Na+-activated K+ channels localized in the nodal region of myelinated axons of Xenopus

D. Koh, P.M. Jonas, W. Vogel, Journal of Physiology 479 (1994) 183–197.


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Abstract
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.
Publishing Year
Date Published
1994-01-01
Journal Title
Journal of Physiology
Volume
479
Page
183 - 197
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Koh D, Jonas PM, Vogel W. Na+-activated K+ channels localized in the nodal region of myelinated axons of Xenopus. Journal of Physiology. 1994;479:183-197. doi:10.1113/jphysiol.1994.sp020287
Koh, D., Jonas, P. M., & Vogel, W. (1994). Na+-activated K+ channels localized in the nodal region of myelinated axons of Xenopus. Journal of Physiology, 479, 183–197. https://doi.org/10.1113/jphysiol.1994.sp020287
Koh, Duk, Peter M Jonas, and Werner Vogel. “Na+-Activated K+ Channels Localized in the Nodal Region of Myelinated Axons of Xenopus.” Journal of Physiology 479 (1994): 183–97. https://doi.org/10.1113/jphysiol.1994.sp020287.
D. Koh, P. M. Jonas, and W. Vogel, “Na+-activated K+ channels localized in the nodal region of myelinated axons of Xenopus,” Journal of Physiology, vol. 479, pp. 183–197, 1994.
Koh D, Jonas PM, Vogel W. 1994. Na+-activated K+ channels localized in the nodal region of myelinated axons of Xenopus. Journal of Physiology. 479, 183–197.
Koh, Duk, et al. “Na+-Activated K+ Channels Localized in the Nodal Region of Myelinated Axons of Xenopus.” Journal of Physiology, vol. 479, Wiley-Blackwell, 1994, pp. 183–97, doi:10.1113/jphysiol.1994.sp020287.

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