International Union of Pharmacology. XLI. Compendium of Voltage-Gated Ion Channels: Potassium Channels

2003 ◽  
Vol 55 (4) ◽  
pp. 583-586 ◽  
Author(s):  
George A. Gutman ◽  
K. George Chandy ◽  
John P. Adelman ◽  
Jayashree Aiyar ◽  
Douglas A. Bayliss ◽  
...  
Keyword(s):  
Ion Channels ◽  
Potassium Channels ◽  
International Union ◽  
Voltage Gated ◽  
Voltage Gated Ion Channels ◽  
Gated Ion Channels

scholarly journals Immobilizing the Moving Parts of Voltage-Gated Ion Channels

2000 ◽  
Vol 116 (3) ◽  
pp. 461-476 ◽  
Author(s):  
Richard Horn ◽  
Shinghua Ding ◽  
Hermann J. Gruber
Keyword(s):  
Ion Channels ◽  
Potassium Channels ◽  
Sodium Channel ◽  
Ultraviolet Irradiation ◽  
Voltage Sensors ◽  
Voltage Gated ◽  
Voltage Gated Ion Channels ◽  
S4 Segment ◽  
Moving Parts ◽  
Gated Ion Channels

Voltage-gated ion channels have at least two classes of moving parts, voltage sensors that respond to changes in the transmembrane potential and gates that create or deny permeant ions access to the conduction pathway. To explore the coupling between voltage sensors and gates, we have systematically immobilized each using a bifunctional photoactivatable cross-linker, benzophenone-4-carboxamidocysteine methanethiosulfonate, that can be tethered to cysteines introduced into the channel protein by mutagenesis. To validate the method, we first tested it on the inactivation gate of the sodium channel. The benzophenone-labeled inactivation gate of the sodium channel can be trapped selectively either in an open or closed state by ultraviolet irradiation at either a hyperpolarized or depolarized voltage, respectively. To verify that ultraviolet light can immobilize S4 segments, we examined its relative effects on ionic and gating currents in Shaker potassium channels, labeled at residue 359 at the extracellular end of the S4 segment. As predicted by the tetrameric stoichiometry of these potassium channels, ultraviolet irradiation reduces ionic current by approximately the fourth power of the gating current reduction, suggesting little cooperativity between the movements of individual S4 segments. Photocross-linking occurs preferably at hyperpolarized voltages after labeling residue 359, suggesting that depolarization moves the benzophenone adduct out of a restricted environment. Immobilization of the S4 segment of the second domain of sodium channels prevents channels from opening. By contrast, photocross-linking the S4 segment of the fourth domain of the sodium channel has effects on both activation and inactivation. Our results indicate that specific voltage sensors of the sodium channel play unique roles in gating, and suggest that movement of one voltage sensor, the S4 segment of domain 4, is at least a two-step process, each step coupled to a different gate.

Zinc and Copper Influence Excitability of Rat Olfactory Bulb Neurons by Multiple Mechanisms

2001 ◽  
Vol 86 (4) ◽  
pp. 1652-1660 ◽  
Author(s):  
Michelle S. Horning ◽  
Paul Q. Trombley
Keyword(s):  
Ion Channels ◽  
Potassium Channels ◽  
Olfactory Bulb ◽  
Membrane Potentials ◽  
Repetitive Firing ◽  
Delayed Rectifier ◽  
Voltage Gated ◽  
Voltage Gated Ion Channels ◽  
Olfactory Bulb Neurons ◽  
Gated Ion Channels

Zinc and copper are highly concentrated in several mammalian brain regions, including the olfactory bulb and hippocampus. Whole cell electrophysiological recordings were made from rat olfactory bulb neurons in primary culture to compare the effects of zinc and copper on synaptic transmission and voltage-gated ion channels. Application of either zinc or copper eliminated GABA-mediated spontaneous inhibitory postsynaptic potentials. However, in contrast to the similarity of their effects on inhibitory transmission, spontaneous glutamate-mediated excitatory synaptic activity was completely blocked by copper but only inhibited by zinc. Among voltage-gated ion channels, zinc or copper inhibited TTX-sensitive sodium channels and delayed rectifier-type potassium channels but did not prevent the firing of evoked single action potentials or dramatically alter their kinetics. Zinc and copper had distinct effects on transient A-type potassium currents. Whereas copper only inhibited the A-type current, zinc modulation of A-type currents resulted in either potentiation or inhibition of the current depending on the membrane potential. The effects of zinc and copper on potassium channels likely underlie their effects on repetitive firing in response to long-duration step depolarizations. Copper reduced repetitive firing independent of the initial membrane voltage. In contrast, whereas zinc reduced repetitive firing at membrane potentials associated with zinc-mediated enhancement of the A-type current (−50 mV), in a significant proportion of neurons, zinc increased repetitive firing at membrane potentials associated with zinc-mediated inhibition of the A-type current (−90 mV). Application of zinc or copper also inhibited voltage-gated Ca2+ channels, suggesting a possible role for presynaptic modulation of neurotransmitter release. Despite similarities between the effects of zinc and copper on some ligand- and voltage-gated ion channels, these data suggest that their net effects likely contribute to differential modulation of neuronal excitability.

International Union of Pharmacology: Approaches to the Nomenclature of Voltage-Gated Ion Channels

2003 ◽  
Vol 55 (4) ◽  
pp. 573-574 ◽  
Author(s):  
W. A. Catterall ◽  
K. G. Chandy ◽  
D. E. Clapham ◽  
G. A. Gutman ◽  
F. Hofmann ◽  
...  
Keyword(s):  
Ion Channels ◽  
International Union ◽  
Voltage Gated ◽  
Voltage Gated Ion Channels ◽  
Gated Ion Channels

International Union of Pharmacology. XL. Compendium of Voltage-Gated Ion Channels: Calcium Channels

2003 ◽  
Vol 55 (4) ◽  
pp. 579-581 ◽  
Author(s):  
William A. Catterall ◽  
Joerg Striessnig ◽  
Terrance P. Snutch ◽  
Edward Perez-Reyes
Keyword(s):  
Ion Channels ◽  
Calcium Channels ◽  
International Union ◽  
Voltage Gated ◽  
Voltage Gated Ion Channels ◽  
Gated Ion Channels
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