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          Institute: MPI für medizinische Forschung     Collection: Abteilung Zellphysiologie     Display Documents

ID: 22429.0, MPI für medizinische Forschung / Abteilung Zellphysiologie
Na+ activated K+ channels localized in the nodal region of myelinated axons of Xenopus
Translation of Title:Na<SUP>+</SUP> activated K<SUP>+</SUP> channels localized in the nodal region of myelinated axons of Xenopus
Authors:Koh, D. S.; Jonas, Peter; Vogel, W.
Date of Publication (YYYY-MM-DD):1994
Title of Journal:Journal of Physiology
Journal Abbrev.:J. Physiol.
Issue / Number:2
Start Page:193
End Page:197
Review Status:Peer-review
Audience:Experts Only
Intended Educational Use:No
Abstract / Description:1. A potassium channel activated by internal Na+ ions (K+Na channel) was identified in peripheral myelinated axons of Xenopus laevis using the cell-attached and excised configurations of the patch clamp technique. 2. The single-channel conductance for the main open state was 88 pS with [K+]o = 105 mM and pS with [K+]o = 2.5 mM ([K+]i = 105 mM). The channel was selectively permeable to K+ over Na+ ions. A characteristic feature of the K+ Na channel was the frequent occurrence of subconductance states. 3. The open probability of the channel was strongly dependent on the concentration of Na+ ions at the inner side of the membrane. The half-maximal activating Na+ concentration and the Hill coefficient were 33 mM and 2.9, respectively. The open probability of the channel showed only weak potential dependence. 4. The K+Na channel was relatively insensitive to external tetraethylammonium (TEA+) in comparison with voltage-dependent axonal K+ channels; the half-maximal inhibitory concentration (IC50) was 21.3 mM (at -90 mV). In contrast, the channel was blocked by low concentrations of external Ba2+ and Cs+ ions, with IC50 values of 0.7 and 1.1 mM, respectively (at -90 mV). The block by Ba2+ and Cs+ was more pronounced at negative than at positive membrane potentials. 5. A comparison of the number of K+Na channels in nodal and paranodal patches from the same axon revealed that the channel density was about 10-fold higher at the node of Ranvier than at the paranode. Moreover, a correlation between the number of K+Na channels and voltage-dependent Na+ channels in the same patches was found, suggesting co-localization of both channel types. 6. As weakly potential-dependent (leakage) channels, axonal K+Na channels may be involved in setting the resting potential of vertebrate axons. Simulations of Na+ ion diffusion suggest two possible mechanisms of activation of K+Na channels: the local increase of Na+ concentration in a cluster of Na+ channels during a single action potential or the accumulation in the intracellular axonal compartment during a train of action potentials.
External Publication Status:published
Document Type:Article
Communicated by:Wulf Kaiser
Affiliations:MPI für medizinische Forschung/Abteilung Zellphysiologie/
Identifiers:URI:http://www.jphysiol.org/cgi/content/abstract/479/2... [Abstract]
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