scholarly journals Batrachotoxin uncouples gating charge immobilization from fast Na inactivation in squid giant axons

1988 ◽  
Vol 54 (4) ◽  
pp. 719-730 ◽  
Author(s):  
J. Tanguy ◽  
J.Z. Yeh
Keyword(s):  
Giant Axons ◽  
Gating Charge ◽  
Na Inactivation

scholarly journals Phosphorylation modulates potassium conductance and gating current of perfused giant axons of squid.

1990 ◽  
Vol 95 (2) ◽  
pp. 245-271 ◽  
Author(s):  
C K Augustine ◽  
F Bezanilla
Keyword(s):  
Steady State ◽  
Voltage Dependence ◽  
Potassium Conductance ◽  
Charge Movement ◽  
Gating Current ◽  
Gating Currents ◽  
Internal Solution ◽  
Giant Axons ◽  
Gating Charge ◽  
Phosphorylation Reaction

The presence of internal Mg-ATP produced a number of changes in the K conductance of perfused giant axons of squid. For holding potentials between -40 and -50 mV, steady-state K conductance increased for depolarizations to potentials more positive than approximately -15 mV and decreased for smaller depolarizations. The voltage dependencies of both steady-state activation and inactivation also appears shifted toward more positive potentials. Gating kinetics were affected by internal ATP, with the activation time constant slowed and the characteristic delay in K conductance markedly enhanced. The rate of deactivation also was hastened during perfusion with ATP. Internal ATP affected potassium channel gating currents in similar ways. The voltage dependence of gating charge movement was shifted toward more positive potentials and the time constants of ON and OFF gating current also were slowed and hastened, respectively, in the presence of ATP. These effects of ATP on the K conductance occurred when no exogenous protein kinases were added to the internal solution and persisted even after removing ATP from the internal perfusate. Perfusion with a solution containing exogenous alkaline phosphatase reversed the effects of ATP. These results provide further evidence that the effects of ATP on the K conductance are a consequence of a phosphorylation reaction mediated by a kinase present and active in perfused axons. Phosphorylation appears to alter the K conductance of squid giant axons via a minimum of two mechanisms. First, the voltage dependence of gating parameters are shifted toward positive potentials. Second, there is an increase in the number of functional closed states and/or a decrease in the rates of transition between these states of the K channels.

scholarly journals Effective Activation of BKCa Channels by QO-40 (5-(Chloromethyl)-3-(Naphthalen-1-yl)-2-(Trifluoromethyl)Pyrazolo [1,5-a]pyrimidin-7(4H)-one), Known to Be an Opener of KCNQ2/Q3 Channels

2021 ◽  
Vol 14 (5) ◽  
pp. 388
Author(s):  
Wei-Ting Chang ◽  
Sheng-Nan Wu
Keyword(s):  
Single Channel ◽  
Slow Component ◽  
Ionic Channel ◽  
Gh3 Cells ◽  
Bkca Channel ◽  
Bkca Channels ◽  
Gating Charge ◽  
Ramp Voltage ◽  
K Current ◽  
The Mean

QO-40 (5-(chloromethyl)-3-(naphthalene-1-yl)-2-(trifluoromethyl) pyrazolo[1,5-a]pyrimidin-7(4H)-one) is a novel and selective activator of KCNQ2/KCNQ3 K+ channels. However, it remains largely unknown whether this compound can modify any other type of plasmalemmal ionic channel. The effects of QO-40 on ion channels in pituitary GH3 lactotrophs were investigated in this study. QO-40 stimulated Ca2+-activated K+ current (IK(Ca)) with an EC50 value of 2.3 μM in these cells. QO-40-stimulated IK(Ca) was attenuated by the further addition of GAL-021 or paxilline but not by linopirdine or TRAM-34. In inside-out mode, this compound added to the intracellular leaflet of the detached patches stimulated large-conductance Ca2+-activated K+ (BKCa) channels with no change in single-channel conductance; however, there was a decrease in the slow component of the mean closed time of BKCa channels. The KD value required for the QO-40-mediated decrease in the slow component at the mean closure time was 1.96 μM. This compound shifted the steady-state activation curve of BKCa channels to a less positive voltage and decreased the gating charge of the channel. The application of QO-40 also increased the hysteretic strength of BKCa channels elicited by a long-lasting isosceles-triangular ramp voltage. In HEK293T cells expressing α-hSlo, QO-40 stimulated BKCa channel activity. Overall, these findings demonstrate that QO-40 can interact directly with the BKCa channel to increase the amplitude of IK(Ca) in GH3 cells.

scholarly journals A Dipeptidyl Aminopeptidase–like Protein Remodels Gating Charge Dynamics in Kv4.2 Channels

2006 ◽  
Vol 128 (6) ◽  
pp. 745-753 ◽  
Author(s):  
Kevin Dougherty ◽  
Manuel Covarrubias
Keyword(s):  
Membrane Potentials ◽  
Charge Movement ◽  
Transmembrane Segment ◽  
Gating Currents ◽  
Voltage Sensing ◽  
Charge Voltage ◽  
Charge Dynamics ◽  
Gating Charge ◽  
Kv4 Channels ◽  
Dipeptidyl Aminopeptidase

Dipeptidyl aminopeptidase–like proteins (DPLPs) interact with Kv4 channels and thereby induce a profound remodeling of activation and inactivation gating. DPLPs are constitutive components of the neuronal Kv4 channel complex, and recent observations have suggested the critical functional role of the single transmembrane segment of these proteins (Zagha, E., A. Ozaita, S.Y. Chang, M.S. Nadal, U. Lin, M.J. Saganich, T. McCormack, K.O. Akinsanya, S.Y. Qi, and B. Rudy. 2005. J. Biol. Chem. 280:18853–18861). However, the underlying mechanism of action is unknown. We hypothesized that a unique interaction between the Kv4.2 channel and a DPLP found in brain (DPPX-S) may remodel the channel's voltage-sensing domain. To test this hypothesis, we implemented a robust experimental system to measure Kv4.2 gating currents and study gating charge dynamics in the absence and presence of DPPX-S. The results demonstrated that coexpression of Kv4.2 and DPPX-S causes a −26 mV parallel shift in the gating charge-voltage (Q-V) relationship. This shift is associated with faster outward movements of the gating charge over a broad range of relevant membrane potentials and accelerated gating charge return upon repolarization. In sharp contrast, DPPX-S had no effect on gating charge movements of the Shaker B Kv channel. We propose that DPPX-S destabilizes resting and intermediate states in the voltage-dependent activation pathway, which promotes the outward gating charge movement. The remodeling of gating charge dynamics may involve specific protein–protein interactions of the DPPX-S's transmembrane segment with the voltage-sensing and pore domains of the Kv4.2 channel. This mechanism may determine the characteristic fast operation of neuronal Kv4 channels in the subthreshold range of membrane potentials.

Preliminary observations on escape swimming and giant neurons in Aglantha digitale (Hydromedusae: Trachylina)

1980 ◽  
Vol 58 (4) ◽  
pp. 549-552 ◽  
Author(s):  
S. Donaldson ◽  
G. O. Mackie ◽  
A. Roberts
Keyword(s):  
Action Potentials ◽  
Giant Axon ◽  
Synaptic Delay ◽  
Giant Axons ◽  
A Value ◽  
Giant Synapses ◽  
Run Up

Aglantha can swim in two ways, one of which, fast swimming, is evoked by contact with predators and serves for escape. The response consists of two or three violent contractions of which the first propels the animal a distance equivalent to five body lengths. Peak velocities in the range 0.3–0.4 m s−1 were measured. Drag is reduced by contraction of the tentacles.Coordination of escape swimming and tentacle contraction is achieved by a system of giant axons. A giant axon runs down each tentacle; action potentials in these elements show a one-for-one correspondence with potentials recorded from a ring-shaped axon lying in the margin near the tentacle bases. The ring giant synapses with eight motor giants which run up the subumbrella innervating the swimming muscles.Conduction velocities in the giant axons may be as high as 4.0 m s−1 in the case of the largest (40 μm diameter) axons. A value of 1.6 ms was obtained for minimum synaptic delay between the ring and motor giant axons.

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