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The Journal of Neuroscience, January 15, 2000, 20(2):511-520

Ultrafast Inactivation Causes Inward Rectification in a Voltage-Gated K⁺ Channel from Caenorhabditis elegans

Richard Fleischhauer¹, M. Wayne Davis², Igor Dzhura³, Alan Neely³, Leon Avery², and Rolf H. Joho¹

¹ Center for Basic Neuroscience and ² Department of Molecular Biology, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9111, and ³ Department of Physiology, Texas Tech University Health Science Center, Lubbock, Texas 79430

The exp-2 gene in the nematode Caenorhabditis elegans influences the shape and duration of the action potential of pharyngeal muscle cells. Several loss-of-function mutations in exp-2 lead to broadening of the action potential and to a concomitant slowing of the pumping action of the pharynx. In contrast, a gain-of-function mutation leads to narrow action potentials and shallow pumping. We cloned and functionally characterized the exp-2 gene. The exp-2 gene is homologous to genes of the family of voltage-gated K⁺ channels (Kv type). The Xenopus oocyte-expressed EXP-2 channel, although structurally closely related to Kv-type channels, is functionally distinct and very similar to the human ether-à-gogo-related gene (HERG) K⁺ channel. In response to depolarization, EXP-2 activates slowly and inactivates very rapidly. On repolarization, recovery from inactivation is also rapid and strongly voltage-dependent. These kinetic properties make the Kv-type EXP-2 channel an inward rectifier that resembles the structurally unrelated HERG channel. Apart from many similarities to HERG, however, the molecular mechanism of fast inactivation appears to be different. Moreover, the single-channel conductance is 5- to 10-fold larger than that of HERG and most Kv-type K⁺ channels. It appears that the inward rectification mechanism by rapid inactivation has evolved independently in two distinct classes of structurally unrelated, voltage-gated K⁺ channels.

Key words: potassium channel; Kv channel; inward rectifier; C. elegans; pharyngeal muscle; Xenopus oocyte

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Copyright © 2000 Society for Neuroscience  0270-6474/00/202511-10$05.00/0

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