ◽  
pp. 291-301 ◽  
Author(s):  
Yoshihiko Wakazono ◽  
Takashi Kurahashi ◽  
Kensuke Nakahira ◽  
Isao Nagata ◽  
Chitoshi Takayama ◽  
...  
Keyword(s):  
Granule Cells ◽  
Cerebellar Granule Cells ◽  
Cerebellar Granule ◽  
Voltage Dependent ◽  
K Currents

scholarly journals Voltage- and time-dependent K+ channel currents in the basolateral membrane of villus enterocytes isolated from guinea pig small intestine.

1994 ◽  
Vol 103 (3) ◽  
pp. 429-446 ◽  
Author(s):  
H Tatsuta ◽  
S Ueda ◽  
S Morishima ◽  
Y Okada
Keyword(s):  
Steady State ◽  
Guinea Pig ◽  
Time Course ◽  
Basolateral Membrane ◽  
Time Dependent ◽  
K Channel ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
K Current ◽  
K Currents

Patch-clamp studies were carried out in villus enterocytes isolated from the guinea pig proximal small intestine. In the whole-cell mode, outward K+ currents were found to be activated by depolarizing command pulses to -45 mV. The activation followed fourth order kinetics. The time constant of K+ current activation was voltage-dependent, decreasing from approximately 3 ms at -10 mV to 1 ms at +50 mV. The K+ current inactivated during maintained depolarizations by a voltage-independent, monoexponential process with a time constant of approximately 470 ms. If the interpulse interval was shorter than 30 s, cumulative inactivation was observed upon repeated stimulations. The steady state inactivation was voltage-dependent over the voltage range from -70 to -30 mV with a half inactivation voltage of -46 mV. The steady state activation was also voltage-dependent with a half-activation voltage of -22 mV. The K+ current profiles were not affected by chelation of cytosolic Ca2+. The K+ current induced by a depolarizing pulse was suppressed by extracellular application of TEA+, Ba2+, 4-aminopyridine or quinine with half-maximal inhibitory concentrations of 8.9 mM, 4.6 mM, 86 microM and 26 microM, respectively. The inactivation time course was accelerated by quinine but decelerated by TEA+, when applied to the extracellular (but not the intracellular) solution. Extracellular (but not intracellular) applications of verapamil and nifedipine also quickened the inactivation time course with 50% effective concentrations of 3 and 17 microM, respectively. Quinine, verapamil and nifedipine shifted the steady state inactivation curve towards more negative potentials. Outward single K+ channel events with a unitary conductance of approximately 8.4 pS were observed in excised inside-out patches of the basolateral membrane, when the patch was depolarized to -40 mV. The ensemble current rapidly activated and thereafter slowly inactivated with similar time constants to those of whole-cell K+ currents. It is concluded that the basolateral membrane of guinea pig villus enterocytes has a voltage-gated, time-dependent, Ca(2+)-insensitive, small-conductance K+ channel. Quinine, verapamil, and nifedipine accelerate the inactivation time course by affecting the inactivation gate from the external side of the cell membrane.

scholarly journals Functional and molecular analysis of transient voltage‐dependent K + currents in rat hippocampal granule cells

2001 ◽  
Vol 537 (2) ◽  
pp. 391-406 ◽  
Author(s):  
Vladimir Riazanski ◽  
Albert Becker ◽  
Jian Chen ◽  
Dmitry Sochivko ◽  
Ailing Lie ◽  
...  
Keyword(s):  
Molecular Analysis ◽  
Granule Cells ◽  
Voltage Dependent ◽  
Transient Voltage ◽  
K Currents

scholarly journals Gonadotropin-Releasing Hormone Inhibits Ether-à-Go-Go-Related Gene K+ Currents in Mouse Gonadotropes

Endocrinology ◽  
2010 ◽  
Vol 151 (3) ◽  
pp. 1079-1088 ◽  
Author(s):  
Wiebke Hirdes ◽  
Crenguta Dinu ◽  
Christiane K. Bauer ◽  
Ulrich Boehm ◽  
Jürgen R. Schwarz
Keyword(s):  
Resting Potential ◽  
Related Gene ◽  
Activation Curve ◽  
Signal Cascade ◽  
Primary Mouse ◽  
Voltage Dependent ◽  
K Current ◽  
Unknown Signal ◽  
Ca2 Channels ◽  
K Currents

Secretion of LH from gonadotropes is initiated by a GnRH-induced increase in intracellular Ca2+ concentration ([Ca2+]i). This increase in [Ca2+]i is the result of Ca2+ release from intracellular stores and Ca2+ influx through voltage-dependent Ca2+ channels. Here we describe an ether-à-go-go-related gene (erg) K+ current in primary mouse gonadotropes and its possible function in the control of Ca2+ influx. To detect gonadotropes, we used a knock-in mouse strain, in which GnRH receptor-expressing cells are fluorescently labeled. Erg K+ currents were recorded in 80–90% of gonadotropes. Blockage of erg currents by E-4031 depolarized the resting potential by 5–8 mV and led to an increase in [Ca2+]i, which was abolished by nifedipine. GnRH inhibited erg currents by a reduction of the maximal erg current and in some cells additionally by a shift of the activation curve to more positive potentials. In conclusion, the erg current contributes to the maintenance of the resting potential in gonadotropes, thereby securing a low [Ca2+]i by restricting Ca2+ influx. In addition, the erg channels are modulated by GnRH by an as-yet unknown signal cascade.

Reduction of voltage-activated K+ currents by forskolin is not mediated via cAMP in pleural sensory neurons of Aplysia

1990 ◽  
Vol 64 (5) ◽  
pp. 1474-1483 ◽  
Author(s):  
D. A. Baxter ◽  
J. H. Byrne
Keyword(s):  
Adenylate Cyclase ◽  
Sensory Neurons ◽  
Water Solubility ◽  
Membrane Current ◽  
Peak Amplitude ◽  
Bath Application ◽  
Voltage Dependent ◽  
K Current ◽  
Derivatives Of ◽  
K Currents

1. Forskolin is often used to activate adenylate cyclase in studies relating adenosine 3',5'-cyclic monophosphate (cAMP) to the modulation of membrane current. There is growing concern, however, that some actions of forskolin are independent of cAMP. With the use of two-electrode voltage-clamp techniques, we compared the effects of analogues of cAMP to the effects of forskolin on K+ currents in somata of sensory neurons that were isolated from pleural ganglia of Aplysia californica. 2. Analogues of cAMP did not reduce the peak amplitude of either the transient K+ current (IA) or the voltage-dependent K+ current (IK.V). Analogues of cAMP did reduce the previously described cAMP-sensitive S K+ current (IK.S). In contrast, forskolin reduced the peak amplitude of both IA and IK.V. Furthermore, both IA and IK.V were reduced by 1,9-dideoxy-forskolin, a derivative of forskolin that does not activate adenylate cyclase. These results indicate that the effects of forskolin and 1,9-dideoxy-forskolin on IA and IK.V were not mediated via cAMP. 3. Bath application of a modified form of forskolin (7-deacetyl-6-[N-acetylglycyl]-forskolin), which has enhanced water solubility and activates adenylate cyclase, reduced IK.S, but did not alter either IA or IK.V. Thus it appears that certain derivatives of forskolin can be used to activate adenylate cyclase and avoid some of the nonspecific actions on membrane current that are associated with forskolin.

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.

Diverse current and voltage responses to baclofen in an identified molluscan photoreceptor

1995 ◽  
Vol 74 (2) ◽  
pp. 506-518 ◽  
Author(s):  
L. D. Matzel ◽  
I. A. Muzzio ◽  
R. F. Rogers
Keyword(s):  
Voltage Clamp ◽  
Action Potentials ◽  
Gabab Receptor ◽  
Outward Current ◽  
Gabab Receptors ◽  
Equilibrium Potential ◽  
K Channel ◽  
Electrode Voltage ◽  
Voltage Dependent ◽  
K Current

1. gamma-Aminobuturic acid-B (GABAB) receptors play a role in the mediation of slow inhibitory postsynaptic potentials in mammalian as well as some nonmammalian species. In identified photoreceptors from the marine mollusc Hermissenda, recent evidence has suggested that GABA, as well as the GABAB receptor agonist baclofen, might simultaneously modulate multiple conductances on the postsynaptic membrane. Here, using intracellular current-clamp and single-electrode voltage-clamp techniques, we have characterized responses to baclofen in the B photoreceptors of the Hermissenda eye. 2. Microapplication of baclofen (12.5–62.5 microM) to the terminal branches of the B photoreceptors induced a slow, concentration-dependent hyperpolarization (approximately 3–8 mV) that was accompanied by a cessation of spontaneous action potentials and a positive shift in firing threshold. Both the hyperpolarization and the shift in spike threshold in response to baclofen were attenuated largely by the K+ channel blocker tetraethylammonium chloride (TEA; 50 mM). 3. Bath application of baclofen (100 microM) decreased the amplitude, duration, and the afterhyperpolarization (AHP) of evoked action potentials. Although baclofen's effect on spike duration and amplitude persisted in the absence of extracellular Ca2+, the reduction of the AHP by baclofen was eliminated, suggesting that multiple conductances mediated the baclofen-induced modification of the action potential. 4. Using a single-electrode voltage-clamp technique, microapplication of baclofen to the terminal branches of the B photoreceptor produced a slow, net outward current (< 0.5 nA) that reversed near the equilibrium potential for K+ and shifted to more positive potentials when extracellular K+ was increased, in approximate agreement with the Nernst equation for K+. 5. Baclofen induced an increase in amplitude of the nonvoltage dependent leak conductance (IL), and the increase was blocked by TEA. The baclofen-induced increase of IL was accompanied by an increase in amplitude and a negative shift in the voltage dependence of a slow, steeply voltage-dependent K+ current (IK), which displays selective sensitivity to TEA but does not normally contribute to leak conductance. The amplitude and steady-state inactivation of a fast, transient K+ current, as well as the amplitude of an inwardly rectifying K+ current were unaffected by baclofen. 6. Both the rate of activation as well as the amplitude of a voltage-dependent Ca2+ current (ICa) were reduced by baclofen. The reduction of ICa resulted in a concomitant suppression of a Ca(2+)-dependent K+ current (IK-Ca) that was sufficient to account for the reduction of the AHP after evoked action potentials.(ABSTRACT TRUNCATED AT 400 WORDS)

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