scholarly journals A scheme to account for the effects of Rb+ and K+ on inward rectifier K channels of bovine artery endothelial cells.

1994 ◽  
Vol 103 (4) ◽  
pp. 549-581 ◽  
Author(s):  
P S Pennefather ◽  
T E DeCoursey
Keyword(s):  
Binding Sites ◽  
Voltage Dependence ◽  
Reversal Potential ◽  
Companion Paper ◽  
K Channel ◽  
Gating Model ◽  
Allosteric Sites ◽  
Voltage Dependent ◽  
Cooperative Process ◽  
Activator Ions

An electrochemical gating model is presented to account for the effects described in the companion paper by M. R. Silver, M. S. Shapiro, and T. E. DeCoursey (1994. Journal of General Physiology, 103:519-548) of Rb+ and Rb+/K+ mixtures on the kinetics and voltage dependence of an inwardly rectifying (IR) K+ channel. The model proposes that both Rb+ and K+ act as allosteric modulators of an intrinsically voltage dependent isomerization between open and closed states. Occupancy of binding sites on the outside of the channel promotes channel opening and stabilizes the open state. Rb+ binds to separate sites within the pore and plugs IR channels. Occupancy of the pore by Rb+ can modify the rates of isomerization and the affinity of the allosteric sites for activator ions. The model also incorporates the proposed triple-barreled nature of the IR channel (Matsuda, H., 1988. Journal of Physiology. 397:237-258.) by proposing that plugging of the channel is a cooperative process involving a single site in each of the three bores, 80% of the way through the membrane field. Interaction between bores during plugging and permeation is consistent with correlated flux models of the properties of the IR channel. Parallel bores multiply the number allosteric sites associated with the macromolecular channel and allow for steep voltage dependence without compromising the parallel shift of the half-activation potential with reversal potential. Our model proposes at least six and possibly 12 such allosteric binding sites for activator ions. We derive algebraic relations that permit derivation of parameters that define simple versions of our model from the data of Silver et al. (1994). Numerical simulations based on those parameters closely reproduce that data. The model reproduces the RS+ induced slowing of IR kinetics and the negative shift of the relation between the half-activation voltage (V1/2) and reversal potential when channel plugging is associated with (a) a slowing of the isomerization rates; (b) an increase in the affinity of allosteric sites on closed channels that promote opening; and (c) a decrease in the affinity of sites on open channels that slow closing. Rb+ also slows closing at positive potentials where open channel blockade is unlikely. Allowing Rb+ to be 1.5 times more potent than K+ as an activator in the model can account for this effect and improves the match between the predicted and observed relation between the Rb+ to K+ mole fraction and the opening rate at V1/2.(ABSTRACT TRUNCATED AT 400 WORDS)

Voltage dependence of conductance changes evoked by glycine release in the zebrafish brain

1995 ◽  
Vol 73 (6) ◽  
pp. 2404-2412 ◽  
Author(s):  
P. Legendre ◽  
H. Korn
Keyword(s):  
Voltage Dependence ◽  
Reversal Potential ◽  
Voltage Sensitivity ◽  
M Cell ◽  
Open Probability ◽  
Similar Time ◽  
Whole Cell ◽  
Glycine Release ◽  
Cell Recording ◽  
Voltage Dependent

1. The kinetics and mechanisms underlying the voltage dependence of inhibitory postsynaptic currents (IPSCs) recorded in the Mauthner cell (M cell) were investigated in the isolated medulla of 52-h-old zebrafish larvae, with the use of whole cell and outside-out patch-clamp recordings. 2. Spontaneous miniature IPSCs (mIPSCs) were recorded in the presence of 10(-6) M tetrodotoxin (TTX), 10 mM MgCl2, and 0.1 mM [CaCl2]o. Depolarizing the cell from -50 to +50 mV did not evoke any significant change in the distribution of mIPSC amplitudes, whereas synaptic currents were prolonged at positive voltages. The average decay time constant was increased twofold at +50 mV. 3. The voltage dependence of the kinetics of glycine-activated channels was first investigated during whole cell recording experiments. Currents evoked by voltage steps in the presence of glycine (50 microM) were compared with those obtained without glycine. The increase in chloride conductance (gCl-) evoked by glycine was time and voltage dependent. Inactivation and reactivation of the chloride current were observed during voltage pulses from 0 to -50 mV and from -50 to 0 mV, respectively, and they occurred with similar time constants (2-3 s). During glycine application, voltage-ramp analysis revealed a shift in the reversal potential (ECl-) occurring at all [Cl-]i tested. 4. The basis of the voltage sensitivity of glycine-evoked gCl- was first analyzed by measuring the relative changes in the total open probability (NPo) of glycine-activated channels with voltage.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics and postnatal development of a hyperpolarization-activated inward current in rat hypoglossal motoneurons in vitro

1994 ◽  
Vol 71 (1) ◽  
pp. 119-128 ◽  
Author(s):  
D. A. Bayliss ◽  
F. Viana ◽  
M. C. Bellingham ◽  
A. J. Berger
Keyword(s):  
Postnatal Development ◽  
Voltage Dependence ◽  
Reversal Potential ◽  
Membrane Potentials ◽  
Time Constants ◽  
Inward Current ◽  
Hypoglossal Motoneurons ◽  
Tail Current ◽  
Cationic Current ◽  
Voltage Dependent

1. Single-electrode voltage clamp recordings in a rat brain stem slice preparation were used to determine the characteristics and postnatal development of a hyperpolarization-activated inward current (Ih) in hypoglossal motoneurons (HMs). 2. In young adult HMs (> P21), a noninactivating, time- and voltage-dependent inward current was evident during hyperpolarizing voltage steps to membrane potentials negative to approximately -65 mV from depolarized holding potentials [Vh = -56.2 +/- 1.0 (SE) mV]. The averaged reversal potential (Erev) of the inward current, estimated using an extrapolation procedure, was -38.8 +/- 2.9 mV (n = 5), suggesting that a mixed cationic current underlies inward rectification in HMs. 3. The voltage dependence of Ih activation was determined from tail current relaxations that followed a family of voltage steps to different membrane potentials. Normalized tail current amplitudes were well-fitted with a single Boltzman function with a half-activation at -79.8 +/- 0.7 mV and slope factor = 5.3 +/- 0.3 (n = 8). 4. Time constants of Ih activation and deactivation were voltage-dependent. Activation proceeded more quickly with larger hyperpolarizing voltage steps; time constants averaged 389, 181, and 134 ms at -69, -82, and -95 mV, respectively (n = 6). Ih deactivated during depolarizing voltage steps from hyperpolarized holding potentials. Deactivation was faster with larger depolarizing steps; time constants averaged 321, 215, and 107 ms at -80, -71, and -62 mV, respectively (n = 4). 5. Ih was sensitive to extracellular cesium but relatively insensitive to extracellular barium. The current amplitude near half-activation (approximately -84 mV) was almost completely blocked (to 11% of control) by Cs+ (3 mM, n = 3) but was reduced to only 85 and 60% in 0.5 (n = 2) and 2 mM Ba2+ (n = 3), respectively. 6. There was a marked increase in the amplitude of Ih during postnatal development of HMs. Measured near half-activation, Ih was approximately 10-fold larger in adult (> or = P21; n = 20) than in neonatal HMs (< or = P8; n = 7). Input conductance (GN) was only threefold higher in the same sample of HMs. There were no apparent differences in the voltage dependence or Erev of Ih between neonatal and older HMs. These results suggest that the increased amplitude of Ih results from an increase in Ih current density.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Permeation of Na+ through a delayed rectifier K+ channel in chick dorsal root ganglion neurons.

1994 ◽  
Vol 104 (4) ◽  
pp. 747-771 ◽  
Author(s):  
M J Callahan ◽  
S J Korn
Keyword(s):  
Dorsal Root Ganglion ◽  
Binding Site ◽  
Dorsal Root ◽  
Reversal Potential ◽  
Dorsal Root Ganglion Neurons ◽  
K Channel ◽  
Delayed Rectifier ◽  
Cation Binding Site ◽  
Voltage Dependent ◽  
Ganglion Neurons

In whole-cell patch clamp recordings from chick dorsal root ganglion neurons, removal of intracellular K+ resulted in the appearance of a large, voltage-dependent inward tail current (Icat). Icat was not Ca2+ dependent and was not blocked by Cd2+, but was blocked by Ba2+. The reversal potential for Icat shifted with the Nernst potential for [Na+]. The channel responsible for Icat had a cation permeability sequence of Na+ &gt; Li+ &gt; TMA+ &gt; NMG+ (PX/PNa = 1:0.33:0.1:0) and was impermeable to Cl-. Addition of high intracellular concentrations of K+, Cs+, or Rb+ prevented the occurrence of Icat. Inhibition of Icat by intracellular K+ was voltage dependent, with an IC50 that ranged from 3.0-8.9 mM at membrane potentials between -50 and -110 mV. This voltage-dependent shift in IC50 (e-fold per 52 mV) is consistent with a single cation binding site approximately 50% of the distance into the membrane field. Icat displayed anomolous mole fraction behavior with respect to Na+ and K+; Icat was inhibited by 5 mM extracellular K+ in the presence of 160 mM Na+ and potentiated by equimolar substitution of 80 mM K+ for Na+. The percent inhibition produced by both extracellular and intracellular K+ at 5 mM was identical. Reversal potential measurements revealed that K+ was 65-105 times more permeant than Na+ through the Icat channel. Icat exhibited the same voltage and time dependence of inactivation, the same voltage dependence of activation, and the same macroscopic conductance as the delayed rectifier K+ current in these neurons. We conclude that Icat is a Na+ current that passes through a delayed rectifier K+ channel when intracellular K+ is reduced to below 30 mM. At intracellular K+ concentrations between 1 and 30 mM, PK/PNa remained constant while the conductance at -50 mV varied from 80 to 0% of maximum. These data suggest that the high selectivity of these channels for K+ over Na+ is due to the inability of Na+ to compete with K+ for an intracellular binding site, rather than a barrier that excludes Na+ from entry into the channel or a barrier such as a selectivity filter that prevents Na+ ions from passing through the channel.

scholarly journals Discovery and characterization of Hv1-type proton channels in reef-building corals.

2021 ◽  
Author(s):  
Gisela Rangel-Tescas ◽  
Cecilia Cervantes ◽  
Miguel A Cervantes-Rocha ◽  
Esteban Suarez-Delgado ◽  
Anastazia T Banaszak ◽  
...  
Keyword(s):  
Voltage Dependence ◽  
Ph Regulation ◽  
Functional Characterization ◽  
Gene Encoding ◽  
Proton Channels ◽  
Gating Model ◽  
Mechanistic Insight ◽  
Voltage Dependent ◽  
Insight Into

Voltage-dependent proton-permeable channels are membrane proteins mediating a number of important physiological functions. Here we report the presence of a gene encoding for Hv1 voltage-dependent, proton-permeable channels in two species of reef-building corals. We performed a characterization of their biophysical properties and found that these channels are fast-activating and modulated by the pH gradient in a manner that makes them interesting models for studying these processes more easily. We have also developed an allosteric gating model that provides mechanistic insight into the modulation of voltage-dependence by protons. This work also represents the first functional characterization of any ion channel in scleractinian corals. We discuss the implications of the presence of these channels in the membranes of coral cells in the calcification and pH regulation processes and possible consequences of ocean acidification related to the function of these channels.

scholarly journals Mechanism of the Voltage Sensitivity of IRK1 Inward-rectifier K+ Channel Block by the Polyamine Spermine

2005 ◽  
Vol 125 (4) ◽  
pp. 413-426 ◽  
Author(s):  
Hyeon-Gyu Shin ◽  
Zhe Lu
Keyword(s):  
Steady State ◽  
Voltage Dependence ◽  
Ion Selectivity ◽  
Inward Rectifier ◽  
Selectivity Filter ◽  
K Channel ◽  
Voltage Sensitivity ◽  
Channel Block ◽  
Head Groups ◽  
Voltage Dependent

IRK1 (Kir2.1) inward-rectifier K+ channels exhibit exceedingly steep rectification, which reflects strong voltage dependence of channel block by intracellular cations such as the polyamine spermine. On the basis of studies of IRK1 block by various amine blockers, it was proposed that the observed voltage dependence (valence ∼5) of IRK1 block by spermine results primarily from K+ ions, not spermine itself, traversing the transmembrane electrical field that drops mostly across the narrow ion selectivity filter, as spermine and K+ ions displace one another during channel block and unblock. If indeed spermine itself only rarely penetrates deep into the ion selectivity filter, then a long blocker with head groups much wider than the selectivity filter should exhibit comparably strong voltage dependence. We confirm here that channel block by two molecules of comparable length, decane-bis-trimethylammonium (bis-QAC10) and spermine, exhibit practically identical overall voltage dependence even though the head groups of the former are much wider (∼6 Å) than the ion selectivity filter (∼3 Å). For both blockers, the overall equilibrium dissociation constant differs from the ratio of apparent rate constants of channel unblock and block. Also, although steady-state IRK1 block by both cations is strongly voltage dependent, their apparent channel-blocking rate constant exhibits minimal voltage dependence, which suggests that the pore becomes blocked as soon as the blocker encounters the innermost K+ ion. These findings strongly suggest the existence of at least two (potentially identifiable) sequentially related blocked states with increasing numbers of K+ ions displaced. Consequently, the steady-state voltage dependence of IRK1 block by spermine or bis-QAC10 should increase with membrane depolarization, a prediction indeed observed. Further kinetic analysis identifies two blocked states, and shows that most of the observed steady-state voltage dependence is associated with the transition between blocked states, consistent with the view that the mutual displacement of blocker and K+ ions must occur mainly as the blocker travels along the long inner pore.

Sweet taste transduction in hamster: sweeteners and cyclic nucleotides depolarize taste cells by reducing a K+ current

1996 ◽  
Vol 75 (3) ◽  
pp. 1256-1263 ◽  
Author(s):  
T. A. Cummings ◽  
C. Daniels ◽  
S. C. Kinnamon
Keyword(s):  
Cyclic Nucleotides ◽  
Cyclic Nucleotide ◽  
Taste Receptor ◽  
Reversal Potential ◽  
Taste Cell ◽  
K Channel ◽  
Cyclic Monophosphate ◽  
Taste Cells ◽  
Voltage Dependent ◽  
K Current

1. The gigaseal voltage-clamp technique was used to record responses of hamster taste receptor cells to synthetic sweeteners and cyclic nucleotides. Voltage-dependent currents and steady-state currents were monitored during bath exchanges of saccharin, two high-potency sweeteners, 8-chlorophenylthio-adenosine 3',5'-cyclic monophosphate (8cpt-cAMP), and dibutyryl-guanosine 3',5'-cyclic monophosphate (db-cGMP). 2. Of the 237 fungiform taste cells studied, only one in eight was sweet responsive. Outward currents, both voltage-dependent and resting, were reduced by all of the sweeteners tested in sweet-responsive taste cells, whereas these currents were unaffected by sweeteners in sweet-unresponsive taste cells. 3. In every sweet-responsive cell tested, 8cpt-cAMP and db-cGMP mimicked the response to the sweeteners, but neither nucleotide elicited responses in sweet-unresponsive cells. Thus there was a one-to-one correlation between sweet responsivity and cyclic nucleotide responsivity. 4. Sweet responses showed cross adaptation with cyclic nucleotide responses. This indicates that the same ion channel is modulated by sweeteners and cyclic nucleotides. 5. The sweetener- and cyclic nucleotide-blocked current had an apparent reversal potential of -50 mV, which was close to the potassium reversal potential in these experiments. In addition, there was no effect of sweeteners and cyclic nucleotides in the presence of the K+ channel blocker tetraethylammonium bromide (TEA). These data suggest that block of a resting, TEA-sensitive K+ current is the final common step leading to taste cell depolarization during sweet transduction. 6. These data, together with data from a previous study (Cummings et al. 1993), suggest that both synthetic sweeteners and sucrose utilize second-messenger pathways that block a resting K+ conductance to depolarize the taste cell membrane.

Permeation and block of dopamine-modulated potassium channels on rat striatal neurons by cesium and barium ions

1996 ◽  
Vol 76 (3) ◽  
pp. 1413-1422 ◽  
Author(s):  
Y. J. Lin ◽  
G. J. Greif ◽  
J. E. Freedman
Keyword(s):  
Dissociation Constant ◽  
Single Channel ◽  
Reversal Potential ◽  
Negative Slope ◽  
K Channel ◽  
Striatal Neurons ◽  
Apparent Dissociation Constant ◽  
Voltage Dependent ◽  
Single Channel Currents ◽  
Inwardly Rectifying

1. In cell-attached patch-clamp recordings from freshly dissociated rat caudate-putamen neurons, an 85-pS inwardly rectifying K+ channel, which was previously found to be modulated by D2-like dopamine receptors, was blocked by externally applied BaCl2 or CsCl. 2. At concentrations between 100 and 500 microM, Ba2+ blockade was voltage dependent, with a greater block at hyperpolarized voltages, in a manner consistent with blockade of the channel pore. Single-channel currents were flickery, with intervening periods of more complete blockade, and block appeared to be time dependent, with an estimated electrical distance of 0.24 and an apparent dissociation constant of 205 microM at 0 mV. 3. At concentrations between 1 and 3 mM, Cs+ blockade was similarly voltage dependent, but without periods of longer blockade, with an electrical distance of 0.81 and an apparent dissociation constant of 625 microM at 0 mV. Cs+ could also permeate this channel at voltages near the K+ reversal potential. The current-voltage relationship displayed an anomalous negative slope conductance, in a manner inconsistent with a single-ion pore. 4. Smaller-conductance, dopamine-insensitive channels were blocked more potently by both Ba2+ and Cs+ than was the 85-pS channel, reflecting differences between inwardly rectifying K+ channels mediating resting conductance and those mediating dopamine receptor responses in striatal neurons.

scholarly journals Na+ Block and Permeation in a K+ Channel of Known Structure

2002 ◽  
Vol 120 (3) ◽  
pp. 323-335 ◽  
Author(s):  
Crina M. Nimigean ◽  
Christopher Miller
Keyword(s):  
High Voltage ◽  
Voltage Dependence ◽  
Low Voltage ◽  
Selectivity Filter ◽  
K Channel ◽  
Voltage Dependent

The effects of intracellular Na+ were studied on K+ and Rb+ currents through single KcsA channels. At low voltage, Na+ produces voltage-dependent block, which becomes relieved at high voltage by a “punchthrough” mechanism representing Na+ escaping from its blocking site through the selectivity filter. The Na+ blocking site is located in the wide, hydrated vestibule, and it displays unexpected selectivity for K+ and Rb+ against Na+. The voltage dependence of Na+ block reflects coordinated movements of the blocker with permeant ions in the selectivity filter.

Novel actions of ryanodine and analogues—Perturbers of potassium channels

1995 ◽  
Vol 15 (6) ◽  
pp. 515-530 ◽  
Author(s):  
H. Vais ◽  
P. N. R. Usherwood
Keyword(s):  
Voltage Dependence ◽  
Reversal Potential ◽  
Bk Channel ◽  
Muscle Membrane ◽  
K Channel ◽  
Similar Data ◽  
Ionic Selectivity ◽  
K Channels ◽  
Quaternary Ammonium Ions ◽  
Ik Channel

The effects of ryanodine, 9,21-didehydroryanodine and 9,21-didehydroryanodol on two types of K+ channel (a maxi, Ca2+-activated, 170 pS channel (BK channel) and an inward rectifier, stretch-sensitive channel of 35 pS conductance (IK channel) found in the plasma membrane of locust skeletal muscle have been investigated. 10−9M-10−5M ryanodine irreversibly induced a dose-dependent reduction of the reversal potential (Vrev) of the currents of both channels, i.e. from ~60 mV in the absence of the alkaloid to ~15 mV for 10−5M ryanodine, measured under physiologically normal K+ and Na+ gradients. In both cases the change in the ionic selectivity was Ca2+-independent. 9,21-didehydroryanodine and 9,21-didehyroryanodol also reduced Vrev, but only to ~35 mV during application of 10−5M of these compounds. Additionally, 9,21-didehydroryanodine reversibly diminished the conductances of the two K+ channels. To test the hypothesis that ryanoids increase Na+ permeability by enlarging the K+ channels, the channels were probed with quaternary ammonium ions during ryanoid application. When applied to the cytoplasmic face of inside-out patches exised from locust muscle membrane, TEA blocked the K+ channels in a voltage-dependent fashion. The dissociation constant (Kd(0)) for TEA block of the IK channel was reduced from 44 mM to 1 mM by 10−7 M ryanodine, but the voltage-dependence of the block was unaffected. Qualitatively similar data were obtained for the BK channel. Ryanodine had no effect on the Kd for cytoplasmically-applied TMA. However, the voltage-dependence for TMA block was increased for both K+ channels, from 0.47 to ~0.8 with 10−6M ryanodine. The effects of ryanodine on TEA and TMA block support the hypothesis that ryanodine enlarges the K+ channels so as to facilitate permeation of partially hydrated Na+ ions.

Serotonin and forskolin modulation of a chloride conductance in cultured identified Aplysia neurons

1987 ◽  
Vol 58 (5) ◽  
pp. 922-939 ◽  
Author(s):  
D. P. Lotshaw ◽  
I. B. Levitan
Keyword(s):  
Cell Culture ◽  
Voltage Clamp ◽  
Primary Cell Culture ◽  
Voltage Dependence ◽  
Reversal Potential ◽  
Aplysia Neurons ◽  
Voltage Dependent ◽  
Cl Conductance ◽  
Dependent Mechanism

1. The effect of serotonin (5-HT) and forskolin on a hyperpolarization activated Cl- conductance (gCl-) was studied using voltage-clamp techniques in identified Aplysia neurons maintained in primary cell culture. 2. The hyperpolarization-activated conductance induced by intracellular Cl- loading was carried by Cl- as determined by the following criteria: the extrapolated reversal potential of the current closely approximated the reversal potential of a cholinergic Cl- conductance, the current was not affected by extracellular ion substitutions other than Cl-, extracellular thiocyanate ions reversibly inhibited the current and the current exhibited slow voltage-dependent exponential kinetics similar to those described for the hyperpolarization-activated Cl- current in Aplysia neurons in situ. 3. In the identified neurons B1, B2, R15, and R2, 5-HT or forskolin reversibly inhibited gCl-, suggesting that 5-HT acted via an adenosine 3',5'-cyclic monophosphate-dependent mechanism. 4. Serotonergic inhibition resulted from a change in the voltage dependence of Cl- channel gating.

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