|
|
|
|
|
|
|
||
Re-examination of the Surface Charge Hypothesis
2 Department of Pharmacology and Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06520
Address correspondence to Edward Moczydlowski, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06520-8066. Fax: (203) 436-4886; E-mail: edward.moczydlowski{at}yale.edu
Incorporation of BK Ca2+–activated K+ channels into planar bilayers composed of negatively charged phospholipids such as phosphatidylserine (PS) or phosphatidylinositol (PI) results in a large enhancement of unitary conductance (gch) in comparison to BK channels in bilayers formed from the neutral zwitterionic lipid, phospatidylethanolamine (PE). Enhancement of gch by PS or PI is inversely dependent on KCl concentration, decreasing from 70% at 10 mM KCl to 8% at 1,000 mM KCl. This effect was explained previously by a surface charge hypothesis (Moczydlowski, E., O. Alvarez, C. Vergara, and R. Latorre. 1985. J. Membr. Biol. 83:273–282), which attributed the conductance enhancement to an increase in local K+ concentration near the entryways of the channel. To test this hypothesis, we measured the kinetics of block by external and internal Ba2+, a divalent cation that is expected to respond strongly to changes in surface electrostatics. We observed little or no effect of PS on discrete blocking kinetics by external and internal Ba2+ at 100 mM KCl and only a small enhancement of discrete and fast block by external Ba2+ in PS-containing membranes at 20 mM KCl. Model calculations of effective surface potential sensed by the K+ conduction and Ba2+-blocking reactions using the Gouy-Chapman-Stern theory of lipid surface charge do not lend support to a simple electrostatic mechanism that predicts valence-dependent increase of local cation concentration. The results imply that the conduction pore of the BK channel is electrostatically insulated from the lipid surface, presumably by a lateral distance of separation (>20 Å) from the lipid head groups. The lack of effect of PS on apparent association and dissociation rates of Ba2+ suggest that lipid modulation of K+ conductance is preferentially coupled through conformational changes of the selectivity filter region that determine the high K+ flux rate of this channel relative to other cations. We discuss possible mechanisms for the effect of anionic lipids in the context of specific molecular interactions of phospholipids documented for the KcsA bacterial potassium channel and general membrane physical properties proposed to regulate membrane protein conformation via energetics of bilayer stress.
Key Words: electrostatics • Gouy-Chapman theory • lipid modulation • phospholipid • Slowpoke
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  T. Vaithianathan, A. Bukiya, J. Liu, P. Liu, M. Asuncion-Chin, Z. Fan, and A. Dopico Direct Regulation of BK Channels by Phosphatidylinositol 4,5-Bisphosphate as a Novel Signaling Pathway J. Gen. Physiol., June 30, 2008; 132(1): 13 - 28. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. K. Lyashchenko and G. R. Tibbs Ion binding in the Open HCN Pacemaker Channel Pore: Fast Mechanisms to Shape "Slow" Channels J. Gen. Physiol., February 25, 2008; 131(3): 227 - 243. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. Yuan, R. J. O'Connell, R. F. Jacob, R. P. Mason, and S. N. Treistman Regulation of the Gating of BKCa Channel by Lipid Bilayer Thickness J. Biol. Chem., March 9, 2007; 282(10): 7276 - 7286. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. T. Lin, D. A. Hessinger, W. J. Pearce, and L. D. Longo Modulation of BK channel calcium affinity by differential phosphorylation in developing ovine basilar artery myocytes Am J Physiol Heart Circ Physiol, August 1, 2006; 291(2): H732 - H740. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Zhang, X. Niu, T. I. Brelidze, and K. L. Magleby Ring of Negative Charge in BK Channels Facilitates Block by Intracellular Mg2+ and Polyamines through Electrostatics J. Gen. Physiol., July 31, 2006; 128(2): 185 - 202. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. A. Sobko, E. A. Kotova, Y. N. Antonenko, S. D. Zakharov, and W. A. Cramer Lipid Dependence of the Channel Properties of a Colicin E1-Lipid Toroidal Pore J. Biol. Chem., May 19, 2006; 281(20): 14408 - 14416. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. I. Brelidze and K. L. Magleby Probing the Geometry of the Inner Vestibule of BK Channels with Sugars J. Gen. Physiol., July 25, 2005; 126(2): 105 - 121. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. J. Crowley, S. N. Treistman, and A. M. Dopico Distinct Structural Features of Phospholipids Differentially Determine Ethanol Sensitivity and Basal Function of BK Channels Mol. Pharmacol., July 1, 2005; 68(1): 4 - 10. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. D'Avanzo, H. C. Cho, I. Tolokh, R. Pekhletski, I. Tolokh, C. Gray, S. Goldman, and P. H. Backx Conduction through the Inward Rectifier Potassium Channel, Kir2.1, Is Increased by Negatively Charged Extracellular Residues J. Gen. Physiol., April 25, 2005; 125(5): 493 - 503. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. Hartel, M. L. Fanani, and B. Maggio Shape Transitions and Lattice Structuring of Ceramide-Enriched Domains Generated by Sphingomyelinase in Lipid Monolayers Biophys. J., January 1, 2005; 88(1): 287 - 304. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Yuan, R. J. O'Connell, P. L. Feinberg-Zadek, L. J. Johnston, and S. N. Treistman Bilayer Thickness Modulates the Conductance of the BK Channel in Model Membranes Biophys. J., June 1, 2004; 86(6): 3620 - 3633. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. I. Brelidze and K. L. Magleby Protons Block BK Channels by Competitive Inhibition with K+ and Contribute to the Limits of Unitary Currents at High Voltages J. Gen. Physiol., February 23, 2004; 123(3): 305 - 319. [Abstract] [Full Text] [PDF]
|
|
|
|
