|
|
|
|
|
|
|
||
Article |
The Interpretation of External Proton-concentration Gradients
Department of Fluid Mechanics, Building 404, Technical University of Denmark, DK-2800 Lyngby, Denmark
We have hypothesized that a major role of the apical H+-pump in mitochondria-rich (MR) cells of amphibian skin is to energize active uptake of Cl– via an apical Cl–/HCO3–-exchanger. The activity of the H+ pump was studied by monitoring mucosal [H+]-profiles with a pH-sensitive microelectrode. With gluconate as mucosal anion, pH adjacent to the cornified cell layer was 0.98 ± 0.07 (mean ± SEM) pH-units below that of the lightly buffered bulk solution (pH = 7.40). The average distance at which the pH-gradient is dissipated was 382 ± 18 µm, corresponding to an estimated "unstirred layer" thickness of 329 ± 29 µm. Mucosal acidification was dependent on serosal pCO2, and abolished after depression of cellular energy metabolism, confirming that mucosal acidification results from active transport of H+. The [H+] was practically similar adjacent to all cells and independent of whether the microelectrode tip was positioned near an MR-cell or a principal cell. To evaluate [H+]-profiles created by a multitude of MR-cells, a mathematical model is proposed which assumes that the H+ distribution is governed by steady diffusion from a number of point sources defining a set of particular solutions to Laplace's equation. Model calculations predicted that with a physiological density of MR cells, the [H+] profile would be governed by so many sources that their individual contributions could not be experimentally resolved. The flux equation was integrated to provide a general mathematical expression for an external standing [H+]–gradient in the unstirred layer. This case was treated as free diffusion of protons and proton-loaded buffer molecules carrying away the protons extruded by the pump into the unstirred layer; the expression derived was used for estimating stationary proton-fluxes. The external [H+]-gradient depended on the mucosal anion such as to indicate that base (HCO3–) is excreted in exchange not only for Cl –, but also for Br– and I–, indicating that the active fluxes of these anions can be attributed to mitochondria-rich cells.
Key Words: active Cl– transport • rheogenic H+ pump • unstirred layer • mathematics of diffusion • proton concentration-profiles outside epithelial cells
Abbreviations: MR, mitochondria-rich
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Facebook 
Reddit 
Technorati 
Twitter What's this?
This article has been cited by other articles:
|
|
 |
|
  M. Grosell, E. M. Mager, C. Williams, and J. R. Taylor High rates of HCO3- secretion and Cl- absorption against adverse gradients in the marine teleost intestine: the involvement of an electrogenic anion exchanger and H+-pump metabolon? J. Exp. Biol., June 1, 2009; 212(11): 1684 - 1696. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Grosell and J. Genz Ouabain-sensitive bicarbonate secretion and acid absorption by the marine teleost fish intestine play a role in osmoregulation Am J Physiol Regulatory Integrative Comp Physiol, October 1, 2006; 291(4): R1145 - R1156. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L. B. Kirschner The mechanism of sodium chloride uptake in hyperregulating aquatic animals J. Exp. Biol., April 1, 2004; 207(9): 1439 - 1452. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Schweigel and H. Martens Anion-dependent Mg2+ influx and a role for a vacuolar H+-ATPase in sheep ruminal epithelial cells Am J Physiol Gastrointest Liver Physiol, June 9, 2003; 285(1): G45 - G53. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. Perry, M. Beyers, and D. Johnson Cloning and molecular characterisation of the trout (Oncorhynchus mykiss) vacuolar H(+)-ATPase B subunit J. Exp. Biol., January 2, 2000; 203(3): 459 - 470. [Abstract] [PDF]
|
|
|
|
 |
|
 N. Nelson and W. R. Harvey Vacuolar and Plasma Membrane Proton-Adenosinetriphosphatases Physiol Rev, April 1, 1999; 79(2): 361 - 385. [Abstract] [Full Text] [PDF]
|
|
|
|
