|
|
|
|
|
|
|
||
The Journal of General Physiology, Vol 101, 153-182, Copyright © 1993 by The Rockefeller University Press
ARTICLES |
DD Doyle, Y Guo, SL Lustig, J Satin, RB Rogart and HA Fozzard
University of Chicago, Department of Medicine, Illinois 60637.
Monovalent and divalent cations competitively displace tetrodotoxin and saxitoxin (STX) from their binding sites on nerve and skeletal muscle Na channels. Recent studies of cloned cardiac (toxin-resistant) and brain (toxin-sensitive) Na channels suggest important structural differences in their toxin and divalent cation binding sites. We used a partially purified preparation of sheep cardiac Na channels to compare monovalent and divalent cation competition and pH dependence of binding of [3H]STX between these toxin-resistant channels and toxin-sensitive channels in membranes prepared from rat brain. The effects of several chemical modifiers of amino acid groups were also compared. Toxin competition curves for Na+ in heart and Cd2+ in brain yielded similar KD values to measurements of equilibrium binding curves. The monovalent cation sequence for effectiveness of [3H]STX competition is the same for cardiac and brain Na channels, with similar KI values for each ion and slopes of -1. The effectiveness sequence corresponds to unhydrated ion radii. For seven divalent cations tested (Ca2+, Mg2+, Mn2+, Co2+, Ni2+, Cd2+, and Zn2+) the sequence for [3H]STX competition was also similar. However, whereas all ions displaced [3H]STX from cardiac Na channels at lower concentrations, Cd2+ and Zn2+ did so at much lower concentrations. In addition, and by way of explication, the divalent ion competition curves for both brain and cardiac channels (except for Cd2+ and Zn2+ in heart and Zn2+ in brain) had slopes of less than -1, consistent with more than one interaction site. Two-site curves had statistically better fits than one-site curves. The derived values of KI for the higher affinity sites were similar between the channel types, but the lower affinity KI's were larger for heart. On the other hand, the slopes of competition curves for Cd2+ and Zn2+ were close to - 1, as if the cardiac Na channel had one dominant site of interaction or more than one site with similar values for KI. pH titration of [3H]STX binding to cardiac channels showed a pKa of 5.5 and a slope of 0.6-0.9, compared with a pKa of 5.1 and slope of 1 for brain channels. Tetramethyloxonium (TMO) treatment abolished [3H]STX binding to cardiac and brain channels and STX protected channels, but the TMO effect was less dramatic for cardiac channels. Trinitrobenzene sulfonate preferentially abolished [3H]STX binding to brain channels by action at an STX protected site.(ABSTRACT TRUNCATED AT 400 WORDS)
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  H. Sun, D. Varela, D. Chartier, P. C. Ruben, S. Nattel, G. W. Zamponi, and N. Leblanc Differential Interactions of Na+ Channel Toxins with T-type Ca2+ Channels J. Gen. Physiol., July 1, 2008; 132(1): 101 - 113. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 F. Brette and C. H. Orchard No Apparent Requirement for Neuronal Sodium Channels in Excitation-Contraction Coupling in Rat Ventricular Myocytes Circ. Res., March 17, 2006; 98(5): 667 - 674. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 Z. Chen, C. Alcayaga, B. A. Suarez-Isla, B. O'Rourke, G. Tomaselli, and E. Marban A "Minimal" Sodium Channel Construct Consisting of Ligated S5-P-S6 Segments Forms a Toxin-activatable Ionophore J. Biol. Chem., June 28, 2002; 277(27): 24653 - 24658. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. K. G. Maier, R. E. Westenbroek, K. A. Schenkman, E. O. Feigl, T. Scheuer, and W. A. Catterall An unexpected role for brain-type sodium channels in coupling of cell surface depolarization to contraction in the heart PNAS, March 19, 2002; 99(6): 4073 - 4078. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. R. Balser Structure and function of the cardiac sodium channels Cardiovasc Res, May 1, 1999; 42(2): 327 - 328. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. S. Gandhi, K. Shuck, J. D. Lear, G. R. Dieckmann, W. F. DeGrado, R. A. Lamb, and L. H. Pinto Cu(II) Inhibition of the Proton Translocation Machinery of the Influenza A Virus M2 Protein J. Biol. Chem., February 26, 1999; 274(9): 5474 - 5482. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K.-J. Shon, B. M. Olivera, M. Watkins, R. B. Jacobsen, W. R. Gray, C. Z. Floresca, L. J. Cruz, D. R. Hillyard, A. Brink, H. Terlau, et al. µ-Conotoxin PIIIA, a New Peptide for Discriminating among Tetrodotoxin-Sensitive Na Channel Subtypes J. Neurosci., June 15, 1998; 18(12): 4473 - 4481. [Abstract] [Full Text] [PDF]
|
|
|
|
