scholarly journals Voltage-dependent gating and gating charge measurements in the Kv1.2 potassium channel

2015 ◽  
Vol 145 (4) ◽  
pp. 345-358 ◽  
Author(s):  
Itzel G. Ishida ◽  
Gisela E. Rangel-Yescas ◽  
Julia Carrasco-Zanini ◽  
León D. Islas
Keyword(s):  
Ion Channels ◽  
Potassium Channel ◽  
Structural Data ◽  
Activation Mechanism ◽  
Voltage Sensitivity ◽  
Structural Interpretation ◽  
Kv Channel ◽  
Gating Charge ◽  
Voltage Dependent ◽  
Electrophysiological Findings

Much has been learned about the voltage sensors of ion channels since the x-ray structure of the mammalian voltage-gated potassium channel Kv1.2 was published in 2005. High resolution structural data of a Kv channel enabled the structural interpretation of numerous electrophysiological findings collected in various ion channels, most notably Shaker, and permitted the development of meticulous computational simulations of the activation mechanism. The fundamental premise for the structural interpretation of functional measurements from Shaker is that this channel and Kv1.2 have the same characteristics, such that correlation of data from both channels would be a trivial task. We tested these assumptions by measuring Kv1.2 voltage-dependent gating and charge per channel. We found that the Kv1.2 gating charge is near 10 elementary charges (eo), ∼25% less than the well-established 13–14 eo in Shaker. Next, we neutralized positive residues in the Kv1.2 S4 transmembrane segment to investigate the cause of the reduction of the gating charge and found that, whereas replacing R1 with glutamine decreased voltage sensitivity to ∼50% of the wild-type channel value, mutation of the subsequent arginines had a much smaller effect. These data are in marked contrast to the effects of charge neutralization in Shaker, where removal of the first four basic residues reduces the gating charge by roughly the same amount. In light of these differences, we propose that the voltage-sensing domains (VSDs) of Kv1.2 and Shaker might undergo the same physical movement, but the septum that separates the aqueous crevices in the VSD of Kv1.2 might be thicker than Shaker’s, accounting for the smaller Kv1.2 gating charge.

scholarly journals A Theoretical Model for Calculating Voltage Sensitivity of Ion Channels and the Application on Kv1.2 Potassium Channel

2012 ◽  
Vol 102 (8) ◽  
pp. 1815-1825 ◽  
Author(s):  
Huaiyu Yang ◽  
Zhaobing Gao ◽  
Ping Li ◽  
Kunqian Yu ◽  
Ye Yu ◽  
...  
Keyword(s):  
Theoretical Model ◽  
Ion Channels ◽  
Potassium Channel ◽  
Voltage Sensitivity

scholarly journals Further studies of ion channels in the electroreceptor of the skate through deep sequencing, cloning and cross species comparisons

2018 ◽  
Author(s):  
William T. Clusin ◽  
Ting-Hsuan Wu ◽  
Ling-Fang Shi ◽  
Peter N. Kao
Keyword(s):  
Amino Acids ◽  
Ion Channels ◽  
Potassium Channel ◽  
Calcium Channel ◽  
Beta Subunit ◽  
K Channel ◽  
Rna Seq ◽  
Α Subunit ◽  
Accessory Subunits ◽  
Voltage Dependent

AbstractOur comparative studies seek to understand the structure and function of ion channels in cartilaginous fish that can detect very low voltage gradients in seawater. The principal channels of the electroreceptor include a calcium activated K channel, whose α subunit is Kcnma1, a voltage-dependent calcium channel, Cacna1d, and a relatively uncharacterized K channel which interacts with the calcium channel to produce fast (20 Hz) oscillations. Large conductance calcium-activated K channels (BK) are comprised of four α subunits, encoded by Kcnma1 and modulatory β subunits of the Kcnmb class. We recently cloned and published the skate Kcnma1 gene and most of Kcnmb4 derived from using purified mRNA of homogenized isolated electroreceptors. Bellono et al. have recently performed RNA sequencing (RNA-seq) on purified mRNA from skate electroreceptors and found several ion channels including Kcnma1. We searched the the Bellono et al RNA-seq repository for additional channels and subunits. Our most significant findings are the presence of two Shaker type voltage dependent potassium channel sequences which are grouped together as isoforms in the data repository. The larger of these is a skate ortholog of the voltage dependent fast potassium channel Kv1.1, which is expressed at appreciable levels and seems likely to explain the 20 Hz oscillations believed to occur in vivo. The second was more similar to Kv1.5 than to Kv1.1 but was somewhat atypical. We also found a beta subunit sequence (Kcnab2) which appears not to cause fast inactivation due to specific structural features. The new channels and subunits were verified by RT-PCR and the Kv1.1 sequence was confirmed by cloning. We also searched the RNA-seq repository for accessory subunits of the calcium activated potassium channel, Kcnma1, and found a computer generated assembly that contained a complete sequence of its beta subunit, Kcnmb2. Skate Kcnmb2 has a total of 279 amino acids, with 51 novel amino acids at the N-terminus which may play a specific physiological role. This sequence was confirmed by PCR and cloning. However, skate Kcnmb2 is expressed at low levels in the electroreceptor compared to Kcnma1 and skate Kcnmb1 (beta1) is absent. The evolutionary origin of the newly described channels and subunits was studied by aligning skate sequences with human sequences and those found in related fish: the whale shark (R. typus) an elasmobranch, and ghost shark (C.milii). There is also homology with the lamprey, which has electroreceptors. An evolutionary tree is presented. Further research should include focusing on the subcellular locations of these channels in the receptor cells, their gating behavior, and the effects of accessory subunits on gating.

scholarly journals Molecular and biophysical basis of glutamate and trace metal modulation of voltage-gated Cav2.3 calcium channels

2012 ◽  
Vol 139 (3) ◽  
pp. 219-234 ◽  
Author(s):  
Aleksandr Shcheglovitov ◽  
Iuliia Vitko ◽  
Roman M. Lazarenko ◽  
Peihan Orestes ◽  
Slobodan M. Todorovic ◽  
...  
Keyword(s):  
Trace Metals ◽  
Voltage Dependence ◽  
Voltage Sensitivity ◽  
Amino Acid Residues ◽  
Voltage Range ◽  
Gating Charge ◽  
Voltage Dependent ◽  
Charge Movements ◽  
The Brain ◽  
Gating Charges

Here, we describe a new mechanism by which glutamate (Glu) and trace metals reciprocally modulate activity of the Cav2.3 channel by profoundly shifting its voltage-dependent gating. We show that zinc and copper, at physiologically relevant concentrations, occupy an extracellular binding site on the surface of Cav2.3 and hold the threshold for activation of these channels in a depolarized voltage range. Abolishing this binding by chelation or the substitution of key amino acid residues in IS1–IS2 (H111) and IS2–IS3 (H179 and H183) loops potentiates Cav2.3 by shifting the voltage dependence of activation toward more negative membrane potentials. We demonstrate that copper regulates the voltage dependence of Cav2.3 by affecting gating charge movements. Thus, in the presence of copper, gating charges transition into the “ON” position slower, delaying activation and reducing the voltage sensitivity of the channel. Overall, our results suggest a new mechanism by which Glu and trace metals transiently modulate voltage-dependent gating of Cav2.3, potentially affecting synaptic transmission and plasticity in the brain.

scholarly journals Cooperative interactions among subunits of a voltage-dependent potassium channel. Evidence from expression of concatenated cDNAs.

1992 ◽  
Vol 267 (33) ◽  
pp. 23742-23745
Author(s):  
R.S. Hurst ◽  
M.P. Kavanaugh ◽  
J Yakel ◽  
J.P. Adelman ◽  
R.A. North
Keyword(s):  
Potassium Channel ◽  
Cooperative Interactions ◽  
Voltage Dependent

scholarly journals Activation-inactivation of potassium channels and development of the potassium-channel spike in internally perfused squid giant axons.

1981 ◽  
Vol 78 (1) ◽  
pp. 43-61 ◽  
Author(s):  
I Inoue
Keyword(s):  
Potassium Channels ◽  
Potassium Channel ◽  
Voltage Clamp ◽  
Time Constant ◽  
Equilibrium Potential ◽  
Giant Axons ◽  
Dependent Inactivation ◽  
Voltage Dependent ◽  
Time Courses ◽  
Calcium Permeability

A spike that is the result of calcium permeability through potassium channels was separated from the action potential is squid giant axons internally perfused with a 30 mM NaF solution and bathed in a 100 mM CaCl2 solution by blocking sodium channels with tetrodotoxin. Currents through potassium channels were studied under voltage clamp. The records showed a clear voltage-dependent inactivation of the currents. The inactivation was composed of at least two components; one relatively fast, having a time constant of 20--30 ms, and the other very slow, having a time constant of 5--10 s. Voltage clamp was carried out with a variety of salt compositions in both the internal and external solutions. A similar voltage-dependent inactivation, also composed of the two components, was recognized in all the current through potassium channels. Although the direction and intensity of current strongly depended on the salt composition of the solutions, the time-courses of these currents at corresponding voltages were very similar. These results strongly suggest that the inactivation of the currents in attributable to an essential, dynamic property of potassium channels themselves. Thus, the generation of a potassium-channel spike can be understood as an event that occurs when the equilibrium potential across the potassium channel becomes positive.

scholarly journals Equilibrium properties of a voltage-dependent junctional conductance.

1981 ◽  
Vol 77 (1) ◽  
pp. 77-93 ◽  
Author(s):  
D C Spray ◽  
A L Harris ◽  
M V Bennett
Keyword(s):  
Steady State ◽  
Rana Pipiens ◽  
Energy Difference ◽  
Ambystoma Mexicanum ◽  
Voltage Sensitivity ◽  
Junctional Conductance ◽  
Voltage Dependent ◽  
Accumulation Mechanism ◽  
Conductance Changes ◽  
A Current

The conductance of junctions between amphibian blastomeres is strongly voltage dependent. Isolated pairs of blastomeres from embryos of Ambystoma mexicanum, Xenopus laevis, and Rana pipiens were voltage clamped, and junctional current was measured during transjunctional voltage steps. The steady-state junctional conductance decreases as a steep function of transjunctional voltage of either polarity. A voltage-insensitive conductance less than 5% of the maximum remains at large transjunctional voltages. Equal transjunctional voltages of opposite polarities produce equal conductance changes. The conductance is half maximal at a transjunctional voltage of approximately 15 mV. The junctional conductance is insensitive to the potential between the inside and outside of the cells. The changes in steady-state junctional conductance may be accurately modeled for voltages of each polarity as arising from a reversible two-state system in which voltage linearly affects the energy difference between states. The voltage sensitivity can be accounted for by the movement of about six electron charges through the transjunctional voltage. The changes in junctional conductance are not consistent with a current-controlled or ionic accumulation mechanism. We propose that the intramembrane particles that comprise gap junctions in early amphibian embryos are voltage-sensitive channels.

scholarly journals Transmembrane Auxiliary Subunits of Voltage-dependent Ion Channels

1996 ◽  
Vol 271 (45) ◽  
pp. 27975-27978 ◽  
Author(s):  
Christina A. Gurnett ◽  
Kevin P. Campbell
Keyword(s):  
Ion Channels ◽  
Auxiliary Subunits ◽  
Voltage Dependent

Control of secretion in anterior pituitary cells--linking ion channels, messengers and exocytosis

1988 ◽  
Vol 139 (1) ◽  
pp. 287-316
Author(s):  
W. T. Mason ◽  
S. R. Rawlings ◽  
P. Cobbett ◽  
S. K. Sikdar ◽  
R. Zorec ◽  
...  
Keyword(s):  
Ion Channels ◽  
Intracellular Calcium ◽  
Anterior Pituitary ◽  
Hormone Secretion ◽  
Cell Types ◽  
Pituitary Cell ◽  
Pituitary Cells ◽  
Calcium Activity ◽  
Anterior Pituitary Cells ◽  
Voltage Dependent

Normal anterior pituitary cells, in their diversity and heterogeneity, provide a rich source of models for secretory function. However, until recently they have largely been neglected in favour of neoplastic, clonal tumour cell lines of pituitary origin, which have enabled a number of studies on supposedly homogeneous cell types. Because many of these lines appear to lack key peptide and neurotransmitter receptors, as well as being degranulated with accompanying abnormal levels of secretion, we have developed a range of normal primary anterior pituitary cell cultures using dispersion and enrichment techniques. By studying lactotrophs, somatotrophs and gonadotrophs we have revealed a number of possible transduction mechanisms by which receptors for hypothalamic peptides and neurotransmitters may control secretion. In particular, the transduction events controlling secretion from pituitary cells may differ fundamentally from those found in other cell types. Patch-clamp recordings in these various pituitary cell preparations have revealed substantial populations of voltage-dependent Na+, Ca2+ and K+ channels which may support action potentials in these cells. Although activation of these channels may gate Ca2+ entry to the cells under some conditions, our evidence taken with that of other laboratories suggests that peptide-receptor interactions leading to hormone secretion occur independently of significant membrane depolarization. Rather, secretion of hormone and rises in intracellular calcium measured with new probes for intracellular calcium activity, can occur in response to hypothalamic peptide activation in the absence of substantial changes in membrane potential. These changes in intracellular calcium activity almost certainly depend on both intracellular and extracellular calcium sources. In addition, strong evidence of a role for multiple intracellular receptors and modulators in the secretory event suggests we should consider the plasma membrane channels important for regulation of hormone secretion to be predominantly agonist-activated, rather than of the more conventional voltage-dependent type. Likewise, evidence from new methods for recording single ion channels suggests the existence of intracellular sites for channel modulation, implying they too may play an important role in secretory regulation. We shall consider new data and new technology which we hope will provide key answers to the many intriguing questions surrounding the control of pituitary hormone secretion. We shall highlight our work with recordings of single ion channels activated by peptides, and recent experiments using imaging of intracellular ionized free calcium.(ABSTRACT TRUNCATED AT 250 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)

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