Modulation of Jellyfish Potassium Channels by External  Potassium Ions

The amplitude of an A-like potassium current ( I Kfast) in identified cultured motor neurons isolated from the jellyfish Polyorchis penicillatus was found to be strongly modulated by extracellular potassium ([K+]out). When expressed in Xenopus oocytes, two jellyfish Shaker-like genes, jShak1 and jShak2, coding for potassium channels, exhibited similar modulation by [K+]out over a range of concentrations from 0 to 100 mM. jShak2-encoded channels also showed a decreased rate of inactivation and an increased rate of recovery from inactivation at high [K+]out. Using site-directed mutagenesis we show that inactivation of jShak2 can be ascribed to an unusual combination of a weak “implicit” N-type inactivation mechanism and a strong, fast, potassium-sensitive C-type mechanism. Interaction between the two forms of inactivation is responsible for the potassium dependence of cumulative inactivation. Inactivation of jShak1 was determined primarily by a strong “ball and chain” mechanism similar to fruit fly Shaker channels. Experiments using fast perfusion of outside-out patches with jShak2 channels were used to establish that the effects of [K+]out on the peak current amplitude and inactivation were due to processes occurring at either different sites located at the external channel mouth with different retention times for potassium ions, or at the same site(s) where retention time is determined by state-dependent conformations of the channel protein. The possible physiological implications of potassium sensitivity of high-threshold potassium A-like currents is discussed.

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Spreading depression (SD) waves in the brainstem can be elicited after blockade of potassium channels – evidence for the role of extracellular potassium ions as a driving force?

Journal of Cerebral Blood Flow & Metabolism ◽

10.1038/sj.jcbfm.9591524.0438 ◽

2005 ◽

Vol 25 (1_suppl) ◽

pp. S438-S438

Author(s):

Frank Richter ◽

Alfred Lehmenkühler ◽

Hans-Georg Schaible

Keyword(s):

Potassium Channels ◽

Driving Force ◽

Spreading Depression ◽

Extracellular Potassium ◽

Potassium Ions

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Dopamine as a Neuroactive Substance in the Jellyfish Polyorchis Penicillatus

Journal of Experimental Biology ◽

10.1242/jeb.156.1.433 ◽

1991 ◽

Vol 156 (1) ◽

pp. 433-451

Author(s):

JUN-MO CHUNG ◽

ANDREW N. SPENCER

Keyword(s):

Motor Neurons ◽

Reversal Potential ◽

Inhibitory Effect ◽

Cellular Level ◽

Potassium Ions ◽

Current Clamp ◽

Polyorchis Penicillatus ◽

Outward Currents ◽

Neuroactive Substance ◽

Current Clamp Mode

Recent studies have shown that nerve-rich tissues in the margin of Polyorchis penicillatus (Eschscholtz), one of the hydromedusae, contain dopamine. The present experiments were conducted to determine the physiological action of dopamine at the cellular level. In the current-clamp mode, dopamine, ranging from 10−8 to 10−3moll−1, applied to cultured swimming motor neurons of this jellyfish produced hyperpolarizations accompanied by a decrease of firing rate or complete inhibition of spiking produced by anodal break excitation. Dopamine in the voltage-clamp mode elicited outward currents at more positive levels than −55 mV, which is the reversal potential of the response. The results of a series of ionic experiments suggest that the inhibitory effect of dopamine is caused by an increased permeability to potassium ions.

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Whole body withdrawal circuit and its involvement in the behavioral hierarchy of the mollusk Clione limacina

Journal of Neurophysiology ◽

10.1152/jn.1996.75.2.529 ◽

1996 ◽

Vol 75 (2) ◽

pp. 529-537 ◽

Cited By ~ 17

Author(s):

T. P. Norekian ◽

R. A. Satterlie

Keyword(s):

Feeding Behavior ◽

Motor Neurons ◽

Prey Capture ◽

The Body ◽

Whole Body ◽

High Threshold ◽

Behavioral Repertoire ◽

Withdrawal Behavior ◽

Cerebral Neurons ◽

Clione Limacina

1. The behavioral repertoire of the holoplanktonic pteropod mollusk Clione limacina includes a few well-defined behaviors organized in a priority sequence. Whole body withdrawal takes precedence over slow swimming behavior, whereas feeding behavior is dominant over withdrawal. In this study a group of neurons is described in the pleural ganglia, which controls whole body withdrawal behavior in Clione. Each pleural withdrawal (Pl-W) neuron has a high threshold for spike generation and is capable of inducing whole body withdrawal in a semi-intact preparation: retraction of the body-tail, wings, and head. Each Pl-W neuron projects axons into the main central nerves and innervates all major regions of the body. 2. Stimulation of Pl-W neurons produces inhibitory inputs to swim motor neurons that terminate swimming activity in the preparation. In turn, Pl-W neurons receive inhibitory inputs from the cerebral neurons involved in the control of feeding behavior in Clione, neurons underlying extrusion of specialized prey capture appendages. Thus it appears that specific inhibitory connections between motor centers can explain the dominance of withdrawal behavior over slow swimming and feeding over withdrawal in Clione.

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Block of Human Heart hH1 Sodium Channels by the Enantiomers of Bupivacaine

Anesthesiology ◽

10.1097/00000542-200010000-00026 ◽

2000 ◽

Vol 93 (4) ◽

pp. 1022-1033 ◽

Cited By ~ 48

Author(s):

Carla Nau ◽

Sho-Ya Wang ◽

Gary R. Strichartz ◽

Ging Kuo Wang

Keyword(s):

Human Heart ◽

Point Mutations ◽

Cell Voltage ◽

Site Directed Mutagenesis ◽

Na Channel ◽

Amino Acid Residues ◽

Na Channels ◽

State Dependent ◽

Positively Charged

Background S(-)-bupivacaine reportedly exhibits lower cardiotoxicity but similar local anesthetic potency compared with R(+)-bupivacaine. The bupivacaine binding site in human heart (hH1) Na+ channels has not been studied to date. The authors investigated the interaction of bupivacaine enantiomers with hH1 Na+ channels, assessed the contribution of putatively relevant residues to binding, and compared the intrinsic affinities to another isoform, the rat skeletal muscle (mu1) Na+ channel. Methods Human heart and mu1 Na+ channel alpha subunits were transiently expressed in HEK293t cells and investigated during whole cell voltage-clamp conditions. Using site-directed mutagenesis, the authors created point mutations at positions hH1-F1760, hH1-N1765, hH1-Y1767, and hH1-N406 by introducing the positively charged lysine (K) or the negatively charged aspartic acid (D) and studied their influence on state-dependent block by bupivacaine enantiomers. Results Inactivated hH1 Na+ channels displayed a weak stereoselectivity with a stereopotency ratio (+/-) of 1.5. In mutations hH1-F1760K and hH1-N1765K, bupivacaine affinity of inactivated channels was reduced by approximately 20- to 40-fold, in mutation hH1-N406K by approximately sevenfold, and in mutations hH1-Y1767K and hH1-Y1767D by approximately twofold to threefold. Changes in recovery of inactivated mutant channels from block paralleled those of inactivated channel affinity. Inactivated hH1 Na+ channels exhibited a slightly higher intrinsic affinity than mu1 Na+ channels. Conclusions Differences in bupivacaine stereoselectivity and intrinsic affinity between hH1 and mu1 Na+ channels are small and most likely of minor clinical relevance. Amino acid residues in positions hH1-F1760, hH1-N1765, and hH1-N406 may contribute to binding of bupivacaine enantiomers in hH1 Na+ channels, whereas the role of hH1-Y1767 remains unclear.

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The conduction pathway of potassium channels is water free under physiological conditions

Science Advances ◽

10.1126/sciadv.aaw6756 ◽

2019 ◽

Vol 5 (7) ◽

pp. eaaw6756 ◽

Cited By ~ 12

Author(s):

Carl Öster ◽

Kitty Hendriks ◽

Wojciech Kopec ◽

Veniamin Chevelkov ◽

Chaowei Shi ◽

...

Keyword(s):

Potassium Channels ◽

Direct Contact ◽

Selectivity Filter ◽

Water Molecules ◽

Potassium Ions ◽

Ion Conduction ◽

Physiological Conditions ◽

Conduction Pathway ◽

Fundamental Process ◽

Dynamics Simulations

Ion conduction through potassium channels is a fundamental process of life. On the basis of crystallographic data, it was originally proposed that potassium ions and water molecules are transported through the selectivity filter in an alternating arrangement, suggesting a “water-mediated” knock-on mechanism. Later on, this view was challenged by results from molecular dynamics simulations that revealed a “direct” knock-on mechanism where ions are in direct contact. Using solid-state nuclear magnetic resonance techniques tailored to characterize the interaction between water molecules and the ion channel, we show here that the selectivity filter of a potassium channel is free of water under physiological conditions. Our results are fully consistent with the direct knock-on mechanism of ion conduction but contradict the previously proposed water-mediated knock-on mechanism.

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Voltage-activated potassium currents in isolated motor neurons from the jellyfish Polyorchis penicillatus

Journal of Neurophysiology ◽

10.1152/jn.1994.72.2.1010 ◽

1994 ◽

Vol 72 (2) ◽

pp. 1010-1019 ◽

Cited By ~ 9

Author(s):

J. Przysiezniak ◽

A. N. Spencer

Keyword(s):

Motor Neurons ◽

Action Potentials ◽

Voltage Dependence ◽

Primary Cultures ◽

Potassium Currents ◽

Whole Cell ◽

Time To Peak ◽

Polyorchis Penicillatus ◽

Slow Onset

1. We describe two voltage-activated potassium currents in the swim motor neurons (SMNs) of the hydrozoan jellyfish, Polyorchis penicillatus. Recordings from neurons isolated in primary cultures were made using the tight-seal, whole-cell technique. 2. One current, IK-fast, turned on rapidly (time to peak = 6–15 ms), was half-activated at -10 to 0 mV, decayed with two exponential phases (tau were approximately 70 ms and approximately 1 s), and was half-inactivated by prepulses around -53 mV. It likely plays an important role in regulating the duration of SMN action potentials. IK-fast has features shared by delayed rectifiers and A-like currents in other invertebrates and vertebrates. 3. Another current, IK-slow, elicited from a holding potential of -30 mV, exhibited a slow onset (tau = 65–250 ms), was half-activated approximately +24 mV, exhibited a shallower voltage dependence than IK-fast, and did not inactivate. It was slower than most known delayed rectifiers.

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The Myelin Sheath Maintains the Spatiotemporal Fidelity of Action Potentials by Eliminating the Effect of Quantum Tunneling of Potassium Ions through the Closed Channels of the Neuronal Membrane

Quantum Reports ◽

10.3390/quantum1020026 ◽

2019 ◽

Vol 1 (2) ◽

pp. 287-294 ◽

Cited By ~ 3

Author(s):

Abdallah Barjas Qaswal

Keyword(s):

Potassium Channels ◽

Action Potential ◽

Myelin Sheath ◽

Quantum Tunneling ◽

Action Potentials ◽

Quantum Physics ◽

Demyelinating Diseases ◽

Neuronal Membrane ◽

Potassium Ions ◽

Axonal Membrane

The myelin sheath facilitates action potential conduction along the axons, however, the mechanism by which myelin maintains the spatiotemporal fidelity and limits the hyperexcitability among myelinated neurons requires further investigation. Therefore, in this study, the model of quantum tunneling of potassium ions through the closed channels is used to explore this function of myelin. According to the present calculations, when an unmyelinated neuron fires, there is a probability of 9.15 × 10 − 4 that it will induce an action potential in other unmyelinated neurons, and this probability varies according to the type of channels involved, the channels density in the axonal membrane, and the surface area available for tunneling. The myelin sheath forms a thick barrier that covers the potassium channels and prevents ions from tunneling through them to induce action potential. Hence, it confines the action potentials spatiotemporally and limits the hyperexcitability. On the other hand, lack of myelin, as in unmyelinated neurons or demyelinating diseases, exposes potassium channels to tunneling by potassium ions and induces the action potential. This approach gives different perspectives to look at the interaction between neurons and explains how quantum physics might play a role in the actions occurring in the nervous system.

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