Original Article

Extracellular Mg²⁺ Modulates Slow Gating Transitions and the Opening of Drosophila Ether-à-Go-Go Potassium Channels

Correspondence to: Diane M. Papazian, Department of Physiology, Box 951751, UCLA School of Medicine, Los Angeles, CA 90095-1751. Fax:310-206-5661 E-mail:papazian{at}mednet.ucla.edu.

Released online: 28 February 2000

We have characterized the effects of prepulse hyperpolarization and extracellular Mg²⁺ on the ionic and gating currents of the Drosophila ether-à-go-go K⁺ channel (eag). Hyperpolarizing prepulses significantly slowed channel opening elicited by a subsequent depolarization, revealing rate-limiting transitions for activation of the ionic currents. Extracellular Mg²⁺ dramatically slowed activation of eag ionic currents evoked with or without prepulse hyperpolarization and regulated the kinetics of channel opening from a nearby closed state(s). These results suggest that Mg²⁺ modulates voltage-dependent gating and pore opening in eag channels. To investigate the mechanism of this modulation, eag gating currents were recorded using the cut-open oocyte voltage clamp. Prepulse hyperpolarization and extracellular Mg²⁺ slowed the time course of ON gating currents. These kinetic changes resembled the results at the ionic current level, but were much smaller in magnitude, suggesting that prepulse hyperpolarization and Mg²⁺ modulate gating transitions that occur slowly and/or move relatively little gating charge. To determine whether quantitatively different effects on ionic and gating currents could be obtained from a sequential activation pathway, computer simulations were performed. Simulations using a sequential model for activation reproduced the key features of eag ionic and gating currents and their modulation by prepulse hyperpolarization and extracellular Mg²⁺. We have also identified mutations in the S3–S4 loop that modify or eliminate the regulation of eag gating by prepulse hyperpolarization and Mg²⁺, indicating an important role for this region in the voltage-dependent activation of eag.

Key Words: gating currents, prepulse hyperpolarization, activation model, voltage clamp

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				M. V. Soldovieri, M. R. Cilio, F. Miceli, G. Bellini, E. Miraglia del Giudice, P. Castaldo, C. C. Hernandez, M. S. Shapiro, A. Pascotto, L. Annunziato, et al. Atypical Gating Of M-Type Potassium Channels Conferred by Mutations in Uncharged Residues in the S4 Region of KCNQ2 Causing Benign Familial Neonatal Convulsions J. Neurosci., May 2, 2007; 27(18): 4919 - 4928. [Abstract] [Full Text] [PDF]

				R. J. G. Cardnell, D. E. Dalle Nogare, B. Ganetzky, and M. Stern In Vivo Analysis of a Gain-of-Function Mutation in the Drosophila eag-Encoded K+ Channel Genetics, April 1, 2006; 172(4): 2351 - 2358. [Abstract] [Full Text] [PDF]

				A. P. Hegle, D. D. Marble, and G. F. Wilson A voltage-driven switch for ion-independent signaling by ether-a-go-go K+ channels PNAS, February 21, 2006; 103(8): 2886 - 2891. [Abstract] [Full Text] [PDF]

				J. P. A. Bannister, B. Chanda, F. Bezanilla, and D. M. Papazian Optical detection of rate-determining ion-modulated conformational changes of the ether-a-go-go K+ channel voltage sensor PNAS, December 20, 2005; 102(51): 18718 - 18723. [Abstract] [Full Text] [PDF]

				G. Wrobel, R. Seifert, S. Ingebrandt, J. Enderlein, H. Ecken, A. Baumann, U. B. Kaupp, and A. Offenhausser Cell-Transistor Coupling: Investigation of Potassium Currents Recorded with p- and n-Channel FETs Biophys. J., November 1, 2005; 89(5): 3628 - 3638. [Abstract] [Full Text] [PDF]

				D. Fernandez, A. Ghanta, K. I Kinard, and M. C Sanguinetti Molecular mapping of a site for Cd2+-induced modification of human ether-a-go-go-related gene (hERG) channel activation J. Physiol., September 15, 2005; 567(3): 737 - 755. [Abstract] [Full Text] [PDF]

				D. R. Piper, W. A. Hinz, C. K. Tallurri, M. C. Sanguinetti, and M. Tristani-Firouzi Regional Specificity of Human ether-a'-go-go-related Gene Channel Activation and Inactivation Gating J. Biol. Chem., February 25, 2005; 280(8): 7206 - 7217. [Abstract] [Full Text] [PDF]

				W. R. Silverman, J. P. A. Bannister, and D. M. Papazian Binding Site in Eag Voltage Sensor Accommodates a Variety of Ions and is Accessible in Closed Channel Biophys. J., November 1, 2004; 87(5): 3110 - 3121. [Abstract] [Full Text] [PDF]

				J. T. Sack, R. W. Aldrich, and W. F. Gilly A Gastropod Toxin Selectively Slows Early Transitions in the Shaker K Channel's Activation Pathway J. Gen. Physiol., June 1, 2004; 123(6): 685 - 696. [Abstract] [Full Text] [PDF]

				D. R. Piper, A. Varghese, M. C. Sanguinetti, and M. Tristani-Firouzi Gating currents associated with intramembrane charge displacement in HERG potassium channels PNAS, September 2, 2003; 100(18): 10534 - 10539. [Abstract] [Full Text] [PDF]

				D. Sigg and F. Bezanilla A Physical Model of Potassium Channel Activation: From Energy Landscape to Gating Kinetics Biophys. J., June 1, 2003; 84(6): 3703 - 3716. [Abstract] [Full Text] [PDF]

				J. Liu, M. Zhang, M. Jiang, and G.-N. Tseng Negative Charges in the Transmembrane Domains of the HERG K Channel Are Involved in the Activation- and Deactivation-gating Processes J. Gen. Physiol., May 27, 2003; 121(6): 599 - 614. [Abstract] [Full Text] [PDF]

				W. R. Silverman, B. Roux, and D. M. Papazian Structural basis of two-stage voltage-dependent activation in K+ channels PNAS, March 4, 2003; 100(5): 2935 - 2940. [Abstract] [Full Text] [PDF]

				M. Tristani-Firouzi, J. Chen, and M. C. Sanguinetti Interactions between S4-S5 Linker and S6 Transmembrane Domain Modulate Gating of HERG K+ Channels J. Biol. Chem., May 17, 2002; 277(21): 18994 - 19000. [Abstract] [Full Text] [PDF]

				J. P. Johnson Jr, J. R. Balser, and P. B. Bennett A Novel Extracellular Calcium Sensing Mechanism in Voltage-Gated Potassium Ion Channels J. Neurosci., June 15, 2001; 21(12): 4143 - 4153. [Abstract] [Full Text] [PDF]

Home | Help | Feedback | Subscriptions | Archive | Search | Table of Contents