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Single-Channel Properties of the Reconstituted Voltage-Regulated Na Channel Isolated from the Electroplax of Electrophorus electricus
Robert L. Rosenberg, Sally A. Tomiko and William S. Agnew
Proceedings of the National Academy of Sciences of the United States of America
Vol. 81, No. 17, [Part 1: Biological Sciences] (Sep. 1, 1984), pp. 5594-5598
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/23954
Page Count: 5
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The tetrodotoxin-binding protein purified from electroplax of Electrophorus electricus has been reincorporated into multilamellar vesicles that were used for patch recording. When excised patches of these reconstituted membranes were voltage clamped in the absence of neurotoxins, voltage-dependent single-channel currents were recorded. These displayed properties qualitatively and quantitatively similar to those reported for Na channels from nerve and muscle cells, including uniform single-channel conductances of the appropriate magnitude (≈ 11 pS in 95 mM Na+), mean open times of ≈ 1.9 msec, and 7-fold selectivity for Na+ over K+. Currents averaged from many depolarizations showed initial voltage-dependent activation and subsequent inactivation. In the presence of batrachotoxin, channels were observed with markedly different properties, including conductances of 20-25 pS (95 mM Na+), mean open times of ≈ 28 msec, and no indication of inactivation. Collectively, these findings indicate that the tetrodotoxin-binding protein of electroplax is a voltage-regulated sodium channel.
Proceedings of the National Academy of Sciences of the United States of America © 1984 National Academy of Sciences