|
|
|
|
|
|
|
||
The Journal of General Physiology, Vol 93, 123-150, Copyright © 1989 by The Rockefeller University Press
ARTICLES |
WF Boron and RC Knakal
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510.
Intracellular pH (pHi) of the squid axon is regulated by a stilbenesensitive transporter that couples the influx of Na+ and HCO3- (or the equivalent) to the efflux of Cl-. According to one model, the extracellular ion pair NaCO3- exchanges for intracellular Cl-. In the present study, the ion-pair model was tested by examining the interaction of the reversible stilbene derivative 4,4'-dinitrostilbene- 2,2'-disulfonate (DNDS) with extracellular Na+ and HCO3-. Axons (initial pHi approximately 7.4) were internally dialyzed with a pH 6.5 solution containing 400 mM Cl- but no Na+. After pHi, as measured with a glass microelectrode, had fallen to approximately 6.6, dialysis was halted. In the presence of both external Na+ and HCO3- (pHo = 8.0, 22 degrees C), pHi increased due to the pHi-regulating mechanism. At a fixed [Na+]o of 425 mM and [HCO3-]o of 12 mM, DNDS reversibly reduced the equivalent acid-extrusion rate (JH) calculated from the rate of pHi recovery. The best-fit value for maximal inhibition was 104%, and for the [DNDS]o at half-maximal inhibition, 0.3 mM. At a [Na+]o of 425 mM, the [HCO3-]o dependence of JH was examined at 0, 0.1, and 0.25 mM DNDS. Although Jmax was always approximately 20 pmol cm-2 s-1, Km(HCO3-) was 2.6, 5.7, and 12.7 mM, respectively. Thus, DNDS is competitive with HCO3-. At a [HCO3-]o of 12 mM, the [Na+]o dependence of JH was examined at 0 and 0.1 mM DNDS. Although Jmax was approximately 20 pmol cm-2 s-1 in both cases, Km(Na+) was 71 and 179 mM, respectively. At a [HCO3-]o of 48 mM, Jmax was approximately 20 pmol cm-2 s-1 at [DNDS]o levels of 0, 0.1, and 0.25 mM. However, Km(Na+) was 22, 45, and 90 mM, respectively. Thus, DNDS (an anion) is also competitive with Na+. The results are consistent with simple competition between DNDS and NaCO3-, and place severe restrictions on other kinetic models.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Facebook 
Reddit 
Technorati 
Twitter What's this?
This article has been cited by other articles:
|
|
 |
|
  W. F. Boron, L. Chen, and M. D. Parker Modular structure of sodium-coupled bicarbonate transporters J. Exp. Biol., June 1, 2009; 212(11): 1697 - 1706. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. Lu and W. F. Boron Reversible and irreversible interactions of DIDS with the human electrogenic Na/HCO3 cotransporter NBCe1-A: role of lysines in the KKMIK motif of TM5 Am J Physiol Cell Physiol, May 1, 2007; 292(5): C1787 - C1798. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. CHESLER Regulation and Modulation of pH in the Brain Physiol Rev, October 1, 2003; 83(4): 1183 - 1221. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L. V. Virkki, I. Choi, B. A. Davis, and W. F. Boron Cloning of a Na+-driven Cl/HCO3 exchanger from squid giant fiber lobe Am J Physiol Cell Physiol, October 1, 2003; 285(4): C771 - C780. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. C. Devor, R. J. Bridges, and J. M. Pilewski Pharmacological modulation of ion transport across wild-type and Delta F508 CFTR-expressing human bronchial epithelia Am J Physiol Cell Physiol, August 1, 2000; 279(2): C461 - C479. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. C. Devor, A. K. Singh, L. C. Lambert, A. DeLuca, R. A. Frizzell, and R. J. Bridges Bicarbonate and Chloride Secretion in Calu-3 Human Airway Epithelial Cells J. Gen. Physiol., May 1, 1999; 113(5): 743 - 760. [Abstract] [Full Text] [PDF]
|
|
|
|
