| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
NEUROSCIENCE |
1 The Cardiac Electrophysiology Laboratories, Departments of Medicine and of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA
Protons are potent physiological modifiers of voltage-gated Na+ channels, shifting the voltage range of channel gating and reducing current magnitude (pKa
6). We recently showed that proton block of the skeletal muscle isoform (NaV1.4) resulted from protonation of the four superficial carboxylates in the outer vestibule of the channel. We concluded that the large local negative electrostatic field shifted the outer vestibule carboxylate pKa into the physiological range. However, block was not complete; the best-fit titration curves yielded an acid pH asymptote of 10–15%, suggesting that the selectivity filter carboxylates may not be protonated. Using HEK 293 cells stably expressing different isoforms, each with varying channel density, we demonstrate that a pH-independent current is found in NaV1.4, but not in the cardiac isoform (NaV1.5). Mutational studies showed that absence of the pH-independent current in NaV1.5 could be ascribed to the cysteine in domain I, just above the selectivity filter aspartate (Cys373). We suggest that this cysteine can be protonated in acid solution to produce a positive charge that blocks the pore. Competition between protons and Na+ did not exist for Na+ concentrations between 1 and 140 mM. The residual current in acid solution, when the cysteine is absent, confirms that over the range of pH values that can be achieved physiologically, the selectivity filter carboxylates are not protonated. The pH-independent current helps to protect activation of skeletal muscle during the acidosis that occurs during exercise.
(Received 20 June 2006;
accepted after revision 26 July 2006;
first published online 27 July 2006)
Corresponding author H. A. Fozzard: PO Box 574, 16 Georgianna Lane, Dana, NC 28724, USA. Email: hafozzar{at}uchicago.edu
This article has been cited by other articles:
|
|
 |
|
  G. M. Lipkind and H. A. Fozzard Voltage-gated Na Channel Selectivity: The Role of the Conserved Domain III Lysine Residue J. Gen. Physiol., June 1, 2008; 131(6): 523 - 529. [Full Text] [PDF]
|
|
|
|
 |
|
 V. P. Santarelli, A. L. Eastwood, D. A. Dougherty, C. A. Ahern, and R. Horn Calcium Block of Single Sodium Channels: Role of a Pore-Lining Aromatic Residue Biophys. J., October 1, 2007; 93(7): 2341 - 2349. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. D. Carrithers, S. Dib-Hajj, L. M. Carrithers, G. Tokmoulina, M. Pypaert, E. A. Jonas, and S. G. Waxman Expression of the Voltage-Gated Sodium Channel NaV1.5 in the Macrophage Late Endosome Regulates Endosomal Acidification J. Immunol., June 15, 2007; 178(12): 7822 - 7832. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. M. McNulty, G. B. Edgerton, R. D. Shah, D. A. Hanck, H. A. Fozzard, and G. M. Lipkind Charge at the lidocaine binding site residue Phe-1759 affects permeation in human cardiac voltage-gated sodium channels J. Physiol., June 1, 2007; 581(2): 741 - 755. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
