Sodium Channel Carboxyl-terminal Residue Regulates Fast Inactivation |
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Authors: | Hai M Nguyen and Alan L Goldin |
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Institution: | From the Department of Microbiology and Molecular Genetics and the Department of Anatomy and Neurobiology, University of California, Irvine, California 92697-4025 |
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Abstract: | The Nav1.2 and Nav1.3 voltage-gated sodium channel isoforms demonstrate distinct differences in their kinetics and voltage dependence of fast inactivation when expressed in Xenopus oocytes. Co-expression of the auxiliary β1 subunit accelerated inactivation of both the Nav1.2 and Nav1.3 isoforms, but it did not eliminate the differences, demonstrating that this property is inherent in the α subunit. By constructing chimeric channels between Nav1.2 and Nav1.3, we demonstrate that the carboxyl terminus is responsible for the differences. The Nav1.2 carboxyl terminus caused faster inactivation in the Nav1.3 backbone, and the Nav1.3 carboxyl terminus caused slower inactivation in the Nav1.2 channel. Through analysis of truncated channels, we identified a homologous 60-amino acid region within the carboxyl terminus of the Nav1.2 and the Nav1.3 channels that is responsible for this modulation of fast inactivation. Site-directed replacement of Nav1.3 lysine 1826 in this region to its Nav1.2 analogue glutamic acid 1880 (K1826E) shifted the voltage dependence of inactivation toward that of Nav1.2. The K1826E mutation also accelerated the inactivation kinetics to a level comparable with that of Nav1.2. The reverse Nav1.2 E1880K mutation exhibited much slower inactivation kinetics and depolarized inactivation voltage dependence. A complementary mutation located within the inactivation linker of Nav1.3 (K1453E) caused inactivation changes mirroring those caused by the K1826E mutation in Nav1.3. Therefore, we have identified a homologous carboxyl-terminal residue that regulates the kinetics and voltage dependence of fast inactivation in sodium channels, possibly via a charge-dependent interaction with the inactivation linker. |
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Keywords: | Ion Channels Membrane Proteins Oocyte Protein Chimeras Sodium Channels Carboxyl Terminus Isoforms Structure-Function Voltage Clamp Voltage-dependent |
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